To Enkei RPF1 or not to??

[CrankyOldMan]

Originally Posted by Jason@SportsCar

The easy button to better performance would just be a tire change with your current wheels. The top 15" street tire in autox for about the last five years has been the 195-50-15 Toyo R1R. It seems small, but it works like a champ on light FWD cars, no other 15" tire has won a ST class Solo championship in years.

This. It's is on my dream list for the coming season. After the helical diff, of course. If you just want stupids amounts of acceleration, smaller diameter is almost as good as lighter. There's some physics involved in it, but I'll skip it since most people start throwing things at me when I start in on it.

I ended up with the Tire Rack house brand 15x7 this past summer, about 13 lbs per wheel. I ran the new BFG Rival in 205/50R15 but had serious acceleration loss compared to my street setup (15x5.5 11 lb Mini Cooper wheels w/205/50R15 DZ101's).

[Lars]

Originally Posted by CrankyOldMan

There's some physics involved in it, but I'll skip it since most people start throwing things at me when I start in on it.

The physics are simple actually!

Two objects of the same weight and "shape/size", the rotational inertia will be lower in the one where the weight is most concentrated close to the rotation center.

So, even if you have two wheels of the same total diameter, same weight, acceleration/braking will be better with the wheels that have a smaller rim, as the weight is closer to the rotation axis (or the biggest part of the weight).

The trade off, I would say, is tire deformation on hard cornering, but in light cars like ours I would say that trade off is not as critical as on big heavy porsches/bmws...