Figuring out Backspace

[Guest LedFoot]

I just had an idea for figuring out the best backspace etc based on a post about 1 to 1.5 years ago. This is probably pretty standard but it may be useful

 

1) Get a wheel ypu have lying around with a tyre diamter you want and that you know the backspace on. Mark concentric circles of 16", 17" etc rims you are looking at getting.

2) Put the wheel on the car with the marks at the top. Measure directly across from the mark to the stut/spring. This gives you how much further in you can get towards the strut based on different rim sizes.

3) Use a flat bar across the rim on the outside to show where the top of the wheel points into the guard. Pack the hub studs with washers until you get it as close as you think it can go but still give enough vertical travel into the guard when going over bumps etc. Measure the stack of washers and that gives you how far out the rim can go based on the current backspace.

4) Put all this ont a big piece of paper and the sizing/backspace should be relatively simple to work out.

 

Also one thing I've heard on the front wheels is to ensure that the pivot point is in the centre of the tire where the tyre touches the ground. This means that there is less leverage on the outer edges of the tyre if you hit a rock etc to try and rip the wheel out of your hands. The same reason also makes steering a little easier as you don't have to supply more tourque to deal with force at a further distance to the edge of the tyre.

 

So add to your cross sectional drawing the point at which the strut intersects the ground when a tire of the right final diameter is on it. Do this by drawing a line extending the strut to where it touches the ground and measure where this is from the edge of the rim. Try to make sure that the tire has equal widths on either side when choosing you rim.

 

Or if you have power steering then forget the last bit and jam in the biggest wheel you can!