Dave. If you want to compare before and after static height of the rear springs you can measure the distance from the centre of the wheel nut to the floor and the vertical distance between the underside of the chassis rail and the floor and then deduct one from the other to get the height of the centre of the axle above the bottom of the chassis rail. Obviously this is then going to vary dependant on fuel load, and weight of the spare wheel etc. At least recording these figures would give a reasonable basis for before and after spring change comparisons and comparisons between similar models fitted with different springs.

Ideally this should be done with the dampers (shock absorbers) disconnected but a gentle bouncing up and down of the rear of the car should settle everything into position. The floor must be absolutely level for this so that all 4 wheels are on the same level. If one of the front wheels is on a different level it would throw additional load on the diagonally opposite back wheel.

On my car the rolling radius of the 195/60 R15 tyres averaged to 292 mm (the distance from the centre of the wheel nut to the floor) I did not worry about pressure but it was probably about 24 psi. It is not really important for the calculation. There was 2 mm difference between left and right.

The height of the lower chassis rail was average 174 mm (there was 2 mm difference due to the tyres, in other words the springs were amazingly equal so a comparison left to right was unnecessary).

By deducting the 174 from 292 we get 118 mm which is the height difference between the centre of the axle and the bottom of the chassis rail. The car was unloaded with half a tank of fuel.

I hope that makes sense.

Peter

[Linked Image]