Thread: Springs

Originally Posted by JDNSW

Yes, I think you are right. The thicker leaves (for the same spring length and number of leaves) obviously increase the rate pretty dramatically - in proportion to thickness everything else being equal, I think - but have two other effects; the one the other manufacturers are looking for, that for the same rate the spring will be lighter and cheaper, and the one that they don't worry about, but Rover apparently did; for the same rate, the spring with thinner leaves can deflect further and/or more often with with less sagging or likelihood of breaking.

John

I think you are right - weight and cost are what the manufacturers are worried about.

Bayside springs had some hoarded thin leaves, a mate got a broken leaf or 2 replaced there with the correct thickness steel.

On the issue of deflection and likelihood of sagging breaking. As you would know, when you deflect a spring leaf, one side is in compression, one side is in tension. The thicker the leaf, the greater the difference between those 2 forces and the greater stress across the leaf. This means that a thicker spring leaf should have fewer cycles to failure, all things being equal. HOWEVER - IME - this is not the case. I have seen heaps of broken leaves in front spring packs (both genuine and aftermarket 5mm), but never any broken rears (e.g. the 7.1 mm leaves used on most LWB rears). Now this may be due to the short front springs on landies and the greater stresses, but parabolics seem to be holding up fine.

Originally Posted by JDNSW

This is probably mainly the effect of the long springs rather than the number of leaves, although the other point I did not mention is that the more leaves the more friction - an important factor if you have no shock absorbers.
The reason most trailers have short springs is to reduce the unsprung weight and reduce the need for damping and sway bars - i.e. overall simplicity and low cost, on the basis that it does not matter if the trailer rides rough - nobody to complain!

John

What about the broken eggs though!

PS - I do have shocks on the trailer also.

Shortening a spring (and keeping all other things equal) increases the rate significantly - just like increasing the leaf thickness does.

Case in point:
LWB front 11-leaf springs are about 270 lb/in
SWB rear 11-leaf springs are about 160 lb/in

Leaf thicknesses are pretty similar.

Some trucks with many-layered leaf packs don't need shock absorbers, because the interleaf friction provides all the damping needed.

This is the main reason parabolics give a smooth ride - no interleaf friction, meaning they respond to bumps rapidly like coils.

Originally Posted by isuzurover

........This means that a thicker spring leaf should have fewer cycles to failure, all things being equal. HOWEVER - IME - this is not the case. I have seen heaps of broken leaves in front spring packs (both genuine and aftermarket 5mm), but never any broken rears (e.g. the 7.1 mm leaves used on most LWB rears). Now this may be due to the short front springs on landies and the greater stresses, but parabolics seem to be holding up fine.

All things are not equal, however! Most broken leaves almost certainly originate from surface defects, and more leaves means more surfaces, hence, you could say, more leaves mean more broken leaves, although the steel quality and surface finish probably varies a lot more than the number of leaves does. But they should sag less, as this does not depend on defects, although it does depend on the steel quality and heat treatment. (and it is noticeable that Rover made sure all their springs had a wrap around second leaf!)

The success of parabolic springs depended on developing techniques for shaping the leaves economically, but also on being able to produce the springs with confidence of being free from both surface and internal defects. And it is noticeable that while some brands of parabolics seem to stand up well, some have had reports of broken springs.


John

Interesting stuff. And as has been alluded to, the springs on Leon are thicker leaf material and less leaves. Standard they should be 10 leaves of 3/16 (just under 5mm) and they are actually 6 leaves of what looks like 5/16 (8mm). So the overall thickness of the spring set is the same, but of course its deflection rate would be vastly different.

I will keep looking.

Originally Posted by numpty

Interesting stuff. And as has been alluded to, the springs on Leon are thicker leaf material and less leaves. Standard they should be 10 leaves of 3/16 (just under 5mm) and they are actually 6 leaves of what looks like 5/16 (8mm). So the overall thickness of the spring set is the same, but of course its deflection rate would be vastly different.

I will keep looking.

If they are about 9/32 then they are LWB springs (albeit with a leaf or 2 removed). In that case, 3 leaves will give you about the same rate as some std SWB springs (160lb/in). I would choose the top 2 and the 4th.

i.e. - like these without the 2nd stage (please ignore the ridiculously long inner clamps):

Sacrilegious it may be but have you measured up a Sierra spring?

They are not LWB springs as they would be too long.