Measuring wheel allignment and tollerance?

[Zedn]

I am currently fine tuning my suspension and chassis allignment before moving on to the motor.

I am taking some measurements as i have been told that more often than not the RCM mounts are in the wrong spot.

The procedure i have used is as follows:
1. Set up a string line on each side of the car.
2. Allign the string line with the rear wheel by measuring the distance from rim to string on front and back of rim.
3. Allign the front wheel with the string line.
4. repeat on other side.
5. Square a line (with the string) from the centre of each hub and mark the string line where they intersect. i.e. inline with the centre of the hub.
6. Measure the distance between the marks on the string.

When i do this i get one side 3mm longer than the other. Seems to be acceptable tollerance to me.

As a final check i measured the distance between the 2 string lines at each end of the car. This came out to be 29mm difference. In other words my string lines tapered in at the front by 29mm over the length of the car (well a bit longer than the car).

If the lines are not perfectly parallel then my distance between wheels is not accurate bacause the centre of the hub will move front to back because of the distance to the ball joints. As i have shortend the control arms at the rear, although i used a jig i made, i cant guarantee they are both 100% straight.

Has anyone got a more accurate way to measure that doesnt involve specialised tools. I just want to make sure it is close enough so it can be fixed with a wheel allignment when the time comes.

Cheers.