I am running stock rubicon tires on my Automatic JK. Currently running 4.10 gears and want to move to 4.56's for better acceleration and more useful in town gears.

Want to figure RPMs at 70 and 80mph in overdrive... is anyone running this setup that can help?

I can't find the final drive ratio to do the math.

Thanks!

 

I think it would be about 10% lower rpm than it is with the 4.10's.



4.10/4.56=0.899=0.9=10%

As this is all you are changing, that would be about right.

I might have a ratio converter soemwhere...but I don't have the stock ratios ans so forth to plug in and check it for you.

What's your overdrive ratio, etc?

Here's one...

Try this:

http://www.4lo.com/4LoCalc.htm

 

Here is the formula I have.

MPH x Gear Ratio x 336 / Tire Diameter = Engine RPM

I.E.

65 x 4.10 x 336 / 35 = 2558 I find it to be within 200 RPM accurate since every vehicle is different and the formula isn't Jeep specific.

That link is pretty handy. I didn't see it until after I posted

 

www.4lo.com



for the money you are spending, you won't notice a big increase. You might want to think about a different gear ratio. There isn't much difference between 4.10 and 4.56.

 

I found the final drive ratio of .69 in OD and 32's.

So: 4.10's at 70 are 2080

4.56's are 2310.

4.88's are 2475 (maybe overkill?)

An extra 230 RPM. Might help with jumping out of OD on hills on the Highway.

Also, I live in rolling hills, so may be some help in 2nd/3rd as well. May go the 33's if anything for the next set of tires...

Any more thoughts?

Thanks!