Originally Posted by
Marc sierra
What I meant was that the springs get relatively closer to the wheels compared to the swing axle because the arms get longer. This does change the ride height at standstill.
The change in motion ratio from 0.63 to 0.73 is not a slight change. The formula for the wheel rate (basically the spring rate as seen at the wheel) = motion ratio^2 * spring rate. The original rear springs on a Sapph are 50 N/mm. So with a standard beam you have a wheel rate of 20 N/mm (50 * 0.63 * 0.63). With a 6 degree beam it becomes 27 N/mm (50 * 0.73 * 0.73). So with a 6 degree beam the rear wheel rate has increased by about 33%.
The weight on a single rear wheel on a Sapph is probably about 250 kg. So with the original beam the wheel will compress 125 mm (250 * 9.8 / 20). With the 6 degree beam the wheel will only compress 93 mm (250 * 9.8 / 27).
The numbers for the motion ratios I used are not completely correct though as I couldn't measure them accurately. The rear definately doesn't sit 32 mm (125 - 93) higher with the 6 degree beam.
hi
those figures look very impressive but like you say they dont work out lol
plus are you sure the ratio alters that amount as you only move the inner point so it still has the pivot point of the outer arm ,have you just done it as a calculation on moving the inner point forward and used that for the outer point aswell ,because its still pivoting about the outer point which has not moved ,or did you fit the same poundage spring in each beam and physically measure it they work out the ratio ,because you said it sat 5mm different but with your calcs it moved 32 mm just interested not having pop
mark