handling with different size wheels/tires

[PT Sportwagon]

I am looking at doing 17s fronts and 18s rear on my wagon. Will it affect the handling? It is stock suspension right now but want to improve it. I can get the tires at a good price. Should I just go with one size for both ends or will it be alright with different sizes? fronts 215/50-17 rears 245/45-18.



Tim

[Henesian]

Best way to think of understeer/neutral/oversteer balance is as a spectrum.

As a general rule, Suspension Grip is different from Tire Grip. When the front suspension is so much stiffer than the rear, the car understeers. The opposite is true with tires. The bigger the tire you have upfront, the more it'll lean the car toward oversteer.

A big enough difference between the sizes of the front tires to the rear tires will make the car understeer or oversteer, according to the spectrum of balance. If the front tires are SOOO small compared to the rears, then it will make the car understeer as a function of tire size difference. You can tune this with tire pressure and suspension, or using tire sizes that are either equal or close.

Also, I wouldn't start to worry about understeer/oversteer balance unless the car was stiff enough.

I'm not going to tell you what you should do. I hate it when people in forums tell you what YOU should do on YOUR car. I think the whole purpose of a forum is to give people enough information to make an educated decision.

[Rod]

I ran a 17/18 corvette combo for a year and the car was built very balanced! when i switched to a 17/17 combo the car over steered and I had to re-tune the suspension for the new set up and now its balanced again, do what you like and remember you're tune will be different than other set ups

[mc84_zz4]

On that Buick you should be able to get 18x8 on all corners, and 245/40/18 as well.
I would even go 18x9, 18x9.5 on the rear with a 275 tire.
If you go 245s all around, it makes it easier to rotate, to avoid rounding off the front tires.

A 215 on the front on a car driven hard is far undersized IMO, you want to get
as much tire under the front-end heavy cars like ours to get them to respond faster.
The 18's will leave you some room to decide to increase your brakes later.
My 2 cents.