Helper springs

[morsan1]

Hey everybody

Do anybody have any experience in working with helper springs insted of changing rollbar setting. I have a theory that if you change to a higher helper spring ratio you will gain the benefit as if you changed the rollbar setting in stiffer direction.
What is your expenrience ?

 

[GregLocock]

Ye, you will increase the roll stiffness. But you'll also increase your ride stiffness, which will affect straight line traction.

Cheers

Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[morsan1]

Hello greg

When the car isnt rolling and is riding strait forward the helper springs should be full compressed and then the ride stiffness shouldnt be affected as you say. Do you agree ?

Thanks

Morten, Denmark

 

[GregLocock]

No. Either I don't understand what a helper spring is, or your idea of how they work is wrong. I was assuming you meant an auxiliary spring, or a constant contact jounce bumper.

Ah, perhaps you meant uncompressed? and a conventional second stage leaf spring or a conventional jb that is not constant contact? Yes, that would work, in a straight line.

Using a non linear springing arrangement for roll control is not ideal, as it tends to unsettle the car as it loads up, but everybody does it whether by accident or design.

The extreme case is when the rebound spring in the shock lifts the inside wheel off the deck. That is again, not very nice, but rather useful.



Cheers

Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[morsan1]

Hello Greg

When we in Europe talk about helper springs, means that you mount an extra springs, and the stiffness/hardness in this spring is much weaker then the main spring. By mounting this spring you will gain a unlinear springing, and when the weight of the car can compress the helper spring to a "solid mass" then the suspension works in the main spring.

My point is that change the helper spring you will change the point where you starts working in the main spring and that will altso affect the rollresistence.
I dont have any experience with leaf springs on racecars because we dont use leafsprings in europe. The most common here is normal spiral springs mountet in struts with the shock inside.

I hope you understand what I mean, or maybe my theory is way out ;-)

Regards
Morten, Denmark

 

[GregLocock]

No, you are fine, we were just talking at cross purposes, and I think I'd got hold of the wrong end of the stick.

The easiest way to work it out is to work out the wheel deflection for each degree of roll, and then the spring lengths and so on.

Now, what is interesting is that you'll get some jacking, which you won't get from a pure antiroll bar. Hmm.





Cheers

Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[morsan1]

What do you mean by jacking ?

I dont use any calculation program for setting up a racecar, I only use dataanalysing for watching the roll of the car and so on. My experience tells me that the car often handles OK when its rolling approx the same front and rear.
What is your experience ?
And do you now some usefuls programs for calculating how the rollbar should be in dimension,armlength, etc ?


Regards
Morten, Denmark

 

[GregLocock]

With non linear roadsprings as the car rolls that end of the car will lift, as well as roll, I think.

I normally set RWD cars up to be stiffer in roll at the front as Milliken/Carroll explain, to give understeer and better traction



Cheers

Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[GregLocock]

Oh, and I don't know of any good cheap programs for roll bar design, I suspect most people use a spreadsheet.

I use ADAMS, which uses a low fidelity beam element model of the sta bar, but that is because production car sta bars have weird shapes, and we are interested in effects that race car people aren't.

Cheers

Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[gt6racer2]

There are a lot of ideas round this concept - Bianchi comes to mind. Rubber bands around the coils which stretch above normal ride height and others. I've even seen designs where the helper is fitted to the shock and designed to compress the helper in both travel directions -a device which can even be preloaded for "on center'. Internal shock rebound springs are now quite common but normally aimed at pitch rather than roll. The issue with all these devices is that they are affected by vehicle ride height vs design - ie payload. For example the "helper" design of the original author has no effect at full load, as the extending spring will still be in the main sporing range. The beauty of the normal "antiroll bar" device is that it largely is not.