Jeep Wrangler Forum banner

35's to 37's...or not

7K views 47 replies 18 participants last post by  SoK66 
#1 ·
Ok here is what I have done with my 2015 Rubicon so far...and what I "think" I need to do to move from 35's to 37's.....opinions and advice please!

Jeep is stock gears at the optional 4.10 ratio

Sleeved and Gusset Front Axle
Mopar Big Brake Kit
Rock Krawler 2.5 Flex w/ added rear Track Bar
Fox IFP 2.0 Shocks
Fox ATS Steering Stablizer
Yeti Tie Rod
Yeti Drag Link
Synergy Ball Joints
Synergy Front Shock Relocation Kit
Poision Spyder Narrow Aluminum Fenders
Rock Slide Eng Slide Steeps
Warn Winch
8.5x17 4.5" backspace wheels
BFG KM2 Mud Terrain 35" Tires

The BFG tires have 26k miles on them. They still have a lot of good rubber and I feel right now I can sell them with in my local Jeep club pretty easy I'm told. They are getting noisy on the road too. I am finding I am not going off-road as much as I like but when I do I find I'd do better, easier going with 37's instead of my 35's.

So I am thinking this is what I should do to go up to 37's
1- Re-gear to 4.88
2- Need strong front Axle Shafts
3- Need Stronger Rear Axle Shafts

4- I'm thinking about getting RCV shafts. They are only a few hundred more than the G2 Placer Gold that I hear are really good.

5- I also believe I should put in the new TeraFlex Ball Joints since there bottom joint has side zerk great fitting and the Synergy Ball Joint does not.

6- Do I need drive shafts yet?

7- due to how much I drive on the street thinking of something like BFG KM2 All Terrain tires instead of Mud Terrain tires for my 37's

Pics for attention..thanks!
 

Attachments

See less See more
4
#2 ·
You axle shafts are fine until you break them, don't swap them until you need to. Gussets and sleeves are fine but sleeves only improve axle strength to bending by about 50%. Add a Artec truss as well and your axle will be as good or better than anything after market until you get to the d60. 4.88 is perfect especially if you ever think about going back to 35's.
 
#4 ·
Well there is not doubt RCV makes a good axle and nothing wrong with being pro-active. Lol, my pro-active pocket book has taken a hit since I retired.
 
#5 ·
I'm 58k on front factory axle shafts and 37s.
Rears lasted less than 20k before the flanges bent.

You'll be fine :thumb: :)

1- Re-gear to 4.88 I regret not going 5.13
2- Need strong front Axle Shafts See above
3- Need Stronger Rear Axle Shafts See above
4- I'm thinking about getting RCV shafts. They are only a few hundred more than the G2 Placer Gold that I hear are really good. RCVs are nice, not gonna lie :)
5- I also believe I should put in the new TeraFlex Ball Joints since there bottom joint has side zerk great fitting and the Synergy Ball Joint does not. Synergy has zirks on top and bottom joints. TF will require some modification to your factory axle shafts, the RCVs I believe will be OK
6- Do I need drive shafts yet? I waited until mine bit the dust
7- due to how much I drive on the street thinking of something like BFG KM2 All Terrain tires instead of Mud Terrain tires for my 37's Tire's are hard... also check out the Cooper STT pro
Good luck!
 
#6 ·
I think you are on the right track, I did gussets and trusses front and rear, I decided that it would be really inconvenient to break an axle, because I knew it would happen at the worst possible time, so I opted to do Carbon axles front and rear, I like the fact that they came fully assembled so it was pretty easy to pull the old one and slide the new ones in.
I would second the cooper sst pro's I really like them 37x13.5x17
 

Attachments

  • Like
Reactions: aqualungs
#8 ·
Pffft those 35's look tiny... get on it!!

I am on 37" KO2's. Daily driver, occasional trail run.

My input:

1. I just went to 5.13 gears. 70-80mph is 2,750-3,250 RPM. If you regularly want over 75mph, 4.88's might be the ticket, but you can never be too low around town or on the trail.

2 - 4. I'd budget for shafts, but priority will depend on how hard you drive and wheel. I guess best case scenario would be to install upgrades BEFORE stock shafts fail so you can keep stock shafts for trail spares. Thing is, if your cognisant of the stock shafts, and drive/wheel accordingly, they'll probably last a long while.

5. I have Synergy ball joints on the work bench for when ready. Stockers are still tight after 8 months and 10k or so miles on 37's.

6. Drive shafts (I think) are more based on lift and clearance, tires won't create an immediate need.

7. KO2's (not KM2's) are the AT. Very safe and good, capable AT selection for mixed use. Typically lighter and a slightly small for a 37.

Others:
- Bumping up to 37's, (size and weight) might just be enough to expose a steering or geometry issue not realized with the 35's. Be prepared for trac bar relocation maybe high steer.

Pics for reference.
 

Attachments

#9 ·
the ko2 are weighing in at roughly 70lbs each, that is lighter than a lot of 35's out there. why all the concern about exploding the front end with this small light 37? i'm torn between these and the cooper st maxx which are 78lbs. still lighter than a toyo mt in a 35 for example.
 
#18 ·
If what you need your tires to do includes daily driving, then weight is a HUGE factor.

Agreed that high steer is related to lift height NOT tire size. I think the general consensus is that at 3" and up lift, raising the DL and TB will reduce tire feedback.

My thought process being, that if one is running close to 3" lift, they are running their DL and TB at the upper range of acceptable angles. That set up might adequately handle feed back from 35's. Going to 37's will produce more feed back so improved DL and TB angles may be benificial.
 
#12 ·
I believe all BFG measure out slightly small. The KM2 and KO2 37's being slightly small,is just fine with me...on my RK 2.5" lift.

Larger tires have nothing to do with having to go to a high steer front end.....that has to do with lift height and how the drag link lines up. On a RK 2.5" lift I do not need high steer...already confirmed that when I installed my Yeti drag link.

When I go off road....here in Florida .....we have mostly trails, dirt, mud and man made hills and rock piles. Most,of the man made rock piles I don't do...so I'd say I do easy to moderate off roading. You can see in my pictures in the first post what my off road looks like

This is why I'm thinking the BFG All Terain KO2 or something similar would be good for me. I'm also planing a long drive out west so I use my Jeep on the road a lot more than off road.
 
#13 ·
For a lot of street miles, mainly pavement driving, wheeling that definitely isn't 37s required territory, and a very long trip - I think in the end, you may be throwing a lot of money at something that will be disappointing for your intended uses going to a 37 inch tire.

All BFGs will run smaller. Nitto, Toyo and a couple others run true or close to true.
 
#15 ·
Sleeved and Gusset Front Axle
8.5x17 4.5" backspace wheels
!
Mike, any thought to trussing the rear? You have no mention of long arm or short arm suspension, is there a goal in the future for this? I mention it because RK long arm kits come with a rear truss so you wouldn't need an artec truss or anything.

With backspacing at 4.5 do you think you will have any rubbing at 37in? I just ordered some wheels and it was recommended 3.75 or less backspacing for 37-40in tires on my Evo kit.

Just some other things to consider.

-Eli
 
#17 ·
I trussed my rear. No reason to do a long arm. 4.5 backspace may be pushing it a hair - I run 4.25 and just graze the sticker on front control arm at full lock. You will always rub somewhere - control arms are beefy enough to take sticker grazing. Better than rubbing frame or body or grill. Or the extra stress on the knuckles etc going super low backspacing under 4. Jeeps are a balancing act - you solve one issue, but that solution creates different issues, key is finding the middle ground.
 
#19 ·
I have to agree with the hydro assist on 37's, if you engage a locker you will wish you had it immediately. I went with 4.5 backspacing and it's been fine so far, I noticed something was hitting just a little when crawling this weekend, it was the fender liner. I have the stock ones in and my husband didn't tighten one of the bolts all the way. Otherwise it was fine. If you plan on going with RCV's I wouldn't bother with installing those ball joints, just run what you have and save that money for the RCV's. I love mine! I have 4.5" lift and ended up shifting the rear back 1". You may have to trim the pinch seam if your at a 2.5 lift. I guess it depends on what tires you end up with. I had 5:13 gears put in and after this weekend I'm so happy with them. I had a big smile the entire time on the trail :) In 4-lo I just put it in 1st and it walked over stuff. I have driven my husbands TJ with the 5:13, but he has the 5:1 Atlas and it's a manual. I love how it crawls and you almost never have to even touch the clutch. My JKU being an auto, I wasn't sure what to expect. I was pleasantly surprised and happy as a clam, lol.

Lisa
 
  • Like
Reactions: mdrums
#23 ·
I'm running 2 S/T Maxx's, and 2 KM2's. Got just over 40,000 miles on them all. The KM2's are at about 20% tread, and the Coopers are at about 40-45%. The KM2's wear like crap if you have a lot of pavement pounding to do. Off-road in mud and rocks, they both are great. I'm on steelies, and I air down to 12psi.

BTW I've been on 37's for many miles, have a D30 with an Aussie locker in it, wheeled it in rocks and all, and haven't broken anything. Jeep has 103,000 miles on it now. It is on it's 3rd set of ball joints. First ones I changed, though, and I went to Spicer HD's. That was about 35,000 miles ago.

Lot's of voodoo talk about stuff you don't *NEED*. It's good stuff to have fo sho, but if you're smart you can make it last.
 
#24 ·
Gonna follow this thread for a bit... I just got 35s (KO2s) last year on a 2" Mopar lift and re-geared to 4.56 from stock 3.73. Installed larger rotors on front and back (courtesy of TF) but after learning BFGs run smaller, I'm wondering if I could do 37" KO2s (since measured diameter would be a true 35"). Primarily an on-road Wrangler with potential for a trail or beach here and there...


Sent from my iPhone using Tapatalk
 
#26 ·
Add Reid Racing knuckles to that list and I think you will be able to keep the breakage to a min as long as you keep the bounce out of your wheeling style. If you stick with the stock knuckles then upgrade your unit bearings to 30 spline and make sure your RCVs are 30 spline inners and outers.
 
#29 ·
so, what can we come with that is based on physics if we look at a 35 inch toyo mt weighing 83lbs vs a less aggressive ko2 weighing 70lbs. toyo has more weight and more aggressive lugs to catch and cause traction on rocks, roots and otherwise. which is in the real world more likely to cause breakage under the same conditions?
 
#30 ·
Anything can cause breakage. Regardless how much your tire weighs.

I would rather have a heavier aggressive tire that is grabbing traction than a lighter less aggressive tire that isn't. That lighter tire is spinning a lot, which means you are probably putting more gas pedal to try to get traction, way more tire spin going on. Skinny pedal + tire spin = source of probably the majority of Offroad carnage. I would go with the tire actually getting traction.
 
#31 ·
Looked at the new General Grabber X3 37's....suppose to be a great tire for off-road but civil with low noise on the highway. However they weight 82lbs!

A heavier tire is more work for the driveline and harder to rotate making acceleration and braking worse.

My BFG Mud Terrain 35's are making me deaf! LOL
 
#35 ·
I just heard about a drop down rear tire carrier that GenRight has. It looks cool and GenRight surely makes great stuff but it seems like you loose the use of the rear door. Has anyone seen this tire carrier or know of any other drop down tire carriers? I googled and couldn't find anything else.

I'm getting a lot of votes for the 37" Cooper STT Pro in my local Jeep club. They say they are quiet and that I'd be real unhappy with the BFG All Terrain off road
 
#36 ·
I initially built my then new '09 JKUR with BFG KM2 35s, which are really just rather large 33s. It was an easy bump to KM2 37s, which are really just plump 35s. Next move was to MTR/K 37s, which are close to true 37s. I was running 4.88s due to an ill informed recommendation and despite it all here in the mountains of SW Colorado the combination was more than livable, even with the gutless 3.8l. I eventually swapped in 5.38s and it was a major performance improvement. After some experience with them on a few other peoples' rigs I tossed the MTR/Ks for 37" MT STZ P3s. These are the best all around tire I've yet used. However they do run a bit small. At street pressure they measure 36.5" diameter.


Sent from AutoGuide.com Free App
 
#37 ·
Thanks @SoK66 I do like my BFG's but I keep hearing that the newish Cooper STT Pro tire is th best way to go...just as good off road some say better than the BFG Mud but a lot better on th highway than the BFG Mud.

I was looking to the chart showing gear ratio's vs tire size for my 3.6 and I think 4.88 ratio will be fine. It will be much like stock with my 4.10 and stock 32's so he crawl ratio will be great again.

I still haven't decided on RCV shafts or something like Force 10 or Carbon U joint shafts.
 
#38 ·
Tangential question, I am replacing my 2016 Sahara OEM D30 Front Axle in 3 weeks with a Dynatrac ProRock D44 w/ ProSteer Ball Joints, Yeti/Griffin High Steer Draglink Assembly, RCV Axle, REID racing knuckles, Detroit TrueTrac, and 4.56 gearing (only because I intend getting Prodigy Stage II turbo in 2 months). He's also installing King 2.5 12" coilovers, I will tell him to return my OME Nitrocharger Sport Shocks, I should be able to resell that < 5k miles when I had MC GC Long Travel Arb edition installed.

Is there ANYTHING else I should ask my mechanic to keep for me that he is taking off, or just tell him to keep/dump it all? I.E. is anything considered trail parts that is worthy to lug around with me, I assume nothing is resellable for any decent value.
 
#42 ·
I love the looks of the 37 and proportion of Jeep to tire. I would never go that big, because I'd need a step

Sent from my iPhone using Tapatalk
I'm close to needing one! I get asked all the time how I get in, lol. I told my husband as long as I can still hop up in, no step. I just hope I don't shrink as I age :(
 
  • Like
Reactions: aqualungs
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top