37" tires
05-06-2018, 07:41 AM
#1
JK Newbie
Thread Starter
37" tires
I currently run 315 70R 17 Duratracs on sevegre wheels with a 3.5 AEV lift on my 2015 Rubicon. I am looking to go to 37" tires. What do I need to do to upgrade the tires? regear? anything else?
05-06-2018, 04:20 PM
#2
JK Freak
Do you need the 37's? In other words, is tire size limiting you out on the trail? If not, don't do it.
If yes, then I'd run through this checklist first:
-Is the rear axle-side track bar bracket raised?
-Does my rear pinion angle look good?
-Are my c's gusseted?
-Are my axles trussed?
-Am I ready to re-gear?
-Are my brakes upgraded?
-Are my ball joints aftermarket? Heavier duty or a kickass warranty?
-Am I running 1 ton steering? If not, am I ready to drop the coin?
-Am I ready to go with hydro-assist?
-Am I ready to drop unexpected $dough$ on driveshafts, axle shafts, and possibly go crazy with my suspension?
If the answer to any of those questions was no, don't do it.
Sure you can slap 37's on any Jeep, so some might disagree with my minimum recommended checklist ^ and go "well I've been running 37's on my stock axles and haven't broken anything yet." It comes down to how you wheel. If you're okay with babying it, then just replace what breaks and make sure you have your AAA card if you unexpectedly find yourself needing a tow home. You'll need the gears at a minimum, and you'll want some bigger brakes ASAP. Expect driveshafts to fail soon (my rear blew out really fast, front is starting to go now). In order to keep your new Adams/Tom Woods/Coast/whatever driveshafts happy, you'll need to adjust your pinion angle out back. While you're doing that you'll find your rear coils are bowing...so order up some Artec coil perches, cut the old ones off, and weld the new perches so your coils are no longer bowing. While you're at it, replace your rear track bar bracket with a beefier raised weld-on such as the Synergy, AND slap a truss on the rear or weld your tubes to the housing at a minimum.
At this point you'll probably have a shimmy in your steering. Use front lowers to adjust your caster to around 4-4.5 degrees. You can't add too much caster, or you'll put too much strain on your driveshaft. The front is a balancing act between caster and pinion angle. After a few hundred miles, maybe a few thousand, you'll find your new 37's have destroyed your ball joints, and you were right on the verge of experiencing death wobble. Remove old ball joints, weld up c-gussets while they're out, hell...weld on the entire Artec armor kit while you're at it. New ball joints and armor welded on, might as well go with 1 ton steering to replace the crappy stock tie rod and drag link.
Now you go wheeling, bend the splines on your rear axle shafts...maybe snap a shaft up front. Time to replace the stock shafts. First real wheeling trip on 37's (blacks and some easier lines on reds) and you'll realize "holy crap I can't turn these things when I'm locked." Now you'll look into hydro-assist, PSC, WTOR, or DIY? Will need to flip your drag link while you're at it, which will also require welding on a raised track bar bracket up front. Now you're realizing your suspension isn't dialed in, and you go crazy frankenlifting it. The "How can I get more droop??" bug will hit, you'll start looking into cramming longer travel shocks under it requiring you to chop/relocate shock mounts. "What coils have the longest free length?" "Well I might as well stretch while I'm at it"
You're opening a can of worms, are you ready for it?
If yes, then I'd run through this checklist first:
-Is the rear axle-side track bar bracket raised?
-Does my rear pinion angle look good?
-Are my c's gusseted?
-Are my axles trussed?
-Am I ready to re-gear?
-Are my brakes upgraded?
-Are my ball joints aftermarket? Heavier duty or a kickass warranty?
-Am I running 1 ton steering? If not, am I ready to drop the coin?
-Am I ready to go with hydro-assist?
-Am I ready to drop unexpected $dough$ on driveshafts, axle shafts, and possibly go crazy with my suspension?
If the answer to any of those questions was no, don't do it.
Sure you can slap 37's on any Jeep, so some might disagree with my minimum recommended checklist ^ and go "well I've been running 37's on my stock axles and haven't broken anything yet." It comes down to how you wheel. If you're okay with babying it, then just replace what breaks and make sure you have your AAA card if you unexpectedly find yourself needing a tow home. You'll need the gears at a minimum, and you'll want some bigger brakes ASAP. Expect driveshafts to fail soon (my rear blew out really fast, front is starting to go now). In order to keep your new Adams/Tom Woods/Coast/whatever driveshafts happy, you'll need to adjust your pinion angle out back. While you're doing that you'll find your rear coils are bowing...so order up some Artec coil perches, cut the old ones off, and weld the new perches so your coils are no longer bowing. While you're at it, replace your rear track bar bracket with a beefier raised weld-on such as the Synergy, AND slap a truss on the rear or weld your tubes to the housing at a minimum.
At this point you'll probably have a shimmy in your steering. Use front lowers to adjust your caster to around 4-4.5 degrees. You can't add too much caster, or you'll put too much strain on your driveshaft. The front is a balancing act between caster and pinion angle. After a few hundred miles, maybe a few thousand, you'll find your new 37's have destroyed your ball joints, and you were right on the verge of experiencing death wobble. Remove old ball joints, weld up c-gussets while they're out, hell...weld on the entire Artec armor kit while you're at it. New ball joints and armor welded on, might as well go with 1 ton steering to replace the crappy stock tie rod and drag link.
Now you go wheeling, bend the splines on your rear axle shafts...maybe snap a shaft up front. Time to replace the stock shafts. First real wheeling trip on 37's (blacks and some easier lines on reds) and you'll realize "holy crap I can't turn these things when I'm locked." Now you'll look into hydro-assist, PSC, WTOR, or DIY? Will need to flip your drag link while you're at it, which will also require welding on a raised track bar bracket up front. Now you're realizing your suspension isn't dialed in, and you go crazy frankenlifting it. The "How can I get more droop??" bug will hit, you'll start looking into cramming longer travel shocks under it requiring you to chop/relocate shock mounts. "What coils have the longest free length?" "Well I might as well stretch while I'm at it"
You're opening a can of worms, are you ready for it?
Last edited by BoraBora; 05-06-2018 at 04:25 PM.
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WVUFAN18 (05-09-2018)
05-06-2018, 06:59 PM
#3
JK Jedi Master
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What is the backspacing on your rims? (Adding spacers? Buying new?)
Gears will be a judgment call based on what you have now, where you live, how you drive, your personal opinion on the power, etc, etc. But yeah, you will want to regear...
And put some thought into what Bora posted. While it is stated in a more worst-case, do you really want to do this way, all of it is worth putting some consideration into.
Gears will be a judgment call based on what you have now, where you live, how you drive, your personal opinion on the power, etc, etc. But yeah, you will want to regear...
And put some thought into what Bora posted. While it is stated in a more worst-case, do you really want to do this way, all of it is worth putting some consideration into.
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WVUFAN18 (05-09-2018)
05-07-2018, 07:37 AM
#4
JK Jedi
I think that in general, Bora Bora’s checklist above is a pretty good assessment, but for most people you probably don’t need all of it. A lot just depends on what you’re going to do with the jeep.
I think that in general, you need:
1) properly BS wheels – 3.5” or willingness to run spacers. Even with a 12.50” tire and 4.5” BS most have, you’ll rub a tiny bit.
2) proper gearing – jumping to 37s is really where it HAS to be addressed.
3) adjustable control arms – especially in the rear….jumping to 37s IMO is where you have to push that axle back some….this then makes you move your rear sway bar back as the links will now hit the axle’s upper control arms as they lean forward, which makes you address your exhaust as well.
4) be ok trimming more pinch seam
You’re steering components will be stressed even further, so if you haven’t upgraded all that, plan on it. Ball joints will likely require a step up to the high end units….and I’m not talking Synergy, TF, Alloy…talking DT or RP’s.
Brakes are highly advised, but I’m still on factory. I’d like larger, and it’s probably next on the checklist, but not end of the world; however, I fully expect that once done it will be an OMG…should have done that sooner moment.
Hydro or HD steering box….nice to have, but it’s not necessarily required. I kinda think the rest of it….if you’re out wheelin hard, you should be addressing regardless of 35s or 37s.
It's a lot like the thought of going from 2.5" lift to 3.5" lift starts costing more....a lot of little things just add up. Going up to 37s starts to require a lot of additional things to be addressed, or planned out.
I think that in general, you need:
1) properly BS wheels – 3.5” or willingness to run spacers. Even with a 12.50” tire and 4.5” BS most have, you’ll rub a tiny bit.
2) proper gearing – jumping to 37s is really where it HAS to be addressed.
3) adjustable control arms – especially in the rear….jumping to 37s IMO is where you have to push that axle back some….this then makes you move your rear sway bar back as the links will now hit the axle’s upper control arms as they lean forward, which makes you address your exhaust as well.
4) be ok trimming more pinch seam
You’re steering components will be stressed even further, so if you haven’t upgraded all that, plan on it. Ball joints will likely require a step up to the high end units….and I’m not talking Synergy, TF, Alloy…talking DT or RP’s.
Brakes are highly advised, but I’m still on factory. I’d like larger, and it’s probably next on the checklist, but not end of the world; however, I fully expect that once done it will be an OMG…should have done that sooner moment.
Hydro or HD steering box….nice to have, but it’s not necessarily required. I kinda think the rest of it….if you’re out wheelin hard, you should be addressing regardless of 35s or 37s.
It's a lot like the thought of going from 2.5" lift to 3.5" lift starts costing more....a lot of little things just add up. Going up to 37s starts to require a lot of additional things to be addressed, or planned out.
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WVUFAN18 (05-09-2018)
05-07-2018, 08:51 AM
#5
Super Moderator
Like the others have said, 37s introduce a new set of possibilities to break stuff. It really depends on your aversion to risk and what you use your rig for. As an example, many folks around me run 37s without much of what BoraBora listed (I agree with that list BTW), but they fall into one of these categories... 1) Don't wheel at all, 2) Wheel only logging trails, 3) Do wheel some of the more advanced stuff and know they are introducing opportunity to break stuff.
A friend of mine on 37s just broke his sector shaft on Saturday, he wheels the advanced stuff and took the gamble that he wouldn't break. He's got a new steering gearbox on the way and will port it and run the WTO hydro assist. Additionally, that same hit also bent his tie rod (and looks like the drag link too), so he'll be shopping for a 1-ton steering set up as well. He just replaced his ball joints like a month ago.
So you can see from that story, that a good amount of the parts that BoraBora listed are now on his list...
A friend of mine on 37s just broke his sector shaft on Saturday, he wheels the advanced stuff and took the gamble that he wouldn't break. He's got a new steering gearbox on the way and will port it and run the WTO hydro assist. Additionally, that same hit also bent his tie rod (and looks like the drag link too), so he'll be shopping for a 1-ton steering set up as well. He just replaced his ball joints like a month ago.
So you can see from that story, that a good amount of the parts that BoraBora listed are now on his list...
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WVUFAN18 (05-09-2018)
05-07-2018, 09:24 AM
#6
JK Jedi
LOL, this is how it typically goes. It's both an addictive and expensive hobby. Regardless of how you're built, go out and do aggressive things one needs to keep in mind that breaking stuff or trail damage is part of the game. Break it, fix it, upgrade it. It's a lot like having a high end remote control beast, cept way way more expensive to fix.
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WVUFAN18 (05-09-2018)
05-09-2018, 07:01 AM
#7
JK Newbie
Thread Starter
Thanks so much for your open and honest assessment, very informative stuff. This is exactly what I was looking for. I guess I have some decisions to make concerning the upgrade. I knew there had to be a lot more to it than just re-gearing.
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05-10-2018, 03:14 PM
#8
JK Enthusiast
BoraBora pretty much nailed it. 35's are the top end of where I'd be comfortable without expecting to go deep into the cost department. Yes, it matters how you drive, yes it matters where you wheel, but it also becomes a matter of when and not if you're going to start breaking things. Regardless of the offroad stuff, you have the safety items to consider, ie steering and brakes, or a really loud horn if you want to go the other route. You can budget and replace things as they break, but keep in mind that typically you're not going to have some kind of massive failure as you turn onto your street, it going to be getting dark, in the middle of nowhere, on the side of a mountain. Pay once, cry once becomes a key motto at this point. Spend the extra money on the upgrades even if you think you don't need them. You will, and it will be dark, in the middle of nowhere, on the side of a mountain. That's just how it seems to work. Good luck!
05-13-2018, 04:35 AM
#9
JK Newbie
Join Date: May 2018
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To give you some applicable advice. I have the AEV lift with 37s on mine. I drive it a few times a week and sometimes to work (mixed highway and city commute of 20 miles) and for running errands around town. My Willy's has the 3.73 gears and honestly - everyone's "You MUST re-gear immediately with 37s" is somewhat comical and just plain silly. I assume with your Rubi you have 4.10s? The older JKs with the 3.8, I can understand the "re-gear NOW" comments. That engine is/was a dog compared to the 3.6. This is going to sound obvious, but it's really all how you drive. I get 16-17mpg with 37s on my 3.73s vs stock was 18-19mpg. (I set cruise at 60-65mph on the highway and my "eco" mode stays on just as it did stock). I am in a lifted Jeep, not a ZR1 Corvette. If you are planning to race people off the line in a Jeep with 37s, then by all means, get your new gears. And trust me, I see plenty of people in lifted Jeeps driving like maniacs, racing, gunning it from every stop light or stop sign...so I know exactly why people on these forums make it sound like you need gears immediately... paying no attention to their rollover hazards. If you are minding your own business and pay no attention to the craziness in how people drive now, then no, your 4.10s will be MORE than sufficient. I have not driven in the mountains, being that Michigan is pretty flat but I can pull out of my subdivision and get up to speed (45-50mph) EASY, and I can easily get up to 70+ on the entrance ramps to highways without straining at all. I don't tow, so I can't give you any applicable advice there.
In the end, be happy with your Jeep. If you want 37's, go get them. I don't want to speak for everyone and their financial situations - but people who lift new $40k Jeeps (like us) aren't worried about having to upgrade more later. Trust me, you won't scare me away by saying "Eventually you will need a new driveshaft or ball joints" Big whoopty doo. I've had to put a transmission in a car with 80,000 miles (thanks FORD!) before... guess what? You fix it. It's part of car ownership. I would rather be happy I went with 37s and have to replace some parts every once in awhile ... versus look at my Jeep and say "I should have gotten 37s, but I'm glad I don't have to do ball joints with my 35s!!"
05-14-2018, 09:17 AM
#10
JK Freak
^ I have to disagree with your comment regarding gears. 3.73 may seem sufficient to you, but I promise you...you don't know what you're missing. My stock gears were drivable with 35's, but they left much to be desired off-road and on hilly roads. Crawl speed absolutely sucked, was constantly riding the clutch, 6th gear didn't exist, and I found myself downshifting more than anything. After gears? 4th gear going 40mph up a hill. I can pass people in 6th gear. 1st gear is very short now, but 6th gear exists again...and I'm getting 18mpg in 6th gear @70mph with 37's and beadlocks. Pretty good.
There's a common misconception that we regear for speed or acceleration, but this doesn't tell the full picture. With bigger tires, especially 37's, it's imperative that you regear in order to take the stress off your transmission/drivetrain. 3.73's and 4.10's will be drivable, but that's about it. Yeah it's a lifted Jeep and it's not meant to go fast, but that doesn't mean you shouldn't regear to the proper ratio if you can afford it.
When it comes to rocks, crawl speed is so important. The absolute best mod you can do to a JK for rock crawling is picking up a Rubi 4:1 tcase. Given that you (OP) already have the 4:1 tcase, pick any gear ratio that will suit your driving needs. I picked 4.56 over 4.88 because I drive my Jeep to the trails and wanted to keep the RPM's down (I usually drive around 80-85) while still having good power. Jeep feels stock now with 4.56 and heavy 37's, but my 2 door is also very weight conscious/light. 4:1 tcase makes it crawl slower than a turtle anyways, so I didn't need or want deeper gears.
There's a common misconception that we regear for speed or acceleration, but this doesn't tell the full picture. With bigger tires, especially 37's, it's imperative that you regear in order to take the stress off your transmission/drivetrain. 3.73's and 4.10's will be drivable, but that's about it. Yeah it's a lifted Jeep and it's not meant to go fast, but that doesn't mean you shouldn't regear to the proper ratio if you can afford it.
When it comes to rocks, crawl speed is so important. The absolute best mod you can do to a JK for rock crawling is picking up a Rubi 4:1 tcase. Given that you (OP) already have the 4:1 tcase, pick any gear ratio that will suit your driving needs. I picked 4.56 over 4.88 because I drive my Jeep to the trails and wanted to keep the RPM's down (I usually drive around 80-85) while still having good power. Jeep feels stock now with 4.56 and heavy 37's, but my 2 door is also very weight conscious/light. 4:1 tcase makes it crawl slower than a turtle anyways, so I didn't need or want deeper gears.