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chapman strut/ mac ferson strut rear suspension

chapman strut/ mac ferson strut rear suspension

chapman strut/ mac ferson strut rear suspension

I intend to use a strut-type suspension in the rear of a car. This is (initially) the engine/trans/suspension from the front of a full size GM car (3.8 + 4-speed automatic)
Will the software suggested for SLA suspensions help with this? How sensitive might this be to tilt of struts, either inward or forward/aft?
What about A-arm pivots- horizontal, or axis tilted forward/back?
Initially I intend to just lock the steering rack in a centered position, later replace with hard point mountings for the (formerly steering) links.
Comments? hazards? show-stoppers?

Jay Maechtlen

RE: chapman strut/ mac ferson strut rear suspension

Tilt is very important, on a McPherson (please note)- the tilt in the YZ plane largely controls the roll centre position. In the XZ plane I think you may have a bit more freedom.

I'd be inclined to keep the A arm square to the strut in side view, and rotate the whole thing about the Y axis to get antidive or prodive.

I don't know about show stoppers, this has been done many times in the past. I'm a bit of a cynic about rear suspensions, so far as I'm concerned they mostly seem to just follow the front around.




Greg Locock

RE: chapman strut/ mac ferson strut rear suspension

"... they mostly seem to just follow the front around"
thanks for the info!

Jay Maechtlen

RE: chapman strut/ mac ferson strut rear suspension

I think you'll at least want to use much more rigid control arm bushings when you swap that front end to the back, and you'll want to avoid toe-out in bump.  Some years back there was a group putting SHO Taurus powertrains in the back seat/trunk areas of Festivas (the "Shogun").  Early testing was reported as somewhat disappointing until somebody figured out that while understeer due to compliance up front was a good thing for keeping your average buyer/driver out of trouble with his FWD Taurus, it became vehicle compliance oversteer when the same parts were plugged in at the rear.


RE: chapman strut/ mac ferson strut rear suspension

Excellent point Norm.

It may be appropriate to soft mount the rack, or make one of the bushes soft, depending one where the rack is relative to the bushes. It is easiest to think about those suspensions which have a lateral arm parallel to the tie rod, and then a leading or trailing link, which can be ignored.

For instance, if the rack is in front of the axle then softening the bush on the lateral arm gives understeer at the front axle. So if you fitted the suspension the same way round in the rear, you'd want to soft mount the rack, to get compliance oversteer on that axle, or vehicle understeer.

And you ALWAYS want compliance understeer, I think.


Greg Locock

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