A 2” drop in ride height. The principle effect of which is the change in angle of the lower control arms (LCA). Using virtual “camber plates”, the upper strut mounting point is moved inward in the “negative” camber direction a total of 2”. For each scenario, figures of a 4 deg. roll are also provided. This would be a rough equivalent to heavy cornering on relatively soft springs.
The diagrams do not take into account reactive caster and resultant chamber changes from steering deflection.
Figure 1
Figure 1 depicts a basic strut suspension, as viewed from the front. Note in the upper left corner “Ride” is ride height, and “Roll” is the degrees of roll. Note the location of the Roll Center (“RC”) at 3.432” above ground, in the center of the front track, marked by a blue X in a brown box. The brown lines denote where the instance centers are located. Note the brown lines coming off the top of the strut are 90 deg. to the strut inclination, and pass through the inner two pivot points in the lower control arm (LCA). They intersect outside the track, the distance of which is noted as Ins.Cen. Negative numbers are to the drivers left and positive to the right. The roll examples would be equivalent to a left-hand turn.
Figure 2
Figure 2 depicts the suspension parameters in Figure 1 with 4.00 deg. of roll. Note that the roll center is above ground and within the front track. The –16.215” tells us that the roll center migrates 16.215” from center under 4.00” deg. of roll while cornering left, and migrates to the inside of the turn.
Figure 3
Figure 3 depicts the suspension parameters in Figure 1, with –2.00” of Ride; a lowered ride height of 2”. Note the angles of the lower control arms (LCA); the inner pivot points are lower than the outer pivot points. The roll center height (RCH) is now -.402” (below ground). Our instant centers have shot out to 145”, from 98”.
Figure 4
Figure 4 depicts the suspension parameters of Figure 3 with 4.00 deg. of roll. Note that the RCH has migrated above ground (it’s off the image to the left), and has migrated 100.149” from the center of the front track, to the left (outside of the turn). Note that prior to lowering in Figure 2, the RC was 16” to the right (inside of the turn).
Figure 5
Figure 5 depicts the parameters in Figure 1, but with the upper strut mounting points moved inward 2”, as would happen if you set your camber plates to “full negative”. Note that the RCH is now at 4.000” vs. 3.432”, a gain of 0.568”. Also, our instant centers have shortened roughly from 98” to 74”.
Figure 6
Figure 6 depicts the parameters from Figure 5, with 4.0 deg. of roll. Our RCH dropped to 3.223” and migrated 12.048” to the inside of the turn. When compared to Figure 2, where the strut inclination axis was left alone, the effect of 4.0 deg. Of roll on both RCH and lateral migration of RC is reduced.
Figure 7
Figure 7 depicts Figure 5 with a 2.0” lowered ride height. So, now we have a lowered ride height and our virtual camber plates set to “full negative”. You’ll note RCH is now above ground at 0.392”, versus what’s depicted in Figure 3 where it is .407”. That’s a change of 0.799” in RCH with the additional strut inclination. Instant centers are also 89”, instead of 145”.
Figure 8
Figure 8 depicts Figure 7 with 4.0 deg. of roll. So, here is a 2” lowered ride height, virtual camber plates set to “full negative”, and 4.0 deg. of roll (in a corner). Note the difference in lateral location of RC as compared to Figure 4; it’s changed a +100” from the center of the front track on the outside of the turn, to -255” to the inside of the turn. A drastic difference, considering only the strut inclination (camber plate position) has changed. Our RCH is also 15.392” below ground, versus 6.477” above ground in Figure 4.
I started this in response to a statement that someone made to me about lowering a car, even without changing anything else is always beneficial to handling due to lowered rollcenters and a lower center of gravity. As shown above, this simply isn't true. In fact, I'm pretty shocked to see that the opposite is true!
Hopefully, I'll have access to some corner scales at the very least and possibly a full chassis dyno soon - then I'll be able to come up with some less generalized conclusions.
I could probably directly measure this stuff to put it in the model, just don't have the time to take shit apart for measurement
