240sx motion ratios?

[nissanman04]

I am trying to decide what spring rates to go with for autocross this year by tuning the front and rear suspension frequencies to my liking. To do this, I need both front and rear motion ratios for suspension travel. I found one post saying that the rear motion ratio is 0.84, but I found no information on the front ratio. I tried taking the wheels off to measure the distances from the control arm pivot point, but it is hard to get a good measurement, and ballpark figures will do me no good in this case. Can anyone confirm the 0.84 in the rear? What about the front ratio? Thanks...

[95lstegman]

figured i'd give this a decent answer for posterity's sake.

i came up with 0.914 and 0.703 front and rear, respectively. those were rough measurements, not too precise, and include the angles of the coil-over-strut. my suggestion though would be to use spring rate to tune natural frequency. that just basically means use spring rate [and dampening] to tune to the track frequency, then use sway bars to tune balance front and rear during steady-state cornering. i'm a fan of ~10% higher front nat'l frequency myself, as it also tends to give better turn-in.

[the converted]

I thought mac strut systems were 1:1?

[crackler]

Damn near, but I *THINK* the motion ratio is taken at the hub face. I could be wrong about that. When talking to a friend of mine who builds custom machined coil overs he said that mac-struts where damn near 1:1, but not quite. he said that the evo's and sti's where roughly in the .97 range, iirc.
Modified by cracker at 6:38 PM 5/31/2008

[the converted]

Ok so I got bored and looked into it. It's the cosine of the kingpin angle plus your camber. So if you had 3 deg of camber you would add that to 12.5 deg for the kinpin angle so cosine of 15.5 deg is 0.9636blahblahblah.