This article was first published in 2006.
Want to tweak the ride height of your car? By
f-a-r the most cost-effective approach is to reset the existing coil springs.
Reset the springs – what’s that, you ask?
Well, as the name implies, it’s a process that
involves heating the springs until they’re red-hot and resetting their free
length to your specification. The process is then finished by quenching,
tempering, shot-peening and powder coating. It’s essentially a remanufactured
There are two main advantages to this approach.
First, resetting the existing coil springs doesn’t affect spring rate, so you can
enjoy a modified ride height with absolutely no trade-off in ride quality. The
second advantage is cost. Resetting a pair of springs costs just AUD$74 plus GST
from Adelaide’s Industrial Engineers and Spring Makers.
The only disadvantage is a degradation of spring
integrity although, in nearly all instances, this doesn’t cause a problem. The
quality of the spring steel, the precision of the resetting process and the
amount of ride height change are the biggest factors determining the amount of
degradation. Note that aftermarket springs manufactured by Industrial Engineers
and Spring Makers have been reset up to three times with no adverse effect. You should be able to reset any spring at least once.
We recently decided to reset the aftermarket
springs fitted to our Mitsubishi Verada. Here’s the process and results...
How Coil Springs are Reset
Before the process can begin, it must be
determined whether the existing springs were originally hot or cold wound. A
hot wound spring (as found in most cars) can be successfully reset but a cold
wound spring cannot. Cold wound springs are sometimes found in small cars with
The other prerequisite is that the spring is in
good condition. A rusty spring isn’t suitable.
If the springs meet these requirements, the next
step is to calculate the spring length that’s required in the early stage of the
resetting process; it’s important to be aware that the spring will shorten as is
goes through later processes. Industrial Springs use a computer program to
calculate the preliminary spring length that will achieve your desired final spring
We requested 20mm elevated springs which meant a
final spring length of 335mm at the front and 350mm a the rear. Computer
simulation determined that preliminary spring lengths of 350 and 360mm were
necessary to achieve this.
Choosing a Spring Length
how do you decide the spring length that’s required to achieve your desired ride
this is still a bit hit-and-miss unless you know the vehicle mass acting on each
spring, the effective spring ratio, spring rate and, where relevant, the amount
of preload when the spring is fitted to a strut. Ride height is also partially
determined by damper characteristics, bush compliance and build tolerances.
the other hand, reset springs are much more likely to achieve your desired ride
height than a set of off-the-shelf aftermarket springs. You’re changing only one
height can be raised or lowered. Changes up to around 25mm can be accommodated
(depending on the characteristics of the spring) but it’s not recommended to
raise OE springs. These tend to sag over time.
The first step in the process is to heat the
springs to make them pliable. The springs are heated in a gas furnace at over
1000 degrees Celsius for around 30 minutes.
Next, each spring is removed from the furnace and
laid on a setting bench. The setting bench incorporates sliding platforms which
are preset to give the preliminary spring length (as calculated by computer).
On the bench, each coil is adjusted using a long
handled tool. The coils are separated so that the spring spans the full length
between the adjustable platforms. It’s important to maintain even coil spacing
to avoid spring bind.
The reset spring is then quenched in an oil bath.
Quenching hardens the spring and achieves the optimal combination of strength
and ductility. The quenching process takes about ten minutes.
Next, the springs are tempered in a kiln operating at
around 480 degrees Celsius. Tempering achieves a finished hardness that will
resist sagging but be ductile enough to prevent breakage. The springs are kept
in the kiln for around 50 minutes.
The springs are now shot-peened. This induces
favourable residual stresses in the outside surface of the spring and
helps avoid cracking.
Now the springs are scragged to improve their
elastic limit and induce more of those favourable stresses. The scragging
process is simple – the springs are compressed to a predetermined height using a
Once scragged, the springs are checked to ensure
they’ve shrunk to the appropriate free length. The scragging process typically
reduces the free length to within a couple of millimeters of your desired
length. Our Verada springs were virtually spot-on.
The final process is painting or powder coating.
We opted for powder coating as it gives a neater and longer lasting finish.
The aftermarket, lowered springs previously installed in
our Mitsubishi Verada gave a ride height that was fine in normal driving but
sometimes caused the front mud flaps to scrape over steep driveways.
In standard form, the springs had a free length of
315mm at the front and 330mm at the rear.
The existing ride height was 370mm at the front and
360mm at the rear (measured from the centre of the wheel to the lip of the wheel
After resetting, spring free length increased
to around 340 and 350mm respectively – an increase of 25 and 20mm. Note that the
captive length of the spring (as fitted to the struts) remains unchanged.
With the reset springs installed, ride height is
brought up adequately to avoid the front mud flaps scraping in almost all
situations. The new ride height is 385mm at the front and 370mm at the rear – an
elevation of 15 and 10mm respectively. The car is also less prone to reach its
bump-stops due to increased bump travel.
Of course, if you want to lower the ride height of
your car none of this really matters. What does matter is you can achieve
your desired ride height at low cost without sacrificing ride quality. And
that’s gotta be a Good Thing.
aware that resetting springs is best left to the experts. Here’s what happens
when a backyarder tries to reheat a spring with an oxy torch... One useless
Industrial Engineers and Spring Makers
+61 8 8346
Footnote – The reset springs were supplied
to AutoSpeed at trade price – AUD$48 (plus GST) a pair.