Tire and Axle Dilema - 37's vs. lightweight 40's

OBJLU

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I'm looking at new tires and I've narrowed it down to two choices:

  • Mickey Thompson 37x12.5r17 Baja Boss - by all accounts an amazing tire, I run the Cooper STT PRO's and everyone I talk to says these are a step up. They weight 81 lbs.
  • Geolander G003 MT 40x13.5r17 - a LIGHTWEIGHT 40 at 87LB's . I used to run these on a different rig and liked them but the Baja Bosses are likely a better performing tire
Here's my axle setup, I have aftermarket driveshafts:

  • Rubicon Axles
    • Front is Trussed and Gussetted if I do the 40's ill truss the rear
    • RCV front Axle shaft
    • Dana/Spicer Cromoly rear shafts
    • Dynatrac Ball Joints
    • 5.13 gears
I built these to run 37's without concern, although I know anything can break. I THINK i can get away with a lightweight set of 40's and still be in good shape. The Yokohamas are only 6 lb's more than the Baja Bosses.

What do you all think?
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OBJLU

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Have you considered 37x13.5x17s? pretty good list of contenders here~
https://simpletire.com/tire-sizes/37-13.50R17
BFG KM3s & Toyo Open Country MTs come to mind :)
Thanks, the STT pro's are practically 13.5 and looking to size up but I think I'm going to go with the Baja Bosses since those are true-to-size so closer to what a "38" would be.
 

Mx5red

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I have no experience, being new to the Jeep world, but increasing diameter of tires (and wheels) puts a lot more forces on the components than just the "scale weight" of the tire itself. So it's not just that the bigger tire weighs 10# more, its the fact it's 10# more AND it's on a longer moment arm.. Like a longer wrench.
So even if they weighed the same, it would still put a lot more force on your components.
Increasing negative offset or pushing wheels out further also adds torque to some components in a similar concept.
Search Rotational Inertia and gyroscopic Precession for examples...

Having said that, sounds like you've made your axles pretty beefy already!
 
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OBJLU

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I have no experience, being new to the Jeep world, but increasing diameter of tires (and wheels) puts a lot more forces on the components than just the "scale weight" of the tire itself. So it's not just that the bigger tire weighs 10# more, its the fact it's 10# more AND it's on a longer moment arm.. Like a longer wrench.
So even if they weighed the same, it would still put a lot more force on your components.
Increasing negative offset or pushing wheels out further also adds torque to some components in a similar concept.
Search Rotational Inertia and gyroscopic Precession for examples...

Having said that, sounds like you've made your axles pretty beefy already!
Yahhh agree 100 percent, if I did 40's I'd try and find the "smallest" and lightest and even explore lighter wheels.
 

Creeker

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Here is some info one some MileStar tires.
This data is from a variety of sources.
Its the best I found.


SizeTypeLoad RangeLoad RangeMax Load ([email protected])Approved Rim Width (in)Tread Depth (in)Tread Width (in)Section Width
(in)
Overall Diameter (in)Maximum psiWeight (lbs)Speed RatingPly Rating
37x12.50R17LTMud TerrainD124[email protected]1019/321012.536.85071.3QD/8PR
38x13.50R17LTMud TerrainC11929981119/321113.637.83682.4QC/6PR
40x13.50R17LTMud TerrainD121[email protected]1119/3213.639.85082.4QD/8PR
 
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OBJLU

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Lol
I knew a girl that weighed 90 and she thought she was obese. I'll say it again, a lightweight 40" tire? LOL
lol well usually they’re 100 lbs plus so yah
 

wibornz

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If you are just going to Lowes or Home Depot, it doesn't matter. If you think that going to 40s and actually wheeling the Jeep, you will find it does matter. I think that if you go to 40s and wheel the Jeep, you must upgrade all the steering components. If you wheel hard, maybe think of hydro assist. The larger diameter tire also will require more braking power. Brake updates would be warranted also.

I thought about going to 40s, but to do it right and have the Jeep be dependable for the type of Jeep travel and wheeling that I do, I was looking at approximately $20,000 to do it right.
 

ChattVol

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If you are just going to Lowes or Home Depot, it doesn't matter. If you think that going to 40s and actually wheeling the Jeep, you will find it does matter. I think that if you go to 40s and wheel the Jeep, you must upgrade all the steering components. If you wheel hard, maybe think of hydro assist. The larger diameter tire also will require more braking power. Brake updates would be warranted also.

I thought about going to 40s, but to do it right and have the Jeep be dependable for the type of Jeep travel and wheeling that I do, I was looking at approximately $20,000 to do it right.
I'm convinced 37/12.50/17 is the sweet spot for wheelin/road trips/all around use in the JL Rubi. Going to a 40" tire only nets 1.5" more clearance...yet it costs exponentially more to support it properly. I can't justify it either and would rather learn to be happy with 37s. I would wager a competent driver with a properly setup JL on 37s can do the majority of the trails that jeeps on 40s run.
 
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OBJLU

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If you are just going to Lowes or Home Depot, it doesn't matter. If you think that going to 40s and actually wheeling the Jeep, you will find it does matter. I think that if you go to 40s and wheel the Jeep, you must upgrade all the steering components. If you wheel hard, maybe think of hydro assist. The larger diameter tire also will require more braking power. Brake updates would be warranted also.

I thought about going to 40s, but to do it right and have the Jeep be dependable for the type of Jeep travel and wheeling that I do, I was looking at approximately $20,000 to do it right.
I wheel alot and I know people who wheel alot running 40's with my setup, one of them just finished a few of the trails out in the hammers in Johnson Valley,. no hydro. Is it ideal? No but job got done.

If I go to 40's I'm going to run those trails too but I also daily it so I've decided to go with the Baja bosses and when I inherit my wife's car for a daily I'll move up to ,40's and plan for tons.
 

Darkseid

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I wheel alot and I know people who wheel alot running 40's with my setup, one of them just finished a few of the trails out in the hammers in Johnson Valley,. no hydro. Is it ideal? No but job got done.

If I go to 40's I'm going to run those trails too but I also daily it so I've decided to go with the Baja bosses and when I inherit my wife's car for a daily I'll move up to ,40's and plan for tons.
So how's the jeep with the baja boss 40s?
 
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