Quote:
Originally Posted by Old Tele man
A 'wide' tyre spreads the weight across (perpendicular to) the direction of travel.
A 'narrow' type, still has some width, but tends to spread the weight more fore/aft (in the direction of) the direction of travel.
There's a 'cross-over' point where the AREA (width×length) of the tyre's 'contact patch' with the road surface reaches a minimum value: That's good for LRR but bad for braking.
Overall, a physically wide tyre presents a larger AREA of resistance than does a narrow tyre; so aerodynamically, a narrow type is better than a wide tyre of equal diameter.
Considering BOTH aero- and pavement (frictional) losses, the narrower tyre presents a smaller aerodynamic and frictional loss than does an overly wide (ala' drag racing slicks) tyre; but, without moving upward to a larger diameter wheel to regain equality in the total fore/aft contact area, the risk of reduced braking ability becomes a problem.
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I like this. Let's see how it plays out with the data we have.
If you will recall, I took some RRC data for the same tire model for different sizes and derived an equation:
Barry's Tire Tech
So if I take 3 different sizes: P235/75R15. P245/70R15, and P255/65R15, all 105 load index, then what ought to happen is the wider, lower aspect ratio tires ought to have a higher RRC.
And just the opposite happens. The wider, lower aspect ratio sizes are ever so slightly worse: 0.15% and 0.3%. Yes, those are really small numbers.
Maybe that is within the error range, and maybe you could call those the same, but I don't think this supports the contention.
Do I have a theory as to why this is so? Perhaps it is because the width of the tread (THEE largest contributor to RR) is some fraction of the overall width of the tire - and that translates into a tiny bit smaller amount of tread rubber in wider tires.
I wish we had more data than this single study. More data would help refine the regression - and might even change it enough to support the above, but that's the data we've got.