Adjustable droop

[hardingfv32-1]

I question the use of droop control when it comes to car handling setup.

Greg or Steven Davis: How do you use an adjustable droop control to effect handling? More droop makes the car loose, etc.?

[brian]

Based on the premise that a vee is usually on the droop stop as soon as it is in a corner, many use the droop to control the grip in the back. Less droop means a car reaches the droop stop quicker and will loose grip. This reduction of grip will rotate the car and reduce the effects of a push. This approach will increase rear tire wear since the car slides more. Basically it's an ok tuning tool but two wrongs don't necessarily make a right. It would be better to reduce the push with better front grip than to reduce rear grip. A real challenge in a zero roll car like our. But it boils down to balancing the car and making it faster. A track like Topeka called for a lot of this kind of tuning because of the sequencing of the turns and getting a car to rotate back and forth quickly without loosing time. Road America is not so critical since the turns aren't in a tight sequence.

[jpetillo]

I would agree that the car is almost immediately pushing on the stop limiter in a corner. I see two thing, the max droop and the "spring rate" of the droop stop bumper. Brian M., what do you run or suggest for a droop stop bumper - softer squishier or a harder stop? What are your thoughts on the two?

About your post, when you said that less droop looses grip faster, do you have a feel for the balance between loss of grip due to camber change vs being up against the limit of the suspension travel and losing compliance?

John

[CitationFV21]

After reviewing pictures of my car in a turn, I realize that my car in NOT getting on the droop stop in the rear.

I also notice that I run the factory recommended rear camber which is around -5.5 degrees. In looking at many other cars, I am guessing that most are running less camber and standing the tires more upright. This leads to more even tire wear, more speed on the straight, but decreases the difference between static setting and droop setting. This makes the car get into the transition faster and harder, which will end up with a less stable car.

So here is the question. If you are running less that -4 degrees of camber, what is your droop set at, and if it is, what sort of stop do you have? It might be time to design some sort of spring stop so that the transition is softer.

ChrisZ

[jpetillo]

Chris, um, I was asking for a friend. Only kidding.

Actually, I really was not talking about my own car per se, just trying to use this thread to better understand what's out there for droop limiters, what people are running, and mostly to see others' opinions and to better understand how it works.

I'm very surprised that you're not up against the stop during a corner, so this is good information, and a benefit, I would think if you can control camber well enough. Was this picture from a 1G sustained corner or a quick corner? Are you running a stiffer rear spring do you think than most? I can see that with sufficient droop and a stiff enough spring that you may not hit the limiter.

I think the first year I ran I was on the limiter at normal ride height. I changed from that. Now it's the same setup, just adjusted differently and not against the stop anymore. I'm sure I'm up against the stop in a 1G corner, though. Um, I mean my friend is.
John

[hardingfv32-1]

First, I assume we want about 1.5 - 2.0 deg total rear camber when all jacked up in a turn on the std bias ply tires we use. That being the case, then you could use 4.0 deg initial camber/2.0 deg droop and stay off the limiter. But why cut it that close if there is no rear cornering power performance to be gained by being on the limiter.

Remember, you are not going to jack up beyond optimum rear camber. Why would the rear suspension keep rising when the cornering force (required for jacking) is going down as you go beyond optimum camber. The question I struggle with is how does the initial camber and spring setting effect where the the camber/jacking stabilizes at. Where the camber/jacking stops might not be where the tire performance is optimized.

It could be that an upright tire makes more drag (more surface contact) on the straights or more camber makes for a softer tread (more heat) and more drag. Looks like we have a couple of curves crossing somewhere here forming a compromise in regard to straight speed.

Transition faster and harder, how it that measured? Simply, we are after more grip, cornering performance, measured as increased G's.

Don't worry about hard or soft limiter snubbers. If you get out to the snubber it will be under shock rebound control, which is slow in this case.

Brian

[CitationFV21]

A few years ago, I played with the lenght of the pushrods on my car. Ended up with about -4.5 degrees static and -2.5 in droop (forgot to check the droop - ). The car was diabolical, especially at a bumpy track like Lime Rock. Probably would not have been so bad at a track like New Hampshire.

y feeling is that you should not use the droop stop to balance the car, and not use limits on the front shocks in the front either, but these are Vees and sometimes you need to do strange things.

Is it better to get to the droop stop or is it better to have some travel left?

ChrisZ

[hardingfv32-1]

A FV's low front roll center, high rear roll center, and rear suspension that jacks are the only major difference with normal race cars.

Lime Rock example: The droop setting was the only abnormality? Diabolical: loose? Was every turn rough? The car could have been picking up the rears over the bumps. Any bumps on the straight (RPM changes)? This could all indicate the we don't want the droop to be at a high number. And why have a high number if it does not improve performance some where else on the track?

As Brian said, if you want to degrade one end to balance with the other, you could use droop. Not the smart way to do suspension setup.

What other road racing car uses front droop limiters for other than holding the springs in their perches? What problem does front droop limiter solve... turn in?

Brian

[jpetillo]

First, I assume we want about 1.5 - 2.0 deg total rear camber when all jacked up in a turn on the std bias ply tires we use. That being the case, then you could use 4.0 deg initial camber/2.0 deg droop and stay off the limiter. But why cut it that close if there is no rear cornering power performance to be gained by being on the limiter.

Perhaps, but the question we haven't answered is whether rear cornering power performance is gained or not by being on the limiter.

Remember, you are not going to jack up beyond optimum rear camber. Why would the rear suspension keep rising when the cornering force (required for jacking) is going down as you go beyond optimum camber. The question I struggle with is how does the initial camber and spring setting effect where the the camber/jacking stabilizes at. Where the camber/jacking stops might not be where the tire performance is optimized.

This is an excellent question. You can jack up beyond optimum rear camber if there is no restoring force that balances it. For example, if it takes 10 lbs of vertical jacking force to bang the suspension to it's upper stop, and you can produce 20 lbs at the optimum camber, then you will go right up on past the optimum camber point. The vee's swing axles rear suspension exacerbates this because, as the rear rises, it takes less side force to give the same vertical jacking force. This is why the vee will rise past the optimum camber angle. It's a combination of the equivalent lever ratio for jacking vs. the force differential between the tires during cornering.

So, you were right that where the camber/jacking stops might not be where the tire performance is optimized. That's why people run droop limiters to hold it at the optimum camber, as far as I understand it.

Don't worry about hard or soft limiter snubbers. If you get out to the snubber it will be under shock rebound control, which is slow in this case.

I don't know that would I agree with this, or perhaps I don't understand what you meant. Under the assumption that we're riding on the droop limiters to hold optimum camber angle, the softness of the snubbers will determine our spring rate and suspension compliance at that point. I believe that this is the compromise when using this suspension setup.

John

[jpetillo]

Is it better to get to the droop stop or is it better to have some travel left?

I think that the front should never get to the droop stop during cornering on a smooth surface, and that, if you do get into a situation where it happens, it will not help cornering. I don't see the benefit to limited droop limits in the front for cornering on smooth surfaces.

A FV's low front roll center, high rear roll center, and rear suspension that jacks are the only major difference with normal race cars.

I agree with this. John

[CitationFV21]

I will throw some more confusion into this. Since we run a zero roll the inside tire is working against jacking. We don't have the same weight transfer as a dual shock, normal suspension. Not only that, but we have a much lower center of gravity. Then look at how some cars (Caracal, D-13, etc,) feed the rear loads low into the chassis, and others (Citation, BRD) have the rocker pivots above the axle pivots......

I will go back and quote Carroll Smith from "Tune to Win" - "Always work with the end of the car that is giving trouble....Unsticking one end to balance the car is for desperate time only." (p135) What Brian said above - "Basically it's an ok tuning tool but two wrongs don't necessarily make a right."

Now I wish I had the time and money to do testing days - I figure most testing is done during a race weekend......

ChrisZ

[jpetillo]

The inside tire working against jacking is true for zero roll or not. But, I agree with you that zero roll resistance unloads the inside tire less (and reduces additional load on the outside tire) than a conventional setup, and that reduces jacking forces.
John

[brian]

I'm not a an engineer and my head starts to hurt when I think too theoretically, but once a car is on the rear droop stop it tends to get loose and I think it's because the car starts shifting weight and the inside rear tire gets light. When I have excessive droop control (less droop), I can feel the car skipping in off camber exits or going over what I call table tops. A table top is where the exit flattens out. Sometimes I will get tire spin cresting over a sharp hill. I usually run between 1 and 1.5 degrees of droop because many of the tracks I run have a lot of elevation changes. If I run higher camber in droop, say 2 or 3 dsegrees, the car will start skipping and it will get nervous under heavy braking. I have run higher droop camber on flat tracks, Topeka comes to mind, and preferred the free rear rotation in combination turn situations. If you have ever run the 11 through 14 combination at Topeka, you know what I mean.

In response to John's question regarding droop rubbers, I always prefer softer but resiliant snubbers. I prefer a progressive feeling from my car. Rigid rubbers and stiff settings make things too sudden for my tastes and talents. Pleiger Plastics makes the urethane suspension parts and they have quite an assortment ph. # 724-228-2244. Some rubber parts at the hardware store won't live very long and you run a chance of them crumbling away during an event. Loosing a droop rubber during a race can be a real eye opener. Hoope this helps.

[Veefan]

A highly complex adjustable droop setup from the United Kingdom...

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[rphillips]

Looks interesting but how does it work?

Ray

[hardingfv32-1]

First, we should be saying "in-car" adjustable droop, as all cars can generally adjust their droop from outside the cockpit.

Unless you can point out something to me that I'm missing, this is NOT an example of an "in-car" adjustable droop. This is just an overly complete way of adding some roll resistance to what would normally be considered a zero roll (resistant) rear suspension. A single steering damper gets you the same results with a lot less hardware.

Why would you want to had roll resistance responsibilities to the rear tires when they are the already at maximum cornering capacity?

Brian

[brian]

The adjustable droop systems I've seen are twist cable set ups, similar to brake bias cables, that move the stop in and out. As was mentioned, changing the length of the pushrods will change the static droop on a one to one basis but, depending on geometry, don't always have a one to one effect on total camber.

The picture shows a suspension that uses secondary shocks on an horizonal plane that alter the parallelogram that carries the main shock and limits the amount of roll. Imagine a square rolling back and forth with pushrods at both corners. Now think of the square changing geometry to resist roll. Mark Edwards has this approach on his Glandring and I think Greq had something similar on Shirley.

Oui, my head is starting to hurt again.

[hardingfv32-1]

Well, that is better than your chest hurting.

Brian

[Veefan]

This one will make your head hurt....

Hey since we considering a Aussie type manifold, maybe we should consider going with this Aussie Airbag suspension... it's got to be 1/2 the price of a Penske 8100... Ok Ok Ok just kidding...

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It's on youtube also...

http://www.youtube.com/watch?v=c5Xd0G6i8lU

[brian]

Don't poo poo that idea. Back in the 60's MG had a suspension called the hydrocylastic system that contained a hydraulic over air bag system that was tied side to side to provide roll resistance. I had a MG 1100 sedan that had the set up and it was fantastic. The rest of the car was pure junk. I can't remember which team but an Indy Roadster team borrowed the system but they ran the 500 with it.

Brian, thanks for the reminder. I ran a double national this weekend and the ticker did very well. Can't say as much for the car, it had a few bugs but I felt rusty but fine.

[smsazzy]

Brian, thanks for the reminder. I ran a double national this weekend and the ticker did very well. Can't say as much for the car, it had a few bugs but I felt rusty but fine.

Rusty enough to set a new track record.....

[DanRemmers]

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That's interesting. They use a fan shroud, and the exhaust runs under the gearbox. I wonder how much ground clearance that car has.

Maybe one day my solo vee will have rear brakes like that. :drool:

[Martinracing98]

That does not look like adjustable droop to me. That looks like roll damping

[Veefan]

With most airbag suspensions, you can remotely control the pressure/length/size of the airbag.

This is posted up on E-bay, it is used on a sprint cars to jack up either side of the car under the coil... if one is installed in a typical zero roll... it would change the length of the shock/coil combo... which would???? ok I'm CPA and not an engineer... no idea if this would work or even fit in a Vee???


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http://cgi.ebay.com/ebaymotors/Shadow-W ... 35a820c407

[fvkartguy]

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This may be a silly question, but are his leading arms basically attached to the transaxle? Is that part of why he has a tube going from the roll hoop to the top of the transaxle, for reinforcement of the transaxle?
If you use the transaxle for structural support, it seems like that would lighten up the back end, but is that a good idea? Can our transaxles take that kind of force... especially with leading vs trailing arms. Or do the arms end up taking much force or just act as more of a pivot?
Thoughts? Maybe this needs a new thread now that I'm getting off the "adjustable droop" topic...