Terry Apple

I'm changing my differential ratio I lost a lot of power when I went from the stock 245/75R16 tires and 4:10 gears and Eaton electric lockers to 35X12.50X17 tires. I want to change to either 4:56 or 4:88 any suggestion on which would be better .

SWHouston

If power is what you're really interested in, then it's the 4.88's.
Of course that's two of um, you are 4WD right ?
I also presume you're going to do OTR/Rock/Towing, or what ?
IOW, what's your objective ?

Terry Apple

Towing and climbing I just lost all my low end torque climbing hills and I have a 40 foot trailer and I drop all the way from 80 to 45 on a 12% grade since I went from the factory I think about 29" to 35 inch tires. I came stock with the 4:10 gears.

SWHouston

Cool !

Then 4.88 is the way to go on both ends (4X4 right ?)
You do understand that your highway speeds are going to drive your RPM way up to stay up with traffic, and more use of Fuel. But, those %'s on grades are going to disappear.

You know what Transfer Case you have ?

Terry Apple

Yes it's a 4X4. It is a NP241C. Yes, I have a 42 gallon tank and even with what I have now I only get about 6 miles to the gallon. I don't do a lot of highway driving. I just want more low end I climb a lot off road. I have Eaton electic lockers and I run out of power way before it slips. I also may go to 37's after these tires wear out but I just got them last month. I've got 120,000 miles on my 350 TBI but when the engine goes I'll go with a 454 Cid.

73shark

You do realize that when you went to the taller tire, you reduced your numerical axle ratio by 20%. That would explain why you have reduced towing power.

SWHouston

Tried to find what ratio your XFer case is, but couldn't. Mine is 2.72 reduction. If yours is the same, a 4.88 dif would give you about a 13.3 drive. That plus whatever the 1st gear ratio is, may get you over some medium sized rocks.
Most of the Rubies generally try to total about 50:1 in low gear, and they do well over some pretty rough surfaces.

One thing for sure is, you won't even know you got a trailer hooked up to your ride.

Also, I see some stuff hanging down under your ride (just from the picture), you might try to clean that up a bit if you're going to be running over rock.
Then, keep in mind those original tires were about 30.5" tall, and the 35's are going to put your Center of Gravity a lot higher.
Be careful, remember your ride weighs about 6000 lbs.

Terry Apple

It says it's a 2.72 reduction.

SWHouston

That's good, and Uoops, I listed my XFer case incorrectly. Mine is 2.72.

What about your Rims, did you get new ones that fit the 12.5 width of those 35" ?

Terry Apple

Yes I got the Black Rhino Warlords. 17X10 with a -12 offset.