Regearing Questions? READ THIS!

[DanNJeep]

if you read that mpg chart you just linked you will notice it bases that number or percentage of highway travel and stop and go traffic. Some of those numbers for stock jeeps did reach the 25 MPG mark, so I'm sure with proper gearing and non-stop travel it is very much possible.

The highest possible mileage is listed under the "user mpg" under the "range". If you take the high column under that you get only one vehicle that gets 25 mpg. The 2000 XJ. No other XJ achieved 25 mpg.

Let's put it this way. Which vehicle requires more energy to push down the road? The heavier, higher XJ or the lighter, lower XJ? To take your hypothesis to it's end I can conclude that if I had a stock XJ and cut the fenders so 35" tires would fit, then changed the gears to 5.13 I would get BETTER mileage? Is this what your're saying? In this example which configuration requires more energy?

Jeep A - 3000 RPM, 35" tires, much higher drag, higher weight
Jeep B - 2250 RPM, 27" tires, lower drag, lower weight

Jeep A requires more energy to move more mass with a higher rolling resistance. What do we use more of to produce more energy?

 

[88 Wagonman]

With 5.13's and 35's, Jes pulls 22-25 on the highway.

Maybe the variable here is the wrong speedo gear? Maybe he still has the stock 36 tooth (I think) instead of the 41 tooth needed. That would make it easy to get more MPG.

 

[saburai]

Maybe the variable here is the wrong speedo gear? Maybe he still has the stock 36 tooth (I think) instead of the 41 tooth needed. That would make it easy to get more MPG.

I'm assuming we are not dealing with idiots...

 

[agent98]

I get almost 30 mpg with 40 in. tires and 3.55 gears.
All I had to do was install un-obtainium 11 electrode spark plugs.
All that torque curve, powerband, gear ratio stuff is nonsense.

 

[muduck18]

I get almost 30 mpg with 40 in. tires and 3.55 gears.
All I had to do was install un-obtainium 11 electrode spark plugs.
All that torque curve, powerband, gear ratio stuff is nonsense.

I'm assuming we are not dealing with idiots...

Idiots ... no

Sarcastic A$$ wipes Yes...:heart: <-- cross section man with chub?

 

[stevieb]

good day all
never posted here before really but read and learnt a lot.
i have had a look at all these supposed gear calculators and they all seem to differ with what anybody on this thread have had to say. i might be sitting on the outside of the ball park but where is the truth? is it driver satisfaction, economy or power related?
is it due to using a auto box compared to a manual box or what is it? i have even had a result using aw4 specs, 33s and it gives me a 3.9>>> ratio to install. this site even made things more complicated.
http://www.grimmjeeper.com/gears.html
then i saw a couple of these charts and differ again like on here http://www.4x4offroads.com/gear-ratio-chart.html
so where is the line pulled?
or is it just user preference?

 

[cal]

good day all
never posted here before really but read and learnt a lot.
i have had a look at all these supposed gear calculators and they all seem to differ with what anybody on this thread have had to say. i might be sitting on the outside of the ball park but where is the truth? is it driver satisfaction, economy or power related?
is it due to using a auto box compared to a manual box or what is it? i have even had a result using aw4 specs, 33s and it gives me a 3.9>>> ratio to install. this site even made things more complicated.
http://www.grimmjeeper.com/gears.html
then i saw a couple of these charts and differ again like on here http://www.4x4offroads.com/gear-ratio-chart.html
so where is the line pulled?
or is it just user preference?

A big thing is a lot of the calculators you find are for 'older' car configs and don't compensate for the overdrive on a cherokee. The Grimmjeeper calculator is the most accurate you will find.

Power and economy usually go hand in hand - the 4.0 does not mind spinning up near 3,000 rpm's on the highway but it will drink the gas when you make it work hard (instead of gearing deep).

From there, it comes down to what the driver is comforatable with.


A good rule of thumb:


4.11:1 - 30", 31", 32"

4.56:1 - 32", 33", 34", 35"

4.88:1 - 33", 35", 37"

5.13:1 35", 37", etc

I tend to gear on the lower side. With 4.56 gears and 32" tires, i was able to do better than 20 mpg on several highway trips. Later I went to 4.88 and 35" tires, and was still able to maintain 17-18 with careful driving.

YMMV.

 

[Goatman]

good day all
never posted here before really but read and learnt a lot.
i have had a look at all these supposed gear calculators and they all seem to differ with what anybody on this thread have had to say. i might be sitting on the outside of the ball park but where is the truth? is it driver satisfaction, economy or power related?
is it due to using a auto box compared to a manual box or what is it? i have even had a result using aw4 specs, 33s and it gives me a 3.9>>> ratio to install. this site even made things more complicated.
http://www.grimmjeeper.com/gears.html
then i saw a couple of these charts and differ again like on here http://www.4x4offroads.com/gear-ratio-chart.html
so where is the line pulled?
or is it just user preference?

You don't want the relative same gear ratio as stock with a lift and larger tires. There is more drag and more power needed to spin the bigger/heavier tires, so lowering the gear ratio more than to relative stock works the best. From there, it's driver preference. I think you'll read that there is a general preference for gears in the lower (higher numerically) range of what is generally accepted for a particular tire size. For example, 4.56's work fine for 33's, but most who have run both prefer 4.88's.

 

[Rutanisgod]

ive been thinking about re gearing to 4.56s. got a 2000 auto 8 inch lift 33s getting about 12 mpg. went to a mechanic to get his opinon on re gearing lower and they were saying i would most likely get worse mileage due to the lower gearing. so now im kinda stuck in the middle of which way to go. the jeep is a daily driver some offroad here and there. Just looking for opinions from you guys that have already re geared with bigger tires. thanks

 

[NW-ZJ-SCOTT]

ive been thinking about re gearing to 4.56s. got a 2000 auto 8 inch lift 33s getting about 12 mpg. went to a mechanic to get his opinon on re gearing lower and they were saying i would most likely get worse mileage due to the lower gearing. so now im kinda stuck in the middle of which way to go. the jeep is a daily driver some offroad here and there. Just looking for opinions from you guys that have already re geared with bigger tires. thanks

going to 4.88s will match 33s alot better then 3.55s

also, another thing that might help is to cut down your lift.. NOBODY needs 8" of lift for 33" tires. hell, 4" of lift for 33"s is perfect!

My advice
A: step up to 35"s and 4.88s
B: 4.88s and bring your lift down to about 5" with 33s

 

[Rutanisgod]

would 4.56s show a decent improvement on gas mileage. future plans would be 35s when i get some more money.

 

[CherBear]

would 4.56s show a decent improvement on gas mileage. future plans would be 35s when i get some more money.

It would depend on what size tire you are using.
You want your cruising speed to be in the low part of the powerband if you want good mileage.

 

[Rutanisgod]

right now im running 33s. what area would be considered the low part of the powerband. i think right now im running around 2000rpms at like 60 or 65

 

[ILLXJ]

Go 4.88's now. Haleyes & I get the same interstate mpg. I have 4.56's & he has 4.88's, both on 33's. His has better low end torque. And it is a better set up if/when the 35's go on. JIM.

 

[Rutanisgod]

thanks, just wondering what kind of mileage do u get right now with the 33s

 

[Darky]

Gas mileage isn't everything. If your gearing is too tall for the tire you're running, you'll be working your engine and transmission too hard while daily driving. Burning up a tranny is expensive.

 

[Rutanisgod]

yeah thats what i figured. i went to a mechanic today to ask him about it and he was certain that putting in a lower gear would actually lower my mpg

 

[ILLXJ]

thanks, just wondering what kind of mileage do u get right now with the 33s

I'm getting 14 mixed & 16 on long highway runs. Hale is getting 16 on the highway, not sure in mixed because he only drives 2 miles to work through town. JIM.

 

[DougJ]

Right now I'm on 245/75R16's (30.5 actual) and 4.56's. The plan is to go to 33/10.50 or 255/85R16. Applying correction to the speedometer since I have already swapped speedo drive gears, I've been averaging about 17 mpg on a BDS 4.5" lift. As you can imagine she's spinning up pretty fast going down the hiway, but the power sure is nice!

 

[89xj]

yeah thats what i figured. i went to a mechanic today to ask him about it and he was certain that putting in a lower gear would actually lower my mpg

did you explain that you were running much larger then stock tires? 33's are roughly 20% larger then stock tires and much heavier.