codygo wrote:
RChung wrote:
1. Pneumatic tires turn out to be pretty damn efficient springs. 2. Suppose you have two tires, A and B. You test them at the same pressure on the same surface at the same speed and find that Crr(A) < Crr(B). Here's an important question: is that true for all pressures, surfaces, and speeds or are there some combinations where Crr(A) > Crr(B)? If not, then testing on a smooth roller is a good predictor of the relative ranking on other surfaces. If so, then what are the conditions?
I agree on both counts, and conjecture that Crr relationships are consistent across dynamics unless someone quantifies wave dynamics in road bike carcasses , which do exist in high speed road vehicle tire theory, but I doubt are significant in bicycling speeds and carcass stiffnesses.
But, what I am suggesting is that merely finding the pressure at which a given rider mass and road surface minimizes rolling resistance is far too constrained by tire aerodynamics limiting tire size, and the fairly limited sidewall heights that this constraint imposes, leading to inadequate compliance on many roads. So decoupling these constraints should allow for a more efficient and comfortable system. More importantly, I just wanna have share this conversation :)
I’d also like to hear thoughts on the “real time” testing scheme i mentioned, for fun.
A few thoughts:
The main argument here as I understand it is that the spring/damper system inherent in a pneumatic tire is not ideally calibrated to be a suspension system for a road bike and the frequencies/amplitudes experienced during a road race.
Therefore it is suggested that adding a suspension system that is better tuned would further decrease rolling resistance vs. the state of the art in tire tech and pressure/Crr knowledge today.
However - to obtain this improvement in the tuning of the dampening, you would need:
1) to allow the mass of the entire wheel to move with the suspension system, decreasing it's effectiveness.
2) to add weight, frontal area, complexity and mechanical losses further decreasing it's overall system performance.
3) you would add cost to already absurdly expensive bikes.
Do you have any data showing that the dampening of a tire vs. ideal calibration of the dampening has a large enough negative effect to overcome these deficiencies of the "solution"? My gut tells me that the improvement obtained in Crr from impedence is not nearly high enough to make the "solution" beneficial.
Finally - bottoming out your tire and pinch-flatting is almost never a problem for road-racing tires when pressurized to the proper lowest point on the Crr curve when taking impedence into account, unless you are on VERY bumpy roads. Like cobbles in Paris-Roubaix or something. Or if you hit a massive pothole or something.
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Ed O'Malley
www.VeloVetta.com
Founder of VeloVetta Cycling Shoes
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