question about tire height for drag racing

[swl987]

Does anybody know generally how many rpms you will drop for every inch in tire height that you go up with 4.10 gears? I have 26" inch drag radials and I am redlining before the traps.thanks

 

[trinity_gt]

Assuming you're in 4th gear (1:1 trans ratio) then you are redlining (6500) at something like 122MPH with a 26" tire (I'm making some assumptions so this is only an approximation...)

If you went to a 27" tire then 122MPH would come in at a hair over 6250RPM.

If you stayed with the 26" tire (e.g. if your class requires it) then a taller gear is in order. A 3.90 would put you just below 6200RPM at 122MPH. FWIW, you'd probably be making better power there too...

 

[Tim2002GT]

I was using a 27" tire on my 11.54 @ 118 pass. At the stripe I was turning just a hair over 6k rpm. I have 4.10's also. You can think of it like this, a 27" tire will make the rpms react like you have 3.90's. A 28" tire will make it react like you have 3.73's. If you have the hp to trap 120+, you will more than likely want the 28" tall tire.

 

[swl987]

The way my car is tuned, I stop making horsepower at 6000rpm. I guess I should go to 28" tall tires.

 

[Stan Weiss]

I have some calculators on my Web Site that will do the Math for you.

Rear Gear Requirements

Calculate Speed (MPH - Km/H) given RPM, Rear Gear Ratio and Trans. Gear Ratio

Calculate RPM given Speed (MPH), Rear Gear Ratio and Trans. Gear Ratio

Calculate Rear Gear Ratio Needed

Automotive Performance Software / Interactive JavaScript Calculators


Stan

 

[Tim2002GT]

^^^ good stuff right there!

I use them all the time!

 

[Stan Weiss]

^^^ good stuff right there!

I use them all the time!

Thanks Tim.

For thoughs on the go. - I have tested these calculators on both an iPad and Android Phone.


Stan