question about motion ratio

[mokinbird87]

so, if I understand this correctly, since our front is a McPherson set up with the strut directly over the front wheels vs the rear double-wishbone set up which have the struts a bit inward from the wheels, our car is generally known to have a ratio of 1:0.75 from front to back? but what about the spring height on the front vs the rear? since the rear springs are a lot shorter, doesnt that negate the inward positioning of the spring and damper, which actually make the rates close to 1:1 or does spring height not play a role in motion ratio? maybe having the engine and transmission in the front which is a big portion of the weight on the car is a reason to have more suspension travel with longer springs, but I`m just curious if spring height has any effect on the motion ratio. please enlighten the noob thank you.

[ZDan]

Originally Posted by mokinbird87

so, if I understand this correctly, since our front is a McPherson set up with the strut directly over the front wheels vs the rear double-wishbone set up which have the struts a bit inward from the wheels, our car is generally known to have a ratio of 1:0.75 from front to back?

MacPherson struts generally have motion ratios in the 0.9 - 0.95 range. I suspension model I made based on unverified FR-S/BRZ geometry yielded 0.925 for the front struts.

but what about the spring height on the front vs the rear?
since the rear springs are a lot shorter, doesnt that negate the inward positioning of the spring and damper, which actually make the rates close to 1:1 or does spring height not play a role in motion ratio?

Spring height doesn't influence motion ratio (though motion ratio will influence spring height indirectly)

maybe having the engine and transmission in the front which is a big portion of the weight on the car is a reason to have more suspension travel with longer springs, but I`m just curious if spring height has any effect on the motion ratio. please enlighten the noob thank you.

With a higher motion ratio, the spring needs to have a greater range of travel, hence the spring is generally longer. That's the relationship. It's not as if the longer spring height give a higher motion ratio.