FLO Gravel Wheel Design Journey Part 3 - Understanding Tire Height & Width

The rolling resistance of cycling tires has been studied extensively. There are great websites dedicated to rolling resistance testing for tires. Tom Anhalt, runs a blog called Blather ‘bout Bikes that describes a rolling resistance testing protocol in great detail if you are interested. Tom helped us with a study we did in 2016 where we combined rolling resistance and the aerodynamic performance of tires to get a full view of their performance for a cyclist.

What hasn’t been studied extensively is how rims affect rolling resistance. It’s known that a wider tire of the same model will typically reduce the rolling resistance of the tire - there is more to this story and we will get into that in a later post. What we wanted to study was how tires behave on different rims and if rolling resistance is linked in a predictable way. For example, if we mounted the same tire on a rims with different internal rim widths, would we be able to predict the tires height and width.

If we could predict the tires measurements on the rim, would we be able to predict the tires rolling resistance as the internal rim width changed. To start the study we collected the following pieces of information for each tire and rim combination.

  1. Tire Brand
  2. Tire Model
  3. Tire Size
  4. Tire Pressure
  5. Internal Rim Width
  6. Tire Width
  7. Tire Height

For each tire and rim combination we measured the height and width for a range of tire pressures. We used our version of the truth to set the tire pressure for each set of measurements taken.

What Did We Find Out About Tire Height and Width?

The results were better than we could have asked for. We found a linear relationship between tire width and internal rim with for the tires we tested. Tire height was minimally affected which was a surprise to us.

Below is a data set taken from the Continental GP 4000 S II in a 23mm size at 90 psi.

 

Continental GP 4000 S II 23mm @ 90 PSI

 

We will have a future blog post that has the data for the full set of tires we tested. This will included road and gravel tires.

Next week we discuss the idea of casing tension and how tire size and rim width affect it.