Does anyone run 37s with 3.21 gears on 2015 JKU? I know this isn't ideal but I'm leaning towards doing this until I can afford to re-gear. I'm only using my jeep as a daily driver, no towing , no rock crawling, and no towing. Would I be ok running these 37s and for how long?
I ran 4.10s on 37s for a year. At first it was OK (at best), then I quickly realized I needed a regear.
I was an effective 3.55 ratio, you'll be effective 2.78 ratio. 2.78 ratio plus the extra weight of the wheel/tire combo.... That would be unbearable to me. But everyone is different
I put light weight 33's & light weight wheels on my Jeep w/3.21 gear - only an increase of about 10 pounds per corner and I can tell a difference - acceleration & breaking - I can't imagine what it would be with 37's!! (wouldn't the breaks need to be upgraded too?)
Auto or manual?
No matter what it's going to be an absolute dog. Might be able to get away with it if you've got a manual - just shorten your clutch life. Wouldn't think of it with an auto.
That is going to be le suck. It has to be awful already with 35s. If you don't think it's a dog, you have never driven a properly geared Jeep. The difference would be astronomical.
I personally also wouldn't even consider 37s on a D30 either, but that's me.
I have 3.21 gears in my JKU and I'll probably go to 33's shortly and I'm looking into light weight tires so I don't mess up the performance. I had 4.10's in my Rubicon and I noticed a power loss with 35's. I wouldn't even consider 37's without a regear first. The D30 is a whole other issue as mentioned above.
Thanks for all the feedback, although I'm disappointed to wait for 37s it's obviously the smart thing to do. I'll just wait till I can afford to do it the right way. I still need to reprogram, what do y'all recommend?
C gussets are very inexpensive insurance. Ball joints are well worth it and necessary even if you run no lift and stock tires, whatever axle your Jeep came with. The stock ball joints are crap, period.
Ive been running 3.73 with my 37s and didnt have any issues at all. I am now down to 35s just because I like the smaller tire but it was all fine for me.
So nobody answered his question - a lot of advice, but no one running 37's on 3.21. Bottom line, it will lower your acceleration a bit, but won't hurt anything. And I get he wants to spend his first dollars on something he can see right away.
LOL, the "nobody's answered his question" comes from the fact that 37s are expensive tires, and not many people run them at all, and those who do have usually built up to that point, and usually have a good bit of experience, and that experience steers them away from such a godawful idea as 37s and 3.21s.
Every enthusiast vehicle has people who try and go for the big mod without spending the necessary supporting mod money. Turbo cars are a great example; it's so easy to turn up the boost to 21 pounds without doing anything else. Your intercooler needs upsized, your fuel injectors need replaced, ditto fuel pump, new tuning program. Then you probably need some upgrades to the rest of your driveline, most notably the clutch. And so on.
So you find "700hp" hits that consist of bigger turbos and a computer flash, and people wonder why they drive like crap and break all the time.
LOL, the "nobody's answered his question" comes from the fact that 37s are expensive tires, and not many people run them at all, and those who do have usually built up to that point, and usually have a good bit of experience, and that experience steers them away from such a godawful idea as 37s and 3.21s.
37's with 3.21s is just stupid. 37's on a bone stock Dana 30 will cause a failure sooner rather than later. It's physics. You can't argue with physics.
Every enthusiast vehicle has people who try and go for the big mod without spending the necessary supporting mod money. Turbo cars are a great example; it's so easy to turn up the boost to 21 pounds without doing anything else. Your intercooler needs upsized, your fuel injectors need replaced, ditto fuel pump, new tuning program. Then you probably need some upgrades to the rest of your driveline, most notably the clutch. And so on.
So you find "700hp" hits that consist of bigger turbos and a computer flash, and people wonder why they drive like crap and break all the time.
Well that escalated quickly, haha. I appreciate all of your opinions and have read all closely. I just need to be sure because it is my daily driver, not off roading yet, and I can't afford to fix something big if it breaks just driving to and from work. Makes me nervous to run 37s without proper equipment after reading all thoughts. I just trimmed up my fenders and imagined how bad ass it would look with 37s, so that part makes it tempting.
If I were to buy 4.56 or 4.88 gears, what are yalls thoughts on buying used? As there are a few being sold online for $100-250.
Also what programmer should I get for what I'm using my jeep for?
Well that escalated quickly, haha. I appreciate all of your opinions and have read all closely. I just need to be sure because it is my daily driver, not off roading yet, and I can't afford to fix something big if it breaks just driving to and from work. Makes me nervous to run 37s without proper equipment after reading all thoughts. I just trimmed up my fenders and imagined how bad ass it would look with 37s, so that part makes it tempting. If I were to buy 4.56 or 4.88 gears, what are yalls thoughts on buying used? As there are a few being sold online for $100-250. Also what programmer should I get for what I'm using my jeep for?
Used gears make zero sense. You might save a little on the gears themselves but the majority of the cost comes from install labor, and chances are a shop is not going to want to install used gears because it's very likely they are going to make noise. Paying $1300 instead of $1500 to use used gears is crazy.
The gears are the only thing I didn't do myself. To me it's more complicated than I wanted to tackle. Generally the shop will purchase the necessary parts. It seems cost is around $1,800 to $2,000 dependent on your area. I'm sure you know, but it needs to be said: you have to re-gear front and rear axles.
The second part is to make sure you're prepared for when items fail because of the extra weight/size. Ball joints and rear axle shafts failed fairly quickly for me (within 25k miles)
Lots of folks don't know that so much is affected by big heavy tires. Your rig was designed and engineered to run 29 or 32 inch tires.
Your brakes are designed to stop stock tires.
Your tie rod, drag link, ball joints, sector shaft and steering box were all designed to steer stock tires.
Your axles and shafts were designed/chosen to turn stock tires.
Your gearing was designed to drive stock size tires (the best stock size tire for 3.21 is 29 inches)
And so on.
Think about it. The good folks at Jeep/Fiat did not say "hey lets design a Jeep to run 37 inch tires and then put 32s on it for fun".
Those who say gearing is "subjective" (typically the folks trying to justify why they didn't spend to do it) have never driven a properly geared Jeep. Especially once you get into oversize tires, the difference is dramatic, and keeps your Jeeps driveline and mechanicals much happier.
Lots of folks don't know that so much is affected by big heavy tires. Your rig was designed and engineered to run 29 or 32 inch tires. Your brakes are designed to stop stock tires. Your tie rod, drag link, ball joints, sector shaft and steering box were all designed to steer stock tires. Your axles and shafts were designed/chosen to turn stock tires. Your gearing was designed to drive stock size tires (the best stock size tire for 3.21 is 29 inches) And so on. Think about it. The good folks at Jeep/Fiat did not say "hey lets design a Jeep to run 37 inch tires and then put 32s on it for fun". Those who say gearing is "subjective" (typically the folks trying to justify why they didn't spend to do it) have never driven a properly geared Jeep. Especially once you get into oversize tires, the difference is dramatic, and keeps your Jeeps driveline and mechanicals much happier.
None of this stuff is subjective; it's all math, engineering, and physics. I find anyone but the engineers behind the design trying to define acceptable tolerances a bit laughable.
It's a simple fact - the entire system is designed to be used with stock components. Change the components and you're now engineering your own system. We all love to mess with our Jeeps so, thankfully, there's tons of knowledge out there to draw from. As always though internet wisdom is exactly that, take it with a grain of salt.
Me? I run 33s with 3.21s on a D30 with stock wheels on spacers. I'm fully aware that I've, to an extent, added stress to the rest of the stock components that I haven't traded out yet. I also fully expect that I've increased my chances for component failure in those stock parts.
I have a buddy running 37's on 3.21's. He has an auto and manually shifts. He states it would be unbearable otherwise. Note, we're in Western NC so mountains are involved.
Did he tell the computer about the tire size change? If you don't, it shifts like crap. Getting the programmer and doing it makes the computer shift smarter.
Yeah, it's still a dog unless he shift manually but he's okay with that since it's just a DD.
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