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4.88 gears 32" tires

L

legmanxj

NAXJA Forum User
Location
Billings, MT
Hi, feel kinda dumb asking this but,,, I have a 98 xj with lots of non performance related mods, most of which just make it heavier. My mechanic put in 4.88 gears to make it feel quicker. I have 32" tires and it does seem like a new rig round town and wheeling but It feels like its gonna explode on the highway. Can i get a transfer case or add on overdrive to help at high speed? I think going to 35" tires are just going make it sluggish again.
 
lots of people run 4.88's with 33's on the highway so i cant imagine it would be much worse with 32's.
 
Just got a new speedo wheel and haven't got it in yet so I don't know how many rpm, but the engine just seem like its screaming going 70 mph
 
4.88s may be a bit much for 32s @70MPG.
I have 4.56s/32s & it is OK, But still a little too much @70MPH. I am going to move up to 33s next time I need tires.
 
4.88's are high for 32" tires if the rig sees regular freeway use.
33's will help but will only shave off a couple hundred rpm's.

I use the Novak-adapt.com gearing calculator.
I went to 4.56 gears with 33's.
 
35's with 488 are perfect for my 89 renix.It feels better now than it did before with 33's on it.This is freeway and around town. go with 35's and don't look back.
 
garr said:
4.88s may be a bit much for 32s @70MPG.
I have 4.56s/32s & it is OK, But still a little too much @70MPH. I am going to move up to 33s next time I need tires.
Click to expand...


Then how do you know you're going 70? ;)

You're at what, like 2700 RPM's? That's the sweet spot for the 4.0 - it may seem high, but its as perfect as it can be.
 
cal said:
Then how do you know you're going 70? ;)

You're at what, like 2700 RPM's? That's the sweet spot for the 4.0 - it may seem high, but its as perfect as it can be.
Click to expand...

2700 is the sweet spot? I was under the impression that it was somewhere between 2300 and mid 2500's.

I run 4.88s with 33x12.50's with an AX-15 tranny and turn 3000 rpms at either 70 or 75 mph ( can't remember... It's when my speedo points straight down lol). When I cruise at an average of 65 mph, I average almost 19 mpg.
 
3000 RPM's should be 76 mph.

http://www.grimmjeeper.com/gears.html

2500. 2700. Its the same thing to the 4.0, it doesn't mind some RPM's. One of our local chapter members used to run 4.88's and 31's, and would make 500 mile highway drives setup that way. Rig never minded.
 
^ good to know. I'll stop trying to keep it around 2500 now lol
 
i have 4.88s with 35s and the NV3550 and it's fine. I had it with 33s before too and it was still fine. I actually preferred how it felt on road with the 33s, more get up and go.
 
cal said:
Then how do you know you're going 70? ;)

You're at what, like 2700 RPM's? That's the sweet spot for the 4.0 - it may seem high, but its as perfect as it can be.
Click to expand...


My speedo is properly calibrated.
I do agree that the 4.0 runs nice & smooth @ that speed, But MPG suffers, I am sure I can pick up a couple of MPG by running it at a lower RPM closer to OEM.
 
i spent most of the day trying to figure out if having a stak transfer case could give me options to make the rig more livable. I saw a post on another site where the guy was talking about an over drive on the stak? Sounds really cool to have a bunch of options. just bought new tires with the gears. Has anyone here switched to a multigear transfer case?
 
I'm running 33s with 4.88s and it's great. I can do 70 just fine and it's got decent pickup down low. 32s won't change that much. It does take some getting used to to have the engine spinning up near 3000, but it's not an undesirable position to be in.
 
Darky said:
I'm running 33s with 4.88s and it's great. I can do 70 just fine and it's got decent pickup down low. 32s won't change that much. It does take some getting used to to have the engine spinning up near 3000, but it's not an undesirable position to be in.
Click to expand...
and Darky knows all about undesirable positions!
 
i ran my rig at 2700 to 3000 rpms for most of a 10k mile trip a couple summers ago. got 15 mpg with 3 people in it completely loaded down with wheeling and camping gear. no issues to this day.
 
I have run mine at 4k and 5k for tens of hours without problems (except the transmission... but I abused it pretty bad) and 2700 is pretty normal.

If you are thinking about a stak overdrive to save on gas and engine repairs, remember that good pulled 4.0s can be had all day for under 300 (I've never paid over 160) and it will likely take you thirty or forty thousand miles to actually see any savings on gas. Don't feel like running the numbers atm but saving a few cents per mile on fuel with a multi thousand dollar transfer case is not a sane investment. If you are just looking for an excuse for a stak, disregard this message :laugh2:
 
I run 4.88 and 31's... I only run 70 MPH because it is a jeep and has many rattles, squeaks, and MT tire on pavement drone.

I do not believe that it is that bad.

Jeff
 
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