4.10 gears and 35's ????

[xdutyxj00]

Just wondering if anybody is running this setup? I currently running 4.88 gears with 35's. The main reason I want to change it is to try to improve gas mileage. Only getting around 220 miles on a tank of gas. Most of my driving is on the highway now. My avg speed is 65-70 mph turning around 2500 rpm.

Specs on my Jeep

4.0L, AW4 trans, 242 t-case
7.5 RE longarm
35" KM2's
15x8 steel wheels
dana 30 & 44 with ARB's

 

[Darky]

Taller gears will make the engine work harder. That's partly why guys are able to build a stroker and get the same or better gas mileage....

 

[MoparManiac]

I've gotten 19 mpg doing a 400mi highway trip on 4.88s and 35s. Calculated and corrected against a GPS.

Doublecheck everything including things as simple as tire pressure, something is wrong.

 

[89xj]

Just wondering if anybody is running this setup? I currently running 4.88 gears with 35's. The main reason I want to change it is to try to improve gas mileage. Only getting around 220 miles on a tank of gas. Most of my driving is on the highway now. My avg speed is 65-70 mph turning around 2500 rpm.

Specs on my Jeep

4.0L, AW4 trans, 242 t-case
7.5 RE longarm
35" KM2's
15x8 steel wheels
dana 30 & 44 with ARB's

2500rpms or a little higher is where the 4.0 should be to get the best mileage, atleast thats the way my 89 renix runs.

are you willing to do a gear swap from 4.88's to 4.10 just for better gas mileage? when will you make your money back?

when was the last tune-up and maintenance?

 

[goodburbon]

I ran 4.10 with my 33's for a while. Even at sea level I had to downshift to go up overpasses and the best mileage I ever got was 19 on full tanks burnt on the highway. It was mostly 14-15. I can't imagine 4.10 and 35 would be any good and compound that for any altitude.

Also the best point raised is 89xj's. If you're doing this to "save money" have you even calculated the break even point in miles with a difference of 2mpg at $2.50 a gallon?

 

[Jeff in VA]

I currently running 4.88 gears with 35's.

do you have the correct speedo gear for your current setup?

Jeff

 

[ktm racer 419]

4.10s will get you worse milage

something else is amiss

 

[jeeperguy21]

I ran 4.10s and 35s for about 2 years before changing to 4.88s. Don't go from 4.88s to 4.10s. You will feel like you have just lost a bunch of power. As was mentioned, your engine works much harder on 4.10s. It seems logical that you would get better gas mileage from 4.10s, but I didn't notice a difference. Maybe the extra work of the motor negates any gains you might have obtained. I dunno.

Basically, what you have right now is the ideal situation for the tire size that you have. 220 miles on a tank on the highway does seem really low. I get that many miles on a tank driving through the city. I'm not sure what else to tell you.

What year Jeep is it?

 

[nochance9]

when will you make your money back?

X2 dropping $800 bucks on gears could buy a lot of gas... not to mention you would then have to live with an under powered rig. 220 isn't right. I've got 35's and 4.56's and manage around 280 on freeway. But i wish i had 4.88s for the extra power. if you do end up swapping gears you know where to send those 4.88s.

 

[kastein]

I've got 32s and 3.55s and I get 250 "miles" to the tank (haven't changed speedo gear), which is actually around 280 miles or so. I was getting 350-360 before the 32s. Check your other stuff - O2 sensors, make sure your TC is locking on the highway, air filter, tire pressures, spark plugs, cap and rotor, etc etc etc.

 

[jeepme]

I run 4.10's and 35's. It sucks!! any little hill and you will be downshifting, not to mention the heat the trans builds up from all that shifting. Dont do it! like mentioned, you got something else going on.

 

[wesleyxcore]

Not to insult your intelligence, but my guess is you didn't change the speedo gear and you're not figuring that into your mpg equation. That would make your odometer read low or slow or whatever you want to call it, making it appear that you're getting terrible mileage. If that's not it, start going through stuff; last tune up, any mechanical issues, tire pressure, etc.

 

[srmitchell]

You didn't mention what year your jeep is.

I'd check
-psi
-spark plugs
-rotor/wires

Oh, and how old is your o2 sensor?

 

[DeathValleyPaul]

I run 4.88s and 35s. I would gladly trade them for 5.13s so I could at least have some power again

 

[WaXJ_Skier]

Just wondering if anybody is running this setup? I currently running 4.88 gears with 35's. The main reason I want to change it is to try to improve gas mileage. Only getting around 220 miles on a tank of gas. Most of my driving is on the highway now. My avg speed is 65-70 mph turning around 2500 rpm.

Specs on my Jeep

4.0L, AW4 trans, 242 t-case
7.5 RE longarm
35" KM2's
15x8 steel wheels
dana 30 & 44 with ARB's

drop your speed a little 55-60 is where I get the best mileage. If you were to try and change gears I would go to 5.13 (build front 44 with hubs)

 

[ROBZ95Xj]

I've got 32s and 3.55s and I get 250 "miles" to the tank (haven't changed speedo gear), which is actually around 280 miles or so. I was getting 350-360 before the 32s. Check your other stuff - O2 sensors, make sure your TC is locking on the highway, air filter, tire pressures, spark plugs, cap and rotor, etc etc etc.

if you run the highway alot use '3' instead of drive, i got 17 out of mine with stock gears and 33's

 

[jeepcomj]

I get 200 on a tank with 35's and 4.10's. less than 15mpg.

decreased by 5mpg just putting the tires on (had 33's). well, and screwing up the steering...

 

[jeepcomj]

...and that's with the correct speedo gear

 

[kastein]

if you run the highway alot use '3' instead of drive, i got 17 out of mine with stock gears and 33's

Yeah, I kinda do this by myself, I just try to avoid using enough skinny pedal to kick it into OD. Occasionally I want to pass someone or something though.

Should be fixed soon, as I am getting closer to being ready for the 8.8 swap, which should get me back to approx stock gearing.

 

[xdutyxj00]

Thanks for all the input.Here are some more details , 2000 model (138,000 miles),I do have the correct speedo gear installed,most of the maintenance is up to date(plugs,filters,t-body cleaned). I run 30 psi in the tires. I do have a noise coming from one of the diffs. Sounds like a gear whine, maybe a bearing. I here it when I let of the gas, thats why I thought about changing gears to 4.10's.