KennyW wrote:
I'm going for smaller levels and wood since I have some gash bits of wood lying around at home.
Race you get done in our weather
Sorry Kenny but I'm going to have to claim victory in this two horse race, and I have the photo finish to prove it.
Here are the scales I made out of a couple of lengths of 25x45mm pine and a bit of scrap plywood for the targets: (click for full image)
Mounting system for the laser: (click for full image)
The mounting system using bungie cords isn't ideal but its what I managed to come up with. The piece of wood extends just past the lip of the rim to sit on top of it but doesn't touch the tyre. I had to do this instead of sitting it inside the lip to be able to clear the center of the rim. To stop things sliding around I put a few layers of rubberised electrical tape on the wood both at the ends and further in, this allows the wood to grip the rim and also the laser level so that things stay stable.
The main drawback of the bungie cords is that I had to jack one side of the car up to turn the wheel so that both wheels were pointing ahead the same time. I couldn't think of an easy way to clamp to the alloys that would give the necessary freedom to turn the laser around to level both at the same time.
Close up of the front left target: (click for full image)
The target size is 100mm wide by 320mm tall, the horizontal line near the top is 290mm which is the axle height of the car, thus the target height when rolling the car backwards and forwards, although anywhere on the visible lines should be ok. Targets were 2 metres from the centre of the wheel since the radius of the hub is 200mm.
To keep things simple I slid one of the targets sideways so that the left hand side was aligned on the same number front and rear - in this case 5, then the difference on the right hand side could be directly read out.
So what was the result ? With the left targets aligned the front right target was on 5 and the rear target on 3.5 (cm) therefore the rear was 15mm narrower than the front, allowing for the 10x magnification that means the tracking is exactly 1.5mm toe out.
I'm both surprised and disappointed by this, I was so sure that it was miles out, and yet it seems to be perfect. I even repeated the measurement about 5 times - rolling backwards and forwards each time, and got exactly the same measurement.
Bear in mind that I have adjusted the centring by more than a turn since they adjusted the tracking since it came back with the steering wheel badly offset. Also I
thought that I had made an increase to the toe out, I can't remember if it was 1/4 turn on both sides or 1/2 turn on both side, in fact I can't even remember for certain whether I did or not.
Somehow after all that the adjustment is spot on, which poses more questions than it answers since the steering is very vague and it does pull erratically to the sides under acceleration.
I guess it must be something else then, most likely the lower arm bushes, which are pretty knackered. Perhaps there was far too much toe out before and that was taking up the slack in the lower arm bushes and now that excess toe out is gone the slack is causing wandering. Oh well, at least I know the tracking is correct.