2018 JLU S Sport and 37" BFG KO2

[OrangeJL15]

This is my first post on a forum. Thank you everyone for your input. I've learned a lot from reading these forums.

I have a question for anyone that has experience with a similar situation.

My build is a 2018 JLU S Sport with 8-speed automatic transmission, D44 rear and D30 front axles with LSD, and Teraflex 3.5" Sport S/T3 suspension lift kit. I'm running 285/75r17 BFG KO2 tires and regeared last year to Dana Spicer 4.56 gear ratio. I'm very happy with its performance both on and off road, although I do admit that the tires look quite a bit smaller than I hoped with the current lift...they measure about 33.5".

My mechanic has recently informed me that he has a set of 37" BFG Ko2 tires that are basically brand-new for a very good price, taken off another Jeep that decided on 39's. He is recommending truss upgrades if I choose larger tires. These tires are advertised as measuring 36.5" diameter from BFG website, but much of what I'm seeing is that they're closer to 35.5" once mounted, and I know that they will tend to run smaller than other advertised 37's.

Has anyone else had a similar set up and what can I expect with the performance? Would my gearing ratio be better at a 4.88 or 5.13? Are there any other upgrades necessary to running these tires, short of a front axle swap (which I may do in the future). My Jeep is a daily driver that I take off-road on moderate trails 1-2 times per month. I currently drive on fairly flat terrain but will be moving to a more hilly part of the country very soon.

Any input will be greatly appreciated!

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[scrape]

This is my first post on a forum. Thank you everyone for your input. I've learned a lot from reading these forums.

I have a question for anyone that has experience with a similar situation.

My build is a 2018 JLU S Sport with 8-speed automatic transmission, D44 rear and D30 front axles with LSD, and Teraflex 3.5" Sport S/T3 suspension lift kit. I'm running 285/75r17 BFG KO2 tires and regeared last year to Dana Spicer 4.56 gear ratio. I'm very happy with its performance both on and off road, although I do admit that the tires look quite a bit smaller than I hoped with the current lift...they measure about 33.5".

My mechanic has recently informed me that he has a set of 37" BFG Ko2 tires that are basically brand-new for a very good price, taken off another Jeep that decided on 39's. He is recommending truss upgrades if I choose larger tires. These tires are advertised as measuring 36.5" diameter from BFG website, but much of what I'm seeing is that they're closer to 35.5" once mounted, and I know that they will tend to run smaller than other advertised 37's.

Has anyone else had a similar set up and what can I expect with the performance? Would my gearing ratio be better at a 4.88 or 5.13? Are there any other upgrades necessary to running these tires, short of a front axle swap (which I may do in the future). My Jeep is a daily driver that I take off-road on moderate trails 1-2 times per month. I currently drive on fairly flat terrain but will be moving to a more hilly part of the country very soon.

Any input will be greatly appreciated!

Sport axle housings are just as strong as rubi axle housings, everything from the pumpkin out (tubes, fad, Cs, knuckles) are identical. In fact sport housings are arguably stronger because they are slightly narrower. If you had a rubicon, would you truss the axles? If the answer is no, then don’t do it to a sport either.

Then as far as gears go. 4.56 is the best ratio in my opinion because it’s the best compromise between reduction and strength. Once you go to a 4.88 you lose a tooth on the pinion gear.

Whether or not you will be happy with 4.56s and 37s on the road is pretty subjective. I personally don’t care if my Jeep never uses 8th gear, but some people are anal about that.

 

[OrangeJL15]

Thank you for your input. It sounds like the 4.56 may be ideal for the 37" KO2's since they're a lighter and smaller than other 37's. Adding trusses won't be too terribly expensive and I don't mind the expense if it will beef the axles up a bit. I'll go ahead and pull the trigger on new tires and post back with my opinion afterwards.

 

[starrs]

Thank you for your input. It sounds like the 4.56 may be ideal for the 37" KO2's since they're a lighter and smaller than other 37's. Adding trusses won't be too terribly expensive and I don't mind the expense if it will beef the axles up a bit. I'll go ahead and pull the trigger on new tires and post back with my opinion afterwards.

For what it’s worth I called AEV inquiring about a turnkey build. I asked about 37s on a 2 door Willys edition. The tech I spoke too explained that they use BFGs and they do run small. A 37” km3 or Ko2 is going to measure almost exactly 35” when on the Jeep and loaded. He said they could do the JL370 kit on a willys. With that upfit they also regear to 4.56 with 37s. So your 4.56 should be perfect

 

[Jamrock]

Please let us know how things work out. Remember to post pictures with the new tires.

 

[OnlyOne]

Thank you for your input. It sounds like the 4.56 may be ideal for the 37" KO2's since they're a lighter and smaller than other 37's. Adding trusses won't be too terribly expensive and I don't mind the expense if it will beef the axles up a bit. I'll go ahead and pull the trigger on new tires and post back with my opinion afterwards.

They are lighter but not really smaller. Most 37's are within a 1/4' of each other give or take. Any 37 you install will have a fairly large impact on just about every aspect of drive-ability. As @scrape said, the housings are the same as a Rubi 44 (just not as wide) so just go easy on the axles and they will be fine. Buy whatever 37 you want because the size is negligible.

 

[OrangeJL15]

I’m very happy with the look and feel of new tires. They ride just as smooth and quiet as the 285’s without any noticeable loss of power.

 

[ChattVol]

They are lighter but not really smaller. Most 37's are within a 1/4' of each other give or take. Any 37 you install will have a fairly large impact on just about every aspect of drive-ability. As @scrape said, the housings are the same as a Rubi 44 (just not as wide) so just go easy on the axles and they will be fine. Buy whatever 37 you want because the size is negligible.

I ran 315/70/17 ko2's on my JL for 15k miles and parked next to my friends jl with same size Milestar Patagonia...both at about 30 psi and 17x8.5 wheels and there was a noticeable difference in size. The ko2's definitely run smaller than milestars in that comparison. I've also seen pics of a unmounted 37" ko2 next to a unmounted 37" stt pro and the ko2 looked to be about 1/2" smaller in height.

 

[OnlyOne]

I ran 315/70/17 ko2's on my JL for 15k miles and parked next to my friends jl with same size Milestar Patagonia...both at about 30 psi and 17x8.5 wheels and there was a noticeable difference in size. The ko2's definitely run smaller than milestars in that comparison. I've also seen pics of a unmounted 37" ko2 next to a unmounted 37" stt pro and the ko2 looked to be about 1/2" smaller in height.

Here are some pics of different 35s......

There really isn't a difference. The point being, don't base your tire purchase on what some people think they measure. Go by whats on the sidewall, not what they "look" to be.

Ko2

STT Pro

Toyo RT

Trail Grappler

Nitto Ridge Grappler

KM2

 

[ChattVol]

Here are some pics of different 35s......

There really isn't a difference. The point being, don't base your tire purchase on what some people think they measure. Go by whats on the sidewall, not what they "look" to be.

Ko2

STT Pro

Toyo RT

Trail Grappler

Nitto Ridge Grappler

KM2

For most tires, I would agree with your logic. IMHO, BFG tires are the exception and run notably small. I'm basing my logic off putting my ko2's right next to a milestar in same size and asking several offroad shops about why my tires are smaller and they all replied that ko2's run small.

Let's do our own test...how about you post a pic measuring your 37" ko2 and let me know tire pressure? I'll match it with my 37" milestars and we can compare.

 

[starrs]

For most tires, I would agree with your logic. IMHO, BFG tires are the exception and run notably small. I'm basing my logic off putting my ko2's right next to a milestar in same size and asking several offroad shops about why my tires are smaller and they all replied that ko2's run small.

Let's do our own test...how about you post a pic measuring your 37" ko2 and let me know tire pressure? I'll match it with my 37" milestars and we can compare.

37” KO2 should come out to a true 35” at around 28-32 psi. My 315 KO2s have always measured just a hair over 33”

 

[OnlyOne]

For most tires, I would agree with your logic. IMHO, BFG tires are the exception and run notably small. I'm basing my logic off putting my ko2's right next to a milestar in same size and asking several offroad shops about why my tires are smaller and they all replied that ko2's run small.

Let's do our own test...how about you post a pic measuring your 37" ko2 and let me know tire pressure? I'll match it with my 37" milestars and we can compare.

30 psi

 

[OnlyOne]

For most tires, I would agree with your logic. IMHO, BFG tires are the exception and run notably small. I'm basing my logic off putting my ko2's right next to a milestar in same size and asking several offroad shops about why my tires are smaller and they all replied that ko2's run small.

Let's do our own test...how about you post a pic measuring your 37" ko2 and let me know tire pressure? I'll match it with my 37" milestars and we can compare.[/QUOTE”]

It amazes me that we are even having this conversation. What I said was 100% correct. All of these tires are within about 1/4” of each other and those that want to choose a tire shouldn’t be picking them based on someone’s theory that anecdotal evidence somehow helps make a decision easier.

You choose a tire based on what the sidewall says. All of these lift companies give their recommendations on sidewall numbers. Not a dick measuring contest on a Jeep forum. If it’s so important that one brand of tire is a 1/4” taller when loaded on a Jeep, then go right ahead. I’m trying to help people make decisions based on common sense. I’ve run almost every tire on this list. They are all about the same. I’m happy you like your milestars and I can’t speak to them because I’ve never used them. I’m sure they’re terrific tires.

 

[starrs]

30 psi

True 35” on a 37” KO2. BFG is grossly undersized on their claims. At least everybody knows this

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