Quote:
Originally Posted by AJI
Thanks, interesting reading. To me though, that "last 4 results" graph showing 235 section tires with six pounds more rolling resistance force than the 175 section tires is quite a difference. The effect of tire width on resistance is fairly easy to demonstrate.
Dump the clutch in a car on narrow tires and then try the same car with fatter tires and it's fairly clear which one has the more resistance (/friction). Fatter tires would make for more rolling resistance and aero drag I would think, by all normal rules of physics. Obviously compound matters too, but like-for-like the narrower tires would have less rolling resistance.
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There are 2 things you have confused:
1) Rolling Resistance has nothing to do with grip (friction). You can not measure RR by doing a burnout. RR is caused by internal (to the tire) friction and the net result is heat.
2) Rolling Resistance Force (RRF) is an important property, but when you apply a tire to a car, the load on the tire doesn't depend on its size - unlike the way the tire is tested. So you need to use Rolling Resistance Coefficient(RRC). If you look at the graph marked "Rolling Resistance Coefficient" (It's the one under the one you were referring to), you'll see that the lowest RRC values occur with fairly large tires and the narrow ones (which also happen to be small) are fairly high. That's why I did the analysis: to find out what was occurring and what was the most sigificant - and while it seems intuitively wrong, wider tires seem to be of benefit.
The problem is that "width" can never be isolated by itself. Every time you go "narrower" you also lower the diameter and the load carrying capacity - and these have negative impact on RRC. If you trade width for aspect ratio - which results in the same load carrying capacity and the same diameter, then that may be true.
But what usually happens is that folks have the space to go wider AND go taller - and both of those are beneficial.