Resetting Springs

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 spring.

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 lightweight coils.

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 length.

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 So how do you decide the spring length that’s required to achieve your desired ride height? Unfortunately, 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. On 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 variable. Ride 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 hydraulic ram.

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.

Results

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 arch).

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.

Do-It-Yourself Spring Resetting? Be 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 spring!

Contact: Industrial Engineers and Spring Makers +61 8 8346 22776 Footnote – The reset springs were supplied to AutoSpeed at trade price – AUD$48 (plus GST) a pair.

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