Is there any calculators available to show what size tire would be best to use for a given combination?

I have a M6 CC306 car with 4.10's and a rev limiter set at 7000. With the 275/40/17 Nittos I was a good ways into 4th gear when i crossed the stripe. But yesterday at M7, I used some 28x10.5x15 ET Drags and I just barely got into 4th gear. Actually on one run I crossed the line in 3rd hitting the rev limiter.

I plan on selling the Prostars with the ET DRags for something different and don't know what size tires would be best.

 

Those Nittos are tiny. They're only 25.66" tall. The MT's are 28.1" tall. Using the taller tires would be like changing those 4.10 gears to 3.73's.

Drag racing never needs to use OD. You should be crossing the finish line at the peak HP in whatever gear is 1:1.

First of all you should decide on the tallest tire that will fit under the fenders. After that you choose the gear ratio that will work best with that tire size so that the engine peaks out at the finish line. The downside is that the 10 bolt has very few gear ratio choices. 3.73, 4.10/4.11 and 4.56 are about the only good performance ratios available.

Gear ratio choice also depends on the altitude of the race track. My current combination uses 4.56 gears and I cross the finish line just as the shift light comes on. When I go to a track at a lower elevation I need a diff with 4.33 gears or my shift light comes on around the 1000' mark.

 

Stephen, I have the 6 speed in my car so my 1:1 gear is 4th gear. I have the 4.10 gears in a Moser 12 bolt right now, but I don't want to change them because this is more of a street car with occasional track use. So I am looking to find a tire size that will maximize traction on the launch but not kill the gear ratio so much as to prevent me from getting into 4th gear. Both the tracks that I run on are around 700' elevation.

Thanks for the information.

 

Sounds like you need a 26" tire. One thing to remember is that with a et drag or et street you will get some tire growth on the top end that you don't experience with a radial tires. This also kills your final drive ratio. You may like the et street as they don't seem to grow as much as a drag tire. Or a 275/50/15 bfg drag radial.

 

Agreed. A 26" tall slick should work best. You'll have to do some measurements to see what the best width would be. ET Street and ET Drag tires have different sidewall measurements. The ET Street is measured across the sidewall section because it's a DOT tire. The ET Drag is measured across the tread because it's a slick.

What rpm do you shift at?

 

My shift light is set at 6800.

Thanks.

 

Ok so with the 25.66" nittos and being a good ways into 4th gear and you shift at 6800. Going to a 26" slick is going to mean you're not going to be into 4th gear as much since the tire is a little bit taller. The even taller 28" slick showed you that already.

Using the 26" slicks and possibly lowering your shift point to 6600 rpm would let you use more of 4th gear in that last 1/8 mile high gear pull.

If tire size, gearing and shift points are all matched together, you should be in high gear 1:1 at or around the 1/8 mile mark and the last 1/8 mile is just a high gear, brute HP pull.

My MPH only increases about 22 mph from the 1/8 mile to the 1/4. Even top fuel dragsters only increase about 50-60 mph from the 1/8 mile to the 1/4. Everything happens in that first 1/8 mile. After that you're just going along for the ride.

 

That makes alot of sense Stephen, thanks! Right now I am gaining between 22-24 MPH in the last 1/8 even Saturday with the 28" slicks I was running 87-88 in the 1/8 and 111 in the 1/4. On a couple of my runs the 60' were in the low 1.8x, the 1/8's were 8.06,8.08,8.09 and the 1/4's were 12.484, 12.49x, 12.52.