wayoflife

Hey guys, if you haven't already heard the great news, Superior Axle & Gear has just finished installing and testing their new 4.88's and 5.13 gears. Click on the link below for more details:

The Very 1st Jeep JK Wrangler 4.88 & 5.13 Gear Installation & Test

Last night, I got to see the installation of the front gears and test them out as well and I'm happy to say that the word is that they will be shipping out in about a week!!

AZCA jeeper

That's sweet!! Thanks Eddie.
Now I don't know very much about mechanics, but what exactly is the ratio?

All I know is 4:88 is better than 4:1, but why?
Am I even talking about the same thing as the main topic?

Superior Axle

No question is a stupid question.

The reason for gearing change is because when you change your tire size (smaller or bigger) from the stock (the ones it came with from the factory) tire, it will indirectly change your drive ratio. Smaller tires will make your RPM higher and larger tires will make your rpm's lower. In order to get the vehicle, in this case your JK, back to a stock performing level we will need to change the differential gearing based on a formula. we do that, by knowing what the rpm we want our rig to run at a given MPH.

example: 65mph X 4.88 X336 = 106579.2 / 35" tire = 3045RPM in 1:1 tranny gear. 3045 X .75 (for your 25% reduction in over drive) = 2283 rpms at 65 MPH. That is perfect. That gets you a couple more rpm's over stock to help keep that additional rolling mass moving and it will give you your best possible performance.

Formula: RPM = MPH X Gear Ratio X 336(given) / tire diameter(inches)

Good Luck!!
Mike

AZCA jeeper

Thank all. You guys are always the people to ask.

So, if I understood this right, If you put larger tires on you will have to rev higher rpm's than you normaly would if it were stock, to get to a certain speed. Putting smaller gears in restores the stock rpm. And if you put even smaller gears, say 5:1, then that brings it down even lower, making it a slower and better crawler. Right?

AZCA jeeper

This may sound weird but it's all I can compare this to.
The re-gearing is like changing gears on a bike. The smaller the gear your in, the slower it goes. I'm even laughing about the comparison

ThinkMud

I can't wait to order some 4.88's!!! I plan on running 35's one day, but will probably keep my 33's for a while (unless someone buys them, hint hint...) but I want the gears before the tires. Awesome right up too!

mbrown2

Wayoflife...I would be interested in what the MPG observed was on the 4.88 combo w/35's before and after the lift....I am assuming they had 4.10's prior to the swap.