Rear Leaf springs 1

[willeng]

Is there any real advantage of replacing the conventional multiple stack leaf spring setup with a (single) rear leaf spring of the same rate. To me it seems like a real headache but others around me think that this is the way to go?
Could someone shed some more light on this subject with the advantages if any & also the disadvantages related to this!
Keeping in mind this is a race car & no rear bar is permitted by the rules in this particular class!

Thanks.

 

[GregLocock]

What advantage(s) do they claim? Are they proposing a tapered spring, or constant depth? Are they tapered in planform?


Cheers

Greg Locock

 

[willeng]

Greg:

No taper in the design at all, basically what they are planning is just like a heavier main leaf spring by itself!
The length of the spring from eye to eye is a little over a
1mtr in length.
When questioned about advantages they will not elaborate, which is suspect to me!

Thanks

 

[patprimmer]

No taper brings two problems to my mind.

1) The spring will be heavier than necessary for it's spring rate.

2) The spring will concentrate the stress near the "U" bolts, as the ends near the shackle will be to stiff, and therefore not share the load evenly.

Regards
pat pprimmer@acay.com.au
eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[GregLocock]

I wouldn't touch it. The only advantages I can think of for a properly designed (ie tapered) leaf spring is that there is no friction between the leaves, and the obvious reduction in part count.

The weight disadvantage of the proposed design is considerable.



Cheers

Greg Locock

 

[willeng]

Thanks guy's

My thoughts exactly!!

 

[Tmoose]

When Chevy went monoleaf on the low-powered Novas or what-not in the (70s?) I recall the abusive road testers complained of wheel hop/tramp and blamed it on extra spring wind-up. I can imagine the lack of leaves and inter-leaf friction might do that, if the springs are being asked to locate the wheels too.

 

[NormPeterson]

Perhaps the design is an intentional end-run around the "no rear bar" racing class rule. A sta-bar that doesn't look like one, being comprised of the axle itself in torsion with the springs in bending plus individual spring torsional components of roll resistance. So perhaps the weight of this design should be balanced against the total weight of a conventional leaf plus the appropriate bar that you would use were it legal. Given that the leaf springs have now assumed the additional duty of sta-bar arms, tapering the leaves in side view is only going to give up some of the added roll stiffness (though it could be used as a rather expensive and fussy way to tune the amount).

Assuming that "supplemental" lateral location devices such as Panhard bars or Watts links are also illegal, you probably wouldn't want these things to be tapered in plan view either.

I think the older Chrysler Corp. cars (circa late 1950's/early 1960's, before some of their cars sported proper rear sta-bars) sometimes used extremely stiff bushings in the front spring eyes for hard cornering applications, which would have added some roll rate. Does this product use a similar attachment point detail?

Norm

 

[GregLocock]

Star for that Norm, makes sense to me. Ah, the never-ending deviousness of racers!



Cheers

Greg Locock

 

[willeng]

Norm:

Thanks for the design concepts, i can tell you, that this design doesn't come close to what you have suggested! But it may be worth a re-think!

Thanks

 

[hford]

since reduction of friction between the leafs reduces( in fact for one leaf, there is no friction) the suspension system should need more high capacity dampers, since this friction acts like a damper.

 

[PTwizz]

"This friction acts like a damper" AAAARGH!!!
We damper manufacturers go to great lengths to reduce friction. It does the opposite of what you want from a damper, in that it is highest at zero velocity, dropping off sharply as motion begins. This is referred to as 'stick-slip'.
Returning to the leaf spring, I use 'parabolic' leaf springs on a Landrover. These are lighter than the originals, even if the same rate is selected. This is because the spring is optimised by reducing it's section toward the ends. They do, however, allow more axle 'wind-up'. I intend to try to remedy this by using a hybrid spring, with a single leaf, tapered toward the shackle end, and parallel (or less tapered) toward the chassis bush end. As Norm suggests, this is probably the aim of the single leaf.

 

[stingc]

Corvettes have had single leaf springs for many years (transversely mounted). They're made out of some composite material, so they're actually much lighter than the equivalent multileaf metal spring.

 

[mikikanazawa]

Yes, but the transverse 'Vette spring does not locate the rear "axle" aside from providing the appropriate ride height/wheel alignment relationship.

 

[willeng]

Results:
After many race & test miles with the single leaf setup of all configurations, best we get a shovel & bury it!!

The conventional stack of springs is much more user friendly for this application & much easier to tune quickly not to mention it stays on the track much nicer & is much more stable under brakes as well!!!