Hey guys,

I'm in the neighborhood for new tires in the next few weeks when the taxes come in and I've got a couple questions.

First off, I've got 15 inch rims and can't afford tires AND rims...so I'm going with tires.

The great book of plus-sizing says I can run a 215/65/15 (stock size) or a 235/60/15 (optional).

Because of my swap from the 305 to a built 350, I want to stay in a "H" rating or higher but the only tires in my size that I like are either the BFGoodrich Radial T/A or the Firestone Firehawk Indy 500 but they are only "S" rated.

I really like the look of either the Goodyear Eagle Response Edge or the new Goodyear Eagle GT. Only problem is, they don't come in my size. The closest I can get is 205/65/15.

My stock tire is 26" diameter. The closest I can get is 25.5".

How will my performance, change, if at all by going with a tire that is 1/2 inch shorter. Also, how will it affect my speedometer (mechanical speedometer) reading? Or is it close enough that I really won't see a difference? If I am doing the math right, I believe it should read "faster" than I am actually going because the tires are just a little shorter.

Any and all help on this subject will be greatly appreciated!

 

235/60-15 would net 26.102" diameter. Changing a half inch in diameter is the equivalent of 16 revolutions per mile difference, or about 40 RPM, or a 0.07 gear ratio change, or about 1.9%.

 

205/65s?? I just threw up in the back of my mouth a little. Bleh!

Keep shopping.

Stock 15" wheels look great with 235/60R-15s mounted. Keep looking for something in that size.

Remember speed ratings are for SUSTAINED speeds, not quick blasts over their speed rating. How often are you going to drive 130 MPH for any length of time?

 

That's a point well taken. I wound up with BFGoodrich Radial T/A with an "S" rating in 235/60/15. I have to admit, they look really good.

The reason I was looking for an "H" or better rating was because my car club is going to the Bonneville Salt Flats this year by wendover Nevada and running their cars. I know be able to hit 130mph with my new motor, if not 140 (hopefully)...but will "S" rated tires, rated for 112mph, last at that speed for the length of the course? 3 miles is the norm.