What is your nominal ride height?

fuse

TJ Enthusiast
Supporting Member
Jun 5, 2018
267
San Diego, CA
I can't remember if I already said it, but my 37s are giving a 18" hub height.
Would rather use tire roll out to measure circumference and use that to calculate tire radius.

But I think we're doing pretty good here for quick and dirty data.
 
OP
toximus

toximus

TJ Addict
Mar 29, 2018
1,400
Northern WI
Your 37s/18" hub vs my 33s (285 75r16s)/15" hub. Do you see it? I'm starting a thread...
My radius is 2" bigger. We have a 3" difference.

A few disclaimers: I suspect my tire pressure is a little high at 25psi. I am also missing a few hundred pounds of fuel, cage, fenders, carpet, top, etc.
 
OP
toximus

toximus

TJ Addict
Mar 29, 2018
1,400
Northern WI
But I think we're doing pretty good here for quick and dirty data.
That was really the intent of this thread, something easy that everybody could measure after work without taking anything more than a tape measure out.
 

mrblaine

TJ Expert
Supporting Member
Nov 20, 2015
3,895
Quail Valley, CA
You should be able to raise the pinion angle without sacrificing wheelbase...the Upper arms control that. Lower arms primarily set the axles fore/aft position, the uppers control rotation, and a trackbar controls the side to side motion. Now...In @jjvw's case, he's running triangulated links, so he doesn't HAVE a trackbar, but his pinion angle is still set with the upper control arms.
Due to the lower mounts being below centerline of the axle tube and thus the center of the tire, you can NOT adjust either the upper or lower arms without changing both wheelbase and pinion angle. That and if you raise the pinion, you won't be sacrificing wheelbase since the axle would move back at the same time the pinion comes up. Raising the pinion adds wheelbase.
 
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dla

TJ Enthusiast
Supporting Member
Nov 25, 2017
177
SoCal
BDS 3" front/2" rear
33X12.50R15 BFG KO's (15 1/4" hub center)
18 1/4" frame height
 
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Mike_H

Rust Belt Heavyweight
Supporting Member
Feb 28, 2017
3,959
Grand Rapids, MI, United States
Due to the lower mounts being below centerline of the axle tube and thus the center of the tire, you can NOT adjust either the upper or lower arms without changing both wheelbase and pinion angle. That and if you raise the pinion, you won't be sacrificing wheelbase since the axle would move back at the same time the pinion comes up. Raising the pinion adds wheelbase.
Thanks. @jjvw mentioned that too, and as I started to think about it, I realized why what I said was incorrect. I should probably go back and delete the comment.
 

mrblaine

TJ Expert
Supporting Member
Nov 20, 2015
3,895
Quail Valley, CA
Thanks. @jjvw mentioned that too, and as I started to think about it, I realized why what I said was incorrect. I should probably go back and delete the comment.
Don't worry about it. I've been fighting that bit of misinformation for years. I've even seen well known smart companies say the same thing.
 

jjvw

0-60 in 18 seconds
Supporting Member
Feb 17, 2018
5,336
Colorado, USA
Here is a the current data. The line graphs are stacked measurements, just like in real life. In the second chart, I reordered the tire, spring and spacer heights to show how each piece adds up to the final frame height. I made a few hub height corrections and educated guesstimates to account for mismatched front/rear lift heights. The top line graph should closely match the frame height. If the top line is higher than the frame height, then a measurement is off.
Frame Heights.JPG


If there are corrections, please let me know. If you know your hub height and/or actual spring measurements, also let me know.
 
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mrblaine

TJ Expert
Supporting Member
Nov 20, 2015
3,895
Quail Valley, CA
Some of the hub heights look a bit odd. If anyone would like a dead nuts accurate hub height without using a tape measure, post up a given verified accurate speed and RPM with year and transmission and we can run that through the gear calculator to get a very accurate hub height.
 
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fuse

TJ Enthusiast
Supporting Member
Jun 5, 2018
267
San Diego, CA
If you know your hub height and/or actual spring measurements, also let me know.
Nice data and charts!

My springs are 12" front and 8" rear (to within the range of manual measurement error).

Also, my tire radius is 14.83" from yesterday's roll out measurement. Looks like that fits well with the other data you have for 31s.
 
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jjvw

0-60 in 18 seconds
Supporting Member
Feb 17, 2018
5,336
Colorado, USA
Something that is hopefully starting to become visible is that these measurements are meaningful and do add up in ways that make sense. The actual tire dimensions (hub height) added to the actual coil/spacer heights will closely correlate to the frame height. This ought to be fairly consistent from TJ to TJ.

If there is one thing for anyone to take away from this, it is that the advertised sidewall and lift measurements are not true to life. We can see these errors in the charts.

If we could get the data actuate enough, an interesting thing we may get to see are the unaccounted height changes found in the spring seats that are in non-stock positions.
 
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mrblaine

TJ Expert
Supporting Member
Nov 20, 2015
3,895
Quail Valley, CA
Something that is hopefully starting to become visible is that these measurements are meaningful and do add up in ways that make sense. The actual tire dimensions (hub height) added to the actual coil/spacer heights will closely correlate to the frame height. This ought to be fairly consistent from TJ to TJ.

If there is one thing for anyone to take away from this, it is that the advertised sidewall and lift measurements are not true to life. We can see these errors in the charts.

If we could get the data actuate enough, an interesting thing we may get to see are the unaccounted height changes found in the spring seats that are in non-stock positions.
We have chatted about this before or at least been in the same threads where it has been discussed. Lift height measurements are predicated on an average based on a specific spring rate for the lift springs. Spring rate is expressed in pounds per inch. As in, if you take a 150 lb per inch spring and stack 150 pounds on it, it will compress 1". If you stack 300 pounds on it, it will compress 2".

It would be rare for most rigs to have the exact same amount of weight on the springs. There are simply too many variables for it to be dead accurate or put another way, if you get 2" of lift out of your 2" lift springs, you have a rig that weighs about the same as the one they used to determine a 2" lift spring height.

What I found the most interesting in all of the data so far is how many are running spacers, very odd to me.
The other item of curiosity is rolling radius.

I also think we could work on another set of dimensions at least for the rear springs which are notoriously difficult to measure in the stock configuration. I'll try to check today and see if I can find out if a top of axle tube to top of frame arch will work to extrapolate backwards to actual spring height.
 
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jjvw

0-60 in 18 seconds
Supporting Member
Feb 17, 2018
5,336
Colorado, USA
...

I also think we could work on another set of dimensions at least for the rear springs which are notoriously difficult to measure in the stock configuration. I'll try to check today and see if I can find out if a top of axle tube to top of frame arch will work to extrapolate backwards to actual spring height.
The rear is especially difficult to measure consistently. In my head, it makes sense to measure at the middle between the seats. It can be hard to get a tape measure in there. But that should average out much of the bow caused by the non-parallel seats. Really, consistentcy in measuring is the most important thing.
 

mrblaine

TJ Expert
Supporting Member
Nov 20, 2015
3,895
Quail Valley, CA
The rear is especially difficult to measure consistently. In my head, it makes sense to measure at the middle between the seats. It can be hard to get a tape measure in there. But that should average out much of the bow caused by the non-parallel seats. Really, consistentcy in measuring is the most important thing.
We measure this stuff all the time doing outboard work and we don't even try to measure the stock rear perches. Even with two guys who have worked together a long time on opposite sides of the rig making sure everything is in the same location we can't get it accurate enough to trust. My middle may not be exactly his middle of the upper perch and since it is sloped, any minute shift front to back will give a different dimension side to side. I'll ponder it some and see if I can come up with an accurate way to measure.
 
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bobthetj03

vibrajeep
Supporting Member
Ride of the Month Winner
Feb 3, 2017
8,020
NorCal
Some of the hub heights look a bit odd. If anyone would like a dead nuts accurate hub height without using a tape measure, post up a given verified accurate speed and RPM with year and transmission and we can run that through the gear calculator to get a very accurate hub height.
2003 TJ, NV3550, @65mph 2500rpm. Speed should be accuarate based on GPS and speedo gear change.
20170125_075340.jpg

Edit: 4.56 gears.