The Truth about Gears and Tires

[dalearyous]

but the pressure i had to hold on the pedal to get there was uncomfortable, keeping the truck at 2600 rpm is not her sweet spot for cruising. So if i wanted to do 75 for a long distance with 4.88s, I had to really hold the pedal down farther than normal. She didnt comfortably cruise at 75. Or 70 for that matter.

2900 rpm to do 75mph is a LOT of rpm to me. I dont think the truck wants to spin at that level for an extended trip either. Or maybe i dont like to hear the engine working harder than it should in a cruising situation.

With 4.10, I would cruise at 75 at about 2k rpm. She was a road trip killer. Now she isnt quite the same cruiser she was, but the overall acceleration is better.

also yes. In NJ people do 80 mph on every highway. If your not up there, you are a slug.

couple things here. holding the pedal down would imply you require more throttle and maybe the jeep wasn't in its optimal power band (HP)? glancing at the pentastar chart this would appear to be true and you were asking a lot from it at that RPM. i dunno, spit balling here.

not wanting to hear the engine working harder than it should? isn't that what a supercharger basically does? i also don't see how you could cruise at 75 mph at 2k rpms. my jeep stock had trouble maintaining 75 because in 6th gear because the RPMs were so low.

now yes, in NJ, you better be driving fast to survive on the highways and i bet it sucks.

anyway a lot of this is circumstantial and i have to agree with snarf, drive what feels best. clearly with your setup 4.56 drives best. it would be very hard to duplicate that as i don't know anyone in person that has a turbo or super charger. and maybe you can get away with 4.56 on 37s BECAUSE of the super charger ... or if you have a free RIPP supercharger i would be happy to be a guinea pig

[JeepLab]

anyway a lot of this is circumstantial and i have to agree with snarf, drive what feels best. clearly with your setup 4.56 drives best. it would be very hard to duplicate that as i don't know anyone in person that has a turbo or super charger. and maybe you can get away with 4.56 on 37s BECAUSE of the super charger ... or if you have a free RIPP supercharger i would be happy to be a guinea pig

"Drive what feels best" is no answer at all. Anyone can agree with that. The driver's goals will dictate what feels best, and with gears you rarely know how its going to feel until you've spent the money and ripped your diffs apart.

Im not against 5.13, please dont take it that way, Tonka, our JK on 40s has 5.13 and no SC and she feels fast. there are different opinions with regard to this related to driving style and location. In NJ you want to be able to drive fast as well as wheel. I also have a 4 to 1 transfer case that gives a little more freedom to run a little less gear.

the best information is for those of us who have actually done it to share with others what our trucks do mathematically now. Then others can get in their trucks and run their RPM up to where we say ours go to maintain highway speed, and see if thats livable for them.