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Discussion Starter · #1 ·
Legal disclaimer: I am not an engineer and at times have faulty logic haha. This is for the "basic" build of a Jeep. Not including bumpers, winch and other goodies, just tires/rims/lift/regear

Here is my Jeep build experience.
The very first thing I should have done is HONESTLY asked myself what is my vision. I lied to myself, "oh I just want some better tires and maybe a lil taller”.

So I went with 285/70(32.7x11.2) from stock 255/75s (32x10) width. Now I rubbed on the inside suspension, so 1.5" adapters. Now I rubbed on fender lip, so 2.5" lift. Vanity struck and got new rims, and ditched the spacers. Still ran into fender rub when flexing (popped rear off 2x), so now flats. The good news is that with all of that I could run 37s. The bad news is because of the D30 front, in my mind I am limited at 35s to have a stable and not too worried about breaking things setup. Hmm GOTTA have 35s which fit nicely on the aftermarket tires.


Now gearing. Knowing that gears and tires will change the "overall effective" gear ratio,
I had to determine the corrected gear ratio to get it back to factory performance. I used http://www.rocky-road.com/calculator.html. In my case; 32(255) vs 35(34.5) calc’d out to a change from 3.73 to 4.0214. Being that, 4.10s would give me a very close factory setup up for speedo and rpms. (NOTE: I recalibrated for the ABD/ESP systems)

Would factory specs be good enough?

Choice of 4.10/4.56/4.88 gears

IMO Gear choice Factors (importance to me 1-3):
Daily Driver (DD) is a 3, 30 miles at avg 65mph 5 times a week to work
Landscape (LS) is a 2 because of the hills
Towing (T) is a 2 due to the amount of time towing a 1700# camper
Off-Roading (OR) is a 2, forestry trails on joy rides and camping
Weight (W) is a 2 because I have added heavy bumpers w/winch


DD, is a long term $$$ factors, rpms and gas mileage: 4.10.
LS, hilly terrain, only need a bit of power: 4.56.
T, 4.88 would be great, but the higher rpms when DDing: 4.56
OR, don’t need 4.88 for crawling or 4.10s for rally: 4.56
W, added a good amount of weight so again 4.88 would be great, but a DD: 4.56

So my choice for my needs is 4.56 because of the underlying overpowering factor of being a DD. If this was a part time “toy” I would have gone 4.88. And now with 4.56 gears, my rpms with BFG KO2 35s are [email protected] & [email protected]

Doing just the tires, rims, lift and regearing cost me shy of $6000 installed.
 
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Nice set up. I went lite. AEV 2" spacer lift. No discernible effect on the handling on the road and I feel better on the trails I like to do. I'm sticking with my stock 32 MTs until they wear out, then I'll go with 33s. Shouldn't be an issue for my 3.73 gearing, and I can keep my stock wheels.

I can do the trails I want and leave the advanced ones for the big boys. Maybe someday I'll go there, but I'd like to have the rig paid for first. In the meantime, I've spent my money on other things: new HU/speakers, steel bumpers, auxiliary lights, some under armor, a hinge tire carrier and a whole bunch of knick knack type stuff to make my Jeep my own. I'm hoping a winch is on Santa's list for me this year.

Just goes to show there's plenty of room under the Jeep tent for everybody, from the hardcore to the mall crawlers and all of us in between.
 

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you also have to factor in the front D30 when regearing, you don't want to go too high numerically

I am getting ProRock 44 front axle installed with Detroit truetrac, 4.56 gears for my KO2 37's (decided on 4.56 since turbo is in my future)
 

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Discussion Starter · #5 ·
you also have to factor in the front D30 when regearing, you don't want to go too high numerically

I am getting ProRock 44 front axle installed with Detroit truetrac, 4.56 gears for my KO2 37's (decided on 4.56 since turbo is in my future)
Yup ". The bad news is because of the D30 front, in my mind I am limited at 35s to have a stable and not too worried about breaking things setup."
 

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One thing people should consider the difference between 4.56 and 4.88 is less than 200 rpms. My 2 door is heavy, this last trip 5800 pounds. I opted for 4.88 but I was worried about performance at 80 mph, how bad would it impact my mpg.

I have track mpg for sometime now that I have an app on my phone. I am happy to say mpg at 80 was really no different than mpg at 65, all within 1 mpg. In fact now that I have plenty of miles on my 4.88's it's get .3 tenth of a mpg better than I did with 4.10's. This is not to say I really enjoy driving 80 mph, mostly because it gets loud with a soft top. 65 mph seems to be the sweet spot though.

Where I was surprised though was once I got about 6000 feet. I spent the better part of 2 days at this altitude and I had wish I had gone 5.13's. The power loss up there is huge, it was like my 4.88's where 4.10's again.
 

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Where I was surprised though was once I got about 6000 feet. I spent the better part of 2 days at this altitude and I had wish I had gone 5.13's. The power loss up there is huge, it was like my 4.88's where 4.10's again.
Where were you at? In state? I'm in Seattle and go to I-90 pass and Walker, but also spend some time over on the peninsula.

Great time of year to get some altitude!
 

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Northern New Mexico, Actually topped out at around 11000 feet.
 

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I wouldn't mind the 4.88's in my auto, but 4.56's do everything i need, onroad or offroad with my 315/70/17 tires.

Remember most 35's are not 35's in reality, if you're looking at the gearing chart, don't look at 4.56 with the 35 intersection, look something in between 33 and 34. my KO2's in 315/70/17 e rated were 33.5" brand new at 32psi (if you measure from the ground to the edge of the tire shoulder, most people measure to the highest point on the thread), my Nitto Trail Grapplers in 315/70/17, D rated, are 33.5" brand new at 28psi.

I use the 33" intersection with the chart, spot on with what i see at 70mph with 4.56's in my auto trans, 2700rpm, at 80mph is about 3100rpm, no issue doing rocks at all with that gearing.
 

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4.56 auto basically the same thing as 4.88 manual.
 

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Discussion Starter · #11 ·
For some reference material
 
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