Rear Alignment Questions

#1

I could have sworn that my car had eccentric bushings in the back for adjusting camber/toe, but the race shop I took it to said the alignment was fixed. So, a couple of questions:

  1. Is there an easy way to visually identify eccentric RTAB’s? I know they should be off center, but do you need to take out any bolts to see it or is there another way to tell at a glance? I do trust these guys, but not sure how many E30’s they see.

  2. My alignment back there is currently 5mm toe OUT. How bad is that going to suck? Massive oversteer, or driveable? I’ve always used a touch of toe-in in the rear.

  3. What’s the current consensus on the best way to add adjustability?

Thanks!

J.

#2

It will oversteer. Can’t remember how much mine was toe’d out but it was driveable. Still I wouldn’t recommend driving it like that, yours might oversteer really badly and it can also handle differently in left and right hand turns.

Mine was bent and I had a frame shop fix it and stayed with the fixed bushings. I prefer to have no adjustability as its just something else than can get out of alignment. I also hate adjusting stuff, setup etc etc.

#3

I’m in the same situation. Lots of toe out in rear. I had it on the alignment rack prior to last weekends race. To help, until I can change to adjusters in the rear, was to disconnect rear bar, front hooked up and go to zero toe in front. Car was a little pushy, but OK last weekend at Homestead. Going to try hooking the rear bar up to see if it helps the push. Going to zero in the front will help.

That’s a band-aid. Ideally you’ll be toe-in rear and slightly toe-out in front, as you would expect. Exact settings depend on preference and driving style.

Hope that helps.

#4

Confirmed with Scott that it does have the AKG eccentric bushings, and he’s sending me the tool to adjust them. That said, anybody know HOW to adjust them?

Shawn, how much toe out did you have on yours?

Thanks for the advice, Simon. I suppose it would be ideal if you could get it where you want it and be certain that it wasn’t going to change!

#5

It’s 5mm of TOTAL toe out? What is the absolute toe?

If it was me I wouldn’t tolerate so much toe out. If one of the rear wheels is straight and the other toes out 5mm I wouldn’t trust the rear end to stay under me when turning such that the toe out wheel is outboard. That’s a lot of toe.

You can ID adjustable rtabs easily enough. Consider that the rtab bushing sort of looks like the letter “I”. Now think of an “I” with an underline. The underline is a thin eccentric nut sort of thing that locates the bushing’s axis. The nut will look around 3mm thick and be a pretty large dia.

5mm of toe with concentric bushings means something is bent. Not a crisis, but good to know.

Eccentric rtabs have their warts. I’d get Ireland’s new weld on kit that has serrations to keep the bushings in place.

#6

my eccentrics are just a through bolt that you turn, then tighten a nut on the other end, no special tool needed. of course, they don’t stay tight and soon shift which makes them relatively useless for any length of time. what were your camber values?

#7

These have a thin nut for turning them. Could do it if you had a thin enough wrench or one that was ground down. Tool is essentially just a flat sheet cut to fit a wrenchish sort of shape.

Here’s what the RTAB adjuster looks like:

Rear camber is a bit much. -4.0L / -3.3R

#8

[quote=“Ranger” post=64271]It’s 5mm of TOTAL toe out? What is the absolute toe?

[/quote]

Hmmm… looking back at their notes it looks like it is 5mm out PER SIDE.

[quote=“Ranger” post=64271]
Eccentric rtabs have their warts. I’d get Ireland’s new weld on kit that has serrations to keep the bushings in place.[/quote]

With these weld-on kits, can you adjust camber and toe individually?

#9

[quote=“juliancates” post=64275]

With these weld-on kits, can you adjust camber and toe individually?[/quote]

Yes. You have to do all 4.

#10

Way more than is acceptable…:S

#11

[quote=“juliancates” post=64275]Hmmm… looking back at their notes it looks like it is 5mm out PER SIDE.[/quote
That is enough toe out to scare god. The car will be extremely loose.

For the most part the weld in kits do make camber and toe independent adjustments. If a big adjustment has to be made on camber or on toe, there can be a slight change in the other setting. But for minor changes they are independent.

#12

5mm absolute toe out on both left and right sides is IMO undrivable.

Adjusting toe and camber with eccentric rtabs is not Infantry simple. A person has to sit down and figure out the geometry. Get a baseball bat or some other kind of long rod and sit behind the car. Use the baseball bat to visualize the axis that one of the rear wheels turns on.

Hmm. I’ll try to describe this in detail for the left rear. Sit behind the left rear of the car with the baseball bat. Put your right hand at the end of the bat and your left hand at center. Now support your left hand on your knee so it can’t move. Then move your right hand in a circle of a dia of 2" or so and note the opposite motions of the other end of the bat which is sticking out to the left.

With the bat replicating the wheel’s axis of rotation, you are replicating what happens to wheel toe and camber when you move the eccentric at the inner rtab for the left wheel.

Now support your right hand on your knee so it can’t move. Then move your left hand around in the same 2" dia circle and note the way the end of the bat moves. Now you are replicating adjusting the outer rtab.

You can see how adjusting rtabs adjust both toe and camber simultaneously. The goal is to get your toe correct while getting your camber as correct as possible. It takes some trial and error.

Now imagine a circle with 3, 6, 9, and 12 o’clock. Consider that as you move the eccentric around 3 or 9 you get a lot of vertical change (camber), but not much horiz change (toe). This is key to making the whole thing work.

For example…lets say you get your toe right, but you need to fix camber. So you have to ask yourself…“where can I get a bunch of vertical change w/o screwing up the horiz change?” Then you look at your rtabs and the outer eccentric is at 6 and the inner eccentric is at 3. So you choose to fool with the inner eccentric because since it’s at 3, you can get a lot of vertical change for your money.

Note that you will have to play with the rtabs a little, rotating them around and around and carefully watching the movement of the bushings. This will allow you to figure out where 12 is on the eccentric. Then mark 12 on the nut in a way that you can keep track of it.

Go get a digital level so you can check camber yourself. It’s little tricky to get absolute camber, but since you already know what your camber is, you can use the level to measure change. For example, what ever the level reads on your 4deg wheel now, if you want to end up with 3deg, then just get a degree less than whatever the level says.

Be sure to get a level that isn’t too tall, otherwise it won’t fit between fender and garage floor. Like mine. Oops.

Whew.

#13

Good stuff, Ranger, the baseball bat visualization is very helpful!

I also took the charts from here: http://e30m3project.com/e30m3performance/tech_articles/susp-tech/ecc_bush/ecc_bush.htm

… made a little cheat sheet:

http://dl.dropbox.com/u/606638/rear_camber-toe_adjust.pdf

I’m hoping that the adjusters are just in a worst case scenario now for toe, and that I can move them around and get some acceptable numbers. It’s not like this is a new build, it’s a car that’s already been made track worthy. Surely it can’t be that egregious back there.

I do have a means to measure camber, and I’ve got a line on some toe plates to measure that. I could set up a string box now, I suppose, and I might go ahead and do that so that I’m not waiting. Just need to be able to adjust the rtab. Trying to figure out what size of a thin wrench I’ll need.

Hopefully it’s apparent what the orientation of the eccentric is by fiddling with it a bit.

Looks like if I rotate the outer bushing to 180* (using the baseline of 0* is pointing toward rear of car) and 0* for the inner I can affect quite a bit of toe change. Here’s hoping that’s correct!

#14

Julian,

I have the same RTAB setup on my M3 and a set of needle nose vice grips works in lieu of the proper wrench. The PO installed mine and didn’t provide the wrench when I purchased the car. Ranger’s explanation is good but I would’nt worry too much about the camber. Just set the rear toe and let the camber be as long as it’s reasonble.

In my experience, using strings and cinder blocks in my garage is much better than an alignment from a shop. I guess I haven’t found the right shop…

#15

Toe plates aren’t an acceptable for a check/set of rear toe. Strings or an alignment rack are the only viable solution.

Think about it. Toe plates could show zero toe, but one rear wheel could be toe’d out and the other toe’d in. That would result in a thrust angle and different handling for left and right hand turns. Fishing line and jack stands are the “poor mans” solution. But understand that the car has to be rolled fore/aft several feet a time or two after an adjustment and the strings reset to tell what the new numbers are.

I use what amounts to “smart strings” that attach to the car. Once set to parallel to the the chassis the alignment of the strings doesn’t change whether I jack up the car or roll it. It is a lot easier to make an adjustment of rear toe or camber with the back end of the car up in the air if you are doing this yourself as that gives you room to work.

#16

You are right of course, Jim. I have a similar string setup, but the bars are set up to hang from my Miata. I re-used the string and weights from my Iron Canyon kit and used the nice toe-stick I have to measure the rears. I came up with 3/16 OUT on one side and 1/8 OUT on the other. So pretty close to each other, but still going the wrong way.

I didn’t have my weight in the car, though, nor did I unhook the sways. Just wanted to get a quick sense of what the shop was seeing. When you have to set them back up every time, strings are a real pain.

Is there a good/easy way to lock the steering straight on the E30’s?

Richard, good idea on the needle nose, I might give those a try. The PO is overnighting me the adjustment tool on Monday, but as slow as I work and with VIR coming up next weekend, I need all the head start I can get.

#17

40lb bags of lime are only $3 or so and work great as driver weight.

#18

Sand is better than lime…

#19

[quote=“jlevie” post=64287]Toe plates aren’t an acceptable for a check/set of rear toe. Strings or an alignment rack are the only viable solution.
[/quote]Toe plates provide only “relative toe” not absolute toe. Fine for the front but not enough for the rear.

I use a laser level and a toe plate to get absolute rear toe. I shoot a laser beam from the rear wheel towards the front. If, for example, the laser beam is 22mm from the rear wheel, then 0 toe is 22mm from the front wheel. This will seem a little tricky at first but with a little practice it’s very quick.

You can’t do it in bright sunshine, a garage is best.

Your reference mark should be tape on the center of the front wheel. That way you can eyeball your front wheels being straight and that’s good enough. If you put your reference tape on your front tire, instead of the center of the wheel, that will introduce error because you can’t be sure the front tires are pointed straight forward.

I’m not sure that made sense. Have someone turn the steering wheel while you watch the motion of the front tire and wheel. Note how the hub of the wheel moves much less than the front and rear of the tire. So if you put the front wheel straight per your calibrated eyeball, you probably didn’t get the tires exactly straight but the hub will be pretty darn close. That’s why you want to put your tape and reference mark on the front hub (or center of wheel) and not the front or rear of the front tire.

The charm of Ranger’s laser method is that any toe error is multiplied by ~x6. This is because toe is normally measured at the rim of the wheel, but I measure it several feet away at the front wheel. This makes it easy to get a very precise toe measurement.

I did my alignment a couple nights ago. My RR is neutral and my LR has 0.5mm toe-in, or 1/50th". That’s more precision than shops will normally do.

#20

I don’t know what size the eccentric nut is but the wrenches in the bmw toolkit are extra skinny and I’ve found that they are a perfect replacement for the my die-grinder chuck wrenches I can never keep track of.

I bought a cheap digital level to do my alignment and it was horribly inaccurate. You could buy 10 alignments for the price of a good one. I wouldn’t trust a spinning construction laser either. Maybe a pen laser that you verified to be straight attached to the rim somehow would work.

You paid for an alignment and they didn’t fix it. I would take it back and get them to finish the job.