New member with questions

J

John A.

New Member
Original poster
Joined
Sep 17, 2020
Messages
15
Location
St. Louis MO Area
Hello. First time poster, long time viewer. I'll apologize now if I accidentally offend anyone or step on any sacred topics. I'll thank @mrblaine and others now for the advice that's forthcoming.

My Jeep. 1997 TJ Wrangler Sahara hardtop. 4.0, 32RH, NP231, Dana 30 / 35... most things are stock and untouched. Has been wheeled gently and infrequently for 10+ years. 3 years ago I did install 1" body & motor mount lift along with a tummy tuck using UCF transfer case / oil pan / gas tank skid. Installed Rancho RS5000X shocks along with bar pin eliminators last year. My situation has changed and I'd like to make this a significantly more capable rig for trails and some rocky areas out West. NOT building a hardcore rig. Want a light rig with a low center of gravity for the wife and I to go exploring. I intend to flat tow this behind my truck to camping / wheeling locations. My first big expense will be getting new axles front / rear. I'm currently considering ECGS Dana 489's. 65", 35 spline shafts, Ox locker, new brakes.

- Recommendation on differential gear? - Low enough that I can crawl when needed, but high enough that I can go fast enough on the straight flat parts of trails. Initially I will use my existing 30" Toyo Open County tires on 15" stock rims. Long term I DEFINITELY want at least 35" tires but would love to get around 37" if I can. Don't really want to re-gear when I get larger tires if I can avoid it. I was thinking 5.13. Thoughts?

- Flat Towing - I plan to disconnect the drive shafts before I do long drives to the mountainous west. I also have a set of new 29" tires on 16" wheels, all season, good for highway, that I'll put on prior to flat towing. It'll keep the Jeep nice and low in the slip stream behind my truck. If I have 5.13 gears, that pinion is going to be spinning at about 4300 rpm towing at 70 mph. Is that too fast? Any concerns on flat towing a trail rig?

- Springs - I want to keep lift to a minimum. Currently have the stock springs. If I am looking for a 1-2" lift, are stock springs with a 1" spacer good enough? Are after market springs that much better if I'm not really wanting any lift?

Thanks in advance.
 
I’m a little confused. You said at the end you want it to stay stock height, but want to go to 35’s or 37’s? That won’t work.

If you’re saying you want stock height now and build to grow, that’s fine. 5.13 with 30” tires you may want to use the http://www.grimmjeeper.com/gears.html. Website to figure what those would Do now and with bigger.

37’s, you won’t get a lot of suggestions to go there on here, 35’s with the TJ is a huge investment, 37’s is more and different investment .
 
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I guess when I said stock height, I should have said stock spring height. I have the 1" body lift already, and would be willing to have a 1" spring spacer lift. That'll give me 2" above the axle of extra space, or 4" extra tire diameter. With the 65" wide axles I should have no problem with width for 35" tires. Not sure if 35" will fit with these or if I need additional space.
 
Another question I forgot to ask. What's the general consensus on running a high pinion in the rear? (or is this a sacred topic not to be discussed?) If I keep the rig light, if I'm not wheeling hard... will it last or is it certain death?

I know the theory, I am curious if anyone has experience with this?
 
John A. said:
I guess when I said stock height, I should have said stock spring height. I have the 1" body lift already, and would be willing to have a 1" spring spacer lift. That'll give me 2" above the axle of extra space, or 4" extra tire diameter. With the 65" wide axles I should have no problem with width for 35" tires. Not sure if 35" will fit with these or if I need additional space.
Click to expand...


I've got 33's on my TJ and 35's on my JK, but I'll be going to 35's next tire buy on the TJ (bought my first 35" BFG Muds in 1991 for my CJ5 at the time) and own all BFGs on any 4x4 for me.

That said, I've been reading a ton on the TJ here for months, and the consensus I've seen is that 1"BL and 1" spacer is not enough to run 35's. You may be right on the 65" axle changing that, but I don't know that. Most threads have said 4" suspension and either 1"BL or flat fenders to run them and really have offroad capability.

Also, and I'm doing this with my 05 TJ:
1. 4" lift
2. 1" BL or Flat flares
3. SYE or SS SYE and DC drivesaft
4. Upgraded axle to Super35 rear
5. Most likely regear (4.88 for me, but depends on your trans)
6. Adjustable control arms to change pinion angle
7. Then adjustable Rear track bar and angled relocation bracket to fit
8. shocks that fit, most likely perch move or cutting perch to fit shocks with axle pinion changed

@Chris has a whole write up on "So you want to put 35's on your TJ" that was a massive bummer when I read it months ago....his reality in his how to's are a buzz kill and costly, but helpful HAA . I kind of miss the days of being young and dumb, throwing on 35's and thinking if I break it.....it was badge of honor.....stupid I was.
 
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Flat flares don't create clearance. Highlines are what you are thinking of.
 
John, if you want 35s, then you need to figure out how to add at least 5" of additional clearence. This will be some combination of spring lift, body lift or body cutting.
 
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Last edited:
Thanks all for the comments. I certainly have a lot to learn. I do not have bottomless pockets, so budget is a factor.

Something that I'm still not understanding. I have 30" tires now, and there is no clearance problems (full flex and full turn). If I want to increase the tire diameter to 35", then that's a 5" diameter change but only a 2.5" radius change. So I need to increase clearance above the tire by 2.5". Am I missing something?

I understand that there is also concerns with tire rubbing when turning. For the sake of simplifying the discussion, lets leave that aside for the moment.
 
John A. said:
...
Something that I'm still not understanding. I have 30" tires now, and there is no clearance problems (full flex and full turn). If I want to increase the tire diameter to 35", then that's a 5" diameter change but only a 2.5" radius change. So I need to increase clearance above the tire by 2.5". Am I missing something?

...
Click to expand...

When you lift, the goal is to at least maintain the factory 4" of up travel. As the lift height increases, so does the shock length. But it isn't 1:1 with the lift height. Which means you are adding lift height, both to accommodate the tire size as well as the required longer shock. There is a balance between the lift height, tire size and shock length that adds up to more required lift than it might appear when looking at the Jeep in the parking lot.

Additionally, as the shock travel increases, so does the travel arc of the articulating tires. This requires more room than it might appear.

On top of that, larger tires are often wider which also required more wheel backspacing. This further increases the travel arc of the articulating tires.

The more you attempt to skimp on the needed clearance for a larger tire, the more compromises you will create. Some of which matter more than others depending on what you want out of the Jeep. The quest for LCoG is an exercise in compromises.
 
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John A. said:
Thanks all for the comments. I certainly have a lot to learn. I do not have bottomless pockets, so budget is a factor.

Something that I'm still not understanding. I have 30" tires now, and there is no clearance problems (full flex and full turn). If I want to increase the tire diameter to 35", then that's a 5" diameter change but only a 2.5" radius change. So I need to increase clearance above the tire by 2.5". Am I missing something?

I understand that there is also concerns with tire rubbing when turning. For the sake of simplifying the discussion, lets leave that aside for the moment.
Click to expand...
The height of the tire is only part of the clearance change. Not only are taller tires wider, they also have to be spaced farther out on the axle to prevent rubbing. The farther the tire edge is from the roll center, the more the tire moves up with an equivalent amount of axle movement. That adds another inch or so of required clearance. (If I flex the axle to 20 degrees, a wider overall axle will require more clearance at the outer edge of the tires than a narrower one.)

In addition, when you go to longer shocks to accommodate the lift, you generally also go to longer travel shocks. The standard 5" of lift and 35s results in about 5.5" up and down travel compared to stock 4" up and down. So there is an extra 1.5" of required clearance.

And since you went with longer travel shocks, the axle can now flex farther and to steeper angles. Thus, the high side tire gets even higher at full flex. That adds probably another inch.

So given your 2.5" taller tire, 1" of extra excursion due to wider outer width, 1.5" of extra excursion upwards due to longer travel shocks, and 1" more due to steeper allowable axle travel, ultimately you get about 5" of extra clearance required over stock.

You can go lower, but you lose the advantage of the longer travel, especially the longer uptravel. The increased suspension travel has a great positive impact on both high speed bumpy driving and low speed rock crawling. In order to go lower, you would probably have to add significant bumpstop extensions and maybe limit straps depending on the shocks used to prevent issues.
 
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jjvw said:
When you lift, the goal is to at the beginning least maintain the factory 4" of up travel. As the lift height increases, so does the shock length. But it isn't 1:1 with the lift height. Which means you are adding lift height, both to accommodate the tire size as well as the required longer shock. There is a balance between the lift height, tire size and shock length that adds up to more required lift than it might appear when looking at the Jeep in the parking lot.

Additionally, as the shock travel increases, so does the travel arc of the articulating tires. This requires more room than it might appear.

On top of that, larger tires are often wider which also required more wheel backspacing. This further increases the travel arc of the articulating tires.
Click to expand...
Dang it you beat me to it...
 
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I think with the tummy tuck your going to have to get a sye with any amount of lift you install. I suppose you could go with highlines and 33s or maybe 35s to avoid the sye
 
Quote from first post "NOT building a hardcore rig". That sounds like 3" SL, 1" BL and 33s. You also mentioned budget. Tire prices go up past 33s and even more past 35s. 33s seem to be the tipping point for cost, but not in capabilities. After wheeling with TJs on 33s, I don't believe there is much performance gain going bigger.
 
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John A. said:
Thanks all for the comments. I certainly have a lot to learn. I do not have bottomless pockets, so budget is a factor.

Something that I'm still not understanding. I have 30" tires now, and there is no clearance problems (full flex and full turn). If I want to increase the tire diameter to 35", then that's a 5" diameter change but only a 2.5" radius change. So I need to increase clearance above the tire by 2.5". Am I missing something?

I understand that there is also concerns with tire rubbing when turning. For the sake of simplifying the discussion, lets leave that aside for the moment.
Click to expand...
Well I am not a suspension guru or a math major but I can tell you 4" of lift is not enough for 35's alone. This is my 05 Rubicon w/ a 4" lift flexing the rear only before I added a 1" BL

1_zps5f5359d7 (1).JPG


11_zps642c32b2.jpg
 
Learning a lot. I now understand some of the added complexity when adding longer springs / longer axles / larger tires. Thanks for sharing.

If I understand correctly.
- Body Lift / Hi Fenders move the axle center line further away from the fender surface, but zero impact to axle / flex geometry.
- Coil spring spacer lift has an impact on axle location and flex geometry, but you keep the same flex length.
- Longer spring impacts axle location and flex geometry, and also impacts total flex length.
- Wider axles needed for larger tires to maintain the same turn angle, leads to higher flex distances required at outside of tire.

Yes, a SYE and new shafts are in my future.

I'm worried about flat towing the jeep at 70 mph for 12+ hrs at a time. That's a lot of bearings spinning at a very high speed (pending a decision on axle gear ratio). Wish I had hub lockouts (front & rear). I'm too cheap to buy a trailer.
 
I imagine you can tow as fast and as far as you can drive. Mine can drive 75mph all day long.
 
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