In the on-going argument about wide tire/narrow tire I found this interesting- partially because it supports my opinion on the matter
Basically, I feel I have always been faster on a slightly wider (21mm at an absolute minimum for tubulars, 23mm for clinchers) tire at a moderate pressure not much more than 130 psi on a tubular and 120 psi for a clincher.
This debate always inflames controversy. This little tidbit is up on cyclingnews.com and I found it insightful:
Mirrors our discussion of the other day . . . my suggestion of 19/22 was a guess though. But, the old adage of it is better to be lucky than good is applicable here.
One thing I just noted with a set of Vitto Chrono cs-20’s is that they measure just over 22mm all around the tire. The S3 lites are a precise 22mm (as advertised) at all points.
I wonder how accurate those vendor’s width numbers are?
Can others check on their tires and let us know how they actually measure?
Since Tom posted those numbers as what he felt “moderate” was, the question was addressed to Tom.
I asked because, for example, Pro Race or Grand Prix 3000 (two popular racing clinchers) tires list maximum air pressures as 120psi, yet for some reason Tom seems to feel that is a “moderate” pressure.
There are hell of a lot of variables in this and tyre selection I feel is made up of so many more factors than just rolling resistance. For a lot of you longer course guys reliability has to be primary. I’m about to start running Michelin Pro Race 2’s having used 1’s for 3 years now with only one puncture incident (and I’m a heavy hard rider). Hopefully the new 2’s have the same level of trust as I’m about to step up in distance soon.
The technology Conti are pushing here though makes sounds sense and I find of great interest. All we need now is a solid number of test subjects to prove it over time…
I asked because, for example, Pro Race or Grand Prix 3000 (two popular racing clinchers) tires list maximum air pressures as 120psi, yet for some reason Tom seems to feel that is a “moderate” pressure.
I am a little confused as well given that the 120 psi on the clincher is close to if not 100% of the maximum rating. This compares to 130 psi for the tubular which is 76% of a tire rated to 170 psi yet Tom considers both to be moderate pressures. Obviously comparing tubulars to clinchers is like apples to oranges, just wondering why the relative pressures are so different?
Tire width is even more of a conundrum in that there seems to be quite a bit of variation between brands, i.e one company’s 23mm is wider than another’s.
I’m a mechanical engineer and actually looking at the formulae for a polyurethane tire’s rolling characteristics for a job I’m working on.
Here is a simplified version of the formula given for rolling resistance (in units of force, ie. pounds, newtons)
R=.51h((W^4*(b-a))/(ESb^2))^(1/3)
h=a material constant
w= wheel load
b and a = outer and inner radii, respectively
E= a material constant
S= tire width
this is for a flat polyurethane tire on a solid steel hub.
the tire width that would pertain to a bike tire would be a function of the spec’d width vs. pressure and rider weight Note that the width is in the denominator of the equation, if the width goes up, the rolling resistance goes down. This seems counter intuitive…by having a wider tire you are decreasing the bearing stress on the contact surface, and you are deforming the tire less (less energy loss) as driving and cornering forces are applied.
The OD of the tire is in the denominator, which would suggest that larger wheels roll more efficiently than smaller ones.
I sort of undertand the rolling resistance piece but doesn’t running a wider tire up mess up your tire - wheel interface? I always heard a fat front tire interferes with laminar flow of deep aero wheels.
I think it is all a conspiracy to keep us guessing and buying new gear…
I think the only way to really test that is in a wind tunnel, which I’m sure manufacturers have done. I’m pretty sure Zipp did this and that was one of their selling points on their 21mm tires.
