I'm kind of surprised more 42RLE Rubicon owners are only going to 5.38 and not to 5.89 to get that 3k RPM
4.56 or 4.88 gears?
- Thread starter TJJeepGirl
- Start date
Nitro, Yukon, G2, Motive, Spicer, SVL (Spicer import brand), and USA Standard all offer 5.89 gears for the Dana 44. They only make them for the 8.5" ring gear that the TJ uses, and not the larger 8.8" JK gears. So you can gear a TJ Rubicon to 5.89, but not a JK unless you convert to the smaller gears.
https://www.summitracing.com/search...le-model/dana-44/ring-and-pinion-ratio/5-89-1
Mobusaki
TJ Enthusiast
If you ever went up or down "one" tire size then that will give about the same feeling as going up or down one gear size. I went from 245/75r16 to 265/75r16 (31's to 32's if you round up) on 4.56 gears and I did not like the difference in performance.
Glad to see others also saying to gear deeper than you think you should. Nothing but an LS swap or stroker engine will make your Jeep feel more badass than being "overgeared."
Mobusaki
TJ Enthusiast
Good to know!
One thing that has not been talked about is MPG with these different ratios, but that's probably because we drive bricks and who really cares about MPG here anyway? But for the sake of being thorough, I suppose you would have a bit better gas mileage on the highway with 4.56 and 33's than 4.88 and 33's. There, we found one thing gearing to the conventional wisdom is better for.
With 35's and 42RLE transmission my mpg went from sub-12 mpg with 4.88 to 14.6 after regearing to 5.38. Higher rpms don't necessarily always mean lower mpg any more than lower rpms always mean higher mpg.
Tldelaney
TJ Enthusiast
The NSG370 is geared lower than the AX-15 and NV3550 which means the highway engine rpms are a little higher with the NSG370 so that's kind of a gray area. If you drive in a flat area and don't have any hills/grades to climb on a regular basis and it's just a daily driver with little to no offroading then 4.56 would work. But for anything else I'd go 4.88.
I plan to go 4.88.
Do you currently have 4.10 gears? If so, 5th gear and 4.10s have the exact same drive ratio as 6th gear with 4.88.
4.88×0.84 = 4.10×1.00
So next time you're out on the freeway, pretend 6th gear doesn't exist, and leave it in 5th. That's exactly what 4.88s will be like in 6th. Want lower RPMs? Go down to 4.56. Want higher RPMs? Consider 5.13.
Tldelaney
TJ Enthusiast
Thanks Jerry, I was reading the old threads on different forums on recommendations ( you, Savvy (Gerald) and others) so I wasn't too sure. This sums it up quite nicely.
Tldelaney
TJ Enthusiast
Ill try this out when I get the LJ back together.
Here is fun calculator to find out what tire, gear and trans combos do verse speed, https://spicerparts.com/calculators/engine-rpm-calculator. This calculator make some transmission ratio assuptions but is still good ball park info.
Making any assumptions on the transmission type is not good as it affects the rpms too much.
This is a calculator that takes the exact transmission type into account... it works superbly. http://www.grimmjeeper.com/gears.html
To show the difference a transmission can make:
70 mph with 35" tires.
32RH 3-speed automatic: 3279 rpms.
42RLE 4-speed automatic: 2263 rpms.
AX-15 5-speed manual: 2591 rpms
That's why you can't ignore the transmission type.
Grimmjeeper.com
And if accuracy matters, the tire size to be entered needs to be the hub height x2.
For example, my 35" has a hub height of 15.75" which means I enter 31.5 as my tire size. Believe it or not. Like it or not. This is accurate to a few rpm.
And if accuracy matters, the tire size to be entered needs to be the hub height x2.
For example, my 35" has a hub height of 15.75" which means I enter 31.5 as my tire size. Believe it or not. Like it or not. This is accurate to a few rpm.
Thanks for the link, I use it regularly but find the Spicer calculator easier for my customers to get the idea of gear ratio vs speed will have on their 4X4's.