Syncro Springs - What's the Ideal Spring Rate

Acknowledgement & appreciation to Steve Schwenk from the US syncro forum for his current post below.
I thought this may be of interest to Oz members, particularly the tech heads and those contemplating spring mods.
Food for thought.
Feedback called for from Steve. Anyone? Cheers.
[] Syncro Springs - What's the Ideal Spring Rate‏
From: on behalf of Steve Schwenk (
Sent: Tuesday, 18 May 2010 6:52:54 AM
I am about to order proto-types for new syncro springs. Betts has moved to a new facility with new
state-of-the-art equipment and after consultation with their engineering dept. numerous other spring
manufacturers, I am going to get some pre-tempered chrome silicon springs made up in a new design, and
hopefully put them into production if all goes right.

The advantage of the chrome silicon is that the manufacturing process is cleaner and more precise, and
the material is better suited to duty as a spring material. This results in fewer springs coming out
of the production line out of spec ... meaning they might settle, especially with the syncro spring
design, which can over-stress some materials, and especially with springs subject to stresses in excess
of what would be anticipated at maximum GVW.

This presents an opportunity to tweak the design that I have been using in terms of spring rate/
stiffness. It is of course impossible to make one spring that provides optimum performance both on and
off the road. THe ideal off-road spring will not perform so great on paved roads and a spring designed
for the pavement will not be the best off road. Generally speaking, softer works better off road and
stiffer works better on the pavement.

You can try to do a variable rate, but even that is a compromise, and often not a good choice. Unless
you reduce the coil thickness and taper it like VW did with the stock rears (which is a very expensive
process), you lose suspension travel by varrying the wind to accomplish a varriable rate. Moreover,
often times the variable coils are very-sensitive to vehicle weight varriations, and when you are
dealing with a range of vehicle weights (pass vans to fully decked out westys), they can be fully
compressed or nearly so under the static weight of the heavier vehicles even if they might work on the
lighter vehicles. This results in a loss of suspension travel equal to the thicknness of the
compressed variable rate coils on the non-tapered design, which is amplified by the suspension geometry
(i.e., a 1 inch spacer above the rear spring raises the vehicle 1.6 inches roughly). So you end up
with little or no variable rate and a not insignificant loss of suspension travel as well. That's not
a good outcome.

It's better in my opinion to pick a straight wind constant rate that offers the best compromise between
on-pavement driving and off-road driving. So the question I have is do you think I should keep the old
spring rate/stiffness, or change it? Should the new springs be softer or stiffer or stay the same?

I had some softer springs made up some years back and have been running them on my van. I like them,
they are a tad softer than the production springs. But they still improve on-road handling and
stability over worn stock springs. They're more supple on the bumps.

I know there are a group of syncro westy folks out there with really heavy vans hankering for a custom
spring that will handle all of their extra weight and still give adequate ride height and also be soft
enough for decent off-road use. But there are also folks with double cabs and pass vans who would
undoubtedly prefer a softer spring. I am thinking of making two versions, but the cost goes up
significantly to do that given the limited market.

But the question for now would be if I just get one spring made, should it be the same spring rate, a
bit softer or a bit stiffer based on your prefferences.

Thanks for any feedback.


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