Droop Limiters - 84 Reynards

[Purple Frog]

OK, it's and old car, but it's affordable.
Pat Prince has been harassing me to install a front droop limiter on the beast. I'm trying to avoid welding on the original frame. Has anyone had any luck creating a bolt-on device?
I have some ideas, but I am willing to forgo "re-inventing the wheel" if there is a simple solution out there.

[Dave]

I have an 84 also. Haven't run it yet so I'm curious as to how to adjust and use the droop limiters.

Come and visit my site at: http://homepage.mac.com/reynardthefox

[Purple Frog]

Read the article at www.formularacingservices.com

It is as good an article on the subject as exists.

[P Calhoun]

You do not need to do any welding to build front droop limiters on a 83/4 Reynard. Pat Prince hounded me years ago too on droop limiters for these cars. Pat can walk you thru it, but it really is very simple.

Basically you fabricate "L" brackets out of 1/4" aluminum angle, which would mount to both the upper & lower shock mounts. You then run a piece of 5/16" threaded rod from the top to bottom "L." Attach at the lower mount w/ a nylock nut and at the top w/ double nuts. This will allow easy adjustment at the top for droop or even adding pre-load into the front springs if desired.

You'll have under $20 in materials when all is said and done.

Peter Calhoun
Reynard FF83/4

[Purple Frog]

Thank you both, Peter and Richard.

After visiting another site I was afraid of what the possible responses would be. I opened this site this morning with fire bottle in hand.

Richard, I kept up with all you wrote. Obviously over the past 15 years the trend has been "stiffer is faster". But, my old beast is set up soft, real soft. While that was great/forgiving for learning (and fast in the rain), it doesn't take advantage of newer tire technology. I know some guys that have installed some much stiffer spring rates on these older cars, with some success (up until the rockers bend).
Unfortunately, due to the current economy, I'm not in a position to experiment with springs. My current setup has been fairly competitive in the last year, but claims of 1 second improvements for less than $20 are hard to ignore. I was thinking about just setting them up without preload and seeing how it felt, then proceeding cautiously.

Soon, I hope to post a question on how to upgrade springs without having to buy 10 sets and 3 track days to get it all sorted out again. But, first I need to go buy a Lotto ticket.

[Purple Frog]

Richard...
I reread what you wrote. I'll have to read it again, I'm sure.
For the springs I have, my car may be well balanced. And, droop limiters may not help. In the last 5 events (Road Atlanta, Roebling, Road America) I don't remember noticing any understeer at turn in. But granted, since my experience is only with a soft old Reynard, and having nothing to compare it to, I may not realize it is pushing.
It is obvious in photos of the car that it is rolling more than newer cars.
If I have understeer at all, it seems to be when I'm on the power. I was thinking that droop limiters would help resist the front lift. The car has the original Bilsteins that I had the factory rebuild mid-season. So it's not like I can dial in a stiffer rebound.
Obviously, this is a low-bucks operation. And it makes little sense to put Penske triples on this old crate. If I had those funds I'd be loading up a pushrod car. But, with that said, I would like to get as much performance out of the car as I can.

[mark defer]

i'm sure richard knows what he's talking about but ..... the last season i competed in my reynard was '94. had a good season, think i won a national or two. we had all the reynard trick stuff, suspension and body mods. near the end of the season i got talking to joe stimola about the car and he talked me into sending him my double adjustable fox shocks. well, ole uncle joe revalved 'em, installed internal droop limiters, and then filled them with his witches brew shock oil [looked and felt like 90wt gear oil]. when he sent the shocks back he also sent a setup sheet along. end result: we ran a 1.27:6 at the runoffs [1.5 sec faster than we had ever gone, and were running 6th before we developed a fuel delivery problem. you can say what you want about droop limiting and preload, but on that car i think it's the hot ticket. by the way, i'm sure uncle joe still has all that info if any of you reynard guys are interested. mark

[Richard Pare]

Droop limiting can work well on softly sprung older cars, but what they are really telling you is that your car is poorly set up and poorly balanced to begin with.

The article is nicely written, but horribly wrong. I don't have a printout of the article to refer to while writing this, so I may miss a point or two, but I'll attempt a simple explanation as to what is really happening.

First off, NOTHING you can do to the car will prevent weight transfer - it's a fact of physics that can't be undone. You CAN lessen weight transfer a bit by lowering the car, or lowering the car's CG, or by widening the track, but you can't stop it from happening.

Weight is transferred by 2 main means - Geometric Transfer, and Roll Transfer.

Geometric transfer happens instantaniously when the wheel is turned or the brakes applied. It is a transfer of weight directly thru the suspension arms from one side to the other, and is a function of roll center height and CG height. It is not the same as the lever arm effect of the CG around the roll axis.

Think of it as being like what happens when you push with our hand on the side of a box. The force that you are pushing with is instantaniously transferred to the contact points between the box and whatever it is sitting on.

Roll transfer is what happens as you continue to push on the box. Assuming that you are pushing at some height above the bottom of the box, your hand acts as a force against a lever, creating a torque moment arond the base of the box. That levering effect transfers the weight of the box to the side away from your hand.

The CG of the car is essentially the same thing as your hand in that example - it is a force located at a certain distance above the roll axis. How effective it is in producing roll is determined by how far above the roll axis it is located. That's the 'lever arm' part of the analogy. The higher the roll center, and/or the lower the CG, the less leverage there is (more geometric, or "built in" roll resistance) and the less the car will roll for any given cornering force. BUT WEIGHT IS STILL TRANSFERRED ACCORDING TO HOW STRONG THE CORNERING FORCE IS.

So what happens in a non-droop limited car when you turn the wheel?

1 - A certain amount of weight is immeadiately transferred thru the suspension arms. G-loading starts, and roll begins.

2 - Roll continues until the forces balance each other. How far the car rolls is determined by CG height, roll center height, track width, roll resistance, and cornering force. How much weight is transferred is a function of the same.

If the car is softly sprung, the car will roll a lot. As a consequence, the roll center position changes according to the suspension geometry. At the front, it will generally get lower,( becase of the "dive" from brking) and will usually move sideways a bit (sometimes quite a bit). As the roll center goes lower, the built in roll resistance is decreased, and the car rolls farther, and so on. At the same time, the rear roll center will rise as the suspension rises from the braking forces. As it rises, it's roll resistance increases, but more importantly, the amount of weight transfer to the front also increases.

If the transfer is too much, the front outside tire has too much weight transferred onto it, and at the same time the front suspension is also being asked to contribute more than it's fair share to the overall roll resistance couple. The result is a sloppy feeling car with a lot of push.

In the droop limited car, Geometric weight transfer also takes place immeadiately, but then things change a bit.

Since the inside wheel is already at full droop, the car can no longer roll about the roll center. If the car is to roll at all, the pivot point becomes the contact patch of the inside tire. This actually will raise the amount of Geometric roll resistance a fair amount, and the car won't roll as far. But more important is what happens to the effecive rate of the sway bar - it is cut in HALF! How?

Remember that the inside wheel cannot go into droop so the lever arm on that side of the bar is now in a fixed position. The only twist introduced into the sway bar is now solely thru the outer lever arm, and so the bar's contribution to roll resistance is cut in half. The overall roll resistance couple is biased more to the rear now, and the car doesn't develop as much push.

Another phenomenon that happens is that more weight stays on the inside wheel, so it can now contribute more traction than it could before. Remember that the contact patch is now the roll pivot point - for the car to roll at all, a certain amount of weight has to be on that patch. If the tire is completely unloaded, the roll pivot point then becomes the outer contact patch. When that happens, the car will stop rolling, and raise the inside tire off of the ground, at which point you can't corner any faster.

If you add preload to the springs, you accomplish 2 things :

1- the nose won't dive as far under braking. Rear-to-front weight transfer still happens,but will be decreased slightly - the max pitch attitude is decreased (the nose doesn't dive as much) so the front roll center stays higher, because the weight transferred first has to overcome the amount of the preload.

2- Roll stops sooner as the inside tire has less droop available.

If the springs are preloaded enough, the amount of Geometric weight transfer is increased, which results in the faster reactions at the front

If the springs are preloaded too much (such as that the nose doesn't dive at all under braking), then the Geometric weight transfer phenomemon becomes the sole means of weight transfer , and quicky overloads the tire contact patches, resulting a "skatey" and "darty" car.

The "sweet spot" is where the car is still able to dive a bit under braking, leaving a bit of droop available for the inside tire. The car will still roll a bit, according to the amount of cornering force produced, but the inside tire will run out of droop travel at exactly the right g-loading where push would usually start ( remember the halving of the sway bar rate & the resultant roll couple balance)

Whew! Sorry I couldn't make that any shorter - it's a really complex set of relationships that is going on when you droop limit. I over-simplified some of it for the sake of brevity, so the description isn't 100% accurate.

While you CAN get good results by droop-limiting, it really is not the right way to balance out the car - it's a crutch. You are only masking the symptom, not curing the problem.

It also can be a real bitch to find that "sweet spot", especially if you aren't really, really consistant in your setups.

But, if you think that is hard, try droop limiting on the rear to cure a loose condition in a particular corner only!

[BrooksHall]

Mark how can I get in touch with Joe, I have the same shocks on my 89 Reynard.

Michael Hall

<BLOCKQUOTE>quote:</font><HR>Originally posted by mark defer:
i'm sure richard knows what he's talking about but ..... the last season i competed in my reynard was '94. had a good season, think i won a national or two. we had all the reynard trick stuff, suspension and body mods. near the end of the season i got talking to joe stimola about the car and he talked me into sending him my double adjustable fox shocks. well, ole uncle joe revalved 'em, installed internal droop limiters, and then filled them with his witches brew shock oil [looked and felt like 90wt gear oil]. when he sent the shocks back he also sent a setup sheet along. end result: we ran a 1.27:6 at the runoffs [1.5 sec faster than we had ever gone, and were running 6th before we developed a fuel delivery problem. you can say what you want about droop limiting and preload, but on that car i think it's the hot ticket. by the way, i'm sure uncle joe still has all that info if any of you reynard guys are interested. mark<HR></BLOCKQUOTE>

[Daniel]

Joe Stimola
SRP Engineering, Ltd.
63 Birch Hill Road
Locust Valley, NY 11560
Phone(516)671-9715
Fax (516)671-1449

[BarryFC99]

Richard/All,
Thank Richard for commenting on my attempt to explain the droop limiter. If its OK with you Richard I would like to update my site with your inputs to the mysterious droop limiter. I hope that in some way my ideas and experiences in using one helped out some folks. Thanks to those that visit my web site.
Barry www.formularacingservices.com