Mcpherson
Mcpherson
(OP)
What geometries effect the bump camber curve of mcpherson struts?
It looks like control arm length (the radius it travels) in relationship to the top strut mount?
It looks like control arm length (the radius it travels) in relationship to the top strut mount?





RE: Mcpherson
Goran
RE: Mcpherson
RE: Mcpherson
If you raise or lower the inboard and/or outboard ends of the arm you can fine tune the shape of the camber vs jounce curve, a bit, for the roll angles of interest (you won't see full jounce on one side and full rebound on the other simultaneously usually).
Note that if you do modify the arm then you'll need to think about your bump steer curve as well.
Cheers
Greg Locock
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RE: Mcpherson
Norm
RE: Mcpherson
With respect to camber curves then, how limited is McPherson compared to Double wish?
I understand some of the other limitations.
Thanks for your time guys, this forum is a great resource.
RE: Mcpherson
In theory MacP is horrible.
In practice it works fine.
This is a classic demonstration of the old motto "In theory, theory and practice are identical. In practice they aren't."
That is if you know what you are doing, judging by BMW's success with MacP, you can make them work well.
I think this has a great deal to do with modern tires.
Cheers
Greg Locock
Please see FAQ731-376: Eng-Tips.com Forum Policies for tips on how to make the best use of Eng-Tips.
RE: Mcpherson
There is often a number of cambercurve discussion on different boards, which is all good. But many times the advantage of camber gain is looked at for only one specific situation. In other situations it might be less desired.
We must look att the whole driving situation for the car.
From that point of view Mcp is ok, but the advantage of doubble A-arms is not only camber related.
Goran
RE: Mcpherson
But, MacP struts are one of the few compromised suspensions that seem to have survived the test of time, at all levels of performance save perhaps open wheeler circuit work, which may be a function of the first para.
Cheers
Greg Locock
Please see FAQ731-376: Eng-Tips.com Forum Policies for tips on how to make the best use of Eng-Tips.
RE: Mcpherson
From what I've gathered they are ignored by manufactures for cost, and packaging reasons. I find it interesting what vehicles you end up finding with SLA suspension, sometimes you even see newer generations of the same vehicle go back to McPherson.
RE: Mcpherson
geometry features. Also, if you look at my frontsuspension
on the picture, the uppright is very deep in the wheel. The KPI is amost zero as well as the scrub. Newer minde why this is so, but it is possible using doubble A-arms. The McP leg would have needed to go throught the wheel and tires.
Goran
RE: Mcpherson
RE: Mcpherson
Cheers
Greg Locock
Please see FAQ731-376: Eng-Tips.com Forum Policies for tips on how to make the best use of Eng-Tips.
RE: Mcpherson
not necessarily true... as far as the scrub is concerned...
MacP struits usually have a large offset between the wheel centerline and lower attachment point for the struit, so there is space to move the upper struit bearing out enoug to get the KPI needed and resulting scrub...
my delta integrale, which is very 80's technology, has zero scrub (as far as I can measure) with a "normal" MacP
as for the geometry change... I did some work on a racing car that used MacP struits in the front and we lowered the ball joint to get the better camber curves. But IMHO, you should look at not only camber change in bump, but combined bump + steer, as there is great scope to adjust your geometry with more castor, which will give you more camber in a turn..
also, I do not know how is current MacP technology, but one of the problems with it, IMHO is that the struit has to resist bending forces in a turn, which affects the resistance and stinction in a damper...
RE: Mcpherson
Again for a mcpherson stetup:
On a paper model it looks like a horizontal (with respect to the ground) control arm is one that will gain and lose camber at the fastest rate. Am I correct?
How then on a Mcpherson setup do you balance both the most exaggerated camber curve with a good roll couple without a really low CG?
RE: Mcpherson
RE: Mcpherson
Cheers
Greg Locock
SIG:Please see FAQ731-376: Eng-Tips.com Forum Policies for tips on how to make the best use of Eng-Tips.
RE: Mcpherson
Goran
RE: Mcpherson
RE: Mcpherson
It is the relation between the leg and A-arm that set the camber gain-loss rate. Not really the A-arm to ground situation. The shorter the leg, the greater the effect.
The A-arm to leg angle both set the rate and the + or - camber effect.
Hmmm, I wish I had the strenght to make some drawing here...
Goran
RE: Mcpherson
Relative to each other? At some point as stated above they change signs, if you're at dead center of the sign change, is that the point in the A-arm swing radius that for a given leg/arm length ratio and angle that the camber change rate is the most accelerated?
RE: Mcpherson
Cheers
Greg Locock
SIG:Please see FAQ731-376: Eng-Tips.com Forum Policies for tips on how to make the best use of Eng-Tips.
RE: Mcpherson
I did, I was trying to verify that I did it correctly. I'll take it elsewhere.
"On a paper model it looks like a horizontal (with respect to the ground) control arm is one that will gain and lose camber at the fastest rate. Am I correct?"
RE: Mcpherson
So, the longer the leg, the greater the Tw change vs camber effect. Tw=wheel sideway movement.
This also means that at 90 dgr you will have the max -camber. So, if the starting point is paralell to ground A-arm and 10 dgr leg tilt, the camber will go - (during bump) until 90 dgr leg to A-arm angle and then go +.
Goran
RE: Mcpherson