The Feb, 1999 Road & Track magazine has an article (including test data)
on plus-sizing.
On a BMW 540i, they used the following tire/wheel combos:
Wheel Pirelli Tire Size
16x7.5 P6000 225/55R16
17x8 P7000 235/45R17
18x 8.5 P Zero 235/40R18
19x8.5 (F) P Zero 245/35R19
19x9.5 (R) P Zero 275/30R19
R&T found, like GRM, not much difference in noise or ride comfort with
the Plus sizes. They generally found the best performance (dry skidpad,
wet braking, wet laps, wet slalom) with the Plus One/17inch combo.
Importantly, in the dry slalom the 19 inch/Plus Three combo gave the
best speed.
Anyway, it is an interesting article but suffers the same trouble as GRM
wherein the larger diameter wheels ALSO have wider tread. And the 19
inch combo weighed almost 10 pounds PER WHEEL more than the 16 inch
combo.
Vincent Vizachero
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