Let's talk optimal build for 31" tires

[MountaineerTom]

31’s really are too big for stock suspension. If you cycle the suspension you can see this. To run a 31 on stock suspension you need a 1” BL or 1/2 to 1” of bumpstop.

@Fishtaco
Diff clearance is variable. Put a tire up on a rock/log/etc and the diff clearance increases.

They just happen to go on 2 or 3 months before I put my lift on.

 

[Irun]

Reason why i ask, is because i am looking at your profile as well as rim in the picture and cant fully figure out if you are on 17" or 15" rim. Not everyone understands that:

On 15", 33s are actually 32.5 , and 31s are somewhere in the 29s area
On 17", 33s are actually 33.1, and 31s are 31.7 (metrics)

15" combo weights less than 17", and 15" 33s are nearly 17" 31s in size.
As far as lift goes, they are almost in need of the same 3" lift. My front is lifted somewhere around 2.7" (a bit higher than 2.5 and just shy of 3 according to the chart), that is splitting hairs to avoid rubbing during the flex on 31.7s

Downsizing from 17" to 15" is next on my list, and going with 33x10.5 should be a straight swap to 31.7 i currently have, seeing your elaboration of your unhappiness with 33s was also beneficial.
Thank you

I run a 15 inch wheel on the TJ I'm building on 31s. My LJ, in the profile,, on 35s has 17 inch wheels.

 

[Sancho]

I'd like to put 33's on, but I don't really want to without re-gearing it. Then that leads to wanting to put a locker (or lockers) at the same time. It's just not in the budget right now, but maybe someday. I don't do any hardcore wheeling, so the 31's with the 2-1/2 spring lift work for me right now. The hardest thing I've done with it is the Dickey Bell hill climb at Uwharrie National forest in NC and I was actually a little surprised the rear bumper didn't drag on anything.

While on 31's... Throw a lunch box locker in the front. Your trail 4x4 ability will spike.

A jeep 4.0 on a 2.5 lift... 31's and a front lunchbox locker will take you many places.

Great thing about building towards a 31 vs 33 or 35.... is the "roi" for 31's is much greater.


The ratio of money to capability is much greater.

 

[MountaineerTom]

While on 31's... Throw a lunch box locker in the front. Your trail 4x4 ability will spike.

A jeep 4.0 on a 2.5 lift... 31's and a front lunchbox locker will take you many places.

Great thing about building towards a 31 vs 33 or 35.... is the "roi" for 31's is much greater.


The ratio of money to capability is much greater.

I have considered putting a Powertrax in the Dana 30. I might end up going that route and if I ever to go to 33’s just leave it in and put a selectable in the rear.

 

[Tob]

Ok, last thoughts here now that I have finished my last day of Moab wheeling. I ran hell’s, fins, TOTW, steelbender, poison spider, gold bar rim, and golden spike. I took nearly all the hardest lines i could find, pushing the Jeep further and further trying to find the limit of what it could do, and where the bottlenecks are. With the exception of some lines on some obstacles that I did not have wheelbase for, I did not find that limit until today on Metal Masher, where I could have benefitted from more tire, slightly more approach angle and more departure angle.

All said and done, this setup has taken me much further than I expected. There is definitely something to be said for building on 31’s.

So to keep things on topic, here is what I imagine as an optimal build built around 31” tires:

• Lockers
• Full flat belly tummy tuck with oil pan/transmission skid
• Obligatory 1” MML and 1”-1.25” body lift to accommodate tuck
• Raised gas tank skid
• High clearance rear bumper (crossmember cap type)
• Stubby front bumper
• Rocker protection
• Steering box protection
• 2.5”-3” suspension lift
• Antirock or swayloc
• Aluminum where applicable
• Out of the normal scope of builds on 31’s, but a small rear stretch and a small front stretch like what @jjvw did recently. This would increase approach and departure angles which the smaller tires do not provide, and mildly increase wheelbase. The caveat to a stretch is that you are messing with the balance between wheelbase and belly height. With that said, in all the hard lines and large ledges I went up and down this week, I don’t think I dragged the belly but once - and only barely.

 

[jjvw]

Ok, last thoughts here now that I have finished my last day of Moab wheeling. I ran hell’s, fins, TOTW, steelbender, poison spider, gold bar rim, and golden spike. I took nearly all the hardest lines i could find, pushing the Jeep further and further trying to find the limit of what it could do, and where the bottlenecks are. With the exception of some lines on some obstacles that I did not have wheelbase for, I did not find that limit until today on Metal Masher, where I could have benefitted from more tire, slightly more approach angle and more departure angle.

All said and done, this setup has taken me much further than I expected. There is definitely something to be said for building on 31’s.

So to keep things on topic, here is what I imagine as an optimal build built around 31” tires:

• Lockers
• Full flat belly tummy tuck with oil pan/transmission skid
• Obligatory 1” MML and 1”-1.25” body lift to accommodate tuck
• Raised gas tank skid
• High clearance rear bumper (crossmember cap type)
• Stubby front bumper
• Rocker protection
• Steering box protection
• 2.5”-3” suspension lift
• Antirock or swayloc
• Aluminum where applicable
• Out of the normal scope of builds on 31’s, but a small rear stretch and a small front stretch like what @jjvw did recently. This would increase approach and departure angles which the smaller tires do not provide, and mildly increase wheelbase. The caveat to a stretch is that you are messing with the balance between wheelbase and belly height. With that said, in all the hard lines and large ledges I went up and down this week, I don’t think I dragged the belly but once - and only barely.

That would be a pretty solid build. From what I've seen, with a good driver that could go pretty far in a place like Moab where axle clearance is less of a concern compared to a place with rocks and boulders.

 

[Fouledplugs]

I don’t think I dragged the belly but once - and only barely.

I understand the concern, but folks who want to rock crawl have to accept that using the skids is ok. It’s going to make noise, a lot of it, but it’s ok.

Also learning how to use the skids without getting further into a bind or hangup is a lesson to be learned as well.

 

[Tob]

I understand the concern, but folks who want to rock crawl have to accept that using the skids is ok. It’s going to make noise, a lot of it, but it’s ok.

Also learning how to use the skids without getting further into a bind or hangup is a lesson to be learned as well.

I agree. My point was that I had more than enough belly clearance for everything I tried, which means with a stretch and same size tires I would actually be putting them to use (which I am more than ok with, ask my GTSP!), but not so much as to high center on everything.

Side note, wheeling with a tuck is AMAZING coming from a factory rubicon skid with 1” drop spacers!

 

[Irun]

Ok, last thoughts here now that I have finished my last day of Moab wheeling. I ran hell’s, fins, TOTW, steelbender, poison spider, gold bar rim, and golden spike. I took nearly all the hardest lines i could find, pushing the Jeep further and further trying to find the limit of what it could do, and where the bottlenecks are. With the exception of some lines on some obstacles that I did not have wheelbase for, I did not find that limit until today on Metal Masher, where I could have benefitted from more tire, slightly more approach angle and more departure angle.

All said and done, this setup has taken me much further than I expected. There is definitely something to be said for building on 31’s.

So to keep things on topic, here is what I imagine as an optimal build built around 31” tires:

• Lockers
• Full flat belly tummy tuck with oil pan/transmission skid
• Obligatory 1” MML and 1”-1.25” body lift to accommodate tuck
• Raised gas tank skid
• High clearance rear bumper (crossmember cap type)
• Stubby front bumper
• Rocker protection
• Steering box protection
• 2.5”-3” suspension lift
• Antirock or swayloc
• Aluminum where applicable
• Out of the normal scope of builds on 31’s, but a small rear stretch and a small front stretch like what @jjvw did recently. This would increase approach and departure angles which the smaller tires do not provide, and mildly increase wheelbase. The caveat to a stretch is that you are messing with the balance between wheelbase and belly height. With that said, in all the hard lines and large ledges I went up and down this week, I don’t think I dragged the belly but once - and only barely.

This is a very solid list. The only major components I'd add would be:

• Adjustable control arms (setting the pinion angle for the tuck)
• Shocks and bumpstops matched to the suspension travel (Requires proper suspension cycling)
• SYE (If you have a 231)
• Driveshafts (To accommodate the lift and tuck)

The 2.5" to 3" suspension lift wouldn't be absolutely required for 31s, given the BL. However, it will provide a wider range of spring choices, resulting in more free length.

 

[Fouledplugs]

I mentioned it in post #26 in my “overkill build” plan post, anyone on 31’s with outboard shocks?

I dont know if any of the 1”or 2.5” springs would support the uptravel and downtravel numbers that a 12” shock can reach, @jjvw might know. Could be money wasted in travel numbers, but would make up for it in ride quality.

 

[Irun]

Well, I ran into a problem during my own 31" tire build. I was able to make a Currie track bar work out back, but not in the front. When I installed the front Currie track bar and cycled the suspension, it hits the Alloy USA cover hard. The result is a need for 2" bump stop. This is unacceptable and I'm looking at ways to make it work.

As a baseline, I then installed a stock track bar and was able to get full bump.

 

[jjvw]

Well, I ran into a problem during my own 31" tire build. I was able to make a Currie track bar work out back, but not in the front. When I installed the front Currie track bar and cycled the suspension, it hits the Alloy USA cover hard. The result is a need for 2" bump stop. This is unacceptable and I'm looking at ways to make it work.

View attachment 249295
View attachment 249296
View attachment 249297

As a baseline, I then installed a stock track bar and was able to get full bump.
View attachment 249298

Bent and cut.

Or pull the axle back.

 

[Irun]

Bent and cut.
View attachment 249301
Or pull the axle back.

Can't pull the axle back anymore. The bottom Savvy arms are adjusted all the way in already. The tops aren't, but they are set for the proper pinion angle. I could trim the gusset on the Currie bar a little, but am hesitant to do so. I'm not sure if that would impact the strength integrity?

 

[jjvw]

Can't pull the axle back anymore. The bottom Savvy arms are adjusted all the way in already. The tops aren't, but they are set for the proper pinion angle. I could trim the gusset on the Currie bar a little, but am hesitant to do so. I'm not sure if that would impact the strength integrity?

I trimmed the gusset on mine about a year ago, before I moved the frame side track bar mount. Both with the help of Blaine. I'm not concerned about either.

 

[Irun]

I trimmed the gusset on mine about a year ago, before I moved the frame side track bar mount. Both with the help of Blaine. I'm not concerned about either.

Seeing how you wheel, that makes me feel better about trimming it!

 

[Irun]

I've done my measurements several times now and looking for "optimal" shocks to pair with the H&R spings is turning out to be a huge headache and time drain. For the front I'm running the H&R 52107 springs, which are paired with a 1" spacer. The combination has netted 2.5" of lift.

FWIW, I'm really trying to go with the best bang for the buck shock here, knowing I will outboard at some point in the furure. This front numbers are the following:

- 14" Compressed
- 24" Extended
- 19" Ride Height

In this case the ride height worked out to a 50/50 split. Looking at all the shocks available, the front choice is fairly obvious. The Rancho RS55239 hits pretty close to these numbers and works with the ride height. Based on the available data, the Rancho numbers are:

- 14.43" Compressed
- 23.84" Extended
- 9.41" Travel

Provided, I'm doing the math correctly, this gives me a 4.57" up travel and 4.7" down travel. If these are corect, I can certainly live with the numbers. As for the rear, it's not so clean and I'll post that one on its own!

 

[TJim]

I've done my measurements several times now and looking for "optimal" shocks to pair with the H&R spings is turning out to be a huge headache and time drain. For the front I'm running the H&R 52107 springs, which are paired with a 1" spacer. The combination has netted 2.5" of lift.

FWIW, I'm really trying to go with the best bang for the buck shock here, knowing I will outboard at some point in the furure. This front numbers are the following:

- 14" Compressed
- 24" Extended
- 19" Ride Height

In this case the ride height worked out to a 50/50 split. Looking at all the shocks available, the front choice is fairly obvious. The Rancho RS55239 hits pretty close to these numbers and works with the ride height. Based on the available data, the Rancho numbers are:

- 14.43" Compressed
- 23.84" Extended
- 9.41" Travel

Provided, I'm doing the math correctly, this gives me a 4.57" up travel and 4.7" down travel. If these are corect, I can certainly live with the numbers. As for the rear, it's not so clean and I'll post that one on its own!

My case is similar. I installed 2" Ome springs, which netter me around 3" actual lift. (My TJ is pretty light)

I installed RS55128/RS55240, but the up travel/down travel ratio is not balanced at all.

My front shock's ride height is quite close to you at 18.75".

I am going to replace my current shocks with RS55239/RS55241 as soon as budget allows.

 

[Irun]

My search for a rear shock has really tested my patience and perseverance. While the front was relatively easy, the compressed length and ride height with the H&R 52107 springs severely limits what shocks can be practically used. Part of this has to do with the fact that I used both the 52107 springs and a 1" spacer up front. I did not use a spacer in the rear, because I wanted to level the Jeep. That said, my current numbers for the rear look like this:

- 13.25" Compressed
- 22.75" Extended
- 17" Ride Height

Although this translates to a 9.5" shock travel, finding an actual shock in that range has turned into a search for a unicorn.

The closest thing I could find is the OME 60049. Its numbers are:
- 13.31 Compressed
- 22.01 Extended
- 8.7 Shock Travel

Not knowing how they compare, I'm not the least bit thrilled about installing different shocks front and rear. Also, my experience with OMEs in the past, while good, has showed me that the OME shock bodies tend to be on the large side. This is a problem, given the rotated axle (for the Savvy UA). Lastly, if I use this shock, my up travel is effectively 3.69". Anything under 4" is unacceptable.

At this point I have three choices:

1. run a Rancho RS55128 rear shock - this one limits my shock travel to 7.98"
2. add the 1" spacer - this opens up my options, but pushes the lift close to the 3" range
3. swap the H&R springs out for a 3" Nth Degree set

Although the Rancho RS55128 puts me close to my minimal acceptable range, it's not good enough. At this point I have no clear path forward and plan to take a step back.

https://wranglertjforum.com/threads/lets-talk-optimal-build-for-31-tires.46071/post-876306

 

[TJim]

My search for a rear shock has really tested my patience and perseverance. While the front was relatively easy, the compressed length and ride height with the H&R 52107 springs severely limits what shocks can be practically used. Part of this has to do with the fact that I used both the 52107 springs and a 1" spacer up front. I did not use a spacer in the rear, because I wanted to level the Jeep. That said, my current numbers for the rear look like this:

- 13.25" Compressed
- 22.75" Extended
- 17" Ride Height

Although this translates to a 9.5" shock travel, finding an actual shock in that range has turned into a search for a unicorn.

The closest thing I could find is the OME 60049. Its numbers are:
- 13.31 Compressed
- 22.01 Extended
- 8.7 Shock Travel

Not knowing how they compare, I'm not the least bit thrilled about installing different shocks front and rear. Also, my experience with OMEs in the past, while good, has showed me that the OME shock bodies tend to be on the large side. This is a problem, given the rotated axle (for the Savvy UA). Lastly, if I use this shock, my up travel is effectively 3.69". Anything under 4" is unacceptable.

At this point I have three choices:

1. run a Rancho RS55128 rear shock - this one limits my shock travel to 7.98"
2. add the 1" spacer - this opens up my options, but pushes the lift close to the 3" range
3. swap the H&R springs out for a 3" Nth Degree set

Although the Rancho RS55128 puts me close to my minimal acceptable range, it's not good enough. At this point I have no clear path forward and plan to take a step back.

https://wranglertjforum.com/threads/lets-talk-optimal-build-for-31-tires.46071/post-876306

How much actual lift have those springs netted you?

If your rear shock's ride height is 17", if I'm not mistaken you have those options:

1) Rancho RS55240 - 4.24" Up travel, 3.04" down travel. The travel is only 7.28".
2) Rancho RS55241 - 3.49" Up travel, 4.67" down travel. The shock travel is 8.16".

I know the second option gives you less than 4" up travel, but consider adding a 10mm (close to 1/2") spacer, or a 3/4" spacer, which will set you almost exactly at 50 50 ratio.

I am not the most experienced person to say if you should install different shocks front and rear. I just know that I wouldn't do it in my rig.

So, if I were you I would probably install the RS55241 rear shocks.

Changing springs is a whole another discussion.

 

[Irun]

How much actual lift have those springs netted you?

If your rear shock's ride height is 17", if I'm not mistaken you have those options:

1) Rancho RS55240 - 4.24" Up travel, 3.04" down travel. The travel is only 7.28".
2) Rancho RS55241 - 3.49" Up travel, 4.67" down travel. The shock travel is 8.16".

I know the second option gives you less than 4" up travel, but consider adding a 10mm (close to 1/2") spacer, or a 3/4" spacer, which will set you almost exactly at 50 50 ratio.

I am not the most experienced person to say if you should install different shocks front and rear. I just know that I wouldn't do it in my rig.

So, if I were you I would probably install the RS55241 rear shocks.

Changing springs is a whole another discussion.

The springs have netted 1.5" of lift front and rear. Since I have a pair of 1" spacers, I'm going to add those this weekend and take a bunch of measurements again. I'm already at a point, with the 1.25" BL and 1.5" suspension lift, where there is more exposed wheelwell space than I would like.