Originally Posted by
Brian Ratliff
The fact is, I don't know. My point is, neither does anyone else. These studies are merely thin cross sections comparing tires in gross ways under artificial conditions.
I don't know how you can say an actual rider riding and actual bike on an actual road is an artificial condition.
[QUOTE=Brian Ratliff;12172207]I have seen nothing that attempts to quantify a physical property to rolling resistance. I haven't seen anything testing the sensitivity of these results to the variables such as rider weight and air pressure. You would think that someone would've at least taken some pictures measuring the tire deformation at the contact patch under different conditions to go with their gross power measurements.
Then I suggest you read some more. Much of what you're looking for is covered in Bicycling Science.
Originally Posted by
Brian Ratliff
For example, many people here subscribe to the notion that increasing air pressure in your tires past, say, 110psi, on real roads (irregular surfaces), doesn't necessarily decrease rolling resistance. Yet it's pretty easy to see on rollers that increasing the air pressure will always decrease resistance; I believe some of the testing results from Jobst Brandt indicates the same. Who is correct here? Or does it depend on the tire brand, road surface, tire pressure, or all of the above and to what extent? What does that mean when put in terms of Mr. Coggan's testing?
I can't help what some people believe. If they bothered to spend any time on the subject they would realize that there is not only one mechanism leading to rolling resistance, and the balance between the mechanisms depends tire, pressure, and normal force. So there is no arbitrary point where rolling resistance starts to increase with pressure but that point depends on the factors just mentioned.
Originally Posted by
Brian Ratliff
Obviously different tires have different rolling resistance. But until this fact is linked to physical properties of the tires in question, then all the ad hoc testing by all the garage scientists in the world won't aid a racer trying to find the best tire for his needs.
Denigrating the authors of peer reviewed articles does little to boost your credibility. The mechanisms and properties controlling rolling resistance are well known and published. Not that it matters. I can weigh something without understand the science of relativity and quantum mechanics which describe the mechanisms by which matter acquires mass. Since you admit tires have different rolling resistance I don't see why you have such trouble admitting that it can be measured.
Coggan has shown that if an individual cares enough, she can measure rolling resistance for tires on a particular road. (Again, I don't see why it's necessary to understand the mechanism to measure the property. I certainly don't understand all there is to know about molecular, atomic and subatomic physics, but I can still use a thermometer to measure the temperature of something.) Coggan has also shown that this measured rolling resistance can be used in a model to predict performance with high accuracy. So if our rider is motivated enough, she can test whatever tires interest her and measure the real-world behavior (both aero and rolling resistance) to optimize performance. However, if she lacks the time or motivation, Coggan and Morrison show that roller data can be transformed to a particular road by taking one data point and then using the scale factor for all other tires tested on rollers.