Thanks for the diagram mole - greatly appreciated. That's what I thought was meant, and it's basically a flawed method. Although it will work, the car has to be basically vertical.
I used one of jimmys photos to illustrate my point. No tyre will have this grip. On 80's style monster trucks, sure method will be fine. But any racing car, C.O.G. is too low.
I think I have a better idea. Basically similar principle, different method. Tilt the car so until you find the point it balances on two wheels. then using something like the chassis plate, measure the angle. Here I put a camber gauge up to show how it would be done, my camber gauge only goes to around 5 degrees though, and I think this car balances around 10. Plenty of other devices would measure this though.
The maths is very easy. Firstly measure the width of the car, then divide by two. This is the adjacent side. The angle you measure will be something like 75 degrees, the tilting angle will be around 15 degrees (i.e you just take away the angle you measure from 90).
These are the two bits you need to know. You will need to use the tan rule. tan(angle) x adjacent = z height of C.O.G.
A working example.
My Kyosho Lazer ZX-5 balances at around 75 degrees, so that's 15 degrees from vertical. It is 240mm wide, so half of that is 120mm which is my adjacent length. tan(15) is 0.2679. If you don't have scientific calc, see
here for table of tan(angle). Excel can easily handle tan.
so:
tan(angle) x adjacent = z height of C.O.G.
0.2679 x 120mm =
32.15mm
Which sounds totally reasonable.