[QUOTE=Rick]
Not that I am doubting you, but what car came from the factory with 16" fronts, and 17" rears? I’ve never heard of this. Different aspect ratio tires F/R yes, different rim sizes, no.
Also better lap times with 15"? The reason for +1 and +2 was to decrease sidewall height, to improve handling. This was before the marketing guys got ahold of the idea. Now you are telling me the reverse is true?
[/QUOTE]
The car is a Lotus Elise with the standard wheels. The optional forged wheels are the same staggered diameters, but wider.
The +1 and +2 options do make the sidewalls stiffer but sidewall compliance is not necessarily a bad thing if properly accounted for during the suspension tuning. Look at the height of the sidewall on an F1 car sometime. The overall reduction in unsprung mass from a lighter wheel/tire combo allows a lower spring and damper rate to be used to keep the tire in full contact with the pavement meaning that the car will be less unsettled by bumps and etc. Also, the lighter wheels take much less power to accelerate. The car is measurably quicker on the lightest wheels.
Part of the problem is that most of the reasonably affordable large diameter wheels are rediculously heavy. Even replacing the relatively light wheels that came stock on the Elise with the forged wheels saves seven pounds a wheel.