05 LJ Rubicon 6 speed. Was going to go 4.56 with 33s. If I go 4.56 with a 305/75/16 (34") the rpms will match up perfect with stock set up. I am happy with stock set up of 245/75/16 and 4.11, decent power and can do interstate at 70 and approximately 2700 rpm. Of course this doesn't factor in the additional tire weight. Opinions on 4.56 vs 4.88 wanted. Thanks
Last question before I commit to gears.
- Thread starter LD68
- Start date
For everything you just said, I'd go 4.56. But then on my Rubi with 33s, I wish it had 3.73s. You are correct tho, the heavier larger tire will not quite give equal performance to the stock set up. 4.88s might improve acceleration, altho 4.56 might improve gaz mileage.
With my TJR, 4.10s, 6spd, 33s. I get great mileage under 55mph. But it plummets if I exceed 60mph. Good gaz mileage seems to like about 2000rpm.
No doubt, the bigger the tire, ie 35s, 37s, or the smaller the engine, ie SEs, the narrower that window gets for acceptable axle ratio performance.
Last edited:
I am very happy with my 4.88 in my 5 speed.
I plugged your numbers into grimmjeeper and it looks like with the 6 speed, 4.56, and 34" tires you will be just about the same as my setup.
@Rob5589 or @Jerry Bransford can point you in the right direction.
I plugged your numbers into grimmjeeper and it looks like with the 6 speed, 4.56, and 34" tires you will be just about the same as my setup.
@Rob5589 or @Jerry Bransford can point you in the right direction.
Keep in mind that the rpms that were appropriate with the small factory size tires will not be appropriate for bigger tires. Like arm muscles that can lift 100 lbs. need to be bigger to lift 150 lbs. In other words, don't gear to produce the same rpms for 35" tires that worked well for the factory 28" or 30" tires.
And it's not a tire weight thing, it's a tire diameter thing. The additional weight of the tires adds to the unsprung weight of the axles but not significantly to how much more effort it takes to rotate that added weight. It's the larger diameter of the tire that causes the extra work. A bigger tire has a larger radius which creates more leverage against the axle shafts and thus the engine. Its that additional leverage a larger tire has that makes brakes and the engine have to work harder to stop or rotate them.
But to waffle on your actual answer, your 6-speed's ratios are a bit lower than a 5-speed which means the engine turns over slightly higher rpms. That simply means you could go either 4.56 or 4.88 for 35's where 4.88 would definitely be the way to go with the 5-speed. If you spend most of your time at high speeds on the highway and relatively little offroad, 4.56 would be fine. But if your highway time is less and your offroad time is more (or more important) 4.88 would be a great choice. Sorry for the less than black & white answer but...
@Jerry Bransford , that is a very good answer, exactly the kind I was looking for. Most of my previous off roading was in the Mississippi River bottom, big block mud trucks, muddy flat... Now that I live in the middle part of TN and have a Jeep things are different. Lots more uneven terrain here and the Jeep is more like a tractor. I drive interstate about 20 miles to get to most of the trails I run so I don't want to over rev. Other than that it's mostly off road or back roads.
Similar threads
