Magazines:  Real Estate Shopping: Adult Costumes  |  Kids Costumes  |  Car Books  |  Guitars |  Electronics
This Issue Archived Articles Blog About Us Contact Us
SEARCH


Spring Swaps!

Upgrading the rear springs in small front wheel drives

by Julian Edgar

Click on pics to view larger images

At a glance...

  • Rear spring swaps
  • Low cost OE wrecker springs
  • What to look for
  • We do it and it works!
Email a friend     Print article
This article was first published in 2007.
Click for larger image

Got a small front-wheel drive with a torsion beam rear axle? If you have, you can make a suspension change that will cost you very little and can provide great benefits. (The approach will actually work on cars with all different types of suspension – but it’s easiest with a torsion beam rear end.) So what sort of benefits then? They can include changed ride height, reduced understeer and a better ride. Course, if you do it wrongly, you can make all those things worse, too!

So what are we on about? Well, with most torsion beam rear ends, removing the springs is dead easy. Unlike cars where the springs are kept captive on MacPherson struts, you won’t need a pair of spring compressors (and the danger involved in using them) and you won’t have to take the suspension assemblies out of the car. In fact, you won’t even have to take off the wheels!

But hold on – why do you need to take the springs out? You want to do that so you can replace them. You should be able to source new springs with your desired characteristics for well under AUD$50 a pair. In fact, I paid $30. And where did I get new springs for fifteen bucks each? Easy - at a big wrecking yard. To do the same you’ll need to take along some measuring tools and expect to spend at least a few hours looking before you find springs from another car that suit the new purpose.

Of course, there are no guaranties – perhaps no off-the-shelf springs are available to suit. But the springs from small cars are often very similar to each other – with just enough variation to allow the desired outcome. And of course the wrecking yard search doesn’t have to limit itself to torsion beam rear axle cars – since you have wrecking yard staff at your disposal, you can always ask to have suitable springs removed from struts...

Swapping Springs

Getting the springs out of most cars with torsion beam axles is as simple as supporting the body on jack-stands and then undoing the bottom retaining bolts of the dampers. The wheels will then droop downwards and the springs will be loose enough to remove by hand. At the most, a simple lever should be sufficient to dislodge them.

Click for larger image

Note: some cars with torsion beam rears use struts, where the coils are captive around the dampers. In these cases the springs may be under a fair amount of preload so the normal safety precautions need to be taken when removing them. See your workshop manual for how to remove the springs - you’ll need spring compressors.

Comparing Springs

When sourcing new springs, you’ll need to maintain the same internal diameter as standard. (And that’s at both ends!)

Click for larger image

When comparing springs of a similar diameter, the stiffness of the spring increases a lot with small increases in wire diameter, and increases more slowly with a reduction in the number of coils. So a new spring with the same wire diameter (you must use calipers to measure wire thickness – accuracy in this is very important), but with more free coils, will be softer. With the same wire thickness and diameter, but less free coils, it will be stiffer. A spring of the same diameter with the same number of coils but thicker wire (even 1mm thicker!) will be stiffer.

The free length of the spring is also very important. If it is longer than standard, the spring will be under greater preload when it is held captive by the dampers. This means that the ride height will be higher than standard. If the preload is great enough (ie the new spring is much longer than standard), there may be no compression under normal vehicle weight – ie there will be zero droop but a lot of bump travel. This is not good!

The following table summarises the difference for springs with the same diameter as standard.

New Spring

Characteristic when compared with old spring

Thicker wire

Stiffer – small changes make a big difference

More Coils

Softer – small changes make little difference

Longer Free Length

Higher preload so car will ride higher, reduced droop but more bump travel

So if you want to lower the back of the car, you’ll need a shorter, slightly stiffer spring (stiffer because there will be less bump travel available). That means you’re looking for a shorter free length, thicker wire and/or less coils. Such a spring selection will normally reduce understeer as well as lowering the rear of the car.

Another aspect to keep in mind is relative vehicle mass. If you grab a spring from the back of an 800kg car and put it in your 1200kg car, the car may appear fine in ride height, etc. However, the stress level in the spring steel will be higher. To counter this, the donor car should be similar in mass (or heavier) and you should make sure the number of coils and/or wire thickness are not reduced too much over standard.

Doing It

It’s starting to sound way complex, isn’t it? But it ain’t – not when you can change springs in 20 minutes!

Click for larger image

So how did I get started on this track? Well over a decade ago, colleague Michael Knowling had a Charade Turbo. At the time he knew very little about cars so I was amazed one day when he told me how that weekend he’d swapped the rear springs for some new ones sourced from a wrecking yard. A fellow Charade owner had told him what model car to take them out of (the other guy had previously found they worked) and so for little money and time, Michael soon found himself driving a successful and low cost upgrade.

That approach stayed in my mind so when I bought a Honda Insight (a car with a torsion beam rear end) and found that the rear suspension was inadequate, I thought of simple spring swaps.

So what was the problem with the Honda? In short, the rear suspension travel in Insights is terrible and the result is that on my rough secondary bitumen roads, the standard rear suspension kept hitting the bump stops. With a heavy passenger in the car, the ride could become very harsh; placing a big car battery in the boot for the trip home from an auto parts dealer was enough to cause the rear suspension to bottom on big bumps.

What I wanted was a slightly stiffer spring. Or maybe more preload. So, either a longer spring of the standard rate, or a spring of the same length but a little stiffer. There are important differences in the outcomes of either approach - and I wasn’t sure which was best to go for. That uncertainty ruled out getting springs made (even the cheapest custom manufactured spring costs well over double the wrecker route!) and so I figured some swaps might be the go.

Toyota Springs

Click for larger image

I removed the rear springs from the Honda and then wandered off to take a pic before heading to the wrecker. But right in front of me lying on my workshop floor was a spring that looked about right! It was from the strut rear of a Toyota Corolla – I’d bought the whole rear suspension when sourcing rear discs for my NHW10 Prius. The Corolla springs were very similar diameter to the standard Honda springs but about 25mm longer – a fair amount of extra preload. The wire was also slightly thicker. (The Corolla spring is at left and the standard Honda spring at right.) But since they were there and the swap was so easy, I bunged them in.

The rear of the car rode higher but since it is normally very low, that wasn’t a huge problem. But by God the ride sure was a problem! I’d wondered what a car would be like with nearly no rebound (droop) travel, but lots of bump travel, and I soon found out. The ride was appalling – incredibly hard and then on the big bumps, completely undamped as the energy stored in the coil quickly overcame the standard dampers. Even if you want more bump travel, I’d not suggest that you go for a longer spring...

So I needed to take a trip to a wrecker.

Wrecker Springs

I took with me to the wrecker the top rubber spring mount from the Honda, a pair of calipers, a tape measure and one standard Honda spring. The Honda is a light car (just 850kg) so I looked at cars like the Mazda 121, Ford Ka, Daihatsu Sirion and Suzuki Swift. (And while I was browsing, I saw plenty of springs that looked suitable for cars up to about 1200kg – so it’s not just the ultra littlies that this applies to.) In the end I settled on the rear springs from a Daewoo Matiz.

Click for larger image

The Matiz springs were the same diameter, the same length, had one more coil but the wire thickness was 1mm greater (the Matiz spring is on the left). That put my rule of thumb calculation as suggesting the new ones slightly stiffer – just what was wanted. I physically pushed down on the original Honda sample and then on one of the Matiz springs and the rule of thumb calculation seemed about right – the Matiz springs were a bit stiffer.

Thirty bucks later, they were mine. (Incidentally, when buying, check on the wrecker’s refund or exchange policy.)

Installation

Twenty minutes after arriving home, the Corolla springs were out and the Matiz springs were in. (I went to the wrecker in another car!) And the result was near perfect. Over the same bumps the car rode more compliantly – despite the stiffer springs. That’s because the suspension travel wasn’t all being used up, so causing a meeting with the bump stops. And, as you’d expect with stiffer rear springs, understeer was reduced. (However, the taller rear ride height gave more rear weight transfer, so more than one thing was happening when cornering!)

Click for larger image

But the springs were noisy, making ‘metallic’ sounds that echoed through the all-aluminium body. Now I know why the standard springs have a rubber compound over the first few coils! But this was easy to fix – up on jack-stands again, springs out and the rubber protectors slipped over the first few coils.

With the springs silenced, I went for a longer drive. Obviously the total suspension travel is unchanged but on the road you’d swear there are inches more travel. Even over speed humps, where previously the car used to bottom-out harshly, full travel is not used. And the car feels far more poised in hard cornering – you’d swear a custom-made rear sway bar had been bolted into place!

All pretty bloody good for thirty bucks....

Conclusion

Click for larger image

Look, I can’t say that you’ll find it easy to whip out the rear springs, even easier to find some excellent on-paper replacements, and then find they work beautifully on the road. But I know one thing: if you don’t try it, you’ll never know!

Did you enjoy this article?

Please consider supporting AutoSpeed with a small contribution. More Info...


Share this Article: 

More of our most popular articles.
An engine that combines both 2-stroke and 4-stroke functions

Technical Features - 16 September, 2008

Stroke of Genius

An aerodynamic undertray - that didn't work!

DIY Tech Features - 28 October, 2008

Trialling a Rear Undertray

Got a 'PD' VW / Audi / Skoda / SEAT diesel? Changing the cam timing can make major differences to performance and economy.

DIY Tech Features - 23 August, 2011

Big Changes from Tiny Adjustments!

Changing the weight of electronically-controlled power steering

DIY Tech Features - 26 February, 2002

Modifying Speed-Sensitive Power Steering

Build your own battery charger for nearly nothing

DIY Tech Features - 21 October, 2008

Dirt Cheap DIY Battery Charger

The story of the wonderful BMW M1 - a purpose-built racer

Special Features - 7 April, 2009

M1 Magnificence

Installing the machinery in a home workshop

DIY Tech Features - 7 October, 2008

Building a Home Workshop, Part 9

First testing results

DIY Tech Features - 23 June, 2009

Chalky, Part 7

DIY knock detection - cheap, easy and very effective!

DIY Tech Features - 18 November, 2014

Hearing Detonation

Part two of an R32 Skyline GT-R modification process

DIY Tech Features - 6 September, 2011

GT-R Unleashed

Copyright © 1996-2019 Web Publications Pty Limited. All Rights ReservedRSS|Privacy policy|Advertise
Consulting Services: Magento Experts|Technologies : Magento Extensions|ReadytoShip