How's it going Daryl?

In order for the mph to be 111.6 at 7800 rpm, you'd need a tire with a rolling circumference of 73.7". Don't think anyone is making one that big, unless you switched to 14 inch tires while no one was watching.

The published diameter and circumference from hoosier and others is normally for a unloaded tire. The numbers are actually lower than that. If you graph rpm vs speed from your dyno runs, it will give you a fairly accurate measure of the rolling circumference on your tires. I usually get 62.7-62.9 for 45 series, around 67.2 for 50 series hoosiers. The tires do grow a bit more on track, I calculate mph for the 45 series based on 63" rolling circumference.
If you pull a baseline run in 5th it lets you verify which 5th gear you have in your trans also, there are several different ones.

Did you get the run file from the dyno shop?


Originally posted by 7'sRracing:
Hi Dave, I was amazed with the on track gains that 7's only got me on the top speed end, car would hit a brick wall at 6700 in 5th with 4:88's before, now it pulls to 7400, not sure what that equates to in MPH. But I do know that 7800 in 4th is 111.06, which I bested on a lap by lap basis at my last race by 500 RPM.