How to measure rear camber? Inner tyre wear

[Grrrmachine]

Swapping my tyres over, I've noticed my rears are wrecked. Inner edge is bald, outer edge still has 4mm on them, so something's really not right.

Beam and trailing arm bushes were renewed 4000km ago, and new standard springs fitted. So I can only guess that something is seriously bent under the car.

How do I go about measuring the camber to confirm this?

[turkeysneck]

It won't be camber, it'll be toe, probably toeing out a country mile.

[Grrrmachine]

This is what they were before I redid the bushes:

Camber: -0.53 and -1.11, when the tolerance is -2.30 to -1.30
Toe: -1.05 and -1.33, when the tolerance is -0.04 to 0.26

Would excess toe suggest something's bent out of shape?

[turkeysneck]

If you have lowered it, the toe will be all over the place. You need check the basics, like the thrust line to see what's going on.

[Grrrmachine]

I'm guessing the only way to measure the thrust line is to take it to a proper geometry place - not the sort of thing you can do at home.

[Brianmoooore]

Both toe and camber change when you lower the back of an E30. Camber goes more negative by
1.75 degrees for 50mm of drop, and toe in increases by about 0.8mm.
Both are easily checked at home, as long as you have a patch of level ground.
For toe you need to tie a piece of string right around the car half way up the wheels, and use small pieces of plywood at the front side of the front tyres and rear side of the rear tyres to lift the string just clear of the wheel rims and to get the strings along the sides exactly parallel. With standard wheels, you should need 4mm more of packers at the front each side, compared to the rear.
When this is all set up, it's just a matter of measuring the distance from the wheel rims to the string to determine toe.
Done properly, this can be every bit as accurate as fancy laser equipment.

For camber you need two 600mm lengths of 2 X 1 batten, and fit a hinge to join them together at one end. Screw two screw partly into one of the pieces of batten space so that their heads rest on the top and the bottom of the wheel rim when the battens are held upright beside the wheel with the hinge at the bottom. Place a spirit level against the batten without the screws and open the hinge up slightly until the spirit level is upright. Measure the gap between the battens at the top end, divide this by 600mm, which will then give you the natural sine or tangent (same at small angles) of the camber of the wheel.

[turkeysneck]

The toe will be a mile more than 0.8mm mill out, to eat the tyres like that they are more likely to be about 10mm toe out.

[Grrrmachine]

That's a sound method, cheers guys.

The more I think about it, I'm wondering if there are other symptoms too. In the last six months that particular wheel has needed a new bearing, and it's also got an occasionally sticking calliper - is there any chance that either of those things could lead to the same sort of irregular tyre wear?

Otherwise I'll have to invest in some new trailing arms

Worth pointing out, I'm not lowering the car, and the tyres are standard 14" balloons.

[Grrrmachine]

Right, some results using Brian's homebrew methods.

For the rear tyres, I've got a camber or 0.84 and 0.98 degrees respectively; 0.98 is the really worn tyre.
For toe, both rears are toeing out; there's a difference of 7mm across one wheel and only 3mm across the really worn one. The front wheel on that side is toeing out by 4mm, and only 1mm on the other, so I'm guessing the front needs setting up properly or the steering wasn't perfectly straight.

Are these numbers drastic? I'm really starting to think it's the sticky caliper causing drag rather than a geometry issue.

[DanThe]

Sounds like your crabbing down the road, 7mm toe out?

[Grrrmachine]

But would that cause massive tyre wear on the other side? I'm trying to get my head around thrust lines and whatnot, but it's all quite new to me.

[Morat]

Can you adjust rear toe?

[Grrrmachine]

Doesn't look like it. I'm concerned because there's a small chance the car has had an impact on the side that's got large toe-out, based on minor panel damage I uncovered during the resto. Of course, there was a chance I was being a spastic setting up all my lines, but there's also the option that the trailing arm is bent.

Don't see how it would cause rapid tyre wear on the other side of the car though.

[harry_p]

Something must be seriously wrong for both sides to toe out, they toe in at the rear as standard which helps with stability, and due to the angles of the arm pivots this toe in increases a the suspension compresses.

With toe out at the rear it must handle like a dog!

I'd certainly be looking very carefully at the rear arms. A bash at the rear due to over enthusiastic drifting could easily knock a wheel toe out.

I wouldn't worry too much about the front for now, as the front wheels will always align themselves to even out toe side to side when the car is in motion. Get the rear sorted out, then get it checked and get the front set properly.

[Grrrmachine]

Well, it wasn't exactly on rails last time I drove it on summer tyres (two years ago) and for the past four months it's been a proper Polish winter so I've been running 14" winter tyres and driving like a granny. It's only as I swapped the tyres to brand new Toyos that I noticed how badly the winters have worn down.

I've got the car booked in for a geometry test tomorrow to confirm my results, and I'll see if they can measure things to see if either of the trailing arms or the rear beam is bent out of shape.

[DanThe]

Its quite easy to see if the beam is out of shape, ive known several cases where the trailing arms have ended up bent

[Grrrmachine]

Got the results back from the professionals.

Rear camber is -1.02 and -1.18 degrees left and right, so I guess that's all fine (although the test sheet says it should be -1.30 to -2.30 degrees).

The toe is -0.45 degrees on the left, -0.33 degrees on the right. So it's toeing out a bit, and close to what my own findings were (not 7mm though - more like 4mm).

The diagnostics bloke also said nothing's bent, it all seems perfectly straight. And the thrust angle is -.06 degrees, so almost bang-on in terms of tolerances. Therefore, I'm stumped

[Brianmoooore]

Your DIY measurements should have been a lot closer than that! I suspect you didn't have the strings parallel down the sides.
I seem to recall your car is lowered a bit, so the camber should be more negative than stock, not less.
It's all within the limits of what can be corrected with offset trailing arm bushes, IIRC, so that's the route I would suggest, then you can experience what an E30 should handle like.

[DanThe]

Looking at those results you just need to lower it to bring it into spec!

[Grrrmachine]

Brian, the car's not lowered at all. I put it on stock springs after the restoration, with stock wheels and tyres (205/55R15). You might be right about the parallel string theory, although it seems a measurement on one side was bang on (3.4mm being 0.33 degrees across a 600mm wheel).

It seems I'd have to lower the car a hell of a lot to pull the wheels in (50mm gives 0.8mm toe in?). Therefore I either need to fiddle with eccentric bushes, or fit these tow-adjustment plates the Yanks seem to love so much.

[Grrrmachine]

Eccentric bushes are increasingly looking like the simplest option, since the current ones have only been on six months they should be fairly easy to get back out again.

However, the Bentley manual says that a pair of eccentrics will only offer 1mm of toe correction, but that's at the trailing arm mounts; I can't find how much toe in/out that corrects at the actual wheel either in mm or degrees.