Upgrade to 3.73 or 4.10 gears with 31" tires?

[Jerry Bransford]

@Jerry Bransford always approves of 1 size up in gearing if you don't care about highway speeds

No, all of my ratio recommendations are always made with highway speeds in mind. Even when I recommend 1 size lower ratio, like 5.13 over 4.88, it's always made with highway rpms in mind as well.

Edit: I just re-read what you said for the third time and think I know what you were getting at. If a Jeep will never be driven on the highway, you can gear to a lower ratio than you'd want if it were also driven on the highway.

 

[Alex01]

No, all of my ratio recommendations are always made with highway speeds in mind. Even when I recommend 1 size lower ratio, like 5.13 over 4.88, it's always made with highway rpms in mind as well.

Your recommendations are dead on for the intended use. Hence why I went with your recommendation for mine. I was joking since he prefers a higher crawl ratio to daily driver.

Would you recommend 4.56 in this particular situation?

 

[Jerry Bransford]

Your recommendations are dead on for the intended use. Hence why I went with your recommendation for mine. I was joking since he prefers a higher crawl ratio to daily driver.

Would you recommend 4.56 in this particular situation?

4.10 is fine with 31's and the OP's engine/transmission combination.

 

[Pat Goode]

I wouldn’t say I will never use it on the highway. Obviously I need to get to and from off road events.
Distances in the uk are much less, as it’s such a small overcrowded place. Our max speed limit is only 70. But most ordinary roads are 50-60, if you’re lucky and the traffic is light.
I know everything is a compromise, but I’d rather compromise on highway running to get the best off road low range setup
My other daily drivers are a Landrover Freelander 2 and a two door Toyota Rav 4
Thanks

 

[jack alexander]

I run 31X10.50 tires with 3.07 gears.
4.0 automatic
Perfect on the highway and off roading.
I read a lot on Jeep forums... it seems to me that no two Jeeps are alike.
I may regret going to 33’s without regearing , yet I have talked to guys who say their rigs run and perform fine with the automatic transmission. ( non overdrive)
Although the torque converter will work harder.

I do not have experience with 5 speeds but I have the best of both worlds with the automatic.

Hi,
Is anyone running on 31" tyres with a 3.73 or 4.10 Diff ratio.
I'm trying to make my mind up as to which way to go. 31" tyres are plenty big enough for the type of off roading I do. In the uk we need to keep the entire tyre within the wheel arch.
It would be easier to re-gear to 3.73 as replacement front axles are readily available off XJ's and the 3.73 is within the carrier break off the, As fitted Dana44 Trac-lok rear diff
I'm fine with the present 3.07 ratio on the tarmac, But off-road in low range the gearing is much to high.
Any observations would be greatly appreciated.
Difficult to find any advice as in the States you all seem to favour 33" or 35" Tires

ere are several things to consider

I ran 31's with a 4.0L and a 5 speed with 3.73 gears. It was acceptable.

 

[Pat Goode]

Hi Alex
I can understand how it would be better in an Auto as you can creep along letting the torque converter control the speed.
However in a 5 speed manual it really is too
fast in first low needing a lot of clutch control during tight manovering. No shortage of power though.
In the ideal world I would have liked an auto but they are fee and far between in the uk.

 

[Dave Carpenter]

My Jeep was factory equipped with 30" tires and 3.73 gears. When I got it, it had been upgraded to 31" tires. I like the combination of 31's, 3.73 gears, and 5 speed. The only problem I have with it on the highway in 5th gear is climbing hills. I can hold 70 MPH, but if traffic slows down, I have to drop back a gear to hold my speed. On the flat or mild climbing, it is just fine. I have no problems with it off road, but I'm not into extreme off roading (rock krawling).

One of the indexes is RPM at highway speed. My RPMs are about 2200-2250 at 60 MPH, about 2500 at 70 MPH.

 

[Jerry Bransford]

My Jeep was factory equipped with 30" tires and 3.73 gears. When I got it, it had been upgraded to 31" tires. I like the combination of 31's, 3.73 gears, and 5 speed. The only problem I have with it on the highway in 5th gear is climbing hills. I can hold 70 MPH, but if traffic slows down, I have to drop back a gear to hold my speed. On the flat or mild climbing, it is just fine. .

Having to downshift out of 5th gear into 4th when climbing hills is absolutely and 100% normal. 5th gear is an Overdrive ratio and it's for maintaining speed when the highway is flat or mostly flat. Climbing hills requires slightly more power which is only possible with higher engine rpms which means you need to shift out of Overdrive (5th gear) into 4th. Don't expect to be able to climb hills in 5th gear no matter what reasonable axle ratio is installed.

 

[astjp2]

I am running 34's and 4.10's in my YJ, and I didnt have to change the speedo. I compensated the low range with a 4.0 atlas though. I still run 3500 rpms at highway speeds, I wish I had a lower RPM or an overdrive. I am going to use the same combination in my LJ...after I rob it from my YJ. I am concerned about highway rpm's because my playground is 175 miles from home and the highway is 80 mph most of the way and only 1 gas stop....not something I would want to run 4.56's or 5.13's and 75/80 mph

 

[jjvw]

I am running 34's and 4.10's in my YJ, and I didnt have to change the speedo. I compensated the low range with a 4.0 atlas though. I still run 3500 rpms at highway speeds, I wish I had a lower RPM or an overdrive. I am going to use the same combination in my LJ...after I rob it from my YJ. I am concerned about highway rpm's because my playground is 175 miles from home and the highway is 80 mph most of the way and only 1 gas stop....not something I would want to run 4.56's or 5.13's and 75/80 mph

What transmission is in the YJ? How does it compare to the transmission in the LJ?

 

[astjp2]

the YJ has a 4.6 stoker and an a999 auto, the LJ has a 4.0 and the 6 speed manual. I would have perfered to get the auto in the LJ but i got it for 6500 as a wreck that needs a fender and a hood. Tim

 

[jjvw]

the YJ has a 4.6 stoker and an a999 auto, the LJ has a 4.0 and the 6 speed manual. I would have perfered to get the auto in the LJ but i got it for 6500 as a wreck that needs a fender and a hood. Tim

You aren't going to like 4.10 gears with the 34" tires and the 6 speed. 4.56 minimum.

 

[astjp2]

Why? there is only 1 overdrive on the 6 speed...

 

[jjvw]

Why? there is only 1 overdrive on the 6 speed...

And there isn't an OD on the a999. Keep in mind that even on the Rubicon, Jeep was using 4.10 with 31" and the 6 speed was arguably the best transmission to have that tire/axle gear combination. You are wanting to go 3 tire sizes larger.

Play around with Grimmjeeper.com and don't be afraid of running the 4.0 at 3k rpm on the highway.

 

[astjp2]

And there isn't an OD on the a999. Keep in mind that even on the Rubicon, Jeep was using 4.10 with 31" and the 6 speed was arguably the best transmission to have that tire/axle gear combination. You are wanting to go 3 tire sizes larger.

Play around with Grimmjeeper.com and don't be afraid of running the 4.0 at 3k rpm on the highway.

It's more like 4K, and that creates a lot of heat and real poor mileage.

 

[jjvw]

It's more like 4K, and that creates a lot of heat and real poor mileage.

Not even close. You're guessing.

This is the lowest you can go with Dana 44s.
NSG370/33.5"/5.38 = 3400rpm @ 75mph

4.10 a bad idea.

 

[astjp2]

The 32rh runs at 3650 at 70, per my GPS in the YJ...and i used to run 4.10's on 37" tires and not have any problems in another vehicle. Peak torque is where I want to run the rpm's at, it leaves a little power left if I want to accelerate. I would be happy for the same performance in the LJ or even lower rpm on the highway, that way if I want to pass someone, I can downshift and have enough power to pass. I also have to deal with 100 degree temperatures and the high rpm's increases the underhood temperatures, even with an aluminum radiator, the stroker keeps the temps right at redline...I dont want that with my LJ. I have the parts to build another stroker, but I am going to leave the LJ engine alone and mess with suspension and drivetrain first. The inline 6 doesnt need run at 3-4K rpms like the 4 banger because it has enough torque to keep it in a more lower range. JMHO Tim

 

[jjvw]

The 32rh runs at 3650 at 70, per my GPS in the YJ...and i used to run 4.10's on 37" tires and not have any problems in another vehicle.

You are not running 4.10 gears with 34" to get 3650rpm at 70mph with the 32rh or the a999. The math does not work out that way. 5.13 adds up to what you are seeing.

What other vehicle are you comparing 4.10/37" tires to a TJ with the 180hp 4.0?

Peak torque is where I want to run the rpm's at, it leaves a little power left if I want to accelerate. I would be happy for the same performance in the LJ or even lower rpm on the highway, that way if I want to pass someone, I can downshift and have enough power to pass. I also have to deal with 100 degree temperatures and the high rpm's increases the underhood temperatures, even with an aluminum radiator, the stroker keeps the temps right at redline...I dont want that with my LJ. I have the parts to build another stroker, but I am going to leave the LJ engine alone and mess with suspension and drivetrain first. The inline 6 doesnt need run at 3-4K rpms like the 4 banger because it has enough torque to keep it in a more lower range. JMHO Tim

I never suggested 3-4k rpm. I do strongly suggest putting your highway cruising rpms closer to 3000rpm. Again, look at grimmjeeper. On a stock 4.0 in good repair, engine temps will right at 210F where they ought to be.

 

[Pat Goode]

Lol, again the talk of rehearing our Jeeps returns to highway speeds.
Want is it with this obsession with gas mileage? From the land of cheap fuel and the home of the V8.

 

[Pat Goode]

Sorry about the spelling, iPhone spell check..!!