Can anyone point me to a web site where I can calculate my engine RPMs with specific gearing and tire sizes? My situation is this: AMC 360, T-18A, Dana 20 t-case, 5:13 gears, 35" rubber. I am currently running 4:10 gears and want to find out what my new safe (without redlining) top speed is going to be limited to with the 5:13's.

Top of this page has a few:
http://www.4lo.com/

RPM= MPH x Tranny ratio x T-case Ratio x Axle ratio x 336 divide this by tire diameter to get MPH..

Originally posted by cpl:
<STRONG>Can anyone point me to a web site where I can calculate my engine RPMs with specific gearing and tire sizes? My situation is this: AMC 360, T-18A, Dana 20 t-case, 5:13 gears, 35" rubber. I am currently running 4:10 gears and want to find out what my new safe (without redlining) top speed is going to be limited to with the 5:13's.</STRONG>

what's your rig? Jtruck, WT chero?

(mphx336xgears)/tire size"=RPMs

e.g., i can hit 2700 rpm with 235/75R15 and 3.31 gears with a 3 spd auto

(70x336x3.31)/28.5=2731

remember that if you are using radials, most companies say 35", but mean 34".

If it is a trail Jeep, this sounds great. If it's a street Jeep, that's going to be awfully low.

Thanks for the replies on this subject. The info was exactly what I needed to get a rough estimate of my RPMs at speed. This will also allow me to see how larger tires will affect my set up as well. Yes, this is stricly a trail jeep, and it will probably be seeing some 37" tires soon. I run Dana 44's front and rear, so these should be able to handle the twisting.

I sent you an email. Try it you'll like it.