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Same here. Bump for more info.
 

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I'm glad I just stumbled upon this (surprisingly the first time) and the engineer inside of me has given so much thought to the double wishbone set-up and the major flaw seems to be in the toe-arm. (I should be shot in the face for posting this up on here because someone could make a lot of money fabricating and selling this idea of mine but I'm a subi guy and I think the community could seriously benefit from what I'm about to throw out there...)

The toe arm is tied into the subframe on the inboard side (very silly as suspension components should be designed to directly interface). Imagine having the toe arm tied into the lower control arm...which would put the reference point or the center of the toe arc in sync with the lower control arm...which depending on the level of compression or depression on the suspension would directly impact the interface of the toe arm and knuckle in reference to the LCA. This would require a beefier LCA and a bit of engineering to do, I do imagine that this would alleviate a lot of the issues being brought up in this thread though.

If this sounds silly at least give me feedback as to why. Hope I just helped someone figure out this age long problem :)

***seeings though I didn't see the few recommended posts before this one I'll clarify how to do this. We would want the LCA and the Toe Arm to operate on the same X, Y, and Z axis...looking from the outside of the wheel directly in we can see that the X axis would have the inner bolt (covers X and Y axis) of the LCA extend forward with some kind of spacer or rib on which to mount the toe arm...the toe arm itself would have to be the same length as the LCA (covers the Z axis).

Now with all of this said...a suspension is at least as complicated as an engine in terms of outside variables and adjustments and so on...and on...and on... Tires, tire pressure, sway bars, bushings, spring rates, ride height, shock stroke, etc... With all of that said I can say that I've always preferred a moderate sway bar (22mm) as opposed to the super flat characteristics of anything bigger (24mm+) as this keeps the car from putting as much weight on the outside wheel...which in the instance of both tires toeing inwards results in the inside wheel still pushing the rear end of the car around the turn a bit...in an outwards fashion but with the outside wheel and tire still having plenty of weight on which to defeat that by pushing the car more towards the apex of the turn than to the outside of it. We also have the effects of camber; in essence a car rolling outwards a bit in a turn brings the effective camber of the outer wheel/tire closer to 90 degrees or perpendicular to the ground...and the inner wheel/tire would actually realize increased camber which would place a much smaller contact patch on the ground on the inner side as opposed to much much larger contact patch on the outer wheel/tire. This being said you can understand that the outside tire in the rear has a lot more influence.

I think with that knowledge we may find a good place to start...real world testing would mean putting a zip tie around the shaft of the rear struts and actually taking it on the track. Find the maximum compression and attempt to zero the toe as the suspension is loaded to that point on an alignment rack. From there we could devise a baseline (we could even do this for just one turn or even on a skid pad). Then we could start by toeing the tire a minute amount, like .2 degrees in and then out and analyzing that data. I'm almost certain that we'd find that a slight toe in would balance the car a little more so and that a slight toe out (remember we're talking under compression) would push the rear end of the car outwards a bit and cause understeer.

Hope I haven't given anyone a headache.
 

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I know I'm late to the party, but what if you moved the mounting pint on the subframe up. The loaded tire would have toe out, and the inner unloaded tire would have toe in. The only problem I see would be bump steer in the rear over harsh bumps, that and idk how complicated it would be moving the inner mounting point.
 

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Re: 2008 rear suspension part II: Toe change/Bumpsteer

The second thing that happens, and this is a big one is that the car will actually dynamically steer against you in a corner.

The loaded tire will quickly toe in (more quickly than stock - remember point 2 to point 3). The unloaded tire will now toe out because the toe arm is approaching parallel to the ground. This will remain the same state until the suspension droops to the point that the arm is parallel to the ground. At that point the tire will toe in.

What this means is that you get passive 4 wheel steering. VERY VERY cool, BUT, and this is a big one, it's in the wrong direction!!!! It's steering the loaded tire into the turn, and the unloaded tire into the turn, but it's at the rear of the car!!! Dangit!!!
Is the solution to *raise* the car then, rather than lower it? If you raise the car, then the loaded side will tend to toe-out, and the unloaded side toe-in. :)
 

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picture links are all broken.

So what happens when you use lift springs? (ie Kings)

- From the travel thread, we'd gain bump, lose droop travel.
- From this thread, it sounds like the lift springs would cause the toe arm to angle down a bit.
- Assuming that an alignment has made this new resting height 0 toe, then:
- the compression side will cause the arm to return to parallel: or toe out (reverse of the toe in from TIC's droop analysis).
- the droop side will go deeper into drop causing a more accelerated toe in.

So will this cause a rotation happy car?
 

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Re: 2008 rear suspension part II: Toe change/Bumpsteer

Is the solution to *raise* the car then, rather than lower it? If you raise the car, then the loaded side will tend to toe-out, and the unloaded side toe-in. :)
This is why a lowered STi understeers so frickin' bad! I couldn't believe how much better my STi drove on coilovers after I had it corner balanced to a more stockish ride height.

Kiddies, if you really need a lowered car, just get a 1991 Civic and be done with it. Paint the wheels pink, get a spoiler and a fart can and be all set with that set of style. Lowering your STi is for the birds!
 

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Re: 2008 rear suspension part II: Toe change/Bumpsteer

This is why a lowered STi understeers so frickin' bad! I couldn't believe how much better my STi drove on coilovers after I had it corner balanced to a more stockish ride height.

Kiddies, if you really need a lowered car, just get a 1991 Civic and be done with it. Paint the wheels pink, get a spoiler and a fart can and be all set with that set of style. Lowering your STi is for the birds!
Absolutely agree....ended up raising rear almost 1/2" to 13.5" wheel hub center to rear fender height and it made a huge difference in handling. I was getting understeer from rear wheel "push" and this change dramatically improved handling.
 

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Re: 2008 rear suspension part II: Toe change/Bumpsteer

Absolutely agree....ended up raising rear almost 1/2" to 13.5" wheel hub center to rear fender height and it made a huge difference in handling. I was getting understeer from rear wheel "push" and this change dramatically improved handling.
Do you remember those 1980's anti-tobacco ads with C3PO and R2D2 saying in a British, protocol droid accent "Don't smoik, iitt's baaad for ya health".

Well don't lower your STi, it's bad for your handling. There are 1,000,001 reasons that it is detrimental for handling. Unless you can engineer a proven setup for a race car that radically alters the suspension geometry to make your mods work like Killer B, EFI logics or Turnin Concepts, stay at stock ride height or you'll regret it.
 

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Tony or Clint,
Does increasing rear, negative camber reduce or exacerbate this issue?
I know this is an old post, but you are DAMN RIGHT IT DOES. Dial a bunch of negative camber in on the rear of your GR (I am using the adjustable rear upper control arm bushings I think they are power flex) and hammer it out of a turn. BE CAREFUL AND LEAVE TRACTION CONTROL ON. It put my nuts in my belly the first time.

For autocrossing, I found running up to -4.0 deg camber in the front to work great, but there is a noticeable loss in braking at the ends of long straights depending on the course. I tried using -2.5deg in the rear to "match" the front and it was far too much. The rear end will snap out when you accelerate out of a turn just when you have it nicely loaded up and start dipping into the boost.

Where is part 3?
 
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