Inside-Out Build—2006 LJ

What is the backspacing in your wheels? I run 1.25" spacers behind 5.25" BS for an effective backspace of 4". More would just trade one interference for another because I'd be into the rear wall of the fender on the tire turned to the outside.

View attachment 292457

I like to run as narrow a stance as possible to keep the scrub radius down and I prefer the way it looks. When I've run 33s I ran a 10.5 on 5+ BS. I've read of some getting away with as much as 4.5" with 35s but I don't know how without losing noticeable turning radius... I'm already hitting the LCAs on both sides now at ride height with more than a washers thickness between the stops.
I measured my wheel this morning my backspacing is 3.5” with a 1.25”spacer. I can probably get away with less of a spacer or steering stop adjustments but that will take a bit to cycle the suspension and check thing. I am considering a suspension upgrade at the moment.
 
I measured my wheel this morning my backspacing is 3.5” with a 1.25”spacer. I can probably get away with less of a spacer or steering stop adjustments but that will take a bit to cycle the suspension and check thing. I am considering a suspension upgrade at the moment.

3.5 including or in addition to a 1.25" spacer? If that's added, for an effective backspacing of 2.25", that's a TON of scrub radius. How does it like the steering wheel being turned while stationary?
 
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I measured my wheel this morning my backspacing is 3.5” with a 1.25”spacer. I can probably get away with less of a spacer or steering stop adjustments but that will take a bit to cycle the suspension and check thing. I am considering a suspension upgrade at the moment.
3.75" is about as far out as you want to go to avoid too much stress on the ball joints and to not mess up the scrub radius more than is necessary.
 
3.75" is about as far out as you want to go to avoid too much stress on the ball joints and to not mess up the scrub radius more than is necessary.
Thanks for the info, I will look at it this weekend to see if I can adjust steering stops and eliminate the spacers
 
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I worked on this last week while I had things apart for the locker install.

I was curious about the factory scrub radius and how different tire and wheel combinations play into it.

First, I put a magnetic angle finder on top of both ball joints, and took the average of the two to account for any slope in my garage floor or difference between jack stands. The result was 9.3° for the steering axis inclination.

Then, I measured the distance from the steering axis to the wheel mounting surface at 5-1/8". I basically just eyeballed where the axis was, I didn't run a string or anything like that. So this is likely plus or minus part of an inch, but it's less important.

I drew this out, viewed from the front, in AutoCAD, which allowed me to measure the stock scrub radius at 1.8", using a factory Canyon or Ravine wheel which has 5.5" BS, and the rolling radius of a 30x9.5" tire calculated from the revolutions per mile published for a BFG KO2 tire.

From there, it's just trig to calculate the change in scrub radius from the 30" tire package.

%2F%2Ftwstatic.net%2Fattachments%2Fscrubradius-png.png


Step 1: Calculate the scrub radius LOST by the increase in tire radius. This happens because as you can imagine in the image above, the intersection of the contact patch with the steering axis moves out as the tire radius grows. As mentioned above, I like to calculate actual rolling radius based on revolutions per mile. It probably doesn't change the result much if you use manufacturer advertised radius instead, but you want to make sure you use the same method for both tire sizes being compared.

Scrub radius change due to tire size = - change in radius*TAN(Steering Axis Inclination)
*Note that if you do this in Excel, you'll need to multiply the SAI by PI()/180 to use degrees instead of radians.

Using my rig as an example, which has 35 and a rolling radius of 16.75" vs the 14.3" of a 30" tire, this value is -0.4".

Then you add the change in scrub radius due to tire size to the difference in wheel offset. A stock 5.5 BS 15x8 wheel has an offset of 25mm or 1". A 4" BS 15x8 has an offset of -12mm or -0.5". So you subtract the new offset from the original offset, and in this example you get 1.5".

-0.4" + 1.5 " =1.1". So I've added 1.1" to the scrub radius from what it would have had with the 30" tire package for an approximate total of 2.9".

Do the calculation for a stock Rubicon with metric 31's and 5" BS Moab wheels, and you get a +0.42" change from the baseline.

Here's a table showing some common arrangements.

1638565479574.png


I thought it was particularly interesting that a 33" tires can maintain an effectively stock scrub radius using a common 5.25" backspaced wheel - the catch is that you have to use a 10.5" to avoid interference at full lock, and probably with the upper rear spring perch as well. On the other hand, the small backspacing required for 12.5" tires combined with a 33" diameter ends up with a +1.5", or 50% more change vs a 35x12.5. Point for pizza cutters!
 
I worked on this last week while I had things apart for the locker install.

I was curious about the factory scrub radius and how different tire and wheel combinations play into it.

First, I put a magnetic angle finder on top of both ball joints, and took the average of the two to account for any slope in my garage floor or difference between jack stands. The result was 9.3° for the steering axis inclination.

Then, I measured the distance from the steering axis to the wheel mounting surface at 5-1/8". I basically just eyeballed where the axis was, I didn't run a string or anything like that. So this is likely plus or minus part of an inch, but it's less important.

I drew this out, viewed from the front, in AutoCAD, which allowed me to measure the stock scrub radius at 1.8", using a factory Canyon or Ravine wheel which has 5.5" BS, and the rolling radius of a 30x9.5" tire calculated from the revolutions per mile published for a BFG KO2 tire.

From there, it's just trig to calculate the change in scrub radius from the 30" tire package.

View attachment 294069

Step 1: Calculate the scrub radius LOST by the increase in tire radius. This happens because as you can imagine in the image above, the intersection of the contact patch with the steering axis moves out as the tire radius grows. As mentioned above, I like to calculate actual rolling radius based on revolutions per mile. It probably doesn't change the result much if you use manufacturer advertised radius instead, but you want to make sure you use the same method for both tire sizes being compared.

Scrub radius change due to tire size = - change in radius*TAN(Steering Axis Inclination)
*Note that if you do this in Excel, you'll need to multiply the SAI by PI()/180 to use degrees instead of radians.

Using my rig as an example, which has 35 and a rolling radius of 16.75" vs the 14.3" of a 30" tire, this value is -0.4".

Then you add the change in scrub radius due to tire size to the difference in wheel offset. A stock 5.5 BS 15x8 wheel has an offset of 25mm or 1". A 4" BS 15x8 has an offset of -12mm or -0.5". So you subtract the new offset from the original offset, and in this example you get 1.5".

-0.4" + 1.5 " =1.1". So I've added 1.1" to the scrub radius from what it would have had with the 30" tire package for an approximate total of 2.9".

Do the calculation for a stock Rubicon with metric 31's and 5" BS Moab wheels, and you get a +0.42" change from the baseline.

Here's a table showing some common arrangements.

View attachment 294062

I thought it was particularly interesting that a 33" tires can maintain an effectively stock scrub radius using a common 5.25" backspaced wheel - the catch is that you have to use a 10.5" to avoid interference at full lock, and probably with the upper rear spring perch as well. On the other hand, the small backspacing required for 12.5" tires combined with a 33" diameter ends up with a +1.5", or 50% more change vs a 35x12.5. Point for pizza cutters!
Thanks for posting this! I geek out on stuff like this. Im going to have to follow along this weekend to see if I can calculate my current scrub radius and determine what BS I need to return to stock.
 
Thanks for posting this! I geek out on stuff like this. Im going to have to follow along this weekend to see if I can calculate my current scrub radius and determine what BS I need to return to stock.

I do too, as you can see. I'm still learning suspension and steering but I use math a lot and I enjoy applying stuff I usually only use for work to my hobbies.

Another example, I'm still definitely a novice welder, but I've been around welding so much with my job (i spent 5 years in a cubicle next to a welding engineer in a welded pressure vessel factory) that I've picked up enough to get a major leg up on someone starting from scratch. I came in already knowing the different processes and much of what makes a weld good or bad, etc so now that I'm getting started I really just need to work on my technique. I got a chance to impress a bunch of my wife's family last weekend when my nephew was welding on some beaver traps and I walked into the shop and could tell it was wrong just based on the sound, walked over to the welder, told him to turn the wire speed up about 6 notches and his helmet down about 2 shades and suddenly his welds became at least passable if still a bit ugly. I didn't volunteer to weld it for him, lest I reveal that I've had about 5 minutes of total arc-on time in my entire life. 🤣
 
Grabbed this shot at the homesite recently. I'd much rather still be living in the mountains, but I will say the sunsets are better when mountains aren't blocking the view, and I sure as hell wouldn't be driving doorless in December at sunset up there.

PXL_20211203_231632529-01-01.jpeg
 
I guess it's not really needed, but it's amusing how I've never received a product from UCF that had any packing material. The tc skid was just the skid with a shipping label stuck to it. The engine skid is in a box, and then the hardware and brackets are loose in a smaller box.

PXL_20211215_174609624.jpg


I should have opened this sooner, because I've been painting my new steering knuckle and I could have painted these brackets at the same time, but completely forgot that the brackets probably wouldn't be aluminum.

The instructions are not in the box, but are available online. I may take some photos of the process and send them back to UCF to add in to the instructions document. It might become clear once I'm looking at things, but just reading this plain text without any pictures it's kinda hard to visualize.
 
I guess it's not really needed, but it's amusing how I've never received a product from UCF that had any packing material. The tc skid was just the skid with a shipping label stuck to it. The engine skid is in a box, and then the hardware and brackets are loose in a smaller box.

View attachment 296434

I should have opened this sooner, because I've been painting my new steering knuckle and I could have painted these brackets at the same time, but completely forgot that the brackets probably wouldn't be aluminum.

The instructions are not in the box, but are available online. I may take some photos of the process and send them back to UCF to add in to the instructions document. It might become clear once I'm looking at things, but just reading this plain text without any pictures it's kinda hard to visualize.

Yep my skid from UCF was the same.

20210918_092002.jpg
 
Yep my skid from UCF was the same.

View attachment 296632
now that's creative...guessing the brackets and hardware were captive between them and contained in that plastic wrap? I wonder if they specifically chose the bolt pattern on the engine skid to match the bolt pattern on the t-case skid so they would go together like that...or if it was just a happy coincidence.

Looks like your t-case skid, like mine, isn't predrilled for the back edge of the engine skid to mount up. The thing is laser cut so it would cost essentially nothing to have those holes in place so we didn't have to drill through 1/4" steel. I love how their site says "you may have to drill the t-case skid" or something along those lines...like, don't sugar coat it, just say I'll have to because that appears to be the case, even when using their skids together.
 
now that's creative...guessing the brackets and hardware were captive between them and contained in that plastic wrap? I wonder if they specifically chose the bolt pattern on the engine skid to match the bolt pattern on the t-case skid so they would go together like that...or if it was just a happy coincidence.

Looks like your t-case skid, like mine, isn't predrilled for the back edge of the engine skid to mount up. The thing is laser cut so it would cost essentially nothing to have those holes in place so we didn't have to drill through 1/4" steel. I love how their site says "you may have to drill the t-case skid" or something along those lines...like, don't sugar coat it, just say I'll have to because that appears to be the case, even when using their skids together.

Yep the braces for the engine skid were bolted and taped with the hardware to the inside of the skid. And as you said no directions but for this it's pretty easy to figure out.
And I would guess they don't cut the holes incase you choose to go with someone else's engine skids?
 
And I would guess they don't cut the holes incase you choose to go with someone else's engine skids?

could be. I'm not sure what the downside would be to having extra holes, unless someone else's engine skid has holes that would overlap with the existing ones but not match well enough to actually use.

Another hole I wish was there is the window the stock skid has to allow you to get a wrench on the front output yoke bolts so it's not such a pain to R&R the front shaft.
 
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could be. I'm not sure what the downside would be to having extra holes, unless someone else's engine skid has holes that would overlap with the existing ones but not match well enough to actually use.

Another hole I wish was there is the window the stock skid has to allow you to get a wrench on the front output yoke bolts so it's not such a pain to R&R the front shaft.

I have transmission and transfer case crossmembers so I don't have to deal with that. I just drop the skid first.
 
How you liking that top?

I found a set of half doors for my LJ recently. Was thinking I'd match that up with a quick-style soft top for summer driving.
 
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How you liking that top?

I found a set of half doors for my LJ recently. Was thinking I'd match that up with a quick-style soft top for summer driving.

It's not as quiet as the one I had on my TJ but I'm still satisfied. If anything it's tighter than that one, so all I have for reasons why is conjecture.

I very much like the functionality of a frameless top. Since I have two kids ages 3 and 6 and we're all of Northern and western European descent, we don't have much occasion for the full top down option offered by a full framed top. The kids get the shade all the time, and I'll flip the sunrider open for the full sky experience in the front seats. This usage style nullifies the common complaint against frameless tops that it's too inconvenient to go fully topless. Even if I wanted to, I'd just take it off at home and stash it, which is easier than putting a framed top down. The only inconvenience of it is that it's too big to keep in the Jeep once you take it off.

Back to the noise issue- what I get is a flapping of the front section at speeds over 45, which noisily slaps the arch. If I run without the arch its not bothersome, but I think without the arch, water would pool there if parked in the rain. My TJ didn't do this, which makes me wonder if the difference is sound pods vs sound bar (sound bar constraining the top better than pods) or if the early TJs lack of a tailgate vent held some interior pressure to dampen the flapping.
 
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I put a new steering knuckle on yesterday to finally deal with the hogged out tie rod hole. The alignment was the most time consuming part of the job; unlike my previous KO2s, these cooper STT Pro's don't have a convenient mold line down the center to use for toe measurements, so I made an alignment tool out of aluminum angle. Rather than matching it to the tire diameter, I just left it at 36" and marked it with what the toe spec would work out to on 36" tires. Regardless of what tire size I actually have, it'll come out to 0.15° +/- 0.06°, straight out of the FSM.

PXL_20211220_031917126.jpg
 
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3.5 including or in addition to a 1.25" spacer? If that's added, for an effective backspacing of 2.25", that's a TON of scrub radius. How does it like the steering wheel being turned while stationary?
The steering while stationary did not seem to be affected, but I did notice a little more wander on the freeway and it trended to pull on way or the other under high speed braking. I pulled the spacers off and put a couple washers under the steering stop to keep the tire away from the air cyl on my swayloc.. I will revisit this when I put some axles in after the holidays.
 
It's not as quiet as the one I had on my TJ but I'm still satisfied. If anything it's tighter than that one, so all I have for reasons why is conjecture.

I very much like the functionality of a frameless top. Since I have two kids ages 3 and 6 and we're all of Northern and western European descent, we don't have much occasion for the full top down option offered by a full framed top. The kids get the shade all the time, and I'll flip the sunrider open for the full sky experience in the front seats. This usage style nullifies the common complaint against frameless tops that it's too inconvenient to go fully topless. Even if I wanted to, I'd just take it off at home and stash it, which is easier than putting a framed top down. The only inconvenience of it is that it's too big to keep in the Jeep once you take it off.

Back to the noise issue- what I get is a flapping of the front section at speeds over 45, which noisily slaps the arch. If I run without the arch its not bothersome, but I think without the arch, water would pool there if parked in the rain. My TJ didn't do this, which makes me wonder if the difference is sound pods vs sound bar (sound bar constraining the top better than pods) or if the early TJs lack of a tailgate vent held some interior pressure to dampen the flapping.
I hear you there - I did the Ancestry.com DNA test and as it turned out, I'm whiter than snow :ROFLMAO: So I too like having something overhead. I was going to go with a bikini top, since that's what I almost extensively ran in AZ, however being in the northeast now, something that offers "oh look it decided to rain" protection is what caught my eye. I figured something that I could run from mid-spring to mid-fall and that would easily store is just the ticket. Soft tops, at least from my TJ experience, are almost harder to store than a hard top. They're floppy, a PITA to clean, are easily chewed by rodents, and the plastic scratches easily (whereas a hard top I can and have simply stored on a pallet in the side yard without any issues whatsoever).
 
Soft tops, at least from my TJ experience, are almost harder to store than a hard top. They're floppy, a PITA to clean, are easily chewed by rodents, and the plastic scratches easily (whereas a hard top I can and have simply stored on a pallet in the side yard without any issues whatsoever).

I alternated tops for 4 years when I was in Colorado. I used a Harken hoist for both tops. To store the soft top, I cut a couple of lengths of 2" PVC that were an inch or two longer than the top is wide, and ran the hoist straps through the pipe. I draped the top over one pipe, hung the windows in a window storage bag from the other pipe, and hoisted it up out of the way and inaccessible to any critters.

Down here I'm running soft top year round. So far our average high since the start of calendar winter has been in the 70s so doorless and windows-out is in play at any time.
 
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