Topic: HOW LOW CAN I GO? SUSPENSION Q and A

Among the favourite tweaks used by tuners to improve road holding are lowering a car's suspension and fitting uprated shocks. But, as with all modifications, there are right and wrong ways of doing this. Technical editor Jake Venter approached suspension guru Ian Glass for some advice…

Most people take the suspension of their motor vehicles for granted. It must convey them safely and comfortably, and it has to perform perfectly for many years with little or no maintenance. When the springs do require maintenance, all replacement parts must be cheap, and restore suspension performance to "as new" specifications. But these expectations show just how little knowledge most of us have about the complexities of modern suspension systems.

One of the most misunderstood components of the suspension system is the shock absorber - or damper, as it should rightly be known, seeing as it is the springs that absorb the shocks… This complex component is often the last thing to be considered when someone is attempting to extract better handling from a vehicle. A good example is a customer who was setting up a rear-wheel drive Ford Escort for drag racing and had spent R15 000 on his engine, R9 000 on a close-ratio gearbox, R8 000 on tyres, R5 000 on an LS diff, and then, finally, spent R2 000 on the correct shocks. The money spent on the shocks gave him the biggest improvement on his quarter-mile times. That is not to say that he should have just spent the money on shocks and saved the rest…

No, the point is that the correct selection of shocks got the whole package working correctly.

More and more vehicle owners are wanting to make their rides look different, and a good way to do this is to lower the ride height. Ian Glass has come across a lot of myths and misconceptions regarding the lowering of vehicles during more than 20 years of involvement with vehicle suspension systems, and deals with ten of the most common questions or concerns facing vehicle owners when wanting to lower their vehicles.

What type of suspension system does my vehicle have?
Most vehicles these days have MacPherson struts at the front. This has the shock absorber and spring as one unit, and is a structural component of the suspension, meaning that the unit bears some of the suspension forces and, if the strut is removed, the suspension will not function.

At the rear of the vehicle there could be a coil spring/damper set-up, coil-over-shock system, or a separate spring and shock set-up. The coil-over and coil spring/damper systems are similar to the strut, except for the fact that it is not a structural part of the suspension, and does not form part of steering - it only damps suspension movement and supports the vehicle. With the separate shock and spring system, the shock can be removed and the vehicle can still be driven (slowly).
Examples of the various systems are:

Strut front and strut rear - Toyota Tazz
Strut front and coil spring/dampers rear - Volkswagen CitiGolf
Strut front and separate shock and spring at the rear - BMW E46 3 Series

By how much should I lower my vehicle?
Spring manufacturers usually offer springs that lower vehicles by between 35 and 60 mm. They argue that a drop of less than 35 mm is not immediately noticeable, and any drop of more than 60 mm causes all kinds of problems that will be covered by the questions and answers that follow. A standard drop would be 40 mm, as these springs can be fitted to standard struts/shocks, provided that the shock is still in good condition, and the spring on a strut unit is still under tension when the unit is at full extension. If the spring is not under tension, a special shock is required. This is usually the case when the 60 mm drop-spring is fitted. These special shocks have a shorter body, reduced extended length, and modified damping curves. Some spring kits opt for a 60 mm drop at the front and a 40 mm drop at the rear, and this "tail up" stance is to compensate for when the vehicle is fully laden, as in that state the greater drop will be at the rear. If a 60 mm drop-spring were fitted at the rear, there would be a risk of bottoming out under full load.

As a general rule, the older designs of vehicles - Volkswagen CitiGolf, Toyota Tazz and Mazda Midge - can handle a bigger drop than newer vehicles. The Volkswagen Golf 4 can only be dropped by 35 mm - any lower at the front, and the driveshafts will foul the anti-roll bar.

Can I use standard shocks with lowered springs?
As stated previously, standard shocks can be used with a 40 mm drop-spring, provided they are in good condition and the spring is under tension. The "spring under tension" requirement is very important, as the spring can become displaced from its upper or lower spring seat if the vehicle is jacked up or becomes airborne while on the road. This condition could seriously compromise the safety of the vehicle. With the 60 mm lowered spring, a special shock is required, with a reduced stroke, shorter body and revised damping. The revised damping is necessary as the lowered spring has to do the same amount of work in a shorter space, so needs a higher spring rate. The higher damping rate means the shock needs less bump (compression) damping, but more rebound (recoil) damping. A standard shock has too much bump damping and not enough rebound damping for a shorter spring. A well-engineered lowering kit will consist of four springs and struts that have a reduced extended length, shorter body and revised damping settings. These struts can then be installed using the original bump rubber - a brown or black concertina component that fits onto the strut rod.

By how much will the short body shock, on its own, lower my vehicle?
It will not lower the vehicle at all, as it is the spring that determines by how much the vehicle is lowered. The only time a short body shock will make a difference is if the bump rubber is in contact with the top of the strut. The shorter body of the shock then allows the suspension to drop further until the spring is at its fully loaded height. This problem often occurs when vehicle owners cut their springs and cut off too many coils from the standard springs.

Can I lower my vehicle by more than 60 mm?
You can lower your vehicle by 100 mm if you want to, but you have to ask yourself how practical it would be. You have to cope with speed bumps, steep driveways or rough roads, to mention but a few things that could rip the sump off your vehicle. For a big drop, you would also have to take the wheelarch clearance into consideration. You may have to go for rims with a bigger inward offset, or modify the body by rolling or flaring the wheelarches, to stop the front tyres from catching when the wheel hits a bump while the steering is not in the straight-ahead position.

Another solution for the front wheels is to run negative camber so they clear the wheelarches when they move upwards. The drawback then is that tyres have to be rotated front to back every 5 000 to 10 000 km to avoid excessive tread wear on the inside edge of the front tyres. The rear tyres should not catch on the bodywork when the vehicle is fully loaded.

The common practice of fitting wider rims just makes this whole problem worse, and I generally advise people to only lower certain vehicles by 40 mm if fitted with 17-inch rims in place of the standard 14-inch units. The bigger rims often come with tyres that have a bigger rolling circumference than the standard tyres, and apart from messing with the carefully selected gearing, they make the vehicle stand higher. This, in turn, demands a bigger drop, which is not possible without major modifications to the wheelarches.

Big drops also introduce undesirable forces on the suspension joints, so that with some big drop kits the suppliers also supply spacers for the lower ball joints (on a MacPherson strut system). This is to bring the lower control arm back to the horizontal, and stop the ball joint working beyond its design range. These spacers are safety-critical, and should only be made by a suspension-tuning expert using the best quality steel available.

Is it a good idea to fit coil-over shocks?
These shocks are great if you are going to be changing the ride height of your vehicle often. A good example would be if you used your vehicle for motor shows. You could then drive to the show and lower it for the event. Generally speaking, coil-over shocks are used on any dedicated track vehicle where the ride height has to be set accurately, and corner weights (using special scales - one at each wheel) are set so that left and right weights are identical. Coil-over shocks are also used to give a vehicle a particular characteristic such as oversteer (making it tail happy). They can also be used to counter undesirable traits such as understeer (nose running wide in a corner), which is achieved by changing front to rear ride height. So the bottom line is that coil-overs on a road vehicle are a bit of overkill. What normally happens is that they are set once and never touched again. Vehicle owners do not often realise that from unladen to laden there is very little weight change at the front of their vehicle, but a very big change at the rear. This is why a few of the top of the range vehicles - Mercedes-Benz, BMW and Audi - only have the fancy self-levelling systems at the back.

Can I just cut one coil off my existing springs?
Yes you can, but this is not wise, because cutting coils off results in the rate of the spring increasing (less coils doing the same work). This increase may be beyond the maximum design rate for the spring, so that it is forced to operate outside the tensile strength of the material, resulting in a broken spring. You cannot undo the act of cutting off coils, so to restore the ride quality back to standard, new OE springs would have to be fitted. Another frequently encountered problem is that when the coil is cut off (using an angle grinder), the cutting disc touches the coil below the cut area. This causes a weakness, and the spring often fractures at this point. Purpose-made lowering springs are always a better option.

Can I have my springs heated up to lower the vehicle?
This is a very bad idea, as springs- coil or leaf - are manufactured to very precise standards to give exact spring rates, so there is little or no variation between the left and right spring on a vehicle. When springs are made they are heated to an exact temperature and cooled (tempered) using a fluid that is also at an exact temperature. Heating the coils on the vehicle with an oxy-acetylene torch is a far cry from the spring manufacturing plant, and heated springs almost always fail where they have been heated. It is best is to stick to the 40 or 60 mm drop, but if a drop of more than 60 mm is required, get the springs to a specialist spring works, where they will be heated and reset to a shorter free height, and re-tempered. This is only necessary if you cannot get standard lowered springs for your vehicle.

This re-tempering of springs can also be used to restore the vehicle to its original ride height. A good example is the rear springs on the Mercedes Benz W123 saloon, which sag over time, but re-tempering will restore the rear ride height. When choosing a spring works, make sure you choose a good one: ask around to find a company that knows what it is doing.

What advantages does a lowered vehicle have?
1. You may get higher cornering speeds, especially if wheel alignment settings, such as camber, castor and toe-in, are re-set after the lowering has been done.

2. The frontal area will be lowered, and this may increase the top speed, as well as the steady speed for the same throttle opening. Fuel consumption may also reduce slightly, as you should use less throttle for the same speed, as long as the same tyres are used.

3. The centre of gravity of the vehicle will be lowered, so that crosswinds will have less effect on it.

Lowered springs have higher spring rates, so the vehicle will roll less in a corner, nose dive less under braking, and squat less under acceleration. This will make the vehicle more responsive and give the driver more control.

4. A well-packaged kit will dial out quirks such as over- or understeer by careful selection of springs matched to the correctly damped shocks. Good quality kits are tested for many kilometres on the road, and on many differing surfaces, before being sold to the public.

5. The suspension will now have less travel from the ride position to full bump (compression), giving better wheel control, which equates to better vehicle control.

6. Coil-overs give adjustable ride height so the vehicle can be trimmed to match local road conditions and varying load situations - for example, adjusting the rear up for a holiday to counter a full back seat (three people) and a packed boot.

7. Settling of the springs can be countered by installing coil-overs and adjusting the settings upwards to restore ride height.

What are the disadvantages?
1. A badly fitted and lowered suspension set-up can result in poor handling and slower cornering than on the standard suspension.

2. Lowered springs matched to incorrect shocks are likely to produce very unsatisfactory results.

3. The lowered ride height increases the risk of damage to the front bumper/skirt, sump and exhaust system.

4. The higher spring rate used for the lowered springs could give the vehicle an unacceptably harsh ride.

5. Some drivers find the increased responsiveness makes the vehicle feel twitchy.

6. The lowered suspension, with its shorter travel, may tend to bump through more violently than on a standard system.

7. Coil-over shocks may be adjusted at purchase and never adjusted again. The buyer then questions why the extra expense of the coil-overs was necessary.

8. Ride height cannot be adjusted on fixed drop suspension set-ups, so any settling of the springs has to be accepted, or the springs have to be changed to restore ride height.

It's important to remember that modifying a car's suspension is a fine balancing act. Keep in mind that you're changing a set-up that was arrived at by the vehicle manufacturer after many hours of testing and a lot of experience. This is why changes to the suspension will yield improvements, but there will be inevitable disadvantages. Suspension packages are available for all major vehicle marques, such as Volkswagen Golf 1, 2, 3, 4 and 5, Polo, Opel Corsa, Astra and Kadett, Fiat Uno, Mazda Midge, Ford Laser, Toyota Corolla, Tazz, RunX, Nissan Sentra and Honda Ballade, V-TEC.

Ian Glass can be contacted at GT Shocks on 021-685-5485 or 083-454-1119.

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Re: HOW LOW CAN I GO? SUSPENSION Q and A

Brilliant write man. Now I know what do.....when i have some cash:|

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Re: HOW LOW CAN I GO? SUSPENSION Q and A

I must agreee! Donnie B our writeup King!

Daily: 3rd Gen 3SGE sw20 MR2, 90 T-Top, Bone stock
Track Project:4AGZE,Sc14 charger 93 "Bubble shape" Corrola
Future project? TWINCHARGE
The Best of both worlds!

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Re: HOW LOW CAN I GO? SUSPENSION Q and A

Great stuff Donnie!

Corolla RXi 20v Blacktop                    87 RSi 4AGE 16v "DBN Stock"- 282Wkw @ 1.8 bar
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Re: HOW LOW CAN I GO? SUSPENSION Q and A

too true...thumbs up for DonnieB ../../extensions/custom_smilies_2/img1/wink

2000 RXiya

Re: HOW LOW CAN I GO? SUSPENSION Q and A

good stuff again

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Re: HOW LOW CAN I GO? SUSPENSION Q and A

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Ian Glass FTW!!!http://i167.photobucket.com/albums/u124/Herschel1_2007/ThumbsUp.gif

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&
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Re: HOW LOW CAN I GO? SUSPENSION Q and A

nice post man!

current : 2005 Xrsi  - 180BHP atw (134kw) with Dastek & Zorst only.... Autotronics Tuned

ex : 97 20v  15.6 matuba 2010
ex : 98 20v stock 16.4 DBN 1st Ave

Re: HOW LOW CAN I GO? SUSPENSION Q and A

sweet post

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Re: HOW LOW CAN I GO? SUSPENSION Q and A

Excellent post! Now where can I get a lowering kit for my Quest?
P.S I'm in Durban.

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Re: HOW LOW CAN I GO? SUSPENSION Q and A

Looking for a good kit for my 98 20V, also in Dbn.
Enjoy driving off the clock on the highway

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Re: HOW LOW CAN I GO? SUSPENSION Q and A

Good stuff their donnie

98'' rolla blacktop rsi
tuned by astral motors

Re: HOW LOW CAN I GO? SUSPENSION Q and A

Top info there...Shot Donnie ...

Now to match shocks to my Koni springs?? wtf

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Re: HOW LOW CAN I GO? SUSPENSION Q and A

Nice post. This is very informative about a car's suspension system and emphasizes the importance of its components such as the shock absorber.

Re: HOW LOW CAN I GO? SUSPENSION Q and A

brandonmillsap wrote:

Nice post. This is very informative about a car's suspension system and emphasizes the importance of its components such as the shock absorber.

I like the part where he says most people take the complex working of modern suspension as nothing.I ran into alot of problems on my previous car when i did the 40mm drop,had to remove it in the end.I then talked to a person who owns a suspension centre,and even if i did not understood everything,the basics became clear..

The author only touched on the complex workings,just the thing around the working of the shock,and its relation the the suspension as a whole,the rebound and damp settings,left me in the dark already.Please go and google this and see..

The bottom line is almost all cars with dropped suspension fails apart from the looks,unless you are a guru like the author no matter what anybody says..

Re: HOW LOW CAN I GO? SUSPENSION Q and A

brandonmillsap wrote:

Nice post. This is very informative about a car's suspension system and emphasizes the importance of its components such as the shock absorber.

I like the part where he says most people take the complex working of modern suspension as nothing.I ran into alot of problems on my previous car when i did the 40mm drop,had to remove it in the end.I then talked to a person who owns a suspension centre,and even if i did not understood everything,the basics became clear..

The author only touched on the complex workings,just the thing around the working of the shock,and its relation the the suspension as a whole,the rebound and damp settings,left me in the dark already.Please go and google this and see..

The bottom line is almost all cars with dropped suspension fails apart from the looks,unless you are a guru like the author no matter what anybody says..