Parabolic Springs?

[ntsqd]

Inter-leaf friction in leaf springs causes slow compliance and reduces the damper valving needed due to their own internal friction acting as a damping agent. Hum, sounds like the perfect pavement trailer spring - no dampers required if the internal friction is high enough compared to the spring rate.

By reading TeriAnn's page I now understand what the differences btwn the "parabolic" leaves and std leaves are. The term "parabolic" may or may not be mis-applied. It would be pretty hard to visually see any difference btwn a parabolically arched leaf and a semi-elliptically arched spring. Which was a point of confusion for me.

These "parabolic" features are also found in the late model 65" GM rear springs. These springs feature the leaf tip pads, which is not all that uncommon, but they also feature a shim/spacer btwn each leaf pair at the center pin that creates an air gap btwn the leaves. So the leaves only touch at the tips, considerably reducing the spring's internal friction. I have found that Bilstein's std leaf spring valve stack is not enough with these springs.
I suspect that this lower overall damping value is what leads to complaints of instability etc.

I think it would be an interesting experiment to install such shims in a "normal" spring pack and see what the vehicle's behavior differences are.

[zimm]

ill be slappin a set of tic 4" paras on the fj 40 soon. ill keep yall posted.

[cruiseroutfit]

As noted it is very interesting that parabolic spring experience vary greatly between the vehicles they are installed on. I know several Landcruiser owners that removed them shortly after install... for what they felt was an unstable and scary handling, poor load capacity, etc. Howevery, just about every old Rover guy I have talked to seems to swear by them.

While parabolics reduce the spring to spring friction, its really neither here nor there as long as the friction is accounted for in the design of the spring (for a particular load capacity) and the matching dampner to go with it.

[Martyn]

While parabolics reduce the spring to spring friction, its really neither here nor there as long as the friction is accounted for in the design of the spring (for a particular load capacity) and the matching dampner to go with it.

Kurt, I'm not certain that parabolic springs reduce friction between the leaves. I think the use of the Teflon pads in this case achieves this. It's a little confusing on the web site in that they define a parabolic spring as;

"Basically a HST Parabolic Spring is a spring that consists of two or more leaves. The leaves touch only in the center, where they are fixed to the axle and at the outer ends, where they are fixed to the vehicle. In between those two points the leaves do not touch each other as they do with conventional leaf springs." (if you placed the same Teflon pads between conventional leaf springs you would achieve the same effect!).

Where as the true definition is more like "....the leaf is tapered, from the center (thick) to the outer ends (thin). This tapering is parabolic..."

Have I made this more confusing or less??

[cruiseroutfit]

Kurt, I'm not certain that parabolic springs reduce friction between the leaves. I think the use of the Teflon pads in this case achieves this. It's a little confusing on the web site in that they define a parabolic spring as;...

Yup, all part of the accounting for the friction I was referring too

OME for example uses greasable teflon pads at each spring end. After a few years of use they can start to wear thin, simply replace them with new ones, under $10/springs

[ntsqd]

I think that the damping was off or mis-matched in those who complained of instability with the parabolics. Then again, everyone has their own definition of what is 'unstable' so a qualitative analysis is sort of doomed from the start.