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

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

Have you read this:

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

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

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.

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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Tom A. wrote:
From that link that stevej pointed...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.

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

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!
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Re: Tire Width (I don't get it) [joshatsilca] [ In reply to ]
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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?

Advanced Aero TopTube Storage for Road, Gravel, & Tri...ZeroSlip & Direct-mount, made in the USA.
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Re: Tire Width (I don't get it) [joshatsilca] [ In reply to ]
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joshatsilca wrote:

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.

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

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

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

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


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

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


Omg......it's beautiful :). That bike is amazing
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Re: Tire Width (I don't get it) [Bonesbrigade] [ In reply to ]
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nice! 650b x 50! that's a bad boy.

Dan Empfield
aka Slowman
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Re: Tire Width (I don't get it) [ridenfish39] [ In reply to ]
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Thanks! It was a fun process and Rob is pretty awesome to work with.

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Re: Tire Width (I don't get it) [Slowman] [ In reply to ]
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Slowman wrote:
nice! 650b x 50! that's a bad boy.


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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Last edited by: Bonesbrigade: Jun 29, 17 10:22
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Re: Tire Width (I don't get it) [joshatsilca] [ In reply to ]
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That was some excellent reading! Thank you!
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