From my DIY thread regarding my adjustable shackle PML:
Before I adjusted anything, the measurements I took were at the seam right below the doors:
2 inch rake front to back, 1 inch rake left to right
Front Left: 19.5" Front Right: 18.5"
Rear Left: 21.5" Rear Right: 20.5"
After some final adjustments and negligence with the bump stop gaps (UCA's in the near future, tires are already bad...so I'll let the bad camber slide temporarily until I get both together) I got the ride height to:
Front Left: 20.5" Front Right: 20.25
Rear Left: 23.0" Rear Right: 22.5"
Interesting observations to note:
The front to back rake was a bit large at 2 inches starting out, now its at 2.5" front to back. I should have gone with the 1 inch setting on the adjustable shackles. Oh well...
I also began with a left to right rake of 1 inch. I tried to adjust the ride height to even it out. However, the front left tire, when maxed out at the bump stop gap (0.5"), was 1 inch higher than the front right tire, when maxed out at the bump stop gap (0.5"). I found it odd that the same bump stop gaps would have different ride heights. I tried to even the front ride height to the same height the best I could (front right bump stop gap maybe 1/4 inch), which in turn brought the rear ride height closer from left to right, but not quite the same.
The tires were just recently rotated and checked for proper inflation at the dealer, but I did realize one thing, which was that 3 out of 4 of my tires are worn and nearing the end of their life. However, the left rear tire was just recently replaced as a temporary measure until I get a fully new set for the Xterra.
My plan as of now is to leave it alone for a month or two until I get the UCA's and a brand new set of tires, and re-adjust as necessary...essentially as of right now, I have leveled an inherently non-level suspension.
Is this rake normal? It appears that the suspension itself is not geometrically symmetric from left to right.
My bumpstop gaps after the PML were different at the same height as well FYI. Couldn't tell you exactly why this is but I suspect the suspension components on either side have just worn differently over time.
__________________ GRANITE 2003 SE SC BUILD THREAD wonton SAS in the works.
It really just blows my mind what else could be going on here...I can't quite explain the lateral rake...it has been repeatedly stated around here that the bump stop gap defines the ride height/lift. My intuition agrees with that seeing as the control arms are identical/symmetrical and rigid connections...so it seems that a UCA on one side at a certain angle (bump stop gap) would produce the same ride height as a UCA on the other side at the same angle. Assuming they are all rigid connections, its just a complicated geometry problem...
I know it has been said when adjusting the torsion bars to ensure tires are evenly inflated and on a flat surface, and that non uniform tire pressure could cause adjustments to be incorrect....perhaps this is the true with the tread as well...
Perhaps I will measure the tire diameters just to get a feel for how much difference the tires are...the left rear tire is definitely larger due to the treading being brand new.
I still keep thinking though...That if the tire height causes the weight to be unevenly distributed, or it affects the position of the control arm, that the uneven ride height would also be reflected by an uneven bump stop gap, whereas I have uneven bump stop gaps for an even ride height.
For instance, take a perfectly level vehicle, new tires, no wear, equal bump stop gaps. Add a higher tread tire to the left rear corner, the car now sits unevenly, and the control arm position is affected. The change in UCA position would then directly correlate to a changed bump stop gap. Adjusting the torsion bar to force the control arms back to the correct bump stop gap should also result in the correct ride height. One torsion bar may have to be adjusted more, or under more torsion load to compensate for the unequal weight distribution, or spring rate degradation etc, but it just seems that the ride height is a direct result of the UCA position which is a direct result of the bump stop gap...
so wouldn't equal bump stop gaps geometrically equal identical UCA positions which would in turn equal identical ride heights?
I'm not sure if I'm making sense, but obviously I am thinking about this too much
I need to quit thinking about this...apparently suspension geometry is a lot more complicated than a bump stop gap.
Free Body Diagram from hell...7 years in school for engineering and this is what happens...you over analyze every little thing trying to answer the single question....WHY?!?!
It's 2am and I still can't stop thinking about it lol
I guess here is my overall question...I know the spring rates can differ and things wear differently etc...but if I am checking the bump stop gaps as the vehicle sits...after all variables and forces are already in place and accounted for and the equilibrium position has been reached, and I make adjustments to force an equal bump stop gap, why is the bump stop gap not a geometric indication of ride height...like in my picture:
Where when you increase the angle of the arms, the ride height is forced up, etc...if the arms on each side are the same shape/size/symmetrical, then the same angle on each side would yield the same lift on each side. And if a t bar wore out and one tire sagged, the angle would also change as the frame falls due to the geometry.
So I guess I'm saying...uneven spring rates or weight distributions would cause the car to sit unevenly, but wouldn't the corresponding gap also be changed accordingly?
I never noticed it before, but ever since I measured the ride height and realized that I have a lateral rake, I notice it every time I walk up to it...even while driving it! It won't let me forget about it!
Well that is a game changer...as I had been told and read in my searching that there shouldn't be a lateral rake.
As I had said, with equal gaps, I ended up with identical lateral rake of about 1 inch with drivers side being higher. Perhaps it is nothing to worry about then...I thought my suspension was abnormal and playing tricks on me.
Should start a poll thread.... I saw TJ's 1/4inch factory spec post, but I wonder how common it is after several years and miles.
Also, I would bet $$ that for everyone who has any lateral rake, its lower on the pass side. This tells me its something from the design/engineering/build/geometry - NOT something that's happened abnormally afterwards.
In your image - the bumpstops do define it, but if your arm's are mounted at all differently to accommodate other parts, the frame sits uneven. The steering is not perfectly symmetrical in the X.
Last edited by ImageOmega; 05-22-2012 at 07:50 AM.
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