Wednesday, April 7, 2010

The latest tire rolling resistance data is out!!

Al Morrison puts all his data together once every year or 2. Al does a big service to the racing community with this.

If you put it into Excel or an other spreadsheet application, you can sort by only new tires, width, clinchers.....

Interesting observations from the data:
  • 25c Pro3 Race are indeed faster than the same tire in 23c, at the same pressure! 
  • Used tires are faster than new. Some get faster than others, depending on how much rubber hey had when new. I always thought that 4000Ss had a bit much rubber on them, and you can see how much they benefit from some miles.
  • Knowing how durable a lot of these tires are, I am still stuck riding Pro3 Race, and 4000Ss, but now have an interest in trying the Bontrager/Trek tires, and maybe the Pro3 Light. 
  • Urethane tubes roll just about as fast as latex without the air loss.
  • There are slower tires that he has not tested, but you can send him some. The fattest one is 27mm. 
If you read his test set up at the top of the document, its done on a smooth 79mm roller, corrected for temperature, and pretty repeatable.  Look at the standard deviations. There is a 12W per wheel difference between his fastest and slowest clinchers at the test speed, 30mph. That's 24W or lost power if you have 2 wheels on the ground. Since rolling resistance is linear with speed, that's 12W of lost power at 15mph. He says real world differences will be 50-100% greater. I am not sure how he got that, as the contact patch is very short and deep in his test set up.

Here is some data he took on a bumpy roller.
More air is almost always faster on smooth pavement, but not when its bumpy.

There has also been some work done by the esteemed Dr. Andrew Coggan correlating Al Morrison's roller data with rolling resistance on the road:

For the test methodology, see this article:

In brief, this is why we believe data taken on rollers is very useful indeed, as it accurately ranks tires in the right order, so you can choose intelligently, not based on marketing hype, or feel.

Anyway, if you want efficient tires, this is very useful data indeed.


  1. Doesn't the power to overcome rolling resistance vary with the square of speed?

  2. No, the power to overcome rolling resistance increases linearly with speed. See Equations 6 & 6a.

  3. ...and here is why we have faith in AFMs Crrr numbers: