Touring Rear Suspn - Correcting Camber?

[e34m50tu]

Is there a way to correct the rear camber on the rear of my touring? It was originally equipped w/the SLS and the PO had removed it and put some Bilsteins in it. When I did my tire rotation I noticed it wore rather severely on the inside.

I know the sedans' rear suspension cannot be aligned, but what about the tourings? If not, then is there a way to manually fabricate some sort of correction for the excessive negative camber? I'd like to make my stock 15" tires last more than 10k miles...

[jetavdk]

Camber is not adjustable even with the M5 subframe. I think you have something else going on if you are having wear problems at 10,000 miles with 15" wheels. Is the car lowered?

[Binjammin]

Is there a way to correct the rear camber on the rear of my touring? It was originally equipped w/the SLS and the PO had removed it and put some Bilsteins in it. When I did my tire rotation I noticed it wore rather severely on the inside.

I know the sedans' rear suspension cannot be aligned, but what about the tourings? If not, then is there a way to manually fabricate some sort of correction for the excessive negative camber? I'd like to make my stock 15" tires last more than 10k miles...

No way to adjust. I'm working on a solution. Pretty sure I've got it worked out, just need free time.

[billygoat777]

Isn't there a camber correction kit?

My autoshop teacher told me that we can make a camber kit for mine sometime in the year. If I ever end up doing it, I'll take pics and try to make a write up.

[e34m50tu]

thanks guys!

[attack eagle]

oh guys.... :)


KMAC.

it isn't the camber that is killing the tires, it is the toe. though I gbet your are runnig 4-4.5 degrees of camber when weighted properly on the alignment rack.

I used to go thru a set of tires in 6,000 miles. 3,000 per shoulder. no problems anymore but it is a BITCH of a job.

ma n RVAe34 both run Kmacs. Side benefit? No more dogbones.

[Binjammin]

The rumor I've heard about kmacs is that they'll reset to 0 on really hard launches. What do you mean no more dogbones btw?

[attack eagle]

you don't use em anymore.

no issue with "resetting them" to 0...

[Binjammin]

Really? From everything I can tell the dogbones are for passive steering, I don't see how putting the camber back to stock would eliminate that.

So far as resetting, it's not a matter of you resetting them, it's that hard launches pull the adjusters and rotate them, changing the adjusted camber back to 0.

[attack eagle]

correct, and because there is far less flex in the kmacs you don't need them for lateral stabilization on the trailing arm... it is all downside if you keep them.
as in the dogbones would pull them out of adjustment possibly.

I havene't had any issues, but then I'm only on 245s.

[Binjammin]

I don't think the dogbones are for stabilization actually. I'm pretty sure the way they work is that as the car leans in a corner, the trailing arm gets pushed up, and as the arm gets pushed up the dogbone, which pushes on the arm to give it a little more toe, causing it to steer out.

[attack eagle]

Cornering torques the arms rear in creating more toe... the dog bones limit lateral deflection.

those OEM TAB bushings are stiff, but not nearly stiff enough to prevent deflection on their own. you can put a screwdriver in em when mounted and move em about slightly.

Dogbones are AFT of the lateral axis... as teh trailing arm moves up or down statically the Ta would be slightly pulled in, correct... which is toe OUT... the exact inverse of what you want except that it some what neutralizes the normal toe in... when limited of course.
but as you load the trailing arm in a corner... that is an ass load more force than simple vertical movement. you could very very easily get the rear shimmy, as you cycle toe in & out as the toe out reduces force returning it to unload and moretoe in, which loads it and causes toe out which unloads it and....

ever notice the design has no panhard bar, though other 2 link designs absolutely require one?

[Binjammin]

Well, it's not a two link, it's an IRS, and it's not a live axle, which is why it doesn't have a panhard bar. I don't know how you'd even think of attaching a panhard bar to an IRS.

[attack eagle]

look under the back of any vette or viper,and you have bar which serves the same function as a panhard bar for IRS control arm types suspensions. look on an early jag and you have a bar which connects in the horizontal axis to the diff carrier. they pivot around the diff like so ( * )

Look at the e34 and you got nada... nothing in the horizontal plane from hub to diff at all. the suspension doesn't move AROUND the diff, it moves like flippers on a scuba diver. the exact same design is used with a live axle rear 2 link suspension...

the camber and toe change when moving up and down is a function of the flexibility of the bushings, and the offset from 0 angle of the "axis" on the leading edge.





it IS a two bar design, a horizontally triangulated one but still... there is free range of motion fore and aft, in and out and up and down on those output shaft cv joints.
the hubs are locked in place on the bar and wheel position in 3 dimensions is completely dependent on the trailing arm position. that is a two bar.

that is why I think they are so very cool. who else ever ran a 2 bar IRS that you know of ?

[Binjammin]

On a jag like what you're talking about, from all the pics I can find, those are control arms, unless there's something I'm missing. They allow the suspension to articulate, and keep the spindle at a relative length to the diff. A panhard bar keeps the suspension in place relative to the body of the car.

[attack eagle]

a panhard bar limits and controls lateral deflection... or a watts link (better)...
has nothing to do with the body THEY DON;T EVEN KEEP THE suspension in the same vertical plane... but they do let you run softer and more compliant busings for a more articulating softer riding rear suspension. and those jag control arms (any U or A shaped control arm) serve the same purpose as a panhard bar. control deflection.

which is exactly what the dogbones do on a STOCK RTAB equipped e34 rear suspension.

this is the IRS version of a 1967 Chevrolet pickup trailing arm rear suspension.
or nascar if you want, since they are based on the same design.

the dogbones are actually mini panhard bars.

you don;t want em or need em when you go stiffer on the rear bushings. it would be un compliant... and that is bad for a two bar rear suspension.

http://static.bmwfans.info/images/epc/NDEyNF9w.png (http://bmwfans.info/original/E34/tou/525i-M50/USA/L/A/1992/03/mg-33/ill-33_0223/)

btw... the INNER is the primary bar in the two link design, not the outer. the outer is a track/toe bar just like the ones on the back of the hub on vettes vipers. It is just static.

[Binjammin]

http://en.wikipedia.org/wiki/Panhard_rod

Actually, keeping an axle in line under the body is exactly what a panhard bar does.

[attack eagle]

nope, it isn't. it doesn't even keep it located under the body. the main suspension does that. A panhard bar without a 3 bar or two bar would be useless. you can run a 2bar or a 3 bar without a panhard bar...

it keeps it within a range of left right motion AND establishes roll center on a straight axle design.

Low and long = low roll center and minimal angularity for minimal shift left right as well as minimal differnces between lefties an righties * which is why dirt track cars run short angled panhard bars.


a tapered two bar design relies on some give in the arm and in the bushings to make it work and establish a roll center. these little dogbones were there to act as limiters on that motion. forces when cornering are primarily horizontal, not vertical. the roll center determines how the car will lean and thus vertical suspension compression.

[e34m50tu]

:eyecrazy

in response to A/E, it's not toe. It's the insides of the tire wearing out, as the suspension is too low.

But from what I gather from this thread, I can't really do much. or am I wrong? I hope I'm wrong...

[attack eagle]

that's toe out brother.

I knoweth of which I speaketh... from experienceth. :)

mine was at 4.5 and 0.2 toe OUT (weighted) before kmacs. ran great, super stable, just needed new rear tires every oil change, wore out only the inner inch or so despite the entire tire touching the ground.

camber will wear them some, but to scrub them down that fast (and especially in only a 1-1.5 inch band) it has to be a toe out problem.

[pspassos]

so, TOE should be ALWAYS neutral or its good to have some TOE IN (or out...)?

[attack eagle]

toe in is what it is designed to have... and VERY minimal at that. .1 degree or something.

Check bentley. Specs are there.

[Jcbe34]

Yep.. I've preached this many a time. I run a lot of camber in the rear but my toe is .2 on both sides and I have slight inner wear but nothing crazy. The downside to KMAC's is the installation.

[pspassos]

Why Jcbe34? whats the big deal with instalation on the kmacs?

[attack eagle]

it's about an 8 hour job... and requires a lift and power tools.

[pspassos]

it's about an 8 hour job... and requires a lift and power tools.

but, at the end, is it worthy? I'm just about to buy front/rear kmacs....

[attack eagle]

front unknown.

rear::: IF you need them there really is no choice. if you DON;T absolutely need the correction then don't do them.

Front? no idea.

ut depending on how much the good front strut mounts cost, they might not cost much more... i certainly need to do my front ones. they is trashed.

[pspassos]

The thing is that I track my car.... its not an everyday use car, its just for track and some ocasional fun on some twist higways.... so my idea was to really change camber.... put soething like -3 on the fronto and -1,5 or -2 on the back.... and, of course, keep changing until I find the correct one.... Does this front kmacs change caster within the change os camber? if so, that is not good....

[attack eagle]

you are already at -2 in the rear. that is stock.

[e34m50tu]

okay so i guess i can buy some time by being more religious about rotating the tires...

[pspassos]

you are already at -2 in the rear. that is stock.

and what is stock at the front?
considering buying olny front kit though....