Rear Suspension Type

[sagero]

I'm looking for some information on this rear suspension setup. Can anybody tell the origin of this; cars it originally came on, designer...

[Mark_Silverberg]

I'm looking for some information on this rear suspension setup. Can anybody tell the origin of this; cars it originally came on, designer...

that is kind of like asking who invented the wheel.

Are you referring to Zero roll resistance rear suspension in general - or the specific implementation of a rear monoshock with push rods and rocker arms?

[sagero]

that is kind of like asking who invented the wheel.

Are you referring to Zero roll resistance rear suspension in general - or the specific implementation of a rear monoshock with push rods and rocker arms?

More specifically, I'd like to know which Vee manufacturer made this particular setup (specifically the same transmission mount and cranks), or which cars it first appeared on (Lynx B, Caracal...?)

[Hardingfv32]

I would say Citation.

Brian

[Steve Davis]

If it was Citation, then Steve Lathrop would know. He's on this board, but if no comment from him, you could PM or call him.
I recognize it as one of MANY 'interpretations' of ZERO ROLL rear suspensions, but doesn't ring any specific mfr with me. Looks a little 'larger?' in the 'wings' to me than most I've seen, but still no reason it shouldn't work.

If you are looking for an "answer" to some specific QUESTION you have, you might still post it here. Most of these types of systems work in the same manner .. just SOME are 'homemade' and this might be one of them - the ONLY ONE of its kind.
Steve, FV80

[R. Pare]

Steve may have more details, but to me, the bellcranks look like Citation, but the trailing links are like none that I ever saw come out of our shop.

[S Lathrop]

The rear suspension is a Citation universal zero roll system. If it was not produced in my shop, it is a very good copy. It is a late version. The original systems had the droop limiter under the shock and spring as Ed Zink had designed the system. On the later versions I moved the droop limiter above the shock and spring. In testing we found that playing with the droop limiting spring system ( the rubber parts) made a big difference in the handling of the car.

[sagero]

The rear suspension is a Citation universal zero roll system. If it was not produced in my shop, it is a very good copy. It is a late version. The original systems had the droop limiter under the shock and spring as Ed Zink had designed the system. On the later versions I moved the droop limiter above the shock and spring. In testing we found that playing with the droop limiting spring system ( the rubber parts) made a big difference in the handling of the car.

Thanks much, Steve.
This set up is on my car. I'm curious about what droop rubber parts you ended up with. I've been using some urethane bushings with a durometer rating of 80 if I recall correctly.

[Steve Davis]

In that type of suspension, there is also a big consideration for the SPRING rate against the RUBBER rate. The higher the spring poundage, the higher duro you need to use on the "rubber", although it's not really RUBBER.. it's much harder and higher duro than one can get from regular rubber. Regular rubber also degrades quite rapidly ... like in 2 race weekends, so you have to go with more sophisticated types of material. You should also look CLOSELY at the spring with regards to coil bind. REAL RACING springs have fewer coils for the same poundage to avoid coil bind. If there is enough flex in a spring such as yours to allow the coils to touch each other at full compression, THAT will cause serious problems when it happens.

[S Lathrop]

For the droop limiting "rubber" I used urethane die springs for the bump stops.

The bump rubbers commonly used with shocks are not even close enough to stiff enough. Metal springs would not work because they would be un-damped and you would need some way to dampen the spring.

I got mine from Reid Tool Supply but when I checked they no longer had them. This might be a source https://www.mwcomponents.com/shop/urethane-springs .

[sagero]

For the droop limiting "rubber" I used urethane die springs for the bump stops.

The bump rubbers commonly used with shocks are not even close enough to stiff enough. Metal springs would not work because they would be un-damped and you would need some way to dampen the spring.

I got mine from Reid Tool Supply but when I checked they no longer had them. This might be a source https://www.mwcomponents.com/shop/urethane-springs .

Could you tell what other materials you used and how they affected handling?

[S Lathrop]

Could you tell what other materials you used and how they affected handling?

With the original zero roll setup where the limiter under the shock, I don't remember what we used but that setup was not sensitive to the spring rate of the medium we used.

I don't remember all the attempts we made to get something to work with the limiter above the shock.. The bump stops that were common to shocks were not stiff enough and we went to the die springs early on. We did find that the length of the die spring was critical. The longer the die spring, the lower the spring rate. So we spent some time playing with different rates.

We did the setup on the rear by putting the car on the ground, setting the main spring to give 2 degrees negative camber at each rear wheel. 4 degrees total is a simpler way to measure. We then set the droop limiter so that we had 2 degrees negative when we jacked the car up off the ground. On the ground, we found that the droop limiter wanted to be loose, just barely in contact with the limiter on either side of the die spring.

It has been many years since I have done a FV setup. But that may change as I am rebuilding a Z12.

[Hardingfv32]

The bump rubbers commonly used with shocks are not even close enough to stiff enough. Metal springs would not work because they would be un-damped and you would need some way to dampen the spring.

The rear shock dampens any movement of the droop rubber. Metal springs work just fine is you have room for one. Bump rubber, etc. do not have a linear spring rate. Linear for say the first half of compression then non-linear for rest of the compression.

It would be my opinion that what you use for the bump rubber is almost irrelevant. Just witness all the different items being used. After three or more decades of zero roll in FV there would be a definitive choice that would have developed by now.

I had very good success using no bump rubber. The shock rebound limit was used to set the droop. The driver never noticed the shock hitting the internal rebound limit. Remember the rear suspension does not move towards the droop limiter in an uncontrolled motion. It is driven toward the droop limit by the rear spring de-compressing and controlled by the rear shock's rebound valving. Nothing uncontrolled or violent about it.

Brian

[S Lathrop]

Brian
If you noticed,one of my last sentences was "It has been many years since I have done a FV setup.".

I can only speak about what I did and the cars that I worked with. That does include 5 SCCA national championships in FV. But those were many decades ago.

One of the characteristics I think happens with the rear end of a FV as it corners, is that the rear jacks up and the car corners with the suspension working against the droop limiter. The shock movement is very short and I think that unless you have very good quality shocks, the damping control is not very much because the shock stroke is very short.

Yes the die springs are rising rate. That is why the length of the die spring is the critical tuning factor in my system. The longer the die spring, the lower the spring rate and the slower spring rate rises. Another feature of my setup is that we do not preload on the main spring.

It has been my practice with all the cars I engineer to minimize rebound damping. I have found that any amount of rebound damping beyond what is called "critical damping", that amount of damping that will allow the spring to return to the initial length and not over shoot, reduces cornering performance. Yes you can use more rebound damping but it does decrease the mechanical grip of the tires. I have seen that proven on a shaker rig and the track both.

In my setup, the car runs on the road spring and the droop limit system only comes into play when the car jacks up in the rear because of the later acceleration in cornering.

In no way am I implying that your system does not work or does not work as well as what I do. In fact your system might be superior to what I do. But I understand what I am doing and how to make it work. I will let my results stand for my approach.