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Quattro Roll Centers
Hello There!
Somebody was asking about the roll centers on our Quattros and I ran the
suspension through the computer and here's what I came up with. (WARNING
this is LONG and I'm tired, the data is correct but I might have been able to
present it better, knowing that here goes!!) All data is computed at 2
degrees of roll.
Front Suspension
(Stock ride height, front crossmember is 7.5" above ground level)
Chassis droop: (Chassis is raised above stock ride height)
Height/R.C. Height/R.C. Lateral/Inner Camber/Outer Camber
+3" 12.28" 2.7" +.49 +2.65
+2" 9.92" 3.29" -.51 +1.8
+1" 7.61" 4.25" -1.43 +1.03
Static 5.28" 6.06" -2.27 +.35
Chassis Bump: (Chassis is lower than stock ride height)
-1" 2.84" 10.52" -3.02 -.23
-2" -.59" 36.54" -3.69 -.70
-3" -.12" -27.59" -4.27 -.1.05
This is not really awful but it ain't great either! Notice that at 3 inches
of bump the roll center lateral has changed the side of the car that it's on,
no longer following the car in roll... this is not good.
Now lets lower the chassis 1.5"
Front Suspension
(Lowered 1.5", front crossmember is 6" above ground level)
Chassis droop: (Chassis is raised above stock ride height)
Height/R.C. Height/R.C. Lateral/Inner Camber/Outer Camber
+3" 8.76" 3.7" 0 +2.37
+2" 6.45" 4.99" -.88 +1.65
+1" 4.09" 7.7" -1.68 +1.02
Static 1.44" 16.44" -2.4 +.49
Chassis Bump: (Chassis is lower than stock ride height)
-1" 8.49" -196.77 (YIPES!!) -3.02 +.08
This is VERY bad
-2" -1.88" -15.18" -3.54 -.20
-3" -4.73" -8.37" -3.95 -.33
The Roll center is obviously much better behaved at the ride height that Audi
wanted but you could fix the problems caused by lowering by modifing the
lower ball joint pickups so that they are lower than the crossmember much
like the like stock set up. (Lower the ball joint 1.75" and your REALLY
Cooking!)
The rear on the other hand is a 'thang of greatness. the roll center's
follow the suspension movement causing no susprises like the front.
Rear Suspension
(Stock Ride Height, Rear crossmember is 9" above ground level)
Chassis droop: (Chassis is raised above stock ride height)
Height/R.C. Height/R.C. Lateral/Inner Camber/Outer Camber
+3" 17.01" -1.36" +8.7 +7.42
+2" 16.83" -1.46" +6.23 +4.15
+1" 16.72" -1.54" +3.37 +.50
Static 16.63" -1.60" +.13 -3.55
Chassis Bump: (Chassis is lower than stock ride height)
-1" 16.56" -1.60" -3.49 -7.99
-2" 16.46" -1.54" -7.52 -12.82
-3" 16.28" -1.41" -11.96 -18.06
The rear roll centers are VERY well controlled at stock ride height.
Unfortunatly the camber gain is incredible.
Lets try lower the rear 1.5"
Rear Suspension
(Rear lower 1.5", Rear crossmember is 7.5" above ground level)
Chassis droop: (Chassis is raised above stock ride height)
Height/R.C. Height/R.C. Lateral/Inner Camber/Outer Camber
+3" 16.77" -1.50" +11.05 +8.58
+2" 16.67" -1.57" +8.00 +4.73
+1" 16.60" -1.60" +4.57 +.48
Static 16.51" -1.58" +.75 -4.15
Chassis Bump: (Chassis is lower than stock ride height)
-1" 16.38" -1.48" -3.49 -9.19
-2" 16.15" -1.31" -8.13 -14.62
-3" 15.77" -1.05" -13.20 -20.44
We See that lowering the rear has very little affect on the roll centers...
Audi did a great job here!
What does this tell us? Well our handling problems are centered around the
fact that the front tires are seriously overloaded. This is due to several
factors; The weight distrubution, the inclined roll axis, the very low front
roll center, the large lateral movement of the roll center and a rear roll
center that is where it needs to be.
I've got several ideas that I'm going to try. Some conventional and some...
well... just a little strange. I'll keep everyone posted.
Sorry for the length. If anyone has any questions, fire away. Friday thru
Sunday I'll be at the Quattro club event at Blackhawk so it may be until the
middle of the week before I can answer you, unless of course your at
Blackhawk!
Eric Fletcher
'87 5KCSTQ (Still stock suspension!)
P.S. A Million Thanks Dan for making this group possible!!!