engine rpm to road speed calculation

is there anybody in here that knows how to figure it out on paper?was just currious as to how many rpm's the engine would be turning with 4.27's vs 5.38's @ 55 mph,bottom line is whether or not it would be worth the swap,the jeep with 5.38's has a top comfortable road speed of about 35 mph,sounds like anything over that is killing the engine,but it will go up to 50 mph,and i am too chicken to run it that way for long

 

The second formula should be what you are looking for.

Formulas for MPH RPM gears & tires:

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

rpm = (mph x gear ratio x 336) / tire daimeter

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

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

 

2500 @ 55 mph with 4.27's sound right with a 32 inch tall tire? if soo WHOOO HOOO it would definitely be worth it to me

 

Is top gear on these transmissions 1:1? I have no idea what they stuck in these old transmissions and that would affect it big time.

Gear ratio includes your transmission, so you need to look at your top gear. If your top gear is 1:1 then you'll be at about 2500 RPM. If your top gear is underdriven then you'll rev higher. If your top gear ratio is say 1.25 then you're looking at 3150 RPM.

 

This is coming up with ~45MPH at 2000RPM, ~55MPH at 2465RPM:

http://www.rocky-road.com/calculator.html

 

All transmissions unless they are overdrive models have high gear as 1 to 1. Transmissions with OD for the most part are a product of the late 70's.

 

didnt want to start a war i knew the were 1:1 ratio in high gear,unless they were od in which case they would be higher than 1:to 1

 

maybe i over reacted in last post but i dont want a conflict going on just the facts and i accept any future descrepancies as my fault in posting. just the facts please.
sincerely, all i want is valuable input. not a war on everything else.

 

All of the work has been done for you.
Go to www.grimmjeeper.com and fill in the blanks.
It will give you more information than you desire.

 

I just wasn't sure, so I wanted to ask. It was as much for me knowing as it was for helping you out.