I currently have 225/55-15 tires(cooper cobras) and have reached their limit of traction going an 11.62 at 120.84mph...so im looking into a set of drag radials.

First question...what kind do you guys reccomend? ive been looking at mickey t's, and nitto. whats your thoughts


Second question...Ive been looking for a 255 or 245 tire but I would have to go from my current tire height of 25" tall to something around 27". I cant find a 255 tire that is 25-26" tall for a 15" rim. So how bad will a 27" tire effect my gear ratio? Will I notice it on the strip? Is it worth going to a 255 over a 235 that I can get in a 26" height?

 

2 inch tire height makes a huge dif. mine, with 26" tires will redline 4th gear about 100ft before 1/4 mile, but with 28s I go through traps about 1,000rpms before redline,

 

With 275 I ran a 13.4 going through the traps at 7400 and with 325 I went 12.8 at 6900

 

what was the difference in height on those tires?

Thats what I was afraid of, I cant find any 245 or 255 tire with a 25-26" height, guess im gonna have to go with a 235/60 or do I go with a taller tire now and then put in a new gear in over the winter like a 3.25:1.

how would my current 3.00 gear with a 25" tire compare to a 3.25 gear with a 26" tire?

 

On a gear calculator both of those setups (3.27 with a 27" tire or 3.00 with a 25" tire) are within 1MPH of each other at 5000RPM in 3rd gear which is probably the RPM your going through the traps at. So go with a taller wider tire and gear accordingly is my advice. I wouldn't dream of running a 235 on a 500hp turbo car. Go with a 275 if you can. If you have the wheels for it I would do a 275/50r15 M/T DR (26") . Unless your doing all street driving I would go with a nitto cause they last longer but have less traction than the MT's.

 

When running a limited tire size most often a tall tire will equal better performance.
The taller tire like create a larger foot print due to the larger diameter.

 

A good approximation for speed as a function of engine speed, tire height and axle ratio is:

speed = (rpm * tire height)/(axle ratio * gear ratio * 335)

you can put that into a spread sheet (or use an online calculator) and get a good guess at what it will do.

It doesn't take into account slipping from a converter, but it is pretty close for manual transmissions.