OK...

I have a set of 15 inch wheels from an '88 Plymouth Lazer. What's the biggest tires I can fit into the rear... and the front? They don't have to be the same size.

K

depends on the width of the wheels. Most 15 inch rims are between 6 and 7 in. wide. Mine are 15x6 and I have 215HR60 tires on.

I run 245/60-15's on my 7" rims (rear of formula).

If you change the rolling diameter of your tires, you also have to regear the speedo. Not only does the speedo use the sender, but the ECM does to.

In other words, don't just stuff a set of tires on a Fiero. You could cause your self some pretty flaky performance problems.

i have 225/50/zr15's in the back(88gt)..in my state(pennsylvania) if your tires stick out past the fenders it's illegal, they barely fit!...plus i have to run with a lower tire pressure(less mpg's) because the tire is wider then reccomended and will go bald in the middle real fast(happened to last set)...my speedo might be off a little but i have had no problems otherwords.

One would have to really go overboard before the rolling diameter would have much effect. The difference in diameter between the 245's and the stock 215's is well over an inch, and it still only results in an error of 5.63%. That would translate to less than 3.5 mph at 60.

Mike

In Pa. the tread can't stick out past the fender! my tire walls stick out past the fender but not the tread

There is a formula to figure out different tire hights according to the width series of tire. I will have to dig it out and post it. For example, on my 71 datsun 510 I run AVS Intermediate 275-35-ZR17's on the rear and they aren't much different than the stock tires that came with it as far as hight goes (the stock ones were 13" rims) As far as wear on the rear inside set your camber to "0". That will help.

i would like to know about that equation if you could dig it out, my friend wants to upgrade his VW with a set of 17's but he's worried about the rolling dia. messing up his speedo(he's the catious type)...thanks.

I found this page very useful for my tire buying decisions:

http://www.miata.net/garage/tirecalc.html

It has some nice graphical calculators that may be just what you are looking for.

Mike