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Re: Tire Width (I don't get it) [Slowman] [ In reply to ]
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You can't run 28s unless you go to disc brakes, right?
I ain't EVAH going to freakin' disk brakes!
(Purist here...)
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Re: Tire Width (I don't get it) [Slowman] [ In reply to ]
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25' are too wide for chain stays.

Team Zoot So Cal
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Re: Tire Width (I don't get it) [Slowman] [ In reply to ]
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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.
Last edited by: cyclenutnz: Jun 27, 17 20:08
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Re: Tire Width (I don't get it) [Tom A.] [ In reply to ]
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Tom A. wrote:
Slowman wrote:
splain me this. and tell me if i've got a problem with my reasoning.

1. 25mm is testing better than 23mm in most rolling resistance tests.
2. in the limited amount of testing i've seen, isn't 28mm outrolling 25mm?
3. wider tires are also likely to be more comfortable (lower pressures).

but...

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

yes, there are aerodynamics to consider as well. is this your argument? or is there something wrong with my chain of reasoning above?


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".

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?
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Re: Tire Width (I don't get it) [Slowman] [ In reply to ]
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Slowman wrote:
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.


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

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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?


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).

Quote:
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?


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 ;-)

http://bikeblather.blogspot.com/
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Re: Tire Width (I don't get it) [devashish_paul] [ In reply to ]
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devashish_paul wrote:
Tom A. wrote:
devashish_paul wrote:
Slowman wrote:
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


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.


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


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?

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.

http://bikeblather.blogspot.com/
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Re: Tire Width (I don't get it) [spookini] [ In reply to ]
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spookini wrote:
You can't run 28s unless you go to disc brakes, right?
I ain't EVAH going to freakin' disk brakes!
(Purist here...)

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.

http://bikeblather.blogspot.com/
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Re: Tire Width (I don't get it) [GreenPlease] [ In reply to ]
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GreenPlease wrote:
Tom A. wrote:
Slowman wrote:
splain me this. and tell me if i've got a problem with my reasoning.

1. 25mm is testing better than 23mm in most rolling resistance tests.
2. in the limited amount of testing i've seen, isn't 28mm outrolling 25mm?
3. wider tires are also likely to be more comfortable (lower pressures).

but...

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

yes, there are aerodynamics to consider as well. is this your argument? or is there something wrong with my chain of reasoning above?


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".

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?

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...

http://bikeblather.blogspot.com/
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Re: Tire Width (I don't get it) [Tom A.] [ In reply to ]
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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?
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Re: Tire Width (I don't get it) [Slowman] [ In reply to ]
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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.
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Re: Tire Width (I don't get it) [Slowman] [ In reply to ]
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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.
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Re: Tire Width (I don't get it) [AG] [ In reply to ]
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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.
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Re: Tire Width (I don't get it) [Slowman] [ In reply to ]
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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.
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Re: Tire Width (I don't get it) [Slowman] [ In reply to ]
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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.
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Re: Tire Width (I don't get it) [Tom A.] [ In reply to ]
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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?
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Re: Tire Width (I don't get it) [Slowman] [ In reply to ]
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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 !!
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Re: Tire Width (I don't get it) [Tom A.] [ In reply to ]
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Tom A. wrote:
spookini wrote:
You can't run 28s unless you go to disc brakes, right?
I ain't EVAH going to freakin' disk brakes!
(Purist here...)


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.

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.)
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Re: Tire Width (I don't get it) [Slowman] [ In reply to ]
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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.

http://www.sfuelsgolonger.com
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Re: Tire Width (I don't get it) [Tom A.] [ In reply to ]
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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?
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Re: Tire Width (I don't get it) [Slowman] [ In reply to ]
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Anything over 23mm on my rear wheel rubs against my BMC TM02 frame. I have no choice.
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Re: Tire Width (I don't get it) [GreenPlease] [ In reply to ]
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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.

GreenPlease wrote:
...and hysteresis losses which should be driven by the compound and casing construction (I think).

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



GreenPlease wrote:
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?

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

http://bikeblather.blogspot.com/
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Re: Tire Width (I don't get it) [RonanIRL] [ In reply to ]
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RonanIRL wrote:
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?

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

http://bikeblather.blogspot.com/
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Re: Tire Width (I don't get it) [duncan] [ In reply to ]
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duncan wrote:
Tom A. wrote:
spookini wrote:
You can't run 28s unless you go to disc brakes, right?
I ain't EVAH going to freakin' disk brakes!
(Purist here...)


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.


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.)

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

http://bikeblather.blogspot.com/
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Re: Tire Width (I don't get it) [jeffp] [ In reply to ]
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jeffp wrote:
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.

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

jeffp wrote:
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?

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...

http://bikeblather.blogspot.com/
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Re: Tire Width (I don't get it) [Tom A.] [ In reply to ]
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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


Last edited by: jeffp: Jun 28, 17 7:50
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