37s vs 40s: Is there really a need for 40s?

[softballnrd27]

Is there really a need for 40s? I would really like some educated opinions on 37" vs 40" tires. I plan to take my jeep all over the US. I always seem to get caught up in keeping up with the Jones. My original build plan for the LJ was 66-69" wide axles, 37s, 4" rear stretch and then I bought 05 super duty axles thinking of going to 40-42" tires. Now I'm 2nd guessing that again.

 

[Steel City 06]

From what I've seen on here, 40s are the standard for competition. Anything beyond that seems to be in diminishing returns. Is this going to be trailered, or driven on the freeway? 40s will be more difficult to keep highway safe and legal, but it can be done

 

[softballnrd27]

From what I've seen on here, 40s are the standard for competition. Anything beyond that seems to be in diminishing returns. Is this going to be trailered, or driven on the freeway? 40s will be more difficult to keep highway safe and legal, but it can be done

I will drive it on the street but not a daily driver, it currently gets trailered and will continue to get trailered to the trails.

 

[Fouledplugs]

A lot of Jeep guys run a 39 and bigger down South on their trailered rig. I'm talking Alabama here, with the soft ground, lots of water, and lots of Jeep traffic. Trails get rutted out, they get washed out, they get worn in. Before you know it, the trial that was perfect for a 35 now needs a 37. There are plenty of trails down here that would warrant a 40 and Im sure that's no different in many other regions.

 

[Fouledplugs]

From what I've seen on here, 40s are the standard for competition. Anything beyond that seems to be in diminishing returns. Is this going to be trailered, or driven on the freeway? 40s will be more difficult to keep highway safe and legal, but it can be done

Maybe you are talking about a 40 inch exclusively on a TJ/LJ.

How tall is a semi truck tire? How tall is a dump truck tire?

It's strange to me (maybe it's just me) that someone thinks a 40 inch tire is so big and drastic in size for the road. Yet, look at the overall diameter of that dump truck tire. Its driven on the road daily and it's normal...All it's missing is the, "aggressive," tread pattern found on most M/T type 40 inch tires.

 

[toximus]

Read through my build thread. I talk about tire size theory in the first few posts.

Building for 37s or 40s requires the same amount of work and money to build for.

 

[Bababooey]

Read through my build thread. I talk about tire size theory in the first few posts.

Building for 37s or 40s requires the same amount of work and money to build for.

This is probably the biggest thing to consider. I run 37's on mine (LJ). Most of the guys I wheel with are on 40's. The only reason I haven't switched to 40's is that it may not clear my garage at that point.

 

[JMT]

Aren’t the returns diminishing past 37’s? You stretch that wheelbase and lose your break over angle IIRC. No benefit going to 40’s IIRC

 

[toximus]

Aren’t the returns diminishing past 37’s? You stretch that wheelbase and lose your break over angle IIRC. No benefit going to 40’s IIRC

The biggest downside is that you loose travel.

 

[mrblaine]

Aren’t the returns diminishing past 37’s? You stretch that wheelbase and lose your break over angle IIRC. No benefit going to 40’s IIRC

It is a fair bit of a dilemma. I wheel in JV. It is rare that 40's can go anyplace that 37's can't with the same effort. The dilemma is when you are done building for 37's, a bit more stretch and the cost difference between 37's and 40's is all that is stopping you from going to the bigger tires. That becomes very bad with a TJ though because about the most you can get for wheelbase is 104 which is just barely enough for 37's. Much easier with a TJ Unlimited where you can run them out to 114" with a tank under the tub and Dana 60's.

The biggest issue with 40's is power to turn them on the highway. Some report good results, I chalk that up to low expectations.

 

[mrblaine]

Maybe you are talking about a 40 inch exclusively on a TJ/LJ.

How tall is a semi truck tire? How tall is a dump truck tire?
View attachment 117612

It's strange to me (maybe it's just me) that someone thinks a 40 inch tire is so big and drastic in size for the road. Yet, look at the overall diameter of that dump truck tire. Its driven on the road daily and it's normal...All it's missing is the, "aggressive," tread pattern found on most M/T type 40 inch tires.

It is just you. That is about the worst apples to apples comparison I've seen yet. There is a reason they run that size and it has more to do with the weight they carry than anything else. The rear axles and tires likely weigh more than an entire rig on 40's.

 

[mrblaine]

Is there really a need for 40s? I would really like some educated opinions on 37" vs 40" tires. I plan to take my jeep all over the US. I always seem to get caught up in keeping up with the Jones. My original build plan for the LJ was 66-69" wide axles, 37s, 4" rear stretch and then I bought 05 super duty axles thinking of going to 40-42" tires. Now I'm 2nd guessing that again.

You can run about 65" wide on 37's. You need to be at least 2" wider for 40's. For our needs, we use 104 minimum for 37's and 108 minimum for 40's and 21-23" frame heights.

 

[Thunderhead]

32's can get you through the same places as 37's, you just have to pick better(?) lines.

 

[derekmac]

32's can get you through the same places as 37's, you just have to pick better(?) lines.

It can be hard to pick a different line on a tight wooded trail with deep ruts when there's only one way through.

 

[JMT]

32's can get you through the same places as 37's, you just have to pick better(?) lines.

I have seen a TJR on 32’s do the Escalator and an LJ on 40’s fail. That instance was an issue of right line.

TJR on 32’s/2” TT

LJ on 40’s, different angle.

But this logic doesn’t hold when clearance is the issue. So, yes, and no, it depends on the terrain

 

[Thunderhead]

I have seen a TJR on 32’s do the Escalator and an LJ on 40’s fail. That instance was an issue of right line.

TJR on 32’s/2” TT
View attachment 117621

LJ on 40’s, different angle.
View attachment 117622

But this logic doesn’t hold when clearance is the issue. So, yes, and no, it depends on the terrain

Yea, that shovel does no one any good, 37's-40's through mud and boulders do so much better.

It can be hard to pick a different line on a tight wooded trail with deep ruts when there's only one way through.

Sometimes you just have to drag your ass through lol

 

[softballnrd27]

108-110" WB will be doable in my LJ. I would like to keep my overall width down to where I'm currently at which fits on a normal car trailer. With the 05+ superduty axles that requires heavy offset wheels which exposes the hub more than I would like to. I've got the axles in my garage but I also came across a complete hub to hub Ford KP 60 with truss and a 14bolt with a shave kit already done and machined 5.13 gears. I'm really leaning towards 37s just need to pop or get off the pot

 

[Fouledplugs]

It is just you. That is about the worst apples to apples comparison I've seen yet. There is a reason they run that size and it has more to do with the weight they carry than anything else. The rear axles and tires likely weigh more than an entire rig on 40's.

While it's not apples to apples, nor was that my intention. I was pointing out diameter and road use. I fully understand the tire size needed to keep the large diff of the ground in ref to weight carrying capes for the dump truck. Agreed that it's not the best example.

 

[LONGJP2]

If you truly plan to wheel all over the U.S., I know there are places where the extra width would be a problem (think trees). Also, are you building to do the hardest obstacle a park has to offer, or wheel different types of terrain in different (scenic) areas of the country?
Personally, I prefer the latter.

 

[softballnrd27]

Sorry for all this, I'm just trying to bounce my ideas off of some more smarter guys than me.