mds

That is a way to think of it. Take two 400lb springs, place them side by side on the floor and stand on them with one foot. You have double the length, but they are side by side. The effective rate is 800lb.

Now, rather than side by side, stack them and stand on the stack. Same total spring length, but now they are stacked. Effective rate of the stack is 200lbs.

So to me, length by itself is not a fundamental factor. The individual spring rates and how they are combined together in series and/or in parallel determines the result.

Adam@Autometrics

We use tender springs on all of our cars with relatively high spring rates, but the purpose is not to develop a progressive rate. In fact, on the rear of a GT3 cup car, the spring will be fully compressed with static load.

The tender comes into play when the damper goes into the rebound direction.
The best way I can describe it is not completely accurate, but you'll get the general idea.

If you Lift up on the fender of a car (by hand) with very soft springs, you can raise the car pretty easily.
Do the same on a car with stiff springs and it won't move.
Adding the tender gives the car a bit more motion in the rebound direction, which ultimately will stop the car from "falling over" if you unload a spring too much.

Porsche would not use them on all of their race cars if they were not necessary.

Geo

Those are helper springs not tender springs. Just trying to keep everybody on the same terminology as the rest of the racing world (see Eibach's site for instance).

Adding neither tender nor helper springs will affect the suspension travel unless the springs were chosen incorrectly. Neither will keep a car from "falling over" in and of themselves, but helper springs will keep the springs seated and keep the springs from falling over on the damper piston at full droop.

There are certainly good reasons for them, but I'm not so sure I'd call them necessary. They serve a purpose and many other racing teams and manufacturers use them as well.

JCP911S

Just to be more precise it is the total length of spring material in the spring not the lheight of the spring.. in other words more coils equals lower spring rate.

kurt M

Yes, in a way...
A spring is a torsion bar that is wound into a cylinder. You can make it with 2 coils and be real big around or 20 coils and be tall and thin. As far as the metal is concerned it is resisting torsion ether way and if both are the same lenght and bar dia they will have ther same rate. Where a spring is different from a T bar is when you set the coils to different gaps so that some of the gaps close up. This shortens the length of the spring (torsion bar). This is where the progression comes into play. When any coils make contact with each other and go into mechanical lock the overall length of the bar is now shorter and the bar will act like a shorter T bar (which it now is). A long T bar will have less torison per inch per degree of twist than a shorter bar. Same with a spring. It's not the # of coils but as you said, the lenght and dia of the coiled bar.

Patrick

I wouldn't insist that there is only one acceptable terminology, especially if I was basing it off a BMW enthusiast site and one spring mfg. site. I did a lot of research on this when the question came up, and from what I can determine, the "rest of the racing world" uses the terms interchangebly, sometimes with distinct meaning and sometimes using both terms for the same spring. In my opinion, Tender makes more sense to describe the spring that keeps the main spring seated, and "Helper" helps with spring rate. But it really does not matter.

Geo

It is not based just open the sites I cited (pun intended).

Geo

Here is some more technical info on this topic from http://www.athon-motorsport.co.uk/co...onsprings.html :

NOTES ON SUSPENSION SETTINGS

A properly tuned spring system provides the muscle needed to transform the power derived from the engine of a racing or rally car onto the road through optimum adhesion. Suspension tuning is always a compromise. On the one hand, the spring system should be soft enough to compensate for road irregularities ensuring permanent road contact and on the other hand the spring system must be firm enough to reduce body roll, squat and dive of the vehicle during cornering, acceleration and braking.

In order to minimize this compromise, Eibach has developed the world famous ERS double spring system. With this system, many different Main and Tender springs can be combined to achieve the best overall suspension characteristic. From a selection of more than 700 different single springs components, the suspension engineer can create nearly unlimited combinations. The ERS double spring system is unsurpassed in performance and flexibility.

The ERS double springs system provides a softer initial rate at the beginning when both the main and tender springs are compressed together and delivers the desired firmer ending rate once the tender spring closes completely leaving only the main spring to deflect further.

The Main spring has a linear-rate characteristic and determines the final rate of the system. The Tender springs are available in a variety of linear-rate as well as progressive-rate characteristics and determine the initial rate of the system.

The Helper spring is used to prevent the Main spring from becoming loose in the spring seat when the wheel is at full droop. The Helper spring unlike the Tender spring, has very little spring rate and therefore, has no effect on the suspension characteristics of the vehicles. Up to 50mm of spring-to-spring seat gap can be covered with the use of a Helper spring.

Connecting Plates are used to connect Main and Tender springs. We offer both inside and outside diameter connection plates depending upon the dimension and function of the specific damper utilized.

Every chassis / suspension / driver is unique therefore we suggest that you utilize the ERS Wizard to fully understand the dynamics of the double spring combination before you go testing. Our page can be used to calculate spring rates that will be close and then below we have listed the formulas for determining the initial and final rate as well as the transition point between the two.

The following formula is used to determine the initial spring rate:
Ci = CM x CT CI = initial spring rate
CM + CT CM = spring rate of Main Spring
CT = spring rate of Tender Spring

The final spring rate (effective after the tender spring is closed) is simply the rate of the active Main spring.

The following formula is used to determine the transition point between the initial rate and the final rate:
TP = (Fc)t TP = Transition Point
CI (Fc)t = Block load of Tender Spring
CI - Initial Rate of Main / Tender Spring Combination

Note: the Main / Progressive Tender spring combination has various rates and transition points and as a result the respective formulas required to determine the rates and transition points are more complex.

Geo

More notes:

From: http://www.pegasusautoracing.com/Pro...p?Product=1876

"Hyperco 2.50 inch Zero-Rate Helper Spring
Also known as Tender Springs, these soft springs are used on suspensions which can travel farther than the chassis spring. When the suspension droops, these springs expand and take up the slack between the chassis spring and the spring perch. This keeps the chassis springs centered on the perch and prevents the ride height from suddenly changing. These short coils have very low spring rates and are coil bound when the suspension is at normal ride height. They will not affect the rate of your chassis springs."

From: http://www.whiteline.com.au/default....faqsprings.htm

"Helper and tender springs are both made from a flat wire spring that are designed to completely compress. In Whiteline's view, the difference is mainly in the application of the spring and at what point they close in the chosen application. This is obviously dependant on spring load, where a helper spring is generally known to close BEFORE normal load is applied, and a tender spring is generally known to close AFTER normal load is applied."

Adam@Autometrics

The Porsche tender springs are around 250lbs/in, so they are not helpers. They are in fact tenders, and Porsche even calls them that. I checked the Cup parts catalog just to make sure.

And if your suspension movement extends to the point to where the spring ever becomes loose in the perches, the car will loose a significant portion of its roll resistance, and you will get alot of body roll quickly. I call that "falling over."
There are other ways to prevent this, but this is the most efficient, IMO.

If you don't believe me, that is fine. But I confirmed this with Claude Rouelle, just a few weeks ago. Go to optimumg.com if you want to make sure he is qualified.

Geo

First of all I was just going by your own description regarding helper/tender regarding your first post.

Secondly (and I mean this sincerely), I don't understand how an spring that is unloading (as in on the side of the car on the inside of the corner) can contribute to roll resistance and how that can be affected when the spring unseats. That's not a smart-aleck comment. I don't see how it works and if you can explain it, I'd be grateful. My first thought is it's dubious, but I'm open to the fact I haven't thought things through enough.

Steve Weiner-Rennsport Systems

Hi George:

I've used tenders for quite some time and one needs some experience with them to understand how they work in practice,...

"Extra cost"?......yessir, but not that much. "Extra complication"?........not really very much at all.

If the main & tender rates are carefully chosen, one doesn't suffer "sudden abrupt changes in spring rates" and its FAR more predictable than rising rate suspensions.

In short, dual-spring (and triple-spring) suspensions are very effective and offer many benefits over single-spring suspensions when the road surface is not smooth.

Just my 2 cents, of course,.......YMMV.

Geo

Agreed. I was just trying to answer the question though. And the complication I was referring to was getting the rates correct. True enough the math isn't that big a deal once you have the formulas. Figuring out what will work well has always been a big question for me.

I will admit to zero experience with them. I've thought about it a bit, but have always been worried about figuring out the best combination of rates and what the transition would be like. If you don't mind sharing, what sort of differentials between the initial rate and the main spring rate have you used?

Adam@Autometrics

It is difficult to explain with just words, but i can try.
The inside spring is contributing to roll resistance.
Look at my first example about lifting stiff vs soft. When you unload the inside spring completely, you now have an infinitely soft spring that lifts very easy.
The entire weight is now being supported by one spring instead of 2.
Like i said, it takes a few visual aids to explain the point defintively and effectively.

hrk

I am interested in this too, but I cannot see Adams logic.
In corner the inside spring is trying to roll the car more, not resist roll.

I get the lifting example difference. Do you mean that inside tire is pushed to road better with these helper/tender springs and thus contributing to keep the car on the road?

Very interesting discussion
hrk