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Better gas mileage with 4.88's vs 4.56's???

T

The Adam Blaster

NAXJA Forum User
Location
Alberta
I just wanted to get everyone's opinion on a statement I just read on another forum.
This is what he said:

I'm running 33 inch tires with 4:56 gears and if I could do it over I would have went with the 4:88s. The guys I know running 4:88s and 33s are actually getting better mileage.

I'm curious what everyone else's experience has been, and whether this guy's statements are actually true.
I'm contemplating switching out the stock 3.55's for my XJ and I have 33's as well. I was thinking 4.10's or 4.56's but if the 4.88's actually get me better fuel economy I would just go with those.
 
Thats pretty accurate. The 4.0 starts to get efficiant around 2400 RPM's and is happy to run up to 2700-3000 on the highway. It would much rather spin fast than work hard.
 
cal said:
Thats pretty accurate. The 4.0 starts to get efficiant around 2400 RPM's and is happy to run up to 2700-3000 on the highway. It would much rather spin fast than work hard.
Click to expand...


I have 33's and 4.88's It spinf 2500 ont he highway and does about 65 at that. closer to 3k and im doing 70 ish. Its not that bad.
 
I'm running 33's and 4.56's also. With the 4.0 and AW4 I'm turning about 2800 at 70 even though the speedo registers 82. I'm not happy with my mileage though.

I'm thinking going to 35's to help on the mileage and also on the speedo reading. Is that thinking right, or wrong?
 
High2by said:
I'm running 33's and 4.56's also. With the 4.0 and AW4 I'm turning about 2800 at 70 even though the speedo registers 82. I'm not happy with my mileage though.

I'm thinking going to 35's to help on the mileage and also on the speedo reading. Is that thinking right, or wrong?
Click to expand...


You're backward, that will make your mileage go down, as the 4.0 will have to work harder.

Re-read the thread - the 4.0 would rather spin fast than work hard. Jes was getting 25 mpg with 5.13's and 35's. I was getting 22 with 4.56 and 32's.

Going to 4.88's could help you, but what is your mileage now?
 
cal said:
Thats pretty accurate. The 4.0 starts to get efficiant around 2400 RPM's and is happy to run up to 2700-3000 on the highway. It would much rather spin fast than work hard.
Click to expand...
Interesting. Would a manual with stock 3.07 gears be any different? I always had the mentality of keeping the RPMs low. I usually shift by 2k RPMs and cruise at that in 5th at around 65-70 mph. Are you saying I should shift into 4th gear instead and cruise around 3k RPMs for the same speed?
 
Transmission has a HUGE bearing on this... both because of the power lost in an automatic, and the gearing differences.

Does Jes have an auto or a manual? That kind of mileage is something I wish I could get with an auto but it's just not happening most likely.
 
crimsondragon said:
Interesting. Would a manual with stock 3.07 gears be any different? I always had the mentality of keeping the RPMs low. I usually shift by 2k RPMs and cruise at that in 5th at around 65-70 mph. Are you saying I should shift into 4th gear instead and cruise around 3k RPMs for the same speed?
Click to expand...


Give it a try for a full tank of gas and see what happens. ;)


Think less about RPM's though and more about how throttle you use. It takes more throttle to push 35's 70 mph than it does 33's 70 mph, and the same goes for having numerically shorter gears (4.10 instead of 4.56).
 
kastein said:
Transmission has a HUGE bearing on this... both because of the power lost in an automatic, and the gearing differences.

Does Jes have an auto or a manual? That kind of mileage is something I wish I could get with an auto but it's just not happening most likely.
Click to expand...


He's got a manual.

With my current jeep I get 15-17, pushing 37's with 5.13's and a stroker, under 7.5" or so of lift.

If I get on the throttle really hard, I can drop it down to 12. ;)
 
crimsondragon said:
I always had the mentality of keeping the RPMs low.
Click to expand...

I was the same way, and that's why going to the 4.88's and getting BETTER fuel mileage didn't make sense to me...
But I guess when certain engines like being at a certain RPM level, that really changes what happens in real life compared to theory. ;)

By the way, I've got an auto tranny, and now it seems like when I get new gears, it will be 4.88's. :D :D
 
Oh, and when I get my rear driveshaft on, I'l fill up the tank and get a good idea as to what my mileage is with the stock 3.55's in there.
It will make a nice baseline for later comparisons.
 
The Adam Blaster said:
Oh, and when I get my rear driveshaft on, I'l fill up the tank and get a good idea as to what my mileage is with the stock 3.55's in there.
It will make a nice baseline for later comparisons.
Click to expand...
Have you corrected your mileage yet? 33s on stock gearing will be fairly inaccurate.

I'm getting 12 right now with 33s and 4.88s. But my alignment is off and I'm fairly certain there are other problems. :)
 
My highway mileage improved when I changed from 4.10 to 4.88 / 33's. But my off road mileage stayed about the same but the performance improved overall.
 
cal said:
You're backward, that will make your mileage go down, as the 4.0 will have to work harder.

Re-read the thread - the 4.0 would rather spin fast than work hard. Jes was getting 25 mpg with 5.13's and 35's. I was getting 22 with 4.56 and 32's.

Going to 4.88's could help you, but what is your mileage now?
Click to expand...

I do understand about the high RPM's versus lugging the thing and that makes sense but I'm getting about 15 MPG's right now. When I was running the stock 3.55 gears with the 33's I was getting about 17. When I hit 45 on the speedo it goes into overdrive. That may be normal, I don't know. All the driving is around town and no highway miles though. It's an educated guess on the mileage because the speedo is off but it's pretty close to accurate. One thing I forgot is that I am running a bored TB. I think that may have more to do with my issues than I thought.
 
On a side note. If your speedo is wrong then the odometer readout will be wrong. You will not be able to get an acurate mileage or mpg number. Get your speedo accurate first. I have a 97 5speed with 35s and 410s and I get between 15 and 17. I got the same with 33s. I will be swapping 44s and 513 in the next month or so. I would really like to see 25 mpg but it's not likely.

As far as 4.56 or 4.88 I don't think you will see a noticable difference. It's only about 150 rpm difference. I would go higher. You get better tourque to the wheels therefore less throttle to maintain speed and less wear and tear on the engine.
 
Last edited:
A large factor is also tire width and weight (mass/resistance). I do not plan on buying 35's because I cannot find a reputable radial in 35x10.5x15, that being said I plan on running 33x10.5

I just bought some 4.56 Yukon gears from Northridge4x4. I was planning to run 4.88's but from the consensus of the board, the 4.88's are generally a weaker gear set in an somewhat compromised front axle (tiny pinion).

Comparing D30 gears to 8.8 gears I understand exactly what the masses are talking about.

This can be "fixed" a number of ways but I did not want the R&P to be my fuse in the equation.

I guess we will see what happens though,
I've drove one XJ with 4.10's and 33x12.5's, it drove like my 3.55 and 31x10.5 setup... hopefully the 4.56 will be a little extra "uphm"
 
J-Roc said:
A large factor is also tire width and weight (mass/resistance). I do not plan on buying 35's because I cannot find a reputable radial in 35x10.5x15, that being said I plan on running 33x10.5

I just bought some 4.56 Yukon gears from Northridge4x4. I was planning to run 4.88's but from the consensus of the board, the 4.88's are generally a weaker gear set in an somewhat compromised front axle (tiny pinion).

Comparing D30 gears to 8.8 gears I understand exactly what the masses are talking about.

This can be "fixed" a number of ways but I did not want the R&P to be my fuse in the equation.

I guess we will see what happens though,
I've drove one XJ with 4.10's and 33x12.5's, it drove like my 3.55 and 31x10.5 setup... hopefully the 4.56 will be a little extra "uphm"
Click to expand...


There hasnt been any real evidence that 4.56 gears are weaker than 4.88's. In theory there is less beef behind them, but if you follow the threads you see as many or more 4.56 gears break as 4.88 gears.
 
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