Difference between 37s and 40s

Blackhawkip

Blackhawkip

Member
Question: What issues arise from going from a Toyo 37x12.50R17 that weighs 83lbs to the Wrangler 40X13.50R17LT that weighs 86lbs? If you have 1350 fr/rr drivelines and are re-gearing anyway, would a PR44 with RSC shafts and Ten Factory rear shafts in a stock Dana44 rear handle the Wrangler 40 with 5.38 gears?

I don't need/want 40s right now but if rolling weight is the primary issue, it seems like 3lbs and the additional diameter wouldn't add that much more stress on the axles. As always, looking for an education from those with the knowledge.

Thx
 
Blackhawkip said:
Question: What issues arise from going from a Toyo 37x12.50R17 that weighs 83lbs to the Wrangler 40X13.50R17LT that weighs 86lbs? If you have 1350 fr/rr drivelines and are re-gearing anyway, would a PR44 with RSC shafts and Ten Factory rear shafts in a stock Dana44 rear handle the Wrangler 40 with 5.38 gears?

I don't need/want 40s right now but if rolling weight is the primary issue, it seems like 3lbs and the additional diameter wouldn't add that much more stress on the axles. As always, looking for an education from those with the knowledge.

Thx
Click to expand...

It's a lot more leverage for breaking shit. I personally wouldn't trust running 40's on less than 1-ton running gear. But also depends on how you're using your jeep.


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Eddie posted a video a while ago where he was running Moby on 40's with a 35 spline upgrade on the rear stock diff if I'm not mistaken. In the end, the ring and pinion proves to little for the pressure placed by those 40's. If you're gonna wheel it, you'll be playing Russian Roulette...


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It's not the weight that is the difference, it's the overall rotating mass and the effect that will have on your ring and pinion, unit bearings, ball joints, braking etc.

You'll need to run 5.38's and the size of the pinion for that gearing on a dana 44 is quite small.

Couple that with the sheer size and what you will need to do for suspension to even maximize the size of a 40" tire, it's scrub radius and the trimming you will need to do to your body especially if you don't have full width axles.

But again, if you just put around town, you should be fine, you'll just run through the above mentioned parts quicker than normal.
 
Agree with everything said. It's not simply a matter of the additional weight of the 40s but rather the mass, rolling resistance and leverage the larger tire will put on your drivetrain and steering components when wheeling. Even if you don't wheel often or hard the smaller components (designed for much smaller tires) will wear out quicker.

If you do wheel it in areas requiring lots of throttle, lots of steering effort and lots of binding or heavy leverage of tires you'll break stuff sooner or later.

As tgoss said if you drive it in a relatively straight line on the street around town you'll likely be OK with minor mods and the required trimming of the fender wells. 40s on standard JK width axle assemblies with stock fenders and full width bumpers isn't going to happen unless you put some insane kind of tall lift on it.

Really comes down to what most have already commented on. What are you going to be doing with it? Are you going to wheel it? How hard? In what kind of terrain? These factors will have a significant impact on recommendations you get from the community here on the site.


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