| Re: [GMCnet] Front suspension geometry [message #124645] |
Thu, 05 May 2011 07:35  |
Gary Casey
Messages: 448
Registered: September 2009
Karma: 0
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Senior Member |
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Hope it's okay if I changed the name of the thread. I'll give a theoretical
answer to Rob's question about suspension geometry. With the upper arm angled
up compared to the lower arm, the wheel will change camber with suspension
travel. It will go to negative camber in jounce (wheel going up) and positive
in rebound (wheel going down). This is typical of more modern vehicles. As
usual, everything is a trade-off and this is no exception. Camber change during
suspension movement will potentially induce a reaction to bumps where a positive
bump will tend to push the front of the vehicle away from the bump, making it
possibly a little more "jittery" on bumpy roads. On the positive side,
roll-induce understeer will be reduced as the tires will "roll" less than the
body and therefore be better able to support the cornering loads. A long time
ago Buick advertised that their upper arms were angled down, making the wheel go
to positive camber in a bump, and they said that this "pulled" the car toward
the bump, making it more stable. Of course, their cars cornered like pigs!
In my opinion the upward angle of the upper control arm is a good thing, but not
by much. I wouldn't worry about it one way or the other.
Gary Casey
Previous post:
subj: Installing Grease Zerks For Front Wheel Bearings
Paul,
I agree with the math, however, I asked a question that no one could answer
when Stan gave a presentation on the conversion at Patterson.
The distance between the upper and lower ball joint mounting points in the
knuckles goes from 9 inches to 11 inches. The angle at which the upper
control arm rides is higher. The angle between the upper ball joint socket
and the ball and shaft is much closer to the inside edge. Has anyone ever
jacked the suspension up as high as possible and verified that the ball and
shaft of the upper ball joint does not hit the upper ball joint socket?
A secondary question is - how does the changed angle between the upper and
lower control arms affect the coaches steering and handling. I'm looking for
a theoretical not empirical response. I realize if it wasn't acceptable
people wouldn't install it!
Regards,
Rob M.
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| Re: [GMCnet] Front suspension geometry [message #124653 is a reply to message #124645] |
Thu, 05 May 2011 08:43  |
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USAussie
Messages: 15912
Registered: July 2007
Location: Sydney, Australia
Karma: 6
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Senior Member |
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Gary,
Thanks!
Now somebody needs to make sure that the ball and shaft of the upper ball
joint does not hit the upper ball joint socket when the upper control arm is
at the max up angle.
Regards,
Rob M.
USAussie - Downunder
AUS '75 Avion - The Blue Streak TZE365V100428
USA '75 Avion - Double Trouble TZE365V100426
-----Original Message-----
From: gmclist-bounces@temp.gmcnet.org
[mailto:gmclist-bounces@temp.gmcnet.org] On Behalf Of Gary Casey
Sent: Thursday, May 05, 2011 8:35 AM
To: gmclist@temp.gmcnet.org
Subject: Re: [GMCnet] Front suspension geometry
Hope it's okay if I changed the name of the thread. I'll give a theoretical
answer to Rob's question about suspension geometry. With the upper arm
angled up compared to the lower arm, the wheel will change camber with
suspension travel. It will go to negative camber in jounce (wheel going up)
and positive in rebound (wheel going down). This is typical of more modern
vehicles. As usual, everything is a trade-off and this is no exception.
Camber change during suspension movement will potentially induce a reaction
to bumps where a positive bump will tend to push the front of the vehicle
away from the bump, making it possibly a little more "jittery" on bumpy
roads. On the positive side, roll-induce understeer will be reduced as the
tires will "roll" less than the body and therefore be better able to support
the cornering loads. A long time ago Buick advertised that their upper arms
were angled down, making the wheel go to positive camber in a bump, and they
said that this "pulled" the car toward the bump, making it more stable. Of
course, their cars cornered like pigs! In my opinion the upward angle of the
upper control arm is a good thing, but not by much. I wouldn't worry about
it one way or the other.
Gary Casey
_______________________________________________
GMCnet mailing list
Unsubscribe or Change List Options:
http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
Regards,
Rob M. (USAussie)
The Pedantic Mechanic
Sydney, Australia
'75 Avion - AUS - The Blue Streak TZE365V100428
'75 Avion - USA - Double Trouble TZE365V100426
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