40" tires... Talk me out of it

[Deleted member 30519]

What's the deal with 38s? It's not mentioned enough. I'm assuming it's because it's a less common size?

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[shrinkhead]

I'm getting around 14mpg now which is down ~1.5pmg since the change from my 37's to 40's. I have basically lost 7th gear but am cruising at 65-70mph at ~2500rpm. I do not offroad at all, unless you count beach cruising. I've upgraded all of my steering components but have not messed with my axles. Im sure there will be some issues that pop up down the road but so far so good.

Always impressed how folks get better MPG on 37s and 40s than I was getting on 35s....i must be doing something very wrong as I never got over 13.5MPG on average highway/ city mixed.

 

[j.o.y.ride]

I have noticed that every every photo of a Gladiator makes the wheels look a little smaller than they appear in person. The 40s I have seen in pics look alright but in person they're a bit comical to me.

I may upgrade to 37s when I get around to doing all that should be done, but I am in no rush to do that stuff for 37s. It's a 'maybe when I get there' sort of thing.

 

[Jeeperjamie]

What's the deal with 38s? It's not mentioned enough. I'm assuming it's because it's a less common size?

Honestly, if a tire manufacturer made a 38 in a 38 12.5 17 I'd probably be running it. I was seriously thinking about getting a set of 39 12.5 17 Kanati mud hogs. Saw a set on Marketplace for $800 with a little over a 1000 miles of driving on them. I went and looked at them but they were just to heavy, 90lbs. Piece. If I could get a 38 12.5 17 and have it weigh around 80lbs I'd be all over it.

 

[Lynn_F]

Always impressed how folks get better MPG on 37s and 40s than I was getting on 35s....i must be doing something very wrong as I never got over 13.5MPG on average highway/ city mixed.

It depends a lot on how a person drives. I drive like a grandpa...I very seldom accelerate hard and mostly keep it under 70. I notice a drastic drop in mpg over 70 vs under 70.

 

[Jeeperjamie]

Always impressed how folks get better MPG on 37s and 40s than I was getting on 35s....i must be doing something very wrong as I never got over 13.5MPG on average highway/ city mixed.

Dang that sucks, I'm getting 17.3 on 37" goodyear MTRs, I guess it comes down to terrain and driving habits and maybe how aerodynamic you make it. I put some thought into the weight of things I added to mine and how they sit on the jeep. That's one of the reasons I went full width bumper with high clearance on the ends to get the bumper up closer to the fenders to fill in the gap like it came factory. Also my tires only weigh 72lbs a piece which was one of the lighter wheels you can get in a 37. I'm moving to a Cooper A/T in a 37 when these wear out And I should see a even higher gain since they only weigh 69lbs and are s A/T.

 

[Dtrues878]

I have noticed that every every photo of a Gladiator makes the wheels look a little smaller than they appear in person. The 40s I have seen in pics look alright but in person they're a bit comical to me.

I may upgrade to 37s when I get around to doing all that should be done, but I am in no rush to do that stuff for 37s. It's a 'maybe when I get there' sort of thing.

What are your prep plans for the 37s?

 

[j.o.y.ride]

What are your prep plans for the 37s?

Ball joints, gears, and front/rear axle shafts are the ones I'd do before anything beyond 35 goes on.

I also would do longer shocks, full under body protection, and front drive shaft before as I would get more benefit there than an extra 1" of tire height. But those are not necessary for the tires, just the order I would go in already having 35s.

 

[j.o.y.ride]

Don't spin the tires in low gear, cause once it catches grip "snap, crackle, pop"

That's the issue on the trail, there's going to be a lot of places (at least where I go), where you will be spinning in dusty dirt trying to get up a granite rock and then it catches and off you go. *BANG*... uh oh. You gotta really really build up the D44 or go a nicely built D60 if you are going to wheel 40s imo. Even 37s would be cause for extra caution.

For me, my #1 thing is to make it out of the trail under my own power. I will rely on skid plates with 35s before maybe snapping something with 40s and all the cost it takes to get there. 37 is still a perhaps to me.

 

[guarnibl]

Heavy 40’s can still break things even with a 60. Significantly less likely of course but not like it’s bullet proof.

I’d avoid 40’s if you don’t have budget to spend $20k for new axles and other components. You’re easily $20k when you factor in a set of Currie axles with the Alcon brakes. Oh and then another $3k for the hydro assist kit. At that point what’s another $35k for a hemi

On a daily basis I’m running 37” KO2’s which are closer to a 36 and weigh basically the same as the stock Falcon 33’s. Still gotta get an alignment, balance, straighten the steering wheel a bit more and install the tazer but then will check gas mileage. Should be decent. May run 40’s in Moab for the week but stay light on the pedal. Going 4.5” springs too — trying my best to keep the bed out of the rocks lol.

absolutely doing axles but hoping to wait until next winter.

 

[Jeeperjamie]

Heavy 40’s can still break things even with a 60. Significantly less likely of course but not like it’s bullet proof.

I’d avoid 40’s if you don’t have budget to spend $20k for new axles and other components. You’re easily $20k when you factor in a set of Currie axles with the Alcon brakes. Oh and then another $3k for the hydro assist kit. At that point what’s another $35k for a hemi

On a daily basis I’m running 37” KO2’s which are closer to a 36 and weigh basically the same as the stock Falcon 33’s. Still gotta get an alignment, balance, straighten the steering wheel a bit more and install the tazer but then will check gas mileage. Should be decent. May run 40’s in Moab for the week but stay light on the pedal. Going 4.5” springs too — trying my best to keep the bed out of the rocks lol.

absolutely doing axles but hoping to wait until next winter.

What do your KO2s measure mounted. I saw a Tacoma the other day that had them mounted for about a month and they were at 35.9 on his truck. I would think that's about what the would measure on ours as well. Just curious because I'm between BFGs and Copper AT3 XLT and it's going to come down to which one measured taller on the jeep, that's after the Goodyears I got now wear out.

 

[guarnibl]

What do your KO2s measure mounted. I saw a Tacoma the other day that had them mounted for about a month and they were at 35.9 on his truck. I would think that's about what the would measure on ours as well. Just curious because I'm between BFGs and Copper AT3 XLT and it's going to come down to which one measured taller on the jeep, that's after the Goodyears I got now wear out.

Mine have about 2000 ish miles on them and show 35.3. But my 37” Nitto’s that came off were about a half inch taller. I also just measured my stock 33” falcons and they came out to 31.8. Surprisingly the KO2’s on my wife’s 2 door are about the same. All of these tires have under 3k miles.

for what it’s worth I typically run 30-32 psi. Nitto will be closest you’ll get to a true 37 but it’s still not even close unless you’re airing them up to crazy town psi. Or maybe I’m just a bad measurer

For me it was important to get the tallest tire I could that was snow rated, light and not loud. That was the KO2. I wish they made it in a 40 — it would probably be mid 70’s weight.

 

[Jeeperjamie]

Mine have about 2000 ish miles on them and show 35.3. But my 37” Nitto’s that came off were about a half inch taller. I also just measured my stock 33” falcons and they came out to 31.8. Surprisingly the KO2’s on my wife’s 2 door are about the same. All of these tires have under 3k miles.

for what it’s worth I typically run 30-32 psi. Nitto will be closest you’ll get to a true 37 but it’s still not even close unless you’re airing them up to crazy town psi.

For me it was important to get the tallest tire I could that was snow rated, light and not loud. That was the KO2.

Wow, 35.3 then they are definitely out. Dang that's small, the Goodyear MTRs I have installed measure 36.2 with 70% life left, 12/32 tread. I was hoping to stay close to that on a A/T, I'll need to find someone running a 37" cooper before pulling the trigger.

 

[guarnibl]

Wow, 35.3 then they are definitely out. Dang that's small, the Goodyear MTRs I have installed measure 36.2 with 70% life left, 12/32 tread. I was hoping to stay close to that on a A/T, I'll need to find someone running a 37" cooper before pulling the trigger.

As I said — I may have not done the best job measuring lol and the tire psi is low so it’s got a fair bit of bulge on the pavement. I’ll try to take some pictures.

just curious though — what’s your use case? It’s tough with the added length of the gladiator so I totally understand wanting the tallest tire possible in AT form.

someone needs to measure all these tires side by side ! Never tried coopers. Had awful experiences with the MTR. Too many flats. Gave up. It’ll be tough for me to consider anything other than trepadors or trail grapplers in the rocks

 

[Jeeperjamie]

As I said — I may have not done the best job measuring lol and the tire psi is low so it’s got a fair bit of bulge on the pavement. I’ll try to take some pictures.

just curious though — what’s your use case? It’s tough with the added length of the gladiator so I totally understand wanting the tallest tire possible in AT form.

someone needs to measure all these tires side by side ! Never tried coopers. Had awful experiences with the MTR

Light trails, daily driver. I want see much mud, just maybe fire roads or stuff like that. Really not planning any rock crawling. I more concerned with on road comfort and performance that does pretty good off road as well. I love BFGs, but I knew they measured smaller, that's why I was looking at another brand when going up to 37's. The Goodyears are great tires but I can tell you a M/T will not be on my daily driver. I am glad I got them for $550 to try out because I would of been upset if I spent $2000 on them.

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