I'm wondering if I'm going to have to reflash the computer going from 255/50-17's on the street to 275/50-15 DR's at the track. The 255's are about 27" tall, the 275's are about 26" tall. Is 1/2" difference in radius going to cause misery?

Edit: sorry, this should have been in GT tech.

 

Lets look at the difference in RPM between the 2 using a 3.27 Gear ratio..

We will drive at 80MPH in 4th gear.

26" radius= 3380RPM

27" Radius=3255RPM

A difference of 125RPM difference.. Not more than 1-2MPH.. I'd say your good to go..

Just so you know, I would love to have an 86GT!! Boy thats awsome man.. All the different crate motors you can put in it! LOL!! You lucky man!!

Isnt this beautiful!!

http://bradbarnett.net/mustangs/timeline/7...THatchback2.jpg

 

A reflash will adjust for speedo correction, I don't know if you can adjust for the stagerred setup so you don't trip ABS.
I don't think the size difference would cause ABS to try to keep the front's spinning the same speed as the back. I doubt it would be that sensitive since I believe a few members here switch for the strip with no problems.
Let us know how it goes at track btw

 

I've been running taller tires in the back for months with no ABS issues... I had 28.5 inch tires in the back and the stock 27 inch tires in the front... No problems at all... I've now got 27.8 inch on the back..

 

I had that same exact car,same color and everything back then! Great car....actually saw it this summer....still running strong!

 

The ABS will be delayed somewhat if you were to need it. The small difference in size may not make it something totally obvious, but it's something to note for those who are running a slightly bigger OD tire in the rear. I bet you won't really notice unless you were at something extreme like at 30"+.