"Stock" Rear Suspension Geometry


Well-Known Member
Here is an analysis of the “stock” Goblin Rear suspension, meant to be a baseline resource for anyone interested.

Wheelbase – 97.25in
Track Width – 58.3in
CG Height – 20.5in
Frame Rake – 1°, Nose down
Tires – Stock LNF SS 225/40R18
Wheels – Stock LNF SS 18inx7.5in, 42mm offset
Bump Travel - 2.5in (limited by spring bind)
Droop Travel - 1.5in (limited by spring preload)

Roll Center Height – 1.6in
Camber Gain in Bump – 0.21°/in
Rear Subframe Ground Clearance – 6.7in
Pro-Squat – 23.9% (Highly Undesirable in all scenarios)
Pro-Lift – (w/ 40% rear brake bias) – 16.2% (Highly Undesirable in all scenarios)


Here we have toe out on bump and toe in on droop. This contributes to roll oversteer in the rear. There are many factors that contribute to the overall balance of the car, and this is just one of them.
Understeer and oversteer are not necessarily good or bad. Some highly skilled drivers may prefer oversteer, because of their ability to adjust and react quickly. Most production cars are setup with understeer, because most drivers are not skilled enough to take advantage of oversteer characteristics.


In general, as this curve approaches horizontal, grip in a corner will go up and grip in a straight line while accelerating or decelerating will go down.
The main drawback of the strut suspension is it's poor camber gain characteristics. The roll camber here is quite low, even by strut standards. This may be a good drag setup, but not ideal for street or track use.

Roll Center Migration:

There is some debate over the importance of lateral roll center migration, but most agree vertical height stability is important. It looks like vertical height stability was not a consideration in the design of this suspension.

If there are any questions or other graphs of interest let me know and I’ll get them added.
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Goblin Guru
What is "Pro Squat" and "Pro Lift"? When you say Highly Undesirable, is 0% the preferred amount of it?


Well-Known Member
What is "Pro Squat" and "Pro Lift"? When you say Highly Undesirable, is 0% the preferred amount of it?
You will more commonly hear the term "anti" geometry.
When a vehicle accelerates forward in a straight line, weight is transferred from the front of the vehicle to the rear. With 0% "anti" geometry, the springs will see 100% of the weight transfer effects, so the front will get lighter, the front springs will decompress and the front of the front of the vehicle will rise. In the rear, the weight increases, the springs compress, and the rear of the vehicle will "squat".
Anti-geometry does not change the weight transfer of the vehicle, but it takes some of the load that the springs see and transfers it into the control arms. So, for example, if you had 100% Anti-Squat geometry, your springs would not compress at all during acceleration, because the additional loads from the weight transfer are taken by the control arms instead of the springs.

In the case of the stock goblin geometry, the geometry actually causes increased loading on the springs, and causes them to compress more than they would otherwise, so "pro" is used instead of "anti".

While "Squat" refers to what the rear is doing during acceleration, "Lift" refers to what the rear is doing during braking - same as above, just different directions.

There are various opinions about anti-geometries, but the desirable range is from 0% to over 100% (over 100% would mean the rear would actually unload the springs some and rise during acceleration). No one, at least from the research I've done, have desired "pro" geometries.
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Desert Sasqwatch

Goblin Guru
To tag on to @Sebnuts discussion, it is desirable to have the front of the lower control arm higher in the front mount than the rear mount locations. This moves the geometry toward the anti-squat direction. Unfortunately the stock Cobalt mounting is set up towards anti-dive as it is the front end of the car, but now moved to a Goblin - so it is in the pro-squat direction as stated above. The front mount on the lower control arm is lower than the rear mount location. This is the reason that some of us have expended lots of time and effort to improve the geometry of the rear suspension to create anti-squat geometry with modifications.