I started wondering about the effect of tire wear on rolling resistance over the week-end. Based on nothing at all, I made the assumption in the past that riding new (or at least newer) tires for a race would be faster. However, some of the lower numbers on the BTR RR charts are from used tires and there doesn’t seem to be much rhyme or reason to their placement versus new. Even just looking at the Pro 2 Light SC’s that were tested, the fastest had 40 miles on it, then it was mixed between new and used.
I believe that the larger the contact patch, the lower the RR because deformation is reduced. If that’s the case, it would seem that a tire that is a older should theoretically have lower RR since tire wear would result in a larger patch. I’m out of my element here, though.
While I appreciate the link, it doesn’t add anything for me. It kind of supports my interpretation that an older tire would be better since, due to wear, it effectively has a wider/shorter contact patch than an unused tire. I’m just not sure if I’m missing something.
While I appreciate the link, it doesn’t add anything for me. It kind of supports my interpretation that an older tire would be better since, due to wear, it effectively has a wider/shorter contact patch than an unused tire. I’m just not sure if I’m missing something.
From that article:
The understanding of the above explanation will go a long way towards understanding why wider tires have lower rolling resistance than narrower tires (for a given tire construction and pressure), why higher tire pressures (to a point) will reduce rolling resistance, why higher “thread count” tire casings (i.e. thinner materials) typically exhibit lower rolling resistance, why thinner tire treads will reduce resistance to rolling, why materials used to enhance puncture resistance can increase rolling resistance, and why certain inner tube materials are faster than others.
The 2 highlighted points above are related to what you are asking about…older tires will typically have slightly wider casings (stretch?), along with tread wear making the tread actually thinner. BOTH contribute to “used” tires having lower Crr.
So…in short, your past assumption of new tires being “faster” is, in general, incorrect.
Another consideration for tires is their shape change with wear.
As the tire wears if the tread shape becomes markedly less round and less aerodynamic it will influence the aerodynamics properties of the wheel it is mounted on.
It would be interesting to quantify those losses with the gains in Crr as the tire wears.
If the shape change has a magnitude worth considering then a ‘slightly used tire’ (100 to 200 miles) might be optimum.