dognights

To further confuse everyone I look at gearing a bit different then probably a good many people. I base my gearing on my needs for my jeep in the most common situation I will find on the road.

For me this is not gearing to do 75 mph on the highway in my Jeep at a given rpm. Heck why would I ever want to go 75mph in my Jeep in the first place. I personally gear for 45mph in 4th gear. I would look for say 2200 -2300 rpm say in fourth gear doing 45mph. This puts me in a nice cruise mode around town without bogging the engine with enough room left to accelerate onto the highway if needed before shifting into highway gears.

I think the 4 to 1 transfer case is plenty enough reduction for the trail regardless of what gears you are running. Heck sometimes I wish I had the 2.72 instead or at least another selector to select a little faster granny mode. Ah well we all use our toys different and like different things.

MTH

Folks reading this thread: Keep in mind autos are different than manual transmissions for pre-2012s. The OP is driving a manual, for which I'd think 4.56 or 4.88 would be good for 35s based on preference. For an auto, either would be too short--5.13 minimum would be appropriate. Just FYI.

Al-Raisi

Gentlemen,
I have searched almost every where but never found any info about Gear ratios for hemi engines.
I'm planing for 6.4 with size 37s.
What ratio would you recommend (mainly desert driving)
I'll really appreciate if you could share your experience and knowledge

duffyboby

Im no expert on this but, ive got an example for you. For jk with the 3.8 engine, peoples who wanted 35 would immediatly swap out their gears to at least 5:13 to regain lost power, BUT, with the pentastar 3.6, people run up to 35 with stock 3:73 or rubi 4:10. So my guess is, since the hemi is SO much more powerful, you might be able to run 37 with 4:10. My understanding of the thing.

JPop

What transmission

Prime8

Love my 5.13s and haven't looked back. According to the rpm charts, you should be running at least 4.88, but preferably 5.13, with 35" tires. Saying yours are 34.5 isn't accurate, they are 35's. EVERYTHING, except the AEV procal, uses the tire size printed on the sidewall, not the actual measurement. So to say your 4.88s don't match up as well with your 34.5" tires as they would with 35" is total nonsense. Not to mention that if you actually did have 34.5 instead of 35, the incremental difference is so minute that it wouldn't matter anyways...

jimk403

For those that live anywhere but sealevel, you might be happier slightly over geared. I know I am, and when we go visit the wifes family in Colorado, having the low gears makes going over the mountain passes less of a drag than stock gears. If we lived in Florida or Texas, 4.88 or 5.13 may be just fine, but up here either one would suck.
Moral of the story, don't believe everthing you read.

Al-Raisi

most probably For a manual transmission (but haven't decided yet)

Al-Raisi

i was thinking exactly the same. Currently I'm running 4.88 on modified 3.8 manual trans but again it might be too much for Hemi.

JPop

The OP was talking about a manual transmission.

All three of the programmers I have owned have used actual tire size. There's a handful of variables for actual tire height, and when you aren't using OEM wheels and tires those numbers could be all over the place.

The OPs tires are not 35s. They are 315/70R17s which should carry a factory measurement of 34.36". They are also running much shorter than that, about 33". That's not an incremental difference, but about a 4% difference which in the OPs case is adding more than a hundred rpms to the cruise speeds expected or hoped for.