Need some advice with regearing

[Centurion07]

FWIW my rig is all purpose, meaning it's my DD and off road go-to. I run 37s with a 4.5" lift, and chose 4.88s to keep it rolling. It keeps up with traffic on west TX interstates with ease, and without that near-death feeling.

Sponsored

 

[limeade]

I just dropped off my JLU Sport S manual, on 35’s, to be regeared today. Going to 4.88. Considered 5.13, but decided to stick with 4.88. IF I decided to get 37’s one day I’ll have to figure it out then, maybe a Rubi transfer case if I can find one.
I’m trussing my D30 front axle while in there too, and adding lockers! So excited to drive it! I’ve been nursing along my powerless rig for a while and can’t wait to have some oomph again!

I think 4.88's are a great choice for 35's. If you ever do go up to 37's, you may like the 4.88's too.

 

[Halstem1]

I just dropped off my JLU Sport S manual, on 35’s, to be regeared today. Going to 4.88. Considered 5.13, but decided to stick with 4.88. IF I decided to get 37’s one day I’ll have to figure it out then, maybe a Rubi transfer case if I can find one.
I’m trussing my D30 front axle while in there too, and adding lockers! So excited to drive it! I’ve been nursing along my powerless rig for a while and can’t wait to have some oomph again!

I’m debating 4.88s for my 37s So you’ll be completely fine if you upgrade and don’t have a super heavy rig.

 

[Halstem1]

I’d rather the rpm be a little higher than lower. These 3.6s don’t make much power and on the highway is where it really needs it. I want my engine working less and having more aggressive gearing helps that. I haven’t seen it in this thread but folks that think it’s ideal to have the hearing mirror stock when you add big, heavy tires aren’t looking at it the way we do. It requires more power to turn those bigger wheels, stock gears and tires are adequate. Lugging a modern gasser is worse than the higher rpms. Also, when on the highway if it doesn’t have the power to hold 8th, it’ll drop to 7th and to me the money spent to regear is now wasted.

Brett

To the shop that asked how fast you like to go on the highway, I like their thinking. That said, I never encourage or condone driving a lifted JL at 80-85 or higher so the gearing consideration is a non-issue with me. Just because you can do it, doesn’t mean you should rings in my head.

Brett, question for you if you don't mind... when you're calculating or evaluating gear ratios, are you supposed to use your tire size on the sidewall or the actual measured tire size when its sitting on the ground? I'm running the BFG KO2 which are known to run smaller than some. My 37's actually measure 35.5" at best. What size do I use when evaluating gear ratios? debating between 4.88 or 5.13. Also considering any future tires... biggest I would go would be a KM3 in a 39 if I beef up my axles enough or a truer to size 37.

 

[gpurp]

OP, I was in your shoes two months ago. I'm running a 2.5 MC lift and 315/70/17 Patagonias. The tires are 34.7" diameter according to the mfg. 8th gear was non-existent and I rarely saw 7th. I chose 4.88s and now see roughly 2300rpm/70mph and 2500rpm/75mph. Highway mileage is right around 18mpg. This works out fine for me because I don't drive over 75mph in the JL. @rustyshakelford did my re-gear and I think he's spot on with his recommendations.

 

[rustyshakelford]

Brett, question for you if you don't mind... when you're calculating or evaluating gear ratios, are you supposed to use your tire size on the sidewall or the actual measured tire size when its sitting on the ground? I'm running the BFG KO2 which are known to run smaller than some. My 37's actually measure 35.5" at best. What size do I use when evaluating gear ratios? debating between 4.88 or 5.13. Also considering any future tires... biggest I would go would be a KM3 in a 39 if I beef up my axles enough or a truer to size 37.

Actual size would give you the most accurate rpms estimates when using a calculator. On my wife’s JL running 37 STT Pros I installed 5.13s and they are perfect and would be fine if we went up to 39s. 40s are kind of my breakover to 5.38s because it’s so much additional rolling resistance, weight and drag that they need all help they can get. 5.38s would be a little much on 37s even with the possibility of doing 40s in the future if that makes sense.

Brett

 

[wibornz]

Do a search on the forum. There is a google sheet that allows you to enter the tire size and then shows you what RPM for speed. I went with 5.13 gears. This is a pic of my guages at 70 mph and the about 2100 rpms. Note I am on 37s.

 

[wibornz]

Ok, look here for the gearing calculator.

https://www.jlwranglerforums.com/forum/threads/gearing-calculator.38206/

 

[Halstem1]

Actual size would give you the most accurate rpms estimates when using a calculator. On my wife’s JL running 37 STT Pros I installed 5.13s and they are perfect and would be fine if we went up to 39s. 40s are kind of my breakover to 5.38s because it’s so much additional rolling resistance, weight and drag that they need all help they can get. 5.38s would be a little much on 37s even with the possibility of doing 40s in the future if that makes sense.

Brett

Would you have any concern going to 5.13 if I’m running “little” 37’s? I’ve been told the SST runs closer to actually 37”. I was using the calculators based one 37” but need to look at with 35” probably. I just wanna be able to run 79 MPH and be at or close to 2500 rpm.

 

[JtwJL]

I just dropped off my JLU Sport S manual, on 35’s, to be regeared today. Going to 4.88. Considered 5.13, but decided to stick with 4.88. IF I decided to get 37’s one day I’ll have to figure it out then, maybe a Rubi transfer case if I can find one.
I’m trussing my D30 front axle while in there too, and adding lockers! So excited to drive it! I’ve been nursing along my powerless rig for a while and can’t wait to have some oomph again!

Whats the update?! Hows 4.88 on 35s? do you think going to 37s will still be fine on that ratio with the 6 speed? Thats my issue, I only want to re-gear once and I don't want to do 37s right away, but I think eventually I will do that... I have 33s right now, but my next set of tires will be 35s when they wear out, and once the 35s wear out I'll either stick with 35s or go 37s.

 

[rustyshakelford]

Would you have any concern going to 5.13 if I’m running “little” 37’s? I’ve been told the SST runs closer to actually 37”. I was using the calculators based one 37” but need to look at with 35” probably. I just wanna be able to run 79 MPH and be at or close to 2500 rpm.

Have you put a tape and level on them to see what they really measured out to? I want to say I set the STT pros to 36.2” or there about when programming them. A 37 that running in the 35s, I’d have an issue with the labeling.

If you’re closer to the 35” size, 4.88s will still be a huge improvement from the stock gearing

Brett

 

[rustyshakelford]

Whats the update?! Hows 4.88 on 35s? do you think going to 37s will still be fine on that ratio with the 6 speed? Thats my issue, I only want to re-gear once and I don't want to do 37s right away, but I think eventually I will do that... I have 33s right now, but my next set of tires will be 35s when they wear out, and once the 35s wear out I'll either stick with 35s or go 37s.

6 speed is a different animal. Settle and get your tires installed then regear to them. It’ll be a dog and not fun to drive for a while so try and line things up if possible

Brett

 

[JtwJL]

6 speed is a different animal. Settle and get your tires installed then regear to them. It’ll be a dog and not fun to drive for a while so try and line things up if possible

Brett

Yeah I know it is, I never see 6th, highway I sometimes need to drop to 4th depending on wind/incline with 33s, I can deal with this for now but once these wear out I'll go 35s which then I definitely will re-gear. My issue is I am eventually going to go 37s and put the prorock 44 in the front when it stops being a DD (probably 4 years ish down the road) but only want to regear once..

 

[Halstem1]

Have you put a tape and level on them to see what they really measured out to? I want to say I set the STT pros to 36.2” or there about when programming them. A 37 that running in the 35s, I’d have an issue with the labeling.

If you’re closer to the 35” size, 4.88s will still be a huge improvement from the stock gearing

Brett

I just measured them the other day with a level and tape. 35 1/4”. I always knew everyone said the BFG ran small but that’s silly.

 

[Roky]

Have you put a tape and level on them to see what they really measured out to? I want to say I set the STT pros to 36.2” or there about when programming them. A 37 that running in the 35s, I’d have an issue with the labeling.

If you’re closer to the 35” size, 4.88s will still be a huge improvement from the stock gearing

Brett

I just measured them the other day with a level and tape. 35 1/4”. I always knew everyone said the BFG ran small but that’s silly.

Nitto ridge grapplers 37s at 30 psi warm on mine are 35 - 3/4” so I’m thinking 4.88s for me. 38s are the tallest I’m going if I change, so I’m thinking I’ll still be good.

Sponsored