Hey, I was just pointing out in response to your snow covered hill scenario that I may have wheeled in the snow a time or two and not on forest service roads. Regardless of what the average is, the pics show we did it, nothing more.
37s vs 40s: Is there really a need for 40s?
- Thread starter softballnrd27
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I will have an LS in front of a th400 or 4l80e/atlas with very little highway driving.
I've always ran 37s on this build, my close buddy runs 39s, we go all the same places, I just have to be more careful with line selection. Same as 33s versus 35s really. I bolted up some Nitto 40s before KOH this year, everything was quite easy. I cleared most everything, it was awesome. 
However, because I built my Jeep with 37s, all the clearances were too tight and had to cut sheet metal, and they were rubbing my bypasses. I dropped down to 38s when I returned.
You're likely not going to make any more obstacles with 40s that you can't with 37s. I would pick the size tire that fits your build and terrain.
However, because I built my Jeep with 37s, all the clearances were too tight and had to cut sheet metal, and they were rubbing my bypasses. I dropped down to 38s when I returned.
You're likely not going to make any more obstacles with 40s that you can't with 37s. I would pick the size tire that fits your build and terrain.
People run larger tires to get more clearance, but you don't gain as much clearance going from 35s to 37s as you'd expect. To run 37s, you need 1 tons, which means you have a larger diff than 35s. So you gain clearance everywhere except at the lowest point on the vehicle.
Fortunately, the axle built for 37s, can handle more than just 37s, so you can gain back that lost clearance. But every time you go up in tire size, you open up a new can of worms.
Fortunately, the axle built for 37s, can handle more than just 37s, so you can gain back that lost clearance. But every time you go up in tire size, you open up a new can of worms.
What wheel size/backspacing would you recommend for for the 37s? And for the 40s? Looking to stay between 76" and 80" overall, if feasible.
Is there an axle width and backspacing combo that would work for 37s, and later change the backspacing to upgrade to 40s if desired?
You act like I've never wheeled in snow in JV.
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Not many days like that in JV.
Backspacing doesn't change and neither does the rim. Typically a 17 x 9 with 4" of back spacing works well for both.
Not in my world. You could make it wider for the 37's and live it it being good for 40's without too much penalty though.
Thanks for the input. You had said 65" axles for 37s, and about 67" for 40s. That would put me at 78.5" wide with 37s (12.5" wide) and 81.5 for 40s (13.5" wide). Unfortunately that sounds like it'll be a bit too wide for me, as I'm trying to stay under 80" overall, closer to 76-78" to fit Washington trails.
That said, would 67" axles with slightly more backspacing be okay with 37s? I don't have a problem swapping wheels if/when I go from 37s to 39s, I just don't want to swap axles again. I'm wondering if there is some leeway with backspacing, or if you want to be right on.
The ideal wheel backspacing is a function of the steering axis inclination. Meaning you ideally want the tire patch to pivot around it's center point. The further you are away from that center point, the more the tire tries to roll (or skid with lockers) during a stationary turn. Lower backspacing also allows steering input from the road due to the increased leverage on the outboard side of the ball joints letting the tire be shoved around. Then there is the reduced life of the ball joints, due to the very same leverage.
From there, the axle width is enough to allow packaging of the coilovers, shock, coils, whichever, and give the tires enough room around the body and frame during suspension articulation.
Is there really nothing between stock axles and tons that would be enough for 37s? Like an aftermarket 44 with the right width and ball joints? Just so you don't have to go to all the effort and expense just to end up with the same or less pumpkin clearance as 35s?
I'm wondering the same thing. I'm planning on going to 37s, just not sure the axle yet.
It looks like JK Rubicon axles are probably enough, but maybe not. ECGS 489s are a little bit better, but at that price you're almost at custom 60s when going to 65 WMS.
I understand the desired outcome, I'm just not sure how to get there.
The tire patch to pivot around the center point... does that mean neutral backspacing (4" backspacing on 8" wide wheels, 5" backspacing on 10" wheels) or the center of the tire over the balljoint? Or something else entirely? How far off can you be before running into issues?
That's why I'm surprised going to 3.75" of backspacing was recommended when the factory was 5.5". I understand that I had to add width due to the tire size, but would it have been better to widen the axles by 3.5" rather than mess with the backspacing? Or am I completely wrong?
Ideal is the center. As you move further away from that, the pain in the ass nature of a highly compromised steering set up begins to rear its ugly head. Someone mentioned JK width and if you fucker the steering on that set up with shallow back spacing, the balljoints that hate 37's are going to just despise that.
You can do 64" on 37's with 4" of back spacing. Very doable, not so much if you are in a hurry and tend to overlook details.
Ideally, you want that dotted line to point to and intersect with the center of the tire patch on the ground. That dotted line is defined by the ball joints. SAI and kingpin angle are the same thing.
If you are changing tire diameters, tire widths and wheel backspacing, then that intersection point on the ground becomes a moving target. At that point, you want the scrub radius to be as equal as is feasible given packaging restrictions. This can be adjusted some through the wheel backspacing.
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I haven’t built one, and really have no idea if it would work, but my feeling is that an axle for 37’s would be a high pinion Dana 44 center section 3” diameter X 1/2” wall tubes and Dana 60 inner C’s and knuckles.
It would be a very expensive axle to build, but I think it would work very well and be very durable. It would also have a good amount of clearance.