Fit.

I don't think anything wider than a 23 on my Flo 30's will fit on my bike.

The results you got are likely heavily influenced by you being so specific - race wheels on your tri bike. Most low crr 23mm tires test faster than 25mm tires when aero is factored in. Plus, many frames still do not fit wide rims with 25mm tires.

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For myself (n=1), it comes down to aerodynamics, what wheels I'm running, and what fits in the bike frame I'm riding. On my old TT bike, a 25mm tire was the widest I could comfortably run in the rear, and this was a 25mm tubular. I'm not sure my current Jet Plus disc with a 23mm Corsa Speed which measures > 26mm on the rim would fit on that bike.

My current wheel setup is a HED 3+ front and a HED Jet Plus Disc. I have a Conti SS 20mm on the HED 3+ which measures around 24mm and a Corsa Speed 23mm on the Jet Plus Disc which measures > 26mm. On my tubular wheel set, I have a 23mm front tire and 25mm rear tire, which more than likely measure narrower than the clincher setup I'm currently running.

For training I run wider tires, but for racing it's balancing aerodynamics, wheel/tire interaction, and rolling resistance.

Fit for me, too. I can't get anything wider than a 23 GP4000 on my bike with FLO 30s.

Also, probably a good chunk of the people who responded with 23mm are using 4000s, which are really almost 25mm on wider rims (limit for many frames).

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23mm GP4000s on my Flos measure just over 26mm, my 2 main bikes can't handle anything larger.

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"I'm thinking of a number between 1 and 10, and I don't know why!"

One thing to consider is that wide-rim clinchers increase the effective tire size. For example, a 25mm-wide (external) / 21mm-wide (internal) Hed Plus rim makes a tire labeled 23mm inflate to about 25-26mm actual. So - is the poll asking about labeled size, or measured size when inflated?

And, frame fit is an issue. I have a custom tri bike that can fit 30mm tires. But it's an extremely rare bird. It was outstanding when I used to live in Michigan, with their abysmal road quality. I never understood how people rode 23mm tires at 100psi or more in that state. Newer tri bikes are slowly accepting wider tires, but it's often capped at about 25mm actual/inflated size.

i'm not disputing you, but do you know this? how many tires have been tested on how many wheels? seems like there must be a lot of aero testing left undone in order to make a broad claim like this. if the 25mm tires on balance outroll their 23mm siblings, then the 23mm tires MUST perform better aerodynamically just to get back to even.

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Dan Empfield
aka Slowman

Aero + fitment.

In my case, they simply came with my bike. When it's time to replace, I'll consider 25s. Edited to say, my current tires are pretty nice (Schwalbe One, tubeless)... so can't really see ripping them off till they're done.

I'm on 23mm GP4000 on SRAM S60/S80.

If anything happened to this wheelset I'd get a wide rim wheelset and 25mm tires, if the tires could clear the frame. But not going to go out of my way to change the wheels for a few seconds over 40Km.

On my road bike running 25mm on a Mavic Ksyrium wheelset. Whole different game there. Frame clearance is better, brakes open to allow wider tires, and rear brake isn't hidden behind the BB making wheel swap a pain in the ass.

Old HED3 front. Which means a 20c. Some things don't change.

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Editor-in-Chief, Slowtwitch.com | Twitter

Brake clearance on the rear brake of my Felt prevents anything wider than the 23.

Fit and ease of use. I tried 25s and experienced frame rubbing, brake rubbing, etc. Cervelo p3c.

Switched back to 23s (4000s) and no issues.

Your reasoning may be fine, but it's incomplete in terms of gauging factors relevant to consumers.

+1

on my Flo 60/90 wheels, 23 Conti GP4000 SII are far wider than 23... 25+ and there is just enough clearance on my 2015 Felt B series.

6 in 10 of us are too poor/cheap to have a wheel/frame setup to take advantage of anything wider than 23. In the big scheme of things, there aren't that many rims with internal widths of more than 17mm (though this isn't much of an issue if you are buying new).

Other factors include the Corsa TLR only being available in 23, up until very recently, some of the TT crowd are still running SS 20s on HED/Specialized Trispokes, and wheels like the Flo 30s being really fat with a 23.

Dan,

For me, it depends on the wheel and the bike. Shiv with RZR92s - 23 (Vittoria tubulars) as manufacturer recommended. With Hed C+, 25 IRCs which measure 30+. With Eurus, 23 Michelins. Reynolds Assaults (old) 23, Enve 3.4s, 23 (measure 26 and 25). Flo 60s, 23 (measure 25).

I was in my LBS the other day. A 25 Conti 4000s2 on Hed Jet 6+, Pinarello FP Quatro was rubbing on the brake. New tire and it was too big. Sadly there were rub marks on the chains stays where the previous 23 had rubbed, too.

What I wonder about all the width testing is, how specifically is it tied to nominal tire width?

25's barely fit on my bike as it is. Its uncomfortably close.

For me it's about bike fit; my B16 from 2012 doesn't fit 25mm tires.

Are there tires that are comparable (i.e., as fast as) to the conti supersonics in casing/tread suppleness in 25mm or 28mm? If yes, let me know.

I think that bottom line is that there is a serious dearth of public data on where exactly the tire/rim width crossover point is for modern bikes and modern wheels and modern super fast tires.

In other words, when exactly does the excess tire/rim width mean an increase in aero drag that exceeds the very small improvement in rolling resistance? I don't know. But my guess is that you can't go that wide without a speed penalty.

And, when people don't know, usually they stick with what they have.

I think that might be the answer to your question.

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Advanced Aero TopTube Storage for Road, Gravel, & Tri...ZeroSlip & Direct-mount, made in the USA.
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The general rule of thumb - based on the results from others, is aero takes a good hit when rim widths are less than 105% of tire widths. I don't think the Crr benefit from wider tires makes up for that.

BUT, I think we will see wider rims paired with wider tires, but we also need more clearance on bikes to accomode this. This is happening though......Flo is going this way for their gravel rim.

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The great Walter Benjamin discussed how and why products have an aura created around them and how that aura becomes the authentic 'thing' and not the product itself. Light reading for your recovery days.

People will go with the first narrative they've created (or agreed with) concerning a product. Judgements about information after that simply serve to justify the opinion.

And when it comes to numbers, people just aren't smart - please believe me, I don't mean that to be condescending. But, Agent K said it best "a person is smart but people are dumb." Read up on why A&W's 1/3 lb burger failed and you'll begin to crack the code of the wider tire. Opinions about tire width, like most things cycling, have nothing to do with the actual thing itself.

i can see now i asked the wrong question. the question i SHOULD have asked is what tire width you feel your next bike should accommodate. i will ask that in the next poll

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Dan Empfield
aka Slowman

But, if speed is the goal, how are we to know what is the optimal tire width that our next frame should accommodate?

Especially when there is no good data.

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Advanced Aero TopTube Storage for Road, Gravel, & Tri...ZeroSlip & Direct-mount, made in the USA.
DarkSpeedWorks.com.....Reviews.....Insta.....Facebook
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If you could fit 28 mm on your bike and they had lower crr and just as aero as thin tires the only remaining reason to not race on 28mm would be rotational weight of the larger tire. Probably the only reason a 28mm tire or 32mm is less aero is the mate structure to rim, and rim depth. The other issue would be brake clearance and if your tire keeps getting bigger your overall wheel does so your gearing kind of changes.

I think it really boils down to what people cant fit and what they have. I don't think any reasonable person is going to go replace their entire wheelset or bike to add 2mm to a tire to maybe save some time.

That being said...

I have 25s on the training wheels for my TT bike, but race on 23s. Because thats what my race wheels can handle.

I have 28 tubless on my road bike...because when I'm riding that I don't care about speed. I just want comfortable time in the saddle and not have to deal with flats.

agreed. and you should do an article with a panel of industry people. it is surprising how limited their designs (still) are.

well, what i'm now seeing is that wider is faster, if you just look at Crr. not because i know. just because i can read. and what it seems to me that i'm reading, altho i haven't gone back and catalogued this, is that we don't really yet know how wide you can go before you stop getting faster. love to see what tom a. has to say about this.

but, as an example, go here and look at the results of the tire most of you are riding. assuming the rim is wide enough to accept the tire with a good config, you tell me why my next tri bike shouldn't be optimized for 28mm tires.

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Dan Empfield
aka Slowman

I think your premises 1 and 2 might be flawed...at a given pressure, yes, but as you point out, wider tires are typically run at lower pressures. For example, from an article right here on this site:


If you look at reasonable pressures for each tire size, you'll see that there isn't much difference in the Crr...in other words, the horizontal yellow line is more reasonable than the vertical yellow line, in regards to how tires are actually run.

So, if that's the case (and there isn't really any great Crr benefits from wider tires), for a RACE bike, I'm going to be following Josh Poertner's "Rule of 105" https://silca.cc/...ure-and-aerodynamics

To me, the driving factor for choosing tire width for a given application is the tire pressure I want to run for a given course. In other words, if the course conditions require lower pressures for comfort reasons, then I'm going to choose a tire width that allows for that pressure without causing other concerns, such as bottoming rims and/or "snakebite" flats. Of course, expected speeds/wind angles also comes into that calculus. This is how I ended up selecting 42mm wide tires for BWR this year...knowing the amount of off-road conditions, I basically wanted to be able to run close to MTB pressures ;-)

That type of thinking is somewhat opposite of how most folks approach the subject (i.e. pick a tire width and then ask "what pressure should I run?"...I like to think that it's not that wider tires allow lower pressures, but lower pressures require wider tires ;-)

Additionally, the ROT that "wider is lower Crr" is mainly only applicable across a given tire model (and at a given pressure, as pointed out above), so there's that. For example, the fastest tire (by far) on my testing chart is a 23C (Vittoria Corsa Speed)...so, I think many are aware that there ARE fast rolling narrower tires, and that could be coming into play. "Wider is faster rolling" is a generality that has some notable exceptions.

Also, as Greg K. points out above, with wider rims, 23s are the new 25s :-) You really should be asking about "mounted width".

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Because it should be optimized for 30mm tires (measured).

Oh shit, anything over about 28mm should have disc brakes. Maybe your next tri bike should be optimized for 30mm tires AND disc brakes. Does anyone know if they are going to start making road/tri bikes any time soon?

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/kj

http://kjmcawesome.tumblr.com/

And that's not even actually a legitimate reason...

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what i see from BRR is that wider tires at high pressures test fast. but then there's the impedance (?) factor, which josh has been testing, maybe you have as well, and i suspect this relates to road surface? for example, maybe 28mm @ 120psi might be a really fast tire/pressure on a very smooth velodrome? as long as the wheel, the bike, and the aerodynamics all played nicely.

the thing is, once you get to a rougher road, it still seems to me that this argues for a larger tire, just @ lower pressure.

i'm asking because i've got bike companies right now in the process of designing their next bikes and they're wondering what to design for. it didn't occur to me that there was so much of a problem with people just not able to put the tires in their bikes, but of course that's true now that i think of it.

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Dan Empfield
aka Slowman

Here's one example of looking at that question:

http://bikeblather.blogspot.com/...t-3-after-party.html

Aero differences of the same tire models in different widths:


What happens when you factor in Crr:


As you can see, just looking at the SW Turbo models, the lower Crr of the 28C model isn't enough to overcome the better aerodynamics of the 26C and 24C models, which are basically "tied" out to 10 deg (BTW, the 22C model of that tire is a pretty huge outlier in regards to Crr for some reason, which is why it's excellent aerodynamics can't be taken advantage of).

Of course, those charts also show that the Turbo Cottons (both 26C and 24C models) outperform the rest due to their significantly lower Crr, despite worse drag at yaws greater than 5 degrees.

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Yeah...you're going to have a problem with that. Good luck getting a 28C tire to stay on a rim at 120psi. The casing tension on that is going to be ENORMOUS.

And yes, I've tested "impedance"...in fact, my first data is what Josh points to. And also yes, that comes into play at all tire widths, and is a function of road surface, load, tire, and speed (i.e. input energy).


No...it argues for lower pressures, which require larger tires "to play nicely" (re-read my post above)


Just tell them to design for the widest measured tire width (and height, in regards to GP4Ks) for the brakes they've selected for the application. For most rim calipers, that's going to be ~28mm, unless they spec mid or long reach calipers, or design their own rim calipers.

For hub calipers (i.e. "discs") then it's basically wide open ;-)

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stipulating that i'm well out of my depth here, do i understand that you tested all of the turbo cotton widths on the same roval CLX64? i ask because i believe i remember specialized making some noise about this wheel being built around the turbo cotton for aerodynamics. so, unless i dreamed that, then it must follow that specialized had a particular width of its turbo cotton in mind and i'd be willing to bet it wasn't the 28mm.

but i don't know if i understood your test to be 3 tires on that same wheel. but if so, then i guess i speculate what could be achieved, theoretically, had specialized gone back and designed another roval optimized now to the 28mm tire. now it no longer has that 21mm internal bead diamater but 23mm or 24mm or whatever. is my reasoning sound or am i off on a wild one?

but it could also be that there's something about a 28mm tire on a 21mm internal bead rim that makes it roll faster and if you placed it on a fatter rim maybe the Crr of that wider tire comes down to earth.

anyway, the point of this speculation is to have a good answer for bike makers who're wondering whether they need to make their new frames and forks to fit 23mm, 25mm, 28mm or what?

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Dan Empfield
aka Slowman

moot point ;-)

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Dan Empfield
aka Slowman

Two reason I still run 23mm tires...

1. I ride older areo wheels so the wider tire look light a light bulb on my narrow rims. Seems like that would negate any areo benefit. (Fix for that of course is me not being so cheap and buying newer wheels that are wider)

2. I ride 650c wheels and Continental doesn't make their 4000s in anything but 23mm for the 650c size. (Fix for that is a whole different bike, which often comes with toe overlap for my height-challenged size)

If that's the case, tell them to design around 50mm width tires...'cuz some dork is going to insist that's what they absolutely need :-P

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I hear you about the Michigan roads! Thankfully I can run 25s on my Felt S22. With latex tubes it is okay, but definitely not great.

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Aaron Bales
Lansing Triathlon Team

I am with you.

This is becoming more well known, and I think wheel/tire systems will develop to recognize this reality.

You need really wide internal measurements to make a bigger tire fit well. A friend builds up Enve m50 mountain rims for his disc road bike because they match well with 28-30mm tires. The overall profile is very smooth.

One of my favorite combos is the zipp 30 course with conti gp4000 28mm tires. Measure out to about 30mm and roll great while soaking up the bumps.

25mm tires rub my frame.

I own a few shops. We measure a lot of tires in order to know what will fit in frames. 23's can easily measure 25-26mm on certain rims. HOWEVER, people mainly buy 23s out of inertia and ignorance. Just FYI, I ran 24mm turbo cottons on a Jet disc and Enve front and they measure around 26. On Rovals they would be 26-27mm(and awesome). The new Tarmac and Emonda will accomodate 28-30s I bet.

+1 Exactly my same set up.

Why? Why not? My engine has more potential for speed gains than my tire choice yet the potential is not reached.... that darn imperfect life thingy going on here. Not all is logical.

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Hillary Trout
San Luis Obispo, CA

Your trip is short. Make the most of it.
https://www.slogoing.net/

Looking at the graphs, for an example, the 0-yaw difference in the SW 22 and 24 look to be right around 0.19 versus 0.199, so let's call it a little less than 10% increase in drag. The difference in width is 9%. This makes me think that the change in Cd is pretty minimal for an aero bike wheel, so the loss in drag for a wider tire is about proportional to the increase in width. If I apply a rough guess of 30 watts Crr, then the wider tire needs to save ~3 watts in rolling resistance for every addition 2-3 mm in width. Seems like you would be lucky to find combinations where you were doing much more than break even. At some point the tire gets so wide you need a really deep airfoil >60-90mm.

I think I will stick with my SS20-H3/Jet disc TLR23 for now.

For me it's what will fit on individual bike. IRun Conti 25mm on my felt and 23 mm on my P3. The 25 on my P3 start to rub when they get heated up

23's barely fit on my P2 and Flo tires. I had a shop install them as I didn't know about the set screw in the drop out and they did a piss poor job...under side of my frame is rubbed to bare carbon after a ride in a light rain. I don't dare go any bigger and extend those set screws anymore as it doesn't look safe

For almost all riding the weight of the tire+tube (rotational weight) is not a concern, unless you are riding a crit or riding an uphill mountain stage finish with a lot of hairpins requiring accelerations. Then those would be the only use cases where the weight at the end of the rim kind of matters "a bit". What do you think?

25s rub on my bike... the rubber fin down the center of new GP4000s in 23 contacts the top of my brake flange. Some serious clearance issues on my bike.. front brake only.

I slapped a Red Aerolink on my bike before a race and it did rub my 23 tire for the entire race, rubbed a groove in the brake and was still rubbing... I'm beating a dead horse but its a clearance issue for me.

This. Labeled tire widths are becoming less and less meaningful given the wide range of rim widths. Actual tire widths vary greatly depending on the internal width of the rim you mount them on. Add to that the fact that one manufacturer's "23mm" tire measures wider than another manufacturer's "23mm" tire and it really becomes a case where you need to know how a particular brand/size of Tire X will actually measure when mounted on a particular brand/internal width of Rim Y.

Mounted on my Bontrager Aeolus TLR wheels, the 23mm Schwalbe Pro One measures at >26mm. The outer rim width of the Aeolus wheels is 27mm. Applying the Rule of 105% to this 27mm rim width, that means I should not use a tire that measures wider than 25.7mm. So even running the "narrow" 23mm version of the tire, I'm really running a tire that is slightly too wide for these wide wheels.

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Amateur recreational hobbyist cyclist
https://www.strava.com/athletes/337152
https://vimeo.com/user11846099

You can't run 28s unless you go to disc brakes, right?
I ain't EVAH going to freakin' disk brakes!
(Purist here...)

25' are too wide for chain stays.

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Team Zoot So Cal

From a piece I wrote a while back

For system weight (bike+rider and gear) of 95kg, on a smooth road at 25mph. Using Zipp aero data and my own CRR testing:


The wider GP4000 definitely faster in the region I care about. But it's irrelevant compared to having a top end narrow tyre.

I would like the next generation of Tri/TT bikes to be designed around 30mm width. That way we've got the room to figure out which is fastest. It may turn out that once fork interference effects, rotational drag and the CRR/translational drag factors are balance that a true 26mm on a rim designed for it is best. But at the moment it's hard to figure that out.

edit: further to that - every aero test I've done on tyres (with modern rims) has shown true width narrower than rim width to be fastest. So my optimum may be a tyre that has relaxed to 27mm after 300km of use, with a 28mm rim to compensate for the wear.

Tom, I've been meaning to ask you this for a while (and possibly recreate the answer myself): what would your CRR spreadsheet look like if you normalized for casing tension? Isn't that what we're really after here? If you look at the BRR article Slowman linked comparing 23mm, 25mm, and 28mm GP4000S IIs, at a fixed pressure on a smooth surface a 28mm tire is going to have lower rolling resistance than a 23mm tire simply by virtue of having more casing tension (ceteris paribus) no?

No, if anything, it was designed with the 22C S-Works Turbo in mind (which measures 24mm wide on that rim), not the Turbo Cottons



It's actually 4 widths if S-Works Turbo and 2 of the Turbo Cottons, not a mere 3 tires...

There may be something to be gained to designing a rim around a 28mm tire (as compared to the same tire on a current rim, and mostly only at higher yaws) but my speculation is that the overall drag curve is going to be higher as compared to an equivalently matched narrower setup (measured tire width to rim external width) due to similar drag coefficients (Cd) but larger frontal area (A).



Thinking about it some more, I think the answer is to tell them to design around being able to fit tires as large as a measured width of 30mm...because, if the course you'll be riding that TT/Tri bike is so rough that it calls for pressures low enough to require tires larger than that, then you probably shouldn't be on a TT/Tri bike for that course anyway ;-)

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I'll tell you what I know:
1. Rotational inertia differences of wheels and tires are exceedingly small fractions of the total inertia of a bike plus rider, and...
2. People, even in an all-out sprint from a low speed, accelerate VERY slowly.

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Not true...most "normal reach" rim calipers will usually accommodate tires up to 28mm measured width, and mid- and long-reach calipers (not to mention cantilevers and V-brakes) will accommodate even larger tires. The caveat is the frames/forks need to be designed for them.

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As I've contemplated roller testing wider tires, I looked into the possibility of normalizing on casing tension. However, while casing tension is linear with measured width, the pressures for significantly wider tires calculated out (normalized to the pressures I test to on narrow tires) to be pretty low as compared to typical pressures run for those width tires.

I'm thinking maybe the Frank Berto recommended "15% drop" technique might be a better approach...

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Just a prediction on my part, if you were to use something like the "15% drop method" to normalize tire pressures, I suspect that "wide" tires would suddenly lose their edge. We're basically dealing with springs (right?) and hysteresis losses which should be driven by the compound and casing construction (I think). The notion of choosing an air pressure for a road condition (as you stated earlier) and then selecting a tire accordingly is more about not destroying the rim (and traction in more extreme cases), correct?

I don't really worry too much about the difference between 23mm and 25mm. Maybe I should. That said, I haven't done any of my own testing, aside from general feel on rough roads and such. Plus looking at what others are saying from a RR/aero standpoint.

Earlier in the year I tried to get some 25mm tires, but they were out of stock so raced on 23mm Schwalbe Pro Ones front and rear. One race I used latex tubes in the tubeless system 'cause I was travelling. I wouldn't do that again.

I'm currently racing with 25mm Schwalbe Pro One Tubeless on the ENVE 7.8 tubeless rear. 23mm on the front. Both set up tubeless. I was in a shop two days ago with the rear wheel and the guy was surprised at how wide the tire was. He measured it at what he called 29mm with a caliper. When I looked I saw 28mm, but chose not to argue his caliper reading. On a Cervelo P5X this works fine.
As for pressure I usually race at around 90psi, and probably more like 80 this coming weekend in Belgium where we hit a few steep cobbled climbs, and it might be wet. You can run some really low pressures without worry of pinch flats on tubeless, but I honestly don't know where 'too low' is with respect to rolling resistance.

I'm pretty happy with that set up, and love the tubeless option once they're on. The only downside is really the initial setup. I've found I need to have the Bontrager Flash Charger pump to make it work, or a compressor that goes to 120psi with a quick release valve. I do believe it could be easier with a different tire. I've seen one brand with an extra piece of material around the bead to help it seal. After a year+ of using tubeless and installing a bunch of Schwalbe Pro One tires on both my and Heather's rims; the key is to have a very clean rim, a solid seal around the valve, soap and water on tire and rim, and a flash charger. If you've got that it's not an issue.

The data will tell you something but perhaps it's not what you really wanted to know. I think you would need to reword the survey to get the result you were looking for.

If I buy a 25c Conti GP 400s knowing that on my wide rim it's going to measure 28 have I bought a 25 or 28? I paid for a 25 but in reality I'm riding a 28.

On my Hed Jet+ wheels my conti force 24mm actually measures 28.7, and my conti gp4000s in 23 mm measure 26.5.

I dont see the benefit of going to a larger tire, especially if the aero gains offset these.

When I bought my tri bike, it was important to me that it could fit 25 mm for the reasons you mentioned. However, it won't fit 28s. Even my road bike will fit some 28, but not all. I run 25 mm on it just so I can swap out tires or only buy one size of tubes.

Is wider faster? I thought the tire width should be 5% less than the wheel width so wheel width is the limiter. For example Flo recommend a continental 23 for my FLO 60 (http://www.flocycling.com/..._front_flo_60_cc.php). To me it makes sense - a wider tire would bulge wider than the rim creating an un-aerodynamic shape. So that's why I'm on 23s.

I'd like to see bikes able to take larger wheels/tires - my old S5 won't even take a GP4000 23, so I feel the pain. But since I'm not going to upgrade my race wheels any time soon I'm still going to stay on 23s for some time.

Sorry for the stupid question but is 23c the same as 23mm?

i.e. 23mm wide at a given pressure on a rim at a given bead width?

After that it's a gong show?

Rim width
Frame Width
Tyre Availability
Trusting the RR tests
Bike/Rider weight
Tyre Pressure
The quality of the road surface.
and Aero for sure.

I would not be happy going above a 23 on the front with maybe 25 max rear. More for Aero reasons. The RR difference between the top tyres are minimal and the test procedures imo don't necessarily match real world conditions.

You wont see any pros with 28mm tyres in an opening prologue TT for the TDF most will be <23 !!

Right, for instance my Canyon Aeroad CF SLX with dual mount brakes will take 28–30 mm tubs. However, designing frame + forks to take a range of tyre sizes from 22–30 mm begs another question concerning whether its possible to optimise of airflow interactions between the wheel and frame/fork for such a large size range? This tied to another question of whether its better aerodynamically to have a small or large gap between the tyre and fork crown or frame? (As a connected aside, I was interested to see that Vroomen and 3T have gone for very minimal gaps on their new Strada.)

When Reynolds tested their Aero wheels they released their findings that the 23mm was the recommended tire to achieve the best aerodynamic properties of the wheel lip. So the way I read it anything wider would offset the gains. So I ride a "modified" 23mm tire.

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http://www.sfuelsgolonger.com

IIRC for a given wheel, rotational drag goes up as tire size goes up. Do you take that into account? Of course, the IIRC may well be wrong or I may have seen a bad source.

That said....what pressure will HED be recommending on 28mm tires when they already suggest 70-80psi for 23mm tires for 170lb riders on the plus rims?

Anything over 23mm on my rear wheel rubs against my BMC TM02 frame. I have no choice.

GreenPlease wrote:

Just a prediction on my part, if you were to use something like the "15% drop method" to normalize tire pressures, I suspect that "wide" tires would suddenly lose their edge. We're basically dealing with springs (right?)

Correct. Josh has a GREAT summary here: https://silca.cc/...r-is-stiffer-harsher

The main takeaways I get from that work are:

1. At a given pressure, larger tires are actually STIFFER (i.e. have less compliance) than narrower tires when pressed against flat/flat-ish surfaces. This implies that for flatter surfaces/features, casing tension has a large effect on compliance.
2. With smaller diameter objects/features/edges, tire width (and thus casing tension) has nearly NO effect, and the overwhelmingly major affect on compliance is air pressure alone.

So...looking at that, especially the second, tells me that if I want more compliance in the system then I want to run lower pressures. Lower pressures, to prevent wheel bottoming and/or tube "pinch" flatting, then require the use of a larger tire.


Correct...and the reason for wider tires having a Crr advantage at a given pressure is more about the width/length of the contact patch (the total area is going to be the same for a given pressure) and it's affect on the resulting retarding torque of the wheel.

http://www.slowtwitch.com/...ling_events_226.html




Exactly...and "comfort". See above :-)

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http://bikeblather.blogspot.com/

Approximately. I'll point to another good Josh article here: https://silca.cc/...-1-how-we-got-to-now

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But, then it would have just been an Exploro ;-)

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http://bikeblather.blogspot.com/

Dunno...I don't recall seeing that...


Well...in reality, they are recommending that pressure for tires that will measure out at 25-26mm wide (or considerably more if they're talking about Continentals) on those rims, so that doesn't seem so unreasonable.

28C tires will measure WELL over 30mm on those rims...

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http://bikeblather.blogspot.com/

https://ir.canterbury.ac.nz/bitstream/handle/10092/1800/thesis_fulltext.pdf?sequence=1&isAllowed=y


I have not looked at exactly what they did(ie same tire brand or not, just size difference in testing on a disk(19 vs 22mm) and don't know how correct this paper is either


tho...they do state larger tires have increased crr due to larger contact area with ground, but i will toss that out since it wasnt actually tested or modelled

Correct! It always bothers me when a fork is designed with the legs too short, or the brake mounting bolt too low (reducing the clearance between the tire and bottom of the fork, and/or inside of the brake). Usually it's only a few millimeters - this is enough to "ruin" a frame or fork. My custom tri bike has standard short-reach calipers, but I've fit tires in that are 29-30mm. The pad adjuster bolts are almost all the way down at the bottom of their adjustment range, and it's great. Plug for Habanero bikes, for getting the details right.

With mid-reach Shimano BR650 brakes and an appropriately designed frame/fork, you could probably fit 33-34mm without a problem. I had a test bike with these brakes a couple years back (Kona Honky Tonk), and it was fantastic. The limited on tire clearance was actually that the chainstays were too short (they since lengthened them), and the Shimano long-arm front derailleur (6800/9000)... which they've since ditched because of this problem. The older FDs also work well.

A lot of folks assume that you need disc brakes to run 28mm tires. It's a shame, because the reason they assume this is that bike manufacturers weren't designing their frames to allow road caliper rim brakes to be used to their full capability. In other words, the tire clearance was always there from the brakes - the frames just had some poor design aspects that narrowed the potential tire size for the user.

4. almost 6 in 10 are choosing 23mm or thinner.


Dan,

As you well know sometimes it's the little least obvious things that make the most impact.

My sense is just generally in the cycling and triathlon population there seems to be VERY poor information about tires and in particular some basics about tires, and how much they impact performance.

I can't tell you how many times, I've been out on rides with either roadies or triathletes and seen people on very expensive bikes with low-grade bad tires on them and almost always 23mm, and way OVER inflated.

Getting top-line tires, with either 25 or even 28mm profile is the single biggest performance up-grade anyone can make for any bike! (Someone please stop the madness with the Gatorskins!!)

Cars are the same. I don't drive a very expensive car - but I always invest in good tires. Makes the car feel, and drive much better, than it does with the lousy OEM tires on it.

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Steve Fleck @stevefleck | Blog

Yup...my old steel '86 Bianchi has PLENTY of clearance at the fork crown for the 28mm+ measured width tires I'm running on it (26C Turbo Cottons on H Plus Son TB14 rims)...and the 1st Gen dual pivot Dura Ace brakes have plenty of clearance as well.

In fact, the limiter on the bike is really the width between the chainstays on the rear...I probably can't go much over 29mm and still fit in there...

BTW, my custom Stinner is set up for at least 30mm wide tires in the rear. Unfortunately, the crown on the 1st Gen Cervelo S5 fork on there doesn't allow tires that large...but, I have considered picking up one of these (a Whisky No. 7 road fork): http://theradavist.com/...s-co-no-7-road-fork/ , but that might not allow me to run my current SRAM Hydro R rim brakes since it requires mid-reach calipers :-(

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http://bikeblather.blogspot.com/

so, turns out based on the early results of the NEW poll that the thing people are complaining about isn't really the thing. it's not that they aren't putting a 25mm or 28mm tire on the bike because they don't have room. they aren't going to put it on there anyway. if they only need a bike that allows a tire that's MEASURED 25mm wide, that's probably a 23mm tire.

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Dan Empfield
aka Slowman

Correct. I had a CAAD10 with ultegra caliper brakes that fit 32c Vittoria XN cyclocross tires without rubbing.

On the other hand, i can't run my Zipp 404 tubies with Zipp Tangente SL Speed tires in a 27c on my p3c because it rubs on the fork crown.

Yes, frame clearance on tri bikes is a huge issue, it is a big limiter.
Plus, if you use rim brakes, actual brake caliper clearance is another significant issue.

But, there are really two tire widths to talk about:

1) the most practical and rideable wide tire/rim for comfort and for fun and for training (where overall speed is not too big of an issue, as long as it is within reason).

2) simply the fastest (optimal combined aero drag and rolling resistance) tire/rim combo for RACING on most, say U.S., roads.

The widths a smart rider would choose for option 1 and option 2 are probably very different.

---

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Anything bigger than 23 on a wide rim will not fit. Would ride wider if it were feasible. So... FIT

I suspect that people are not thinking about their answers in the new poll. Those that pick 25 probably did not consider that means a 23 tire.

Never thought I'd see Walter Benjamin quoted on ST :)

At tter at the pointy end of the field will want s different tire than a mid pack triathlete doing an iron man.

Dan,

Most are on the tire width that they think is fastest. And some are right, but probably not 90% of us. There is additional information sprinkled around out there that suggests some changes could be made.

1) Aero - probably Flo Wheel testing and widely read here that said the 23s were the most aero (with their wheels/rims) could be the single biggest driver in the poll.

However RIM SIZE will dictate the aeroness of TIRE SIZE. Narrow rims need narrow tires to be aero and large rims can use a large tire (probably not larger than the the rim though) to be more aero.

2) Rolling resistance - Road buzz or impedance is underestimated in importance. Many tests were run with relatively smooth surfaces and not real roads. Here is a site that shows how much road surface and road resistance matter. https://silca.cc/...stance-and-impedance

RIM SIZE dictates TIRE SIZE for aero and rolling resistance. Picking a tire irregardless of the rim is a mistake.

I learned the hard way.

Over inflated tires for performance led to as many flats as under inflated tires. Plus the physical strength expended in absorbing road shock. Wanting to steer clear of even relatively minor road bumps was also unsafe.

Bought some 28 tubeless tires (because my bike can take them) and mistakenly put them on too narrow a rim. The ride was soft; yet, something was wrong. A tire too big for a rim can act like a parallelogram on the road. The tire shifts sideways and slows one while cornering and increases the odds of getting sidewall cuts/punctures.

The good news is that the data is out there. The auto/truck tire industry is way ahead of us. Cycling is catching up. It seems like the new Mavic wheel and tubeless tire SYSTEM is there from what I've read and recently saw on a GCN video. Mavic said that just 1mm between rim and tire makes a difference in fit, performance and aero.

Which leaves us with the problem that we have separate wheel/rim manufacturers and tire manufacturers. Hardly any do both and they may not be talking to each other or creating alliances and sharing data. So we the users are getting in between results trying to match tires to rims and then we disagree about which is better on ST. We also continously spend money searching for a better result that is not as in between. ;)

We really don't have enough data to guide us to the richt answer in tire and rim selection given all the possible combinations (including rider weight) out there. So we try this and that depending on what we've read on ST and else where.

My guess is that your poll probably correlates well to the number of time 23 and 25 have been mentioned on ST.

What about weight?

Don't you have to factor that into the benefit/lack of benefit to using a wider tire in addition to any rolling resistance or aero impacts?

Tom,

Do you think the 105 rule applies to the front and rear equally or would there need to be another calculation based on the seat tube geometry and proximity?

Cheers!

Yes you do. Spin those little things in the horizontal dropout. My rear race tire measures 28mm on a Time Machine. I could go even bigger if the brake wanted to cooperate.

So I think we have a lot of factors converging here:

1. Acceptance/belief: I travel a LOT and talk to A LOT of people and I'd say 98% of people out there still know little and care little about tire Crr or wheel/tire aero. Most people want to purchase the solution to what THEY think is the problem. With 30 years under our belts, frames and wheels aren't in a bad place: "I ride this frame because it's the fastest, this wheel..fastest.. etc." But with tires, not everybody knows/cares/believes about Crr or tire aero and so almost nobody in the real world (not on ST) is yet spending a lot of time/energy on this. People are generally shocked..and I mean dis-believing shocked when I tell them that their Gatorskins/Armadillos are doing as much or more harm to speed than their aero wheel set is doing to improve it..and even after our conversation I'd be shocked if most people make changes as the fear of flatting (more accurately the fear of changing a flat) is SO HIGH for most people that they'll accept the penalties.

2. That number on the sidewall vs the Actual Measurement: I'd say 90% of people I talk to about measured vs actual disbelieve it. I get this. It says 23mm... that like, means 23mm, right? This can be one of the toughest points in all of this to make because of the language used to discuss it... it's hard to argue that a 23mm tire measures 25mm when we are forced to constantly refer to it as a '23mm tire'. To really move on from this, we need to adopt a new standard like the one Josh Deetz developed some 10 years ago that combines bead width of rim and circumferential length of tire casing to create an install size. I'd say for most people it's actually the diameter increase that causes the real problems here. As we've shown in our pressure blog, the tire diameter also grows when moving to a wider bead width... My first experience with this was doing the early Zipp carbon clinchers and we were experimenting with bead widths and people would have a prototype with 15mm bead with and 23mm tire and we'd give them an identical wheel and tire only with 17.5mm bead width, and now we're rubbing the caliper, or seat-tube.

3. Disconnect between how we talk about Crr and Aero and their actual orders of magnitude: We say 'Wider is faster' and for a given tire construction, wider is generally faster (in Crr), but with diminishing returns.. So maybe the first 2mm of width get you 1Watt..the next 2mm gets you 0.8Watt and then next two might net 0.6, etc.. (these are made-up numbers but consistent with real data..). In my experience with real world testing on pavement there seems to be some sort of cross-over point in the 28-32mm zone where the benefits of further widening the tire seem to disappear. At this point, with the data we have, I'd say that somewhere in here we find the sort of max optimal width for road/tri tires.

In the mean time, what I tell everybody from the local triathlete to Peter Sagan is this:

1. Run the widest tire that doesn't violate the Rule of 105% for your rim AND will also fit in your frame with 3mm+ clearance on all sides. This will allow you the most tunability for your overall setup while also remaining close to optimal aero.
2. Test and optimize your pressures for various surfaces in training. A 23mm tire measuring 25mm is ~4% stiffer than a 23mm tire measuring 23mm at the same pressure, so going wider without lowering pressure very likely costs you more watts in Crr than are being saved by the wider tire. Test pressures in training to find your optimal pressure for various types of surface (should be smooth and feel like the tire is absorbing the harsh edges, yet not bouncy). Knowing ahead of time that you can comfortably adjust PSI depending on the course in front of you takes some of the guess work and stress out. We have 4 pre-set pressure 'Zones' for Team Bora and can quickly scan the parcours and make a decision.. no guess work, no stress.
3. When in doubt: let it out! Remember, 5psi above optimal can cost you twice as many watts as 5psi below optimal for a given surface.. so unless pinch flatting is a real concern, we always recommend dropping a few psi rather than adding.

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I saw that on the poll and though it weird too. Although I cannot remember the study, but it showed 25 faster than 23 but 28 about the same as 23.

I put the Bontrager 26mm tubeless on my flo wheels, and have been enjoying them.

My new Speed Concept even came with 25mm from the factory, so Trek has started shipping 25mm instead of 23mm with their tri bikes.

No. Asked and answered above.

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http://bikeblather.blogspot.com/

It will never happen, but with rim widths varying so much these days, the designations "23mm," "25mm," "28mm," etc. just are not that meaningful anymore.

What would be a lot more helpful would be for tires sizes to be listed by their cross section measured bead-to-bead ("B2B") out of the box and laid flat. I'm sure some tires inflate "higher" or "wider" than others given a particular B2B, but I doubt there is much variation due to "inflated shape" and you can pretty safely assume that a tire with a wider B2B will result in a wider inflated tire (rather than simply a "taller" tire and yes that is despite what we know about the GP4000SII and its "magic aero" properties). And of course a tire with a given B2B will result in a wider inflated tire when mounted on a wider rim (internal bead width).

Below is a list from a thread on the Internets showing exactly this, the B2B of a variety of tires. You can see that for various "23mm" tires, the B2B can vary from as narrow as 56mm to as wide as 60mm. And then you have some "24mm" tires that measure as wide as 64mm. So you can have an 8mm swing just moving from a "23mm" tire to a "24mm" tire. And then of course these tires will all measure out quite differently when mounted on different width rims.

So what we really need is tires listed in B2B, and then for the rim/wheel manufacturers (or Slowtwitchers armed with their digital calipers) to tell us what range of B2B works best for a particular rim's width (both external and internal). Generally speaking, we would expect the "ideal" B2B to be the B2B that results in the measured width of the inflated tire equaling 95% of the external rim width. This way, we are obeying the Rule of 105 while at the same time using the widest tire for lowest rolling resistance.

OK fine, we all know tire manufacturers are not going to give up on the "23mm-25mm-28mm" designations in the same way that we know they are not going to stop reporting aero results in terms of "watts saved" because in both cases these are measurement units that consumers can get their heads around - a lot more than B2B and CdA. But if we can get manufacturers to report CdA in addition to "watts saved," can we get manufacturers to report B2B in addition to "23mm-25mm-28mm?" It's a lot more informative.

| Mfr | Size | Model | B2B |
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| Bontrager | 700X23 | Race X Lite Silica | 60 |
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| Clement | 700X28 | Strada LGG | 68 |
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| Continental | 700X24 | Grand Prix | 64 |
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| Continental | 700X25 | GP4000s | 70 |
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| Continental | 700X22 | GP Attack | 54 |
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| Continental | 700X23 | GP3000 | 58 |
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| Continental | 700X23 | Force | 57 |
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| Deda | 700X23 | TRE RS | 58 |
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| Hutchinson | 700X23 | Fusion 2 Triathalon | 59 |
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| Michelin | 700X23 | Speedium 2 | 64 |
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| Michelin | 700X25 | Pro4 Race SC | 70 |
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| Michelin | 700X23 | Pro4 Race SC | 60 |
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| Michelin | 700X23 | Pro3 Race SC | 60 |
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| Michelin | 700X25 | Krylion | 72 |
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| Michelin | 700X25 | Pro3 Race SC | 72 |
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| Michelin | 700X23 | Krylion | 64 |
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| Michelin | 700X25 | Pro Optimum | 72 |
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| Michelin | 700X23 | Pro4 Endurance | 59 |
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| Panaracer | 700X23 | Type-A | 56 |
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| Schwalbe | 700X28 | One Tubeless | 77 |
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| Specialized | 700X23 | Pro all conditions | 56 |
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| Vittoria | 700X24 | Diamante Pro Radiale | 64 |
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| Vittoria | 700X24 | Open Pave Evo | 64 |
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| Vittoria | 700X23 | Rubino Pro 3 | 60 |
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| WTB | 700X23 | Camino Alto | 59 |


The last number for each is the measured B2B.

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Amateur recreational hobbyist cyclist
https://www.strava.com/athletes/337152
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I assume it applies more to front wheels than rear...mostly because its based on wheel-only tunnel data.

One can probably "afford" a smaller percentage on a rear wheel with less adverse affect...

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http://bikeblather.blogspot.com/

You're right about caliper expansion. When I started riding in the 70s we rode clement del mundo tubies. Every bit of 30mm. But today's tri bikes, magura hydraulics on a p5-6, speed concepts, ain't like it was in the good old days.

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Dan Empfield
aka Slowman

Thanks. Couple Qs:

1: 105% means inflated tire, as measured, cannot exceed what? Brake track width?

2. Based on what you wrote in your post it sounds like you would've checked the 30mm box in the current poll running. If not the 32mm box. Am I understanding?

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Dan Empfield
aka Slowman

I don't know. I asked Josh on his blog last year and didn't get a reply. I asked again on ST after one of his awesome blog post discussions and don't recall a reply. I'm assuming brake track, but that's 100% assumption. It just seems like something shaped similar to a sideways figure 8 with a tail hanging off the back doesn't make sense aerodynamically.


I did check 30mm. I don't need it, but would prefer for training tires. I have started my own outdoor testing, but am still new enough to it that I am not confident enough to really discuss 'findings' here. I started replying to Trevor Wurtele's post that he absolutely should try 80 psi front and rear as my *limited* testing at 185-190lbs on nearly the same setup was getting faster and faster on bumpy midwest roads down to 80. I don't think we (as a community) have a great understanding of how much our road surfaces are slowing us down. The Josh P. stuff from last year was just awesome, but we still have so much of ST telling everybody to buy 23mm GP4000's, fill em up to at least 100, then buy an Aerohead to make up for how much you're slowing yourself down with vertical oscillation.

Yes, but what I called "normal reach" are actually considered "short reach" (i.e. the new normal).

Apparently the mid-reach (47-57mm) brakes were actually referred to as "standard reach".

My old Bianchi, even with "short reach" DA brakes can easily fit 30mm tires. The rear of my Stinner currently has a tire that measure just over 30mm wide, and there's still plenty of clearance to the SRAM Hydro R caliper (even though they only claim up to 28mm of clearance). On the front fork, I'll hit the crown with anything measuring over 26-27mm...

So yeah, the clearance "issues" on road/TT/Tri bikes for tires up to 28-30mm in width seem to be more about frame/fork design than anything else...although, there ARE some brake designs that have issues at smaller widths.

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http://bikeblather.blogspot.com/

I'm fairly certain it's in reference to maximum wheel width, not brake track outer width...but, Josh can correct if I'm wrong.

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http://bikeblather.blogspot.com/

I think this one is fairly easy. Do you NEED anything wider than 25c on your tri bike? I guess if it's your only bike and primarily ride on crappy roads. For road bikes, I'm happy my Evo Hi-Mod can take up to 30c. That gives me flexibility for where I'm going to ride it. Would I ever do something like BWR on a tri bike...no, but I might use my road bike.

The increasing manufacture of bikes with disc brakes allows wider tires to be used. I still feel like this is marketing creating a problem for a problem that exists for very few cyclists. Remember the days when we only had to worry about whether wheels had a Shimano or Campy freehub? Now you also need to make sure the hub spacing and width fit your bike, you have tires that properly match the rim, and are tubeless ready (if you go that route).

As someone who works in marketing, I have no issue with bike companies doing this. However, as a bike consumer, I like to have as few of standards as possible. Thankfully, there are minimal standards when it comes to tire (diameter, width, type).

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"Most of my heroes don't appear on no stamps"
Blog = http://extrememomentum.com|Photos = http://wheelgoodphotos.com

I thought about maximum but on toroidal shapes that means the tire can be pretty fat relative to the brake track. Air goes around the tire, dips in, goes around the fat part of the rim, follows the reverse path on the way out?

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Dan Empfield
aka Slowman

That is odd, maybe I have this wrong, but I thought that on toroidal shaped rims (as well as more classic shaped aero rims), the tire should be narrower (or at least be no wider) than the brake track ...

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Advanced Aero TopTube Storage for Road, Gravel, & Tri...ZeroSlip & Direct-mount, made in the USA.
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Have you read this:

https://silca.cc/...ure-and-aerodynamics

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blog

From that link that stevej pointed you to:

"The Rule of 105 states that the rim must be at least 105% the width of the tire if you have any chance of re-capturing airflow from the tire and controlling it or smoothing it." (Italics added by me).

The way I read that, it implies maximum rim width...especially since Josh references a rim "widest point" two sentences in front of that.

Like I said, Josh can clarify when he has a chance.

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http://bikeblather.blogspot.com/

Well now I'm interested again. I see my question was posted on that link last August. It just makes sense to me that we're talking brake track width.

The other thing is, when this was tested......were toroidal rims being used yet? I don't know my aero wheel history enough to know!

1.So the 'Rule of 105%' is a pretty old school type rule of thumb. I conceived it in the early 2000's when we were experimenting with V shaped, parabolic, hybrid toroidal and early toroidal rims.. basically we found that they all would sort of work as long rim was at least 105% of the tire width measured almost anywhere on a deep rim. Granted there are differences in effectiveness of this which are the pillars upon which the various wheel companies have built their respective empires, but really, the rule holds from a very binary good/bad sort of perspective.

That is to say that there is more or less a near zero change of your wheel/tire system being fast if the wheel and tire are of equal width.. it really only works if the rim is wider. (and really only works if the rim is at least 105% of measured tire width)

This makes sense if you think about it from the point of view of the air... the tire is the leading and trailing edge of the wheel system and by the nature of it being built on an inflated casing..it really can't be aerodynamically optimized... so you need a rim shape that collects the separated air and smooths it out when you are looking at the front half of the wheel and a shape that delivers the air onto the tire in a way that it it most likely to 'close the gap' when you are looking at the rear of the wheel.. and to do either of these, much less both of them, the rim has to be a good bit wider than the tire.

As far as where the rim is widest is a sort of shell game...you can do it all at the brake track which makes the front half of the wheel very efficient in both drag and lift...but then the rear half of the wheel is less efficient and you have very forward centers of pressure and potentially unstable handling in cross-winds. You can move it to the middle of the rim and get pretty neutral handling but potentially at the cost of higher drag as the tire gets larger..or you can move it more toward the spoke bed which can do some cool things for handling, but can make some tire shapes no longer work well... so much that even tires within the rule of 105% don't work so well.. so we seem to be at a point where there are tradeoffs between total drag and handling, but for the average person were are talking pretty small differences in both.

2. So my point about the asymptotic relationship of width to rolling efficiency was mostly meant to point out that the 'wider is better' mantra isn't exactly true if you are considering pavement. As the returns are diminishing with width increase, there is very little benefit of say going from 30mm to 32mm and even less going from 32-34mm...and on smooth pavements, the difference is often immeasurable. The point here really being that there is some real benefit in rolling resistance and comfort moving from 23mm to 25mm and slightly less, but still measurable moving from 25 to 28mm but as you keep widening, the curve is so flat that the differences appear to be minimal to non-existent.. whereas the costs of getting there become ever higher. So for something like a Tri bike, the actual benefit (if any) of moving from a 28 to a 30 or 32mm tire is so small that it's almost certain to be wiped out by all of the other compromises that have to be made to get there...in particular, there just aren't really any aero rims that will work all that well with 30-32mm tires.

Now if you begin to consider other factors and surface conditions this will change. Our data looks primarily at various roughnesses of pavement and the Crr curves relative to tire width are pretty flat by the time you get to 28-32mm of tire width. However, if you move onto dirt, or gravel, or cobbles, the curves change and you find that wider tires suddenly have huge advantages again. This is where a bike like the new 3T Strada is pretty interesting and very fun (full disclosure, I am good friends with those guys so my opinion is likely colored by that!). Here is a bike that is built as an aero road bike that can handle tires at what seems to be the max width for both Crr and Aero when considering paved and related surfaces.. And when the surfaces move to gravel or dirt or worse, you move to something like and Exploro or an OPEN UP which can handle 40+mm tires which are smoking fast on the rough stuff.

3. Personally, I ride 28mm Corsa G+ on Zipp 303 rims which measure 29.8mm at 62-64psi and fit nicely inside Campy Calipers. This is a nice blend of comfort at some aero expense for our bad roads here in Indiana, but more importantly it adds some comfort to my daily driver which is a 1993 Team Issue Eddy Merckx MX Leader (Molteni paint scheme for those wondering). This bike is completely irrational, way too heavy, too stiff, terribly un-aero, and too overbuilt for most anybody ever (mine was originally built for the Eddy Merckx Podio team) but at the same time, makes me smile to look at and also very happy when I ride it. For me, the wider tires at lower pressures are of great benefit on our terribly rough roads full of pavement seams and such as they offer excellent handling and comfort (plus latex tubes.. oh so nice!)

If I were racing or at all serious about going fast, I'd likely generally be on 26-28mm tires (measured) on one of the very aero bikes out there for most events (likely run at 75-90psi depending on surface) and in the right conditions or the right events with high quality pavements I'd happily move to something like the Vittoria Corsa Speed TLR at 23mm (will measure 24.8-25.0 on wider bead seat rim which means I'd likely run 85-95psi depending on surface quality) for the combined Crr and aero benefits. The real key is having options and knowing when/where to use them and having wider rims and frames that can accommodate, certainly allow for more options.

---

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Hi Josh,
Any idea of what some of the fastest (lowest measured rolling resistance) 25mm (as printed on sidewall, not necessarily actual measured size) tires are? Say, the top 3 to 5 tires?

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This is pretty far off the path of the OP but do you think this is what Knight is doing with their rim shape? They claim (and I've heard) that their rims handle really well in the wind and they talked about optimizing the trailing edge... and the rims are pretty damn wide. So, without seeing a rim profile, could one assume they moved the wide point closer to the trailing edge?

I moved down to the 22mm Attack because my old 23mm GP4000sII was too wide and rubbed.
I would run 28s if I could, in fact I plan to buy a gravel bike frame for road riding so that I can get big tires in without fear of rubbing.

Which non-disc brake TT bikes will comfortably fit a 28mm tyre front and back?

Just to add some data to the discussion:

I run 23 mm conti tt, which are at 120 psi at the front 25,5mm wide and at the rear 26 mm.

I have an 808 firecrest at the front which has as widest width 27 mm. That is thus 106% of the tirewidth and should be ok following the 105% rule.

At the back I have a citec 8000 disc which is basically slimmer than the tire, it only gets broader rather near the axle. According to the 105% rule the tire is thus even still too wide.

All in all I should be ok and indeed it seems that the 23tt is in use actually wider.

Here is what I would want if I went out and bought a tt bike.
Front and rear rim shapes different.
The rear disc wheel would be shielded by the frame at the front so it only makes sense that it should be optimised for the trailing edge shapes.
I would want a conti 28 size tyre whatever the real measurement is and the rim width designed accordingly.
I am happy with the ride of the current conti 25 front and see no reason to go wider than this and suspect that there will be aero penalty to do so.
So front rim designed to be better stability so that a higher depth rim can be used and width appropriate to the tyre.

If really wide rims and tyres, like more than 30mm can actually be made more or as aero, then I'll have at that too.

On my road bike I currently ride 404's with gp4000 25's and I think I give up aero for the tyres, but the superior cornering and the feeling that very little rolling is lost when surfaces change to rougher, means I will wear that aero penalty happily.
But my next set of wheels will be wider and my next frame will accommodate them and I am not upgrading until frames do.

There is still only a smattering of frames out there now that really do 25's well, let alone 28's.
Wheels are only now getting wide enough for 25's and none of them are right for 28's yet.

So my current steed and wheels will just keep rolling until bike manufacturers take their many small steps as they are all afraid to evolve.

Mountain bike riders have asked for many years for longer, slacker head angle bikes that fit fit wider rubber and are only now just started to be given bikes close to what we have asked for.
I bet the road going bikes will take another two generations to get to be where I want them.

Speaking of all this.... I just stumbled across Zipp's instagram story. It looks like Tony Martin is running a 25 mm TT on a super 9. Width of a super 9 is 27.5 mm..... 27.5/1.05 = 26.19 mm. I don't have calipers or else I would do this myself, but what's the width of a 25mm TT tire mounted on a super at say 90 psi? IIRC, the 25mm TT is actually quite big when mounted.

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it looks to me from what i've observed of others' Crr drum testing that you can move down a full bar in pressure and the wider tire rolls as fast or faster than its 2mm or 3mm narrower cousin. and if you drop the pressure a bar you'll get a better ride, that is, you're testing would indicate considerably less stiffness, yes?

so:

1. either my reasoning above is off, or...
2. why aren't we all clamoring for tires that measure 30mm wide with bikes and wheels made to aerodynamically accommodate these?

i'm sure there's a good reason. i'm just not seeing it. yet.

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Dan Empfield
aka Slowman

I've run the 25mm TT on a Super 9 and it measured just over 26mm at 100psi (which was surprising as I thought it would be more)

On my rear 404 NSW a 25mm GP TT measures just shy of 27mm IIRC. Keep in mind there's not much of an aero penalty for the tire being wider than the rim in the rear. The air back there is quite "dirty."

2. A lot of us are clamouring for exactly that. Rims, frames, and forks need to be optimized for this first though. Tires are pretty much there already. My personal opinion is that 95% of the cycling population just isn't there yet - and the industry knows this.

Flo has been hinting at optimizing a rim shape/width to favour gravel-size tires - so it is slowly happening. What is discussed on ST is NOT representative of the general cycling population.

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What is your definition of high quality pavement? Did you see this article I just posted today where Lisa Norden explained that 1.5km of that 25km national TT she just won was on tricky terrain?

http://www.slowtwitch.com/...isa_Norden_6428.html

I think that if the consumers had all the data and knowledge to fully understand and appreciate this, then we all would be clamoring for that bike..but it doesn't work that way and the industry will end up moving piecewise in that general direction slowly as it takes the entire village getting on board both in terms of the products to really optimize this as well as the sales/marketing to make it happen.

1. Your point 1 is spot on and in some ways has played against this trend due to the way many people execute this strategy. Seems that many to most people don't understand the pressure-stiffness relationship so they go to wider tires because 'wider tires are more comfortable' but then fail to reduce pressure. I'm shocked at how many people I talk to who went from 23mm to 25mm tires and still run 120psi because 'I've always run 120psi'. So for a lot of the potential converts, their first hand experience has been sort of meh.. But yes, you are correct, the extra width allows you to reduce pressure beyond the point of equivalent tire stiffness while maintaining similar or better bottom-out energy which is the key to protecting your rim. If you look at the combination of stiffness data and the energy data HERE we see that yes, 1bar lower pressure makes the tire less vertically stiff while still requiring considerably more energy to bottom out when we look between the 23, 25 and 28.

Also factor that most people are accustomed to associating high frequency road buzz with 'FAST'. No secret on this forum that I was not a fan of working with Contador during my Zipp days and mostly for this reason. He was one of those old-school guys that 'knew what he felt' so we had all sorts of crazy experiences with him 'feeling' things to be faster that that the data just showed were not. If I can't get a pro who's success and livelihood to believe that lower tire pressures and smoother ride on cobbles is faster..and we are using $50,000+ in advanced on-board data acquisition to help prove it.. then you begin to see the challenge in undoing 100 years of conventional wisdom for everybody else.

2. I think that we all will be clamoring for 30mm tire road/tri bikes in the next 5 years or so. The trend will be similar to what we saw with OPEN and the UP... that bike was seen as something a bit crazy and gimmicky and too niche for most people when it was launched..but now it's the bike almost everybody else is trying to follow for adventure/gravel/groad..type riding and I know that in my circle of friends we have a handful of people who've replaced 2-3 other bikes with that one. I imagine the same will happen with the Strada and bikes yet to come which will be similar.. people will start buying them because they are novel and fill a really unique niche of fat-road, but then very likely find themselves not riding their road/tri bikes anymore because of all the benefits offered by those big tires. Then riders on group rides are going to realize that they aren't just dropping the folks on the fat-road bikes and slowly the beliefs of old will die off...it just takes time.

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http://www.SILCA.cc
Check out my podcast, inside stories from more than 20 years of product and tech innovation from inside the Pro Peloton and Pro Triathlon worlds!
http://www.marginalgainspodcast.cc

I would say that they should optimize for 25mm but per HED (my wheels) they recommend a 22mm tire on a plus rim for maximum benefit. So I would think that it depends on the wheels etc...but they should be able to accommodate a 25mm tire. I know on my older Felt DA the HED's were a tight squeeze.

The custom builders are benefiting from the lag in the industry which is how I came to my English. It has clearance for 700x42 and 660bx50 with road geometry.

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Omg......it's beautiful :). That bike is amazing

nice! 650b x 50! that's a bad boy.

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Dan Empfield
aka Slowman

Thanks! It was a fun process and Rob is pretty awesome to work with.

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I haven't had a chance to try my compass 650bx48mm yet - Jan Heine actually still has our club's demo wheels. He's supposed to be sending them back soon!

One issue with using an etap FD and wide tires is that the battery doesn't clear (it sits inboard a bit)! So...I've had someone design me a battery harness where the battery is mounted elsewhere - it works well in my limited testing so far. Hopefully SRAM redesigns their etap FD to accommodate really wide tires.

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That was some excellent reading! Thank you!

Do you have an estimate on max tire width that works with the eTap FD? Was this only for the 650b wheels? I'm working on a gravel bike build now and was planning on using eTap. The plan was Compass 700c x 35 or 38.

Thanks!

My compass 700x35 and 700x38 both fit - My Schwalbe G-ones did not fit (41mm). My chainstays are 415mm, so that is a factor.

650bx42 should fit, but I haven't tried it.

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Great info! Thank you!

Here is my hacked etap battery clearance solution if anyone is interested:

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Of the ones I've rolled, the top 5 are:
1. Continental GP TT (states 23, but measures 24.6mm on a narrow rim)
1. Specialized Turbo Cotton (pick either 24 or 26)
2. Continental Force (states is a 24, but actually measures 25mm on a narrow rim)
3. Zipp Tangente Speed 25C
4. Continental GP4KS2 25C

As you can see, even with this list, asking for "printed on sidewall" sizes isn't very helpful...

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http://bikeblather.blogspot.com/

And really, in the sense of a wheel being "fast" in regards to the "rule of 105", you're really talking about at higher yaw angles, right?

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http://bikeblather.blogspot.com/

How much do you want to bet that they tell you to just ditch the front derailleur? ;-)

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http://bikeblather.blogspot.com/

Slowman wrote:

nice! 650b x 50! that's a bad boy.

Don't need to go custom or super-expensive to get that...my Fuji Jari can accommodate 650Bx2.0" (~51mm)

http://www.fujibikes.com/usa/bikes/road/adventure-and-touring/jari

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http://bikeblather.blogspot.com/

Ha, true. The shifting on the etap FD is awesome. The Yaw FD on my road is also great. People dog on SRAM for poor FD shifting, but I don't see that.

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This was first attempt a few years ago using 650b racing Ralph's. I had Walt make me a custom fork for the conversion

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Yeah, forks like the 3T Luteus and the Fuji FC440 are real "godsends" for these types of rigs...

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http://bikeblather.blogspot.com/

I would add to Tom's list:
1. Vittoria CorsaSpeed TLR 23 (measures 24.6mm on 17c rim and is fastest tire we've ever tested..)
2. Michelin Power Competition 23mm which also measures 25mm on 17c Rim.

Also Tom asked:
And I'd say that this gets really dependent on rim design. For a really well designed rim, the Rule of 105 is mostly about the stall angle..which will be out at the higher yaw angles..but for many non-excellent rim shapes, the Rule of 105 can be the difference between air separating at 2 degrees yaw or 10 degrees yaw. The rule was actually formulated in 2001-2002 when we were doing a bunch of general-science type of tunnel work to figure out the next generation of aero and is what put us on the path to bringing Full Toroidal rims to market. Good example of the genesis of the rule would be my Original Campagnolo Shamals with silver aluminum rims circa 1994. With an 18 mm tire they behave almost like a modern aero rim as we see the drag drop with increasing yaw out to about 5-6 degrees yaw, but with a 21mm tire, the drag climbs from zero.. so you are talking 2-5 watts difference out 2.5 and 10 degrees. The tire narrower than rim isn't making the simple V shape work like a modern rim, but it is at least giving you decent flow over the windward rim faces and helping close up the void off the trailing edge of the tire that much faster.

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http://www.SILCA.cc
Check out my podcast, inside stories from more than 20 years of product and tech innovation from inside the Pro Peloton and Pro Triathlon worlds!
http://www.marginalgainspodcast.cc

Dan, your questions is a good one and it is the root of a big research project we are currently doing. We are in the process of collecting thousands of measurements in an attempt to optimize the entire wheel tire system.

All that said, the reason most people choose 23mm tires and the reason we still primarily recommend them (even though we've proven 25s are faster on our wheels) is because the frame industry has not caught up with the current wheel technology. Wider tires/wheels simply do not fit on a lot of the bikes.

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Chris Thornham
Co-Founder And Previous Owner Of FLO Cycling

go look at the current thread on kiley's test. and the comments about disc brakes. what i said 2 years ago, and before, and since then, is that one real value of disc brakes is the ability to make a wheel, and a frame, that do not contemplate the needs of rim braking.

it's becoming evident now how to make the fastest tri bike. it's clear what will be the fastest tri bike. what's not clear is who is going to finally make the fastest tri bike (wheels and tires inclusive).

everybody likes to rag on the old man! but i've got a bit of a track record when it comes to stuff like this ;-)

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Dan Empfield
aka Slowman