Topic: Gearing

[No Luck]

Hello all, new to this board. Here is the deal, I got a 97 tj with a 2.5 and a 5spd awhile back for a steal 1500 it was suppose to have a bad motor but just had a blown water pump. Anyways I picked up another 2.5 that had been in a project for years and was never finished, got everything for 400, put in a new clutch when I replaced the motor. $2100 jeep

I,m going to put 31-10.50s on it and plan on going with 4.56 or 4.88. My question is will the 4.88 be to low?

[sharpxmen]

Hello all, new to this board. Here is the deal, I got a 97 tj with a 2.5 and a 5spd awhile back for a steal 1500 it was suppose to have a bad motor but just had a blown water pump. Anyways I picked up another 2.5 that had been in a project for years and was never finished, got everything for 400, put in a new clutch when I replaced the motor. $2100 jeep

I,m going to put 31-10.50s on it and plan on going with 4.56 or 4.88. My question is will the 4.88 be to low?

4.88 will be fine, don't bother with 4.56. Pretty much everyone here will tell you the same thing

[Torch_Ind]

4.88's for 31's?

[97 TJ - I dont wave]

4.88's will be way too low with 31's.
I have the 2.5l with 35's and I run 4.88's.
With 31's you are better off with 4.11's.
If you are going to go with 33's or 35's in a year or so then go with 4.88's.

[sharpxmen]

4.88's for 31's?

4.88 and 33s would be like stock, same for 4.56 and 31s

there's no harm in going to 4.88s and 31'' tires, he'll just be able to use the 5th more, aside of that have a better overall ratio - difference in rpm is really not an issue once you hit 5th, you're limited by the lack of power to hit high rpm on the highway anyway, unless you see a different reason i don't think he should go to 4.56 if he's going to spend the money.

4.88's will be way too low with 31's.
I have the 2.5l with 35's and I run 4.88's.
With 31's you are better off with 4.11's.
If you are going to go with 33's or 35's in a year or so then go with 4.88's.

what's your rpm in 5th at top speed? and what's the top speed you reach in 5th?

[sharpxmen]

4.88 and 31'' tires / 4.56 and 31'' tires
(i rounded them to the closest 50 rpm to make it easier to compare)

rpm at speed in 4th
55mph - 2900 rpm / 2700 rpm
60mph - 3200 rpm / 2950 rpm
65mph - 3450 rpm / 3200 rpm
70mph - 3700 rpm / 3450 rpm
75mph - 4000 rpm / 3700 rpm
80mph - 4250 rpm / 3950 rpm

rpm at speed in 5th
55mph - 2450 rpm / 2300 rpm
60mph - 2700 rpm / 2500 rpm
65mph - 2900 rpm / 2750 rpm
70mph - 3150 rpm / 2950 rpm
75mph - 3400 rpm / 3150 rpm
80mph - 3600 rpm / 3350 rpm


assuming you get to 80mph, neither 4250 rpm in 4th nor 3600 rpm in 5th seems way too high to me, so i'm not sure why would you think 4.88 and 31 is way too low - it's between 200 and 300 rpm difference in 4th or 5th between 4.56 and 4.88, really no major difference at all.

EDIT: and i forgot to mention better crawl ratio in 4low

[No Luck]

4.88's will be way too low with 31's.
I have the 2.5l with 35's and I run 4.88's.
With 31's you are better off with 4.11's.
If you are going to go with 33's or 35's in a year or so then go with 4.88's.

It has 4.10s with 235/75-15s which are 28.5 and it sucks bad, it works best in fourth gear fifth not so much, to get it back to stock with those tires it would take 4.56s I'm really leaning toward the 4.88s with 31s just not sure.

[sharpxmen]

It has 4.10s with 235/75-15s which are 28.5 and it sucks bad, it works best in fourth gear fifth not so much, to get it back to stock with those tires it would take 4.56s I'm really leaning toward the 4.88s with 31s just not sure.

in 5th
4.10 and 235/75x15 / 4.56 and 31 / 4.88 and 31
55mph - 2250 rpm / 2300 rpm / 2450 rpm
60mph - 2450 rpm / 2500 rpm / 2700 rpm
65mph - 2650 rpm / 2750 rpm / 2900 rpm
70mph - 2850 rpm / 2950 rpm / 3150 rpm
75mph - 3050 rpm / 3150 rpm / 3400 rpm

like i said, you'll just get to use 5th more, not much difference with what you had before if you go 4.56 and 31 (100 rpm, so almost the same) and you already got that experience

[No Luck]

in 5th
4.10 and 235/75x15 / 4.56 and 31 / 4.88 and 31
55mph - 2250 rpm / 2300 rpm / 2450 rpm
60mph - 2450 rpm / 2500 rpm / 2700 rpm
65mph - 2650 rpm / 2750 rpm / 2900 rpm
70mph - 2850 rpm / 2950 rpm / 3150 rpm
75mph - 3050 rpm / 3150 rpm / 3400 rpm

like i said, you'll just get to use 5th more, not much difference with what you had before if you go 4.56 and 31 (100 rpm, so almost the same) and you already got that experience

That was my thought as well, 4.88s it is thanks for the push in the right direction 

[No Luck]

Well installed my RC 2.5 lift last week, and got my 31s on yesterday... all I can say is with the factory 4.10s I have all but lost 5th gear on anything but flat ground.

ordered up the 4.88s for a hp 30 and 8.8 plus all the brackets to install it.

This is my first four banger, my other two have the 4.0 I do like driving it though kind of fun.

[Jeffy]

Well installed my RC 2.5 lift last week, and got my 31s on yesterday... all I can say is with the factory 4.10s I have all but lost 5th gear on anything but flat ground.

ordered up the 4.88s for a hp 30 and 8.8 plus all the brackets to install it.

This is my first four banger, my other two have the 4.0 I do like driving it though kind of fun.

Make sure you recalibrate your speedometer.

[RT]

4.88's with 31's?.....oh god that would suck that's waaay to low for a tire that small

[FourbangerYJ]

4.88's with 31's?.....oh god that would suck that's waaay to low for a tire that small

3150 RPM at 70 MPH. That is about spot on IMO.
With 205-75-15 and 4.10's it's 3050 RPM at 70MPH. (came from Toledo this way)

See for yourself. http://www.grimmjeeper.com/gears.html

[sharpxmen]

4.88's with 31's?.....oh god that would suck that's waaay to low for a tire that small

what is your statement based on?

[jfrabat]

4.88's with 31's?.....oh god that would suck that's waaay to low for a tire that small

Why?  Have you ran like this?  I did, and it was plain AWESOME!  I would cruise in 5th at 70mph just a hair north of 3K RPM's, which is where the 4 banger likes to be.  I drove all throughout FL this way without any issues.  Since I swapped my tires to 33's, I actually miss all the torque i had, and now wish I could go to 5.13's without having to swap my axles!