Rear droop

[DD16]

Two questions.

What is the camber you shoot for at full droop?

Looking at the pictures for cars shown in the For Sale listings it looks like it is evenly divided between cars that have a "rubber" bushing on the shaft controlling droop when full droop occurs and those that apparently use shock travel or a separate rod without a bushing at full droop. What are the pros and cons for running without a bushing? What durometer reading is the rubber bushing?
Thanks

[Darren Brown]

There is really no right answer the question. I think everybody does a little something different to achieve the same result.

My general settings have worked well for every make of Vee I have raced over the years. This included the push rod mysterians and Vortech as well as the pull rod Vector and Adams.

I have always ran between 4.5 and 5 degrees of total camber at ride height with driver weight in the car and the droop snubber is just under a slight bit of pressure.

On the droop I usually run between 2 and 2.5 degrees.

As far as droop materials, I am not so sure it really matters. The only difference I notice is just the abruptness as to when you start pulling against the limiter. I have used the supplied snubbers from the builders of what ever chassis I had at the time, washer stacks, small diameter compression springs and in a pinch sway bar bushings from a local auto parts store. I truly never noticed much difference except when the limiting rod would fail completely.


I imagine you will get a lot of different answers, this is what has worked well for me over the years.

Darren

[jphoenix13]

Brian McCarthy told me that the rubber bushing provides a soft landing for the droop limit when you hit it, provides some “leniency” for the suspension change when it reaches that limit, much better than an abrupt STOP that might upset the car.

The droop limiter bushing that he installed on my car when he built it, I still use - on the new car that I built in 2016. Regarding durometer - it’s soft, seems about the same as a 32 gram shock bumper.

[S Lathrop]

When we were doing the development work on the Citation FV, we found that the droop limiter spring medium was important. Now on the Citation setup, the droop limiter is above the spring and shock and has a larger motion ration than the spring and shock. Therefore I used rubber die springs. Rubber because it is self dampened.

I think that as the car is cornering, the rear jacks up and the car goes around the corner just touching the droop limiter, or riding against the limiter.

[Doug FST 5]

When you are hard on the brakes the rear suspension is likely at the droop limit. The back end settles back to the running camber per the valving of the shock when you release the brakes and begin the turn. You can tune the turn in feel of the car by making changes to both the droop camber and the valving.

[problemchild]

There is no right answer to either question.

The droop and shock rebound settings control the maximum amount of rear grip that can be generated. So the droop value is dependent on suspension design and driver technique. Best to start with what other drivers use in their cars with the same design and tune from there.

On most FVs, the droop material or lack of, effects how the car feels as it approaches maximum grip levels, and is totally driver preference.

On some FVs. like D-13s, Adams, and any car that I tuned, the bump stop is longer and softer, and is applying some preload at static ride height. I could not begin to understand or explain all the dynamics involved. Having had a D-13, and then an Adams, I found some settings that worked well and I use the "droop limiter" to set preload rather than droop. I would think this method would be best left to advanced users, and requires different shock settings.

[DD16]

Thanks for all the answers. It seems a consensus that some sort of cushion is important. Locally it appears that 2 degree droop is fairly common. I have a starting spot for both droop and the cushion now. I need to look around and find some cushion material. Now the testing begins. Thank you all very much.

[Hardingfv32]

The goal at the rear suspension is to hit the ideal rear camber when cornering at max corner force. The ideal camber is not known precisely, but is probably close to neg 2 degrees total for the Hoosier slick.

This camber setting is achieved when the rear suspension is fully jacked up. Make sure you get this clear in your mind. The FV rear suspension does not hunker down while corner hard, it jacks up.

Roughly three things go into the mix when determining how much the rear is going to jack. The rear spring and jacking force from the swing axle layout provide the lifting force. The droop limiter provides a counter lifting force. For a given cornering situation you can consider the jack (lifting) force to be a constant. So that leaves you with the rear spring and droop setting to work with. You can achieve the optimum rear camber WITHOUT using a rear droop limit, but the most common is the rear spring in combination with the droop limiter. The use of a soft rear spring usually requires a droop limiter as the rear spring is providing too much lifting force when at optimum rear camber.

In general the rear camber static sitting is just as important as the droop setting. There is more than one ideal combination for achieving the proper dynamic rear camber setting. That is why you are going to hear such a variety of opinions about rear suspension adjustments.

Brian

[jpetillo]

That was well said! John

[FVRacer21]

One thing to keep in mind, whatever setting you use, is that the droop rod not bind in any way during its travel. Look for polished spots or nicks in the rod where it goes through pivot/stop or suspension parts.

Early Citations had a small plate that could tilt and grab the rod. I put a tube extension on to keep the plate at right angles. On another setup, the rod was threaded too far so that the threads caught on the pivot point. Making a new rod solved that problem.

ChrisZ