Correct gear for 37's and manual

[Wardell]

The reason I'm asking is that I know the engine runs best at a certain rpm, temp and speed, like at work we trim an engine for standard day conditions (elevation-temp and pressure) and that's where it runs optimally. This is why I'm trying to get as close to the factory rpm and speed range as possible.
I really use the Jeep probably 3 or 4 times a year down south at Windrock and Jelico (easy trails) but use the hell out of it during bow season so I'd say 95% highway with about 5% offroad.

Don't forget either that there are three different gear ratios available from the factory: 3.21, 3.73 and 4.10. Since the rest of the stock drivetrain doesn't change much (aside from a small size difference in tires depending on the trim level), your stock RPMs at that speed may differ.

The best way to get an idea of tire size to RPMs might be to look at it in a table, though I agree 4:88 or 5:13 would be the ratios to look at for 37" tires depending on if you have to contend with hills or how much power you may need. I'm personally leaning towards 5:13 (which would also be more comparable to the 4:10 gearing my JKUR came with stock).

 

[slammer121]

I have a 15' JKU 3.6L Manual transmission and I'm running 4.88 on 37's. It's perfect, great balance between running on/off road. I have no complaints! from what I can tell it is very close to stock ratios.

 

[BlueBox]

Thanks for the replies,
Wayoflife, I've heard the same thing but wanted to get some real world advice from people running the same set up.
Troy-built and BlueBox, could you tell me your rpm's at 65 mph?

I'm at 2500 at 65 mph