Cycling News tire test

[Mikej]

Let’s face it - something like rolling resistance of 2 dozen tires is quite the undertaking- in fact, I, as a test engineer, couldn’t quote a test like this for a reasonable amount of money. I would say in the arena of 200k. So, let’s take this with a grain of salt.

[marciero]

Originally Posted by Mark McM

The causes (model) of the breakpoint phenomenon may not be well understood, but it has been observed in multiple independent tests. However, the Silca pressure calculator does not rely on using a model of this phenomenon, instead it is based on experimental data. Josh Poertner has worked with several pro teams to to empirically determine the effect of tire pressure under different scenarios to maximize performance (speed), and from this experience he has lots of test data. What the Silca pressure calculator actually does is interpolates/extrapolates its pressure recommendation from the empirical test data, So it should probably actually be called the "Silca Pressure Interpolator".

One possibility also is that it really is a smooth phenomenon, with terms from the "impedance" dominating at higher pressures.

Originally Posted by Mark McM

As far as whether the Silca pressure calculator works for MTB, Poertner himself has admitted he isn't an expert on MTB riding/racing, and probably has little MTB tire pressure test data. It's entirely possible that when the parameters stray far away from the test data (mostly gathered under road conditions), the Silca pressure calculator's extrapolations break down and become invalid.

Indeed. Extrapolation is usually a bad idea with any statistical model (They still have to use some math/statistical model to fit the data and do the interpolation or extrapolation). The error bands on estimates/predictions are narrowest near the center of the data and get wider at the ends. Outside the range you dont know what you might get, and you cant simply extrapolate the error band trend.