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gears again

4.56 or 4.88
 
cherowagon said:
anybody have experience with the 5spd? the new rubicons come with 4.10's and 31's. guys are jumping to 33's no problem.
Click to expand...
Just because they don't have any problems doesn't mean its the best option.
 
My '88 MJ 5-speed is set up with 3.73s and 31x10.50s. The RPMs to MPH is exactly the same as a stock XJ automatic, with 3.54 gears. I put the 3.73s in because I had them, but the gears were bought with the intention of using them on the XJ with 30" tires.

So to get any gearing advantage over stock (automatic) gearing with 31" tires, you need at least 4.10 gears. With 33" tires, you need at least 4.56 gears, and 4.88s would be better unless you spend most of your time on the highway.
 
xjj33p3r said:
4.56 if you want stock power and similar gas mileage to stock. Top speed will be limited with 4.88's
Click to expand...

Yup, your top speed will be limited to about 75~80mph. I've had 4.88's in my XJ with the 33's since June and I love the setup. I get about 15~16mpg, but then again I've always been getting 15~16 mpg (even with 31's and 4.11's). In any case, if you can go to 4.88's do it or you'll be kicking yourself later (the limitation comes from your rear axle, and on that note: if you have a D35, consider upgrading to 8.25 or D44)
 
Eagle said:
My '88 MJ 5-speed is set up with 3.73s and 31x10.50s. The RPMs to MPH is exactly the same as a stock XJ automatic, with 3.54 gears. I put the 3.73s in because I had them, but the gears were bought with the intention of using them on the XJ with 30" tires.

So to get any gearing advantage over stock (automatic) gearing with 31" tires, you need at least 4.10 gears. With 33" tires, you need at least 4.56 gears, and 4.88s would be better unless you spend most of your time on the highway.
Click to expand...

even with the 5spd?
 
cherowagon said:
linky no worky
Click to expand...
should be: http://www.intercotire.com/html/table.htm
Couple things that those tables do not take into account though:
With stock gearing you're ussually lighter and lower to the ground. By the time you're regearing, you've lifted the rig and have more front air resistance then you used to. Your tires are also a factor as they're harder to move then the smaller ones. You've also added extra weight to the rig.
So just looking at those items you should realize that the straight out calculation based on the increase in the tire size should not be used to get the gears. It is a good starting point, but taking everything in consideration you need to go deeper then the table says (oh, and did I mention that stock XJ with manual transmissions were undergeared?)
 
yeah, i still think you should go w/4.56's it is a happy medium good offroad perfomance,good on road manners. you might want to drive a little bit and note what your rpm's are at. and take a look at that again. see if that helps or gives you a little contrast. maybe do some more searches for gear ratio calculators. there are a lot of other gear manufacture out there that have info ,hope that helps
 
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