Aurelia Rear Wheel alignment / adjustment

[williamcorke]

This weekend my B10 had its wheel alignment checked - this was to make sure the front toe-in was as it should be.

We also looked at the rear wheels and found that one was toeing-in by 1 degree, the other toeing out be 4 degrees.

I have been wondering if moving the rear wishbone/trailing arm  on the two bushes that attach it to the body of the car would change alignment. The wishbone arm where the bush mounts is 40mm wide, and the bush is 75mm in length, so there is potential for lateral re-positioning.

Does anyone have any knowledge or experience of this? I couldn't find any reference to it in the workshop manual.

[williamcorke]

Looks like I'll have to reply to my own question...

Having gone into this further, it seems obvious that the rear suspension on the S1 (trailing arm) Aurelia is designed to allow final set-up of toe-in/out with the wishbone/wheel on the car. I expect the factory will have done this with each car (unless dealers did it).

Some schoolboy geometry calculations gave me the result (correctly I hope) that for each degree of toe adjustment, you'd need to move the wishbone arm on the bush by c. 8mm. There was 2.5 m of toe-out at the (metal) rim of the RH rear wheel which I make to be 0.68 of a degree, so I moved the arm on the bushes by a bit over 5mm. When the car's alignment is measured again in a few weeks, we'll see if the problem has been sorted.

The technique I used was to undo the pinch bolts and (with the outer surface of the bushes greased), 'encourage' sideways movement in the desired direction. Not too much encouragement (with a hammer) was needed, but I took the precaution of removing the suspension spring first, so the wishbone was swinging free. I'm not sure this was strictly necessary.

Final word on this - before alignment measurement at least - is that the change had no discernible effect on the car's behaviour on the road. Oh well.

[Charles]

What a clever chap De Virgilio was.

[peteracs]

Hi William

If you use the string method of checking the alignment you can get a good idea of where they are at home before you go for a professional alignment. I did this on my Spider with good results.

Peter

[Jay]

Interesting setup, so what stops the wishbone/tailing arm moving on its own over time, is the geometry slightly out so creating extra friction?  Having sorted a few cars with string and lasers and found that you need to roll the car back and forth by a fair amount to ‘settle’, each time you make adjustment. It’s definitely not a quick job.       

[Dikappa]

Very intresting thoughts, never thought of that when assembling my rear suspension at the time, I think I just put all bushings in the middle....looking forward to the results of the alignment checks!

[GG]

Interesting discussion. As you likely know, the mounting lines for rubber bushes are not co-linear with each other. This raised many questions at the time, but the general sense was it worked well. While not explicitly discussed, it seems likely that De Virgilio was designing in anticipation of wear in the bushes, and thus the non-co-linear alignment would keep things fresh and on point, even if there was some wear.
That seems clear enough.

What is less clear is the toe-in adjustment you are referencing. It doesn't seem like it was designed for this, but perhaps it was. We are always learning! 

[williamcorke]

Great drawing, thank you Geoff.

Why have bushes so much longer than the wishbone clamps is the question I still have.

When my mate with a 4-wheel alignment kit next comes over we'll do some measuring and testing and report back.