Running 40's

[Discount Tire]

A lot of good information to help people thinking about going to larger tires.

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[cannonFodder]

I've been running 40s daily for a year and a half and the people complaining about axles getting wrecked by 40's are making a mountain out of a molehill.

As long as you're not driving like a jack wagon, you can definitely get up and go without needing axles.

Gearing upgrades, sure. Axle upgrades, maybe but not necessary.

 

[RhinoJT]

Good info. It’s one of those hit or miss kind of situations. Over time, you are going to wear out consumables, ie. Ball joints, wheel bearings and such much quicker. Still may be cheaper overtime than going full tons. We all have seen the news out there. People running them for years with no issues, then those that put them on, back out of the driveway and snap.( mutilple tire sizes included). This is the oldest and longest discussion topic in the community. It can be done, as long as you realize there are limitations.

Now for those of us that want to drive like jackwagons( sometimes you just have to “send it”)

I give you BEEF!

 

[guarnibl]

I finally got the 40's installed on my Gladiator last week. First impressions, it looks great! Ride is pretty good I think it can be better. I went with 40x13.50x17 Cooper's. I have 17x9 Method wheels. I do have a slight rub at full lock. The installer had a hell of a time getting the old 37's off and dinged up my wheels. They ordered me some new ones but they struggled getting the tire off the bead, because of the bead gripper. I am running them at 32 psi right now and might go lower, I will chalk test when I get a chance. I do have a little road wander and vibration at 55MPH. They used balancing beads instead of weights, anyone have an opinion on this? I'd also like to hear opinions on what upgrades I should be considering to keep this thing safe, reliable, and as roadworthy as possible? (Apex booster, sector shaft brace?) It currently has a Clayton 3.5 ride rite which has been great. I don't do any rock crawling but do get it off road a bit, hunting/snow etc. I'll be honest its mostly a pavement princess.

Assuming pavement princess, I don't think there's much you need to do (maybe wheels with less backspacing). 32 PSI is likely too much. My guess is you'll settle mid to high 20's.

Are you able to still hit 8th gear after programming it to the tire size on the highway going 65-75? Ultimately, that's the question I ask when deciding on regearing. If it can't hit and hold 8th, it's time to regear. For me, on 37" KO2s and stock wheels, there's zero need to regear, as it holds 8th just fine without issue. I'd imagine if you ran KMC's and 40" Nittos, you'd immediately regret not regearing, even w/ the diesel. That combination is nearly 150 pounds per corner, vs the KO2 setup at 90 pounds per corner. Hell, even 39" KO2's are ~97 pounds per corner.

If I were to regear, I'd likely just sell my axles and buy the ones that come with 4.56's (and then beef them up while it's down). I don't think you'd need more gear than that even on 40's with the diesel.

 

[Drooler]

A lot of good information to help people thinking about going to larger tires.

Thanks to everybody for sharing their advice in this post.

Quick question. What is the min size backspacing needed to accommodate 40” by 13.5” by 17” tires?

Have a 2023 FarOut edition EcoDiesel with standard Rubicon axles. Will be modding with Truss, Gusset, 4.88 regear, etc.

Will start out with 38” by 13.5” tires but if all goes well on my trail rides (Moab once a year), I hope to move up to 40” tires knows these wear out.

I used to skinny pedal all the time. Decided slow and steady is the better approach. And I have no qualms about being winched over (versus breaking an axle).

Trying to get set of tires that look like the below, but most of them have -12 offset which clearly isn’t enough “poke”. Trying to figure out what is the min offset I need without going overboard with the “poke”.

Went to my local discount tire, but I tjink they usually deal with normal cars, low profile tires, etc.

Not used to Jeep folks asking for 38”, 39” or 40” tires.

Thanks in advance

 

[rharr]

Thanks to everybody for sharing their advice in this post.

Quick question. What is the min size backspacing needed to accommodate 40” by 13.5” by 17” tires?

Have a 2023 FarOut edition EcoDiesel with standard Rubicon axles. Will be modding with Truss, Gusset, 4.88 regear, etc.

Will start out with 38” by 13.5” tires but if all goes well on my trail rides (Moab once a year), I hope to move up to 40” tires knows these wear out.

I used to skinny pedal all the time. Decided slow and steady is the better approach. And I have no qualms about being winched over (versus breaking an axle).

Trying to get set of tires that look like the below, but most of them have -12 offset which clearly isn’t enough “poke”. Trying to figure out what is the min offset I need without going overboard with the “poke”.

Went to my local discount tire, but I tjink they usually deal with normal cars, low profile tires, etc.

Not used to Jeep folks asking for 38”, 39” or 40” tires.

Thanks in advance

Look at the rock krawler suspension website, they have back space recommendations for tire sizes and lift.

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