Still on the wheel size dilemna. I'd like to go 18" on the VR SF-Challenges; I'd prefer to have them both 18x8.5, except they only make them in 18x8.0 and 18x9.0. The Rays Engineering website recommends a staggered 18x8.0 up front and 18x9.0 in the rear, with 225/40 tires up front and 245/40 in the rear (i.e. not the same diameter).

If I used this staggered set up, would it counteract the understeer if I were to use 245/40/18 sized tires on all four corners? Or would I be better off sticking to 18x8 all the way around or 18x9? Or should I just bite the bullet and get the bigger (and heavier) 19s?

 

OK I've just about decided. I'll see if I can get them in 18x8.5, and if not we'll try the 18x8 and 18x9 set up with matching 245/40/18 tires. The recommended setup yields a phat 2" lip in the rear. And if that setup induces unbearable understeer I'll just get a bigger rear sway bar (I currently have the MS front and rear sway bars).

 

There will be more understeer with a narrower tire up front...

...If you use the same size tire on all four but stagger the rims there will also be understeer, though not as bad as with the different size tires.

The reason is that a 245 tire on an 8" rim has a greater slip angle than a 245 on a 9" rim. And while a 225 tire on an 8" rim may have less slip angle than the 245, there is still more rubber (and thus more grip) on the 245 tire.

Now to really blow your mind... Go with 275 on all 4 regardless of 8" or 9" or both options :D

 

i think the staggered rim setup will work just fine. you can tune the steer characteristic of the car in other ways. driving technique can compensate for pretty wide differences in the car.

i can make pretty much any car understeer or oversteer all the way around a course just from driving it differently. so little differences like a rim width difference wont matter much. typically i go for the maximum total traction and find a way to make the car work. in other words, id rather have a faster car than a perfectly balanced car.

james