im planning on buying some rims and tires for my car and i want to make sure i get the right offset first. i want the widest possible tires without and rubbing issues. im going to get the low profile IRS bolts as well. the main thing i want is rear wheels that are going to fill up the back fender because i cant stand the look of the stock wheels on there. does anyone know what offset and what width tires i should buy?

 

You can fit a set of 315's out back on an 18"x10.5" wheel according to several on this forum. The bolt can come into play, but you are obviously already aware of that.

As for off-set, I hate using that so I prefer back-space. I think the '99~'04 IRS is the same as the '99~'04 SRA. I am and running a 10.5" wheel with a 6~7/8" back-space. Not sure you could squeeze the 11"s I am running, but the 10.5"s are not an issue if back-space is correct.

I have seen MANY Cobras running 10.5"s, but mostly in 17" wheels.

Jazzer

 

I got a solid axle, and running 10.5 x 18's on my rear, on a dished fr500 rim...

 

and yeah, those are 315/30/18's...

 

the widest you can go on a 99 or 01 cobra is a 17/10 if you want to do 17/10.5 you will have to get a new irs bolt which you can order from american muscle or you can run 18/10.5 with the stock irs bolt. i prefer to stick with a 17" wheel because you won't mess up your speedo and imo i like them better than 18's.

 

like i said, go with a dished rim, and you can run a 10.5 just fine...

 

If the overall tire diameter is the same you will not have any speedometer accuracy issues. If the tire is 1/2" smaller/larger, you will have about 5 MPH difference at 70 MPH.

I am with mfj here, I think an 18" wheel is the way to go on Stangs. Hell, I am running 315/30's on 11" out back

Either way, a tuner can correct a speedo issue easily

Jazzer

 

Also depends on whether and how much you are lowered. The 18" wheels are actually less of a problem in clearing the IRS bolt than the 17's. With an 18" wheel the bolt head is actually well inside the wheel diameter when the suspension is loaded. If you size your tires correctly the speedo isn't an issue, even without a tuner to correct it the difference is only like 3% for 315/30R18's which would go on a 10.5" width wheel. At 70mph that's only off 2 mph.