Poly subframe spacers... side effects?

[huntz0r]

I have noticed that since I installed my set of Whiteline subframe spacers below the frame, the rear of the car now sits slightly (maybe 1" or less) lower than the front. The reason why is pretty obvious, as by compressing the bushings it pushes the subframe closer to the body.

However, I have begun to wonder if this has any adverse effects. I hadn't really given it much thought before, since everything is attached to the subframe it shouldn't affect the suspension geometry... except for one thing, the spring is getting compressed an extra .5-1" isn't it? Being stock linear-rate springs I would guess that it doesn't matter (the spring rate doesn't change), but I really don't know. Would that make the rear effectively stiffer? Or would the angle actually make it more prone to squat? The suspension is just stock springs with new GR-2s and all poly bushings in the rear.

Of course, it also looks a little doofy with an anti-rake, but I can probably get over that if it's the only issue... just another reason to upgrade the springs at some time :)

[Dousan_PG]

here's some info on it from Freshalloy



Don (PDM) says:

There's enough "slop" in the rear subframe bushings that under load, or deflection, they bend and twist enough to measure over 3/4".
The subframe bushings are not solid - they look kind of like a front wheel drive car's engine mounts, where there is only 3 sections of the bushing that is attaching the inner section to the outer. They are poured into the subframe at the factory. (many older S13's may find that if they take off the cup washers holding the subframe in place, their bushings may no be connected at all, and slopping around a TON !!)
The "pineapple's" or subframe donuts, are used to either go underneath the "cup" washers to squash the subframe up into the unibody...

Or they are strategically placed on top and underneath to affect the rear alignment for drag (reducing rear camber) or drift (toeing out the rear wheels)

The Whiteline kit comes complete with 6 bushings, 2 already cut so that you can jack up the rear end, and insert them very easily.
Also, Whiteline worked with me on the durometer of these donuts, so they are firmer than the Euras donuts made in Japan.

Super simple install, and positive results for very little work. (beats removing the entire rear subframe, diff, and suspension to burn out the stock rubber ones, and install delrin or aluminum or Cusco ones.

and in another thread about it, ruf posted:

Originally posted by ruf:
As Greaser pointed out, put them on TOP for drag/drift, BOTTOM for circuit (grip style...hahaha).

Reduced camber gain is useful for drag and drift for different reasons. On a drag car, you launch relatively straight (or you try to) so the car squats straight with little or no body roll. By reducing camber gain under suspension compression, the wheel stays more parallel to the vertical axis of the car, you maintain a larger contact patch = more rear traction.

When drifting, you have a lot of sideload on the car and a lot of body/chassis roll. Typically camber gain compensates for this roll and maintains a relatively flat contact patch. By reducing camber gain, the wheel again stays more parallel to the vertical axis of the car (which is leaning), so the wheel will "roll over" more, reducing contact patch = less rear traction = dori dori. You want the opposite of this for circuit.

<cheezy ASCII diagrams>

Drag:
|=o|o=|

Drift:
\=o\o=\

Circuit:
|=o\o=|
--------------------------------------------------------------------------------

FOOT IN MOUTH...

So it's not the first time nor the last time I will be wrong. The characteristics that I described above about the PDM/Whiteline subframe spacers (also known as "drift pineapples") is WRONG. The spacers act in a different manner. They do not alter roll center at all, but they change the level of anti-squat in the rear. The drag setting is with the spacer on top of the subframe in front and underneath in back. This reduces anti-squat so that the car will squat more under acceleration. This means more weight transfer to the rear and better launches. For drift, you do the opposite and jack up the anti-squat. Since the rear suspension isn't acting in the same plane (or less so) as the car's displacement, it is effectively stiffer and doesn't transfer weight as well. This gives less rear traction hence drifting easier. For neutral performance, you just leave them both underneath in front and rear to preload the stock bushings.

I was stupid and didn't stop to think that the upper control arms are also connected to the subframe and not the frame so there can't possibly be any roll center change made by moving the subframe because the LCAs and UCAs don't change position in relation to each other. The S15(and S14?) subframe swap however is a roll center change.

[huntz0r]

Interesting, thanks for the info... so I guess the only alteration is of the rear ride height, due to the fact my stock bushings squished up nicely, heh.

I did put them all on the bottom because I didn't really have a desire to change the subframe angle, plus it was a whole lot easier to get them on that way. The thought occurs to me of removing and reinstalling all four on top (slitting two as necessary), so the rear is slightly higher rather than slightly lower... if nothing else it would simply look better. But maybe I'm just being silly at that point. And the springs are probably better pushed down an inch below normal than let up the same distance above...

[mrdirty]

Does anyone have any pics of these installed?
I still can't quite visualize where they are...

[Dousan_PG]

pics from DriftinJim on FA

http://www.team140.net/~jimmy/pics/sub-spacer-circle.jpg

http://www.team140.net/~jimmy/pics/sub-spacer.jpg

[mrdirty]

Thanks!

[Bliss]

Originally posted by mrdirty
Thanks!

Yeah, thanks ALOT. I couldn't envision it, but those pics were extremely helpful.