Suspension Design Question

[scubachef]

I’ve had a question rattling around my head i don’t have the knowledge base to understand and can’t seem to search the answer. Essentially, what effect does upper link length have on four link suspension design? I have a 69 Camaro so I’m thinking from the perspective of a first gen.

if we use DSE Quadralink and Roadster Shop SPEC chassis as the examples, why do both those designs work well with Quadralink needing the links to extend into the back seat area, and the roadster shop chassis using much shorter links?

I don’t know dimensions, it it seems like one link is 1/2 the length of the other, and they look to have relatively similar mounting points and design for the rest of the suspension, so does it matter and why does it matter what length the upper links are?

Thanks.

[marolf101x]

Primarily the upper link would affect pinion angle change when compressing/extending the suspension.
The shorter the link, the more the pinion angle changes.
The longer the link, the less change.

[scubachef]

Thanks for the reply. So it doesn’t affect travel as much as pinion angle. Does that mean you have to compensate for that variation in pinion angle somehow as the suspension moves?

[stab6902]

Too much pinion angle will cause vibration issues and reduce u-joint life. Longer and closer to equal length links will allow for more travel, but will be harder to package. I personally prefer DSE's approach. It allows for more suspension travel (without much pinion angle change), which lets you run lower spring rates for better ride on the street. In a more track focused car with stiff/low travel suspension, either approach will work.

[marolf101x]

You only need 5 inches of overall wheel travel for good ride quality. All major players on this site have 5 inches of travel, so I don't think that's an issue or determining factor.

The geometry does change the rear end angle (when viewed from above). Shorter links cause more angle change, longer links cause less change.
However, this is not that big of a deal as you are able to get bars in there long enough to not cause huge problems.

[scubachef]

Thank you!

[stab6902]

I agree that the 5" of travel, 3" compression and 2" rebound, is a good rule of thumb for pro-touring type cars, and it's not easy to do better than that with coilovers on our old platforms. If you like the way a well setup lowered 4th gen Camaro rides, you'll be happy.

I prefer more of a "touring" ride (think modern sporty sedan... CTS-V, 335i, E500, etc), and I find that hard to achieve with 5" of travel. Compression travel is often limited by ride height, but I take all the rebound travel I can get. I usually go with firmer stock type coil springs, adjustable shocks, rubber bushings, and a modern bump stop setup.

Like everything else, it all depends on your goals for the car.

[dhutton]

i agree that the 5" of travel, 3" compression and 2" rebound, is a good rule of thumb for pro-touring type cars, and it's not easy to do better than that with coilovers on our old platforms. If you like the way a well setup lowered 4th gen camaro rides, you'll be happy.

I prefer more of a "touring" ride (think modern sporty sedan... Cts-v, 335i, e500, etc), and i find that hard to achieve with 5" of travel. Compression travel is often limited by ride height, but i take all the rebound travel i can get. I usually go with firmer stock type coil springs, adjustable shocks, rubber bushings, and a modern bump stop setup.

Like everything else, it all depends on your goals for the car.

x2.