Weight Weenies

120psi is even low'ish for the roadrace. For TT I run 160r/155f on 22r/20f tubulars.

I get that it feels faster, put in reality you are just wasting precious watts...

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Tony Martin used same disc wheel with same tub and pressure. Of course I use that pressure for ideal tarmac only.

Here's what Nick Legan says about tire pressures: http://velonews.competitor.com/2010/11/ ... ent_149851" onclick="window.open(this.href);return false;
of course, tire pressure may change for time trials, but I'm pretty certain Tony Martin doesn't use 150+ psi for TT's because he's moved to clinchers.

Back on the original topic of wide wheels, Hed claims that their wider c2 clincher lowers rolling resistance as it spreads out the contact patch more, so I assume this would be true of most wide rim wheels.

shjames96 wrote:Here's what Nick Legan says about tire pressures: http://velonews.competitor.com/2010/11/ ... ent_149851" onclick="window.open(this.href);return false;" onclick="window.open(this.href);return false;
of course, tire pressure may change for time trials, but I'm pretty certain Tony Martin doesn't use 150+ psi for TT's because he's moved to clinchers.

Not anymore on clinchers, but when he used same tub/disc(mine is HTC team disc used by Patrick Gretsch) same pressures were used, so I'm not crunching numbers out of the cosmos.

Good discussion so far - if only someone could find some definitive data!
So many possible and probable theories as well as the usual smoke and mirrors claims from manufacturers.

DMF wrote:All magazine tests I've seen in recent years put that number way closer to the 75-80psi range (23mm clincher) for a mid-weight rider (65-70kg) most likely lower than most of us are willing to go in fear of puncture and some very scary cornering, at least on 19mm rims.

I've yet to see any test of this except for what Tom Anhalt did. Wheel Energy probably has the lab equipment to do it, but they don't make their results public.

Can you link to the sources or post some of the results?

Hi,

Kasparz wrote:

shjames96 wrote:Here's what Nick Legan says about tire pressures: http://velonews.competitor.com/2010/11/ ... ent_149851" onclick="window.open(this.href);return false;" onclick="window.open(this.href);return false;" onclick="window.open(this.href);return false;" onclick="window.open(this.href);return false;
of course, tire pressure may change for time trials, but I'm pretty certain Tony Martin doesn't use 150+ psi for TT's because he's moved to clinchers.

Not anymore on clinchers, but when he used same tub/disc(mine is HTC team disc used by Patrick Gretsch) same pressures were used, so I'm not crunching numbers out of the cosmos.

Do you think that would work for the rest of us too?

Ciao,

WMW wrote:

DMF wrote:All magazine tests I've seen in recent years put that number way closer to the 75-80psi range (23mm clincher) for a mid-weight rider (65-70kg) most likely lower than most of us are willing to go in fear of puncture and some very scary cornering, at least on 19mm rims.

I've yet to see any test of this except for what Tom Anhalt did. Wheel Energy probably has the lab equipment to do it, but they don't make their results public.

Can you link to the sources or post some of the results?

Sorry, as said it's magazine tests from way back. I don't keep old numbers of magz for more than a few months before they're binned. But in all fairness, this really has been tested multiple times and I'm pretty sure german mag Tour has put the final nail in the coffin on this more than once...,

Maybe I'm imagining it, but when I lower my tires from 100 psi to 95-90 psi they definitely sound different.

I'm 90 kg on a steel bike riding Pro Race 4 Endurance clinchers on the HED C2 rims.

A supple casing allows the tire to more easily deflect and therefore compared to a stiffer casing at the same tire pressure it will ride smoother and when it does deflect it wastes less energy because it's more receptive to being moved the amount that it did.

Higher tire pressure reduces the amount the casing will deflect and therefore reduces movement in the casing and thus reduces that form of casing related energy loss. Then at some variable point the roughness of the surface will dictate when too much pressure is being used - the bike is tossed about, more difficult to control, traction is compromised, and it's a pain to ride. Velodrome tracks don't have rough surfaces so it's a perfect place to capitalize on ultra high/ultra efficient tire pressure. Cyclocross is the opposite - you need that softening of the ride that lower pressure brings otherwise traction, handling, and comfort suffer.

But bottom line, lower air pressure is not lower crr with respect to the tire. Case in point is a tire at 20 psi - very, very sluggish. But in the correct range, lower air pressure could offer an increased efficiency in terms of traction, handling, comfort, but still will never be a winner in the crr arena.

Al Morrisons' tire testing has several tests with those garden hose Tufo's. He does it at various pressures. It aligns with the recent velo news test. That lower pressure might ride nicer but it brings with it higher crr. http://www.biketechreview.com/tires_old ... g_rev9.pdf" onclick="window.open(this.href);return false; go to page 4 at the bottom.

My understanding the wider vs narrow tire is that a wider tire can be run at a slightly reduced pressure than the narrow for the same security of knowing that it is properly supporting the weight of the rider. Think for instance if you had a tubular tire the size of the truck tire that is pumped to 120 psi. When you get on that bike the tire will deflect almost zero compared to sitting on a bike with tires that are 5mm wide at the same pressure. So you have a "safe-to-operate" range for each size of tire. The lower pressure brings with it a bit more comfort. At the lower pressure you generally will see some added crr to some extent compared to a narrower tire at it's slightly higher pressure. So if you pump that wider tire to the same psi as the narrow tire (like they do in those roller tests) then you have less casing deflection on the wider tire and it will win the crr battle......but the ride should be (very) slightly more "rough" than the narrow tire. So it's horses for courses. Are you heavyweight or someone who rides rough roads who needs a tire to not bottom out and be comfortable - go wide. Are you a lighter build and good roads + aero does come into play - then the traditional 21/22 mm casing is still a winner. What you are seeing the wheel folks then doing is selling wide rims to fit well with wide tires so the profiles of each stay fairly even....and there are a lot of heavy people spending cash on go fast bikes these days....

DMF wrote:Sorry, as said it's magazine tests from way back. I don't keep old numbers of magz for more than a few months before they're binned. But in all fairness, this really has been tested multiple times and I'm pretty sure german mag Tour has put the final nail in the coffin on this more than once...,

I keep my ears open and look at every test I'm aware of (lots of tests by Tour) and survey several bicycling forums... and I've never heard of a psi of 75-80 being optimal for road riding. 90-120 yes...

Not trying to market a product in any sense here, but this article provides some good data/perspective on the effect a wide rim and tire pressure have on the contact patch of a tire along with the moment that contact patch creates on a spinning wheel.

http://flocycling.blogspot.com/2011/11/ ... er-is.html

shapeofthings wrote:according to this laboratory, wider is better/faster:

http://www.bikeradar.com/gear/article/bicycle-tires-puncturing-the-myths-29245/

Spot on, tnu has done a couple of studies and came up with similar results ! Not sure why we ride with 23 mm tyres ?

michel2 wrote:
Spot on, tnu has done a couple of studies and came up with similar results ! Not sure why we ride with 23 mm tyres ?

Everything is a tradeoff, the difference in aerodynamics between a 23mm tire and a 25 or 27mm tire on some wheels is quite big:

http://velonews.competitor.com/files/20 ... s-Zipp.png

The drag we're talking about can be pretty significant.

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