How to calculate trap RPM

[429244]

Is there a formula for calculation trap rpm for both 1/4 mile and 1/8 mile track when you only know the rear gear ratio, transmission type, and tire diameter? For example, my '06 has a stock TR3650, rear gear is 3.55, and tire diameter is 28" tall. My engine will be at what rpm when I cross the finish line? If I change to a 26" tall tire, what is the change in rpm at the finish line?
Thanks.
Edit: I am looking for a formula but if you know from experience, please let me know.

 

[stkjock]

Yes

Did u try Wallace Racing's site?

wallaceracing.com

http://www.wallaceracing.com/calc-gear-tire-rpm-mph.php

 

[GTAmuscle]

http://www.wallaceracing.com/gear-speed.php?no_redirect=true
If you know your MPH you can interpolate and get a rough guess

 

[lindertw]

rpm = (mph x final gear ratio x 336)/tire diameter

If you're crossing the stripe in 3rd gear with those 3.55's then it would be:

rpm = (mph x final gear ratio x 1.32 x 336)/tire diameter

 

[kdanner]

You can get somewhat in the ballpark. 2 things you won't know:

1. If it is an auto trans without a locking converter, you won't know how to account for converter slip.
2. You won't know what your tire diameter is under load and at speed.

 

[429244]

Thanks for the info & link. There is a lot on that site.

 

[hotrod_renegade]

Here is another calculator I've found that works really well. Allows you to also put in your trans. gear ratios and compare two different setups.

http://www.teammfactory.com/gearcalculator.php?kmh=0&tirewidth=275&tireprofile=50&wheelsize=15&tirediameter1=25.83&maxrpm1=6600&finaldrive1=3.73&gearratio1=2.87&gearratio2=1.89&gearratio3=1.28&gearratio4=1.00&gearratio5=0.82&gearratio6=&trannytype=&tirewidth2=275&tireprofile2=50&wheelsize2=15&tirediameter2=25.83&maxrpm2=6600&finaldrive2=3.73&gearratioa=2.87&gearratiob=1.89&gearratioc=1.28&gearratiod=1.00&gearratioe=0.64&gearratiof=&trannytype=&tranny=Calculate+Transmission+1+%26+2

 

[blk12wls]

1/2 tire radius / 168 x rpm / gear = mph

gear ratio is trans gear(1.23) x rear end gear(3.55)= 4.366

my stock V6 is 13.8/168x5400/4.366=101.59mph dead on.