Tires and Rims

[johnpr]

the reason the lighter wheel is usually less aerodynamic is because they have more holes in them which allows air in to cause drag, this would be combated by either wheel skirts or flat covers (yep kill the cool effect)

out of curiosity have you seen the list of lrr tires, you may want to check into those.

so yes the first 3 points are accurate generalities with number 4 almost always being true (if i understand though there is a point of diminishing returns)

[abshnasko]

Yea theres a good wikipedia article on LRR tires... I'm assuming that's the list you're talking about. Whichever rims I choose to upgrade to, I'll be sure they can accommodate one of the tires on that list.

yea, part of the reason for my upgrade is looks, admittedly, so I think the wheel skirts are out. front wheel dams I can deal with though.

[aerohead]

Originally Posted by abshnasko

so in conclusion (correct me if im wrong):

1. a larger rim + tire combo CAN be lighter if attention is paid, helping FE
2. larger rim is generally less aerodynamic and takes a wider tire, hurting FE
3. larger rim size means that more of the LRR tires will fit (possible negating the effect of #2?), helping FE
4. larger rim and OD reduces rpm's, helping FE

about a larger rim being less aerodynamic... would some of this be countered some if I installed dams in front of the wheels? Or would it have to be skirts...

(1) Right! If the overall mass is less,and the mass is not concentrated out near the tread,the wheel/tire will be lighter "flywheel". (2) the larger rim need not be less aero if it is more like an optimized disc ( pie-pan ).If the wheel is WIDER,then it will a larger frontal area,crashing into more air as it goes. (3) yes,although it didn't work for me in the case of the Michelin MXV Green-X radials. (4) Only a larger overall circumference of the tire will effect revolutions per mile,and typically,in a clean-sheet design for a high-mpg car,engineers would spec out a slow-turning tire for the LLR.