FAQ: Lets Look @ Springs!
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FAQ: Lets Look @ Springs!
A simplified guide to what component does what in the whole suspension chassis equation. Or, enough information to make you dangerous!
This is by no means the definitive guide as each sub section alone can justify a volume of books let alone all the components we have not covered yet. So, if you're interested in finding out more, let us know and we can recommend some other texts for you to read. Naturally this FAQ will be expanded as more questions are asked and we get round to answering them.
Springs
What Aftermarket Springs will and won't do?
Will Aftermarket springs lower my car 1 1/2" or 37.5 mm?
Will my tires scrub after fitting lowered springs?
What is "spring rate" and why should I know about it?
Motion Ratio, what are we talking about?
I want "progressive springs", but can you tell me what they are first?
Why don't I just cut my existing springs?
How low should I go – Control vs Flatout?
Bumpstops - are they important?
Coil-Overs and Height Adjustable suspension
What are they?
How do they work?
What are the Pro's and Con's?
What about the shocks?
So what's available?
What should I buy?
A Tender spring or a Helper spring?
What Aftermarket Springs will and won't do?
Springs models recommended WILL make your car handle better if matched with appropriate shocks and they WILL deliver a lower sporting look however I DO NOT condone cosmetic lowering solutions.
That is, rates and heights are calculated to try to deliver the optimum ride/handling outcome. I would not try to "even out" front to rear fender gaps as these are generally different for a reason. To do so would be to disproportionately lower one end more than another which could result in poor handling and ride through unwanted changes to weight and geometry.
We do sometimes change the front/rear height balance on some vehicles as part of an overall handling strategy but again, improved handling is the main target. Fender gaps are a misleading way to asses "rake" (the amount of angle rear to front). The only way to measure this accurately is at the bottom of the sill or rail under the doors. If a car looks even at the fenders, it will almost always have a VERY significant downward rake to the front.
Having said that though, I often refer to separate ranges of springs for popular vehicles. Street range springs are designed to deliver an optimum ride and handling compromise with an increase in spring rate coupled with a moderate decrease in ride height. This will vary between 25-40 mm depending on model as some cars are quite low from the factory. Also, factory sports options may already have a significant height reduction so the spring may not lower more than 15 mm but will have an increased rate tuned for sharper response.
If low is the goal I usually say go with a "race" spring. Though still acceptable for controlled road use, they are more suitable for track use where the surface is smooth and predictable. However, they offer the lowest ride height available in the range, up to 60 mm for some applications
Will X brand springs springs lower my car 1 1/2" or 37.5 mm?
Probably neither!
Irrespective of brand, it is impossible to confirm or guarantee how much a pair of springs will lower because of the variable starting point. That is, any cars standard height can vary enormously start including accessories and other modifications to the equation and we have a very complicated problem.
Add a few years or km’s of use (or mistreatment) and an absolute starting point becomes impossible to predict
Therefore, claims that any pair of lowered springs lower a vehicle a fixed or precise amount are wrong and misleading. However, there is some data that we can provide and that is the resultant fitted heights using Known Springs with a tolerance of +/- 5 mm. Note that this can only relate to a relatively standard vehicle as even mono-tube gas shocks can have an effect on the final height. Add sub-woofers or aftermarket strut top camber adjusters and this height can vary by 25 mm.
These fitted height measurements are taken from the centre of the wheel to the lip of the guard (fender) cut-out, measured at all 4 corners with the car parked on level ground.
These measurements are published in our kit Fact Sheets where available. We always encourage our customers to use these measurements to compare their existing heights with the proposed lowered height prior to purchase. This way there is no misunderstandings about the outcome.
Firstly, they are used to hold the weight of the car and secondly to deflect when required at a specified rate i.e. when the vehicle hits a bump or starts to pitch forward and back. In reality they work as an energy store. The spring is there to minimize the transfer of loads from the unsprung mass to the sprung mass. Or, to absorb as much of the shock, bump and pitch load the car is subjected to with out influencing or affecting the body and occupants. The damper or "shock absorber" then dissipates this stored energy. This process is also critical in maintaining tyre contact with the road. With out springs the car would simply bounce from bump to bump.
Springs should not be designed to limit body roll. When the vehicle is in roll the spring needs to be soft enough to absorb bumps. If the spring is stiff enough to control roll then it will be far too stiff when you have roll and a bump at the same time. The result again would be a car that jumps around requiring constant steering adjustments. Unlike many other springs, our Whiteline Springs range is designed to be as soft as possible for this very reason.
Will my tires scrub after fitting lowered springs?
Provided standard wheels and tyres are used and the manufacturer had provided clearance between the tyre, suspension and body work at FULL suspension travel, then lowering the ride height will not cause tyre-to-body interference or "scrubbing". That is, if you follow manufacturers maximum recommended options etc, everything should be fine. Lowering the vehicle simply relocates the wheel and tyre to a different point of its travel arc, it does not change the travel arc.
However, when fitting bigger wheels and tires it is important to keep within the original overall outside diameter and width relative to wheel offset. That is, fitting larger diameter tyres which dramatically increased overall diameter will probably lead to scrubbing problems. As will increasing width excessively or using the wrong offset. Simplest rule of thumb is that if it scrub now when loaded, it will scrub even more if you lower it but that's not the springs fault.
What is "Spring Rate" and why should I know about it?
A spring will be compressed when a load is applied. The distance it is compressed (deflected) for that given load is referred to as the spring rate. Spring rate is specified in terms of force applied per distance of deflection. Typically, the units of spring rate are pounds force per Inch or using the metric Sl system - Newton's per millimeter. We can just as easily convert the pounds into kilograms and measure the deflection in millimeters.
If a load of 1 kg deflects a spring 1-mm, each additional 1-kg will deflect it another mm. For each kg removed from the load the spring will return one mm toward its original state. The spring may be loaded at the rate of 1 kg per mm until it is deflected beyond its capacity. This means the spring will become damaged and will not resume its original characteristics when the load is removed. This point is called the elastic limit. A spring loaded beyond the elastic limit is deformed permanently.
In this example using linear design coils, both springs have 125 kg's of force applied to them. The standard spring has deflected 150mm from its original height. It therefore has a spring rate of 125 kg's per 150 mm, or 0.833 kg's/mm.
The replacement coil however with the same force only deflects 100 mm. Its rate is therefore 125 kg's per 100 mm or, 1.25 kg's/mm. It is a heavier spring.
Even though the replacement spring is 50 mm shorter, given the same weight, the ride height will be the same. However, because the spring is of a heavier rate, it will sag less, handle greater loads and often perform better in performance applications. A lowered heavier rate spring may be shorter again to deliver a lowered ride height with a heavier rate.
Motion ratio, what are we talking about?
Probably the most misunderstood component of the spring design function. The effective spring rate at the wheel is the only relevant number when discussing spring "rates". The actual rate of the spring itself is irrelevant without the knowledge of the effect of the motion ratio on that rate.
That is, it is rare that the spring moves up and do over the same distance as the actual wheel. For example, a HQ Holden front wheel may move up 50mm when hitting a bump but the spring will only move (compress) around 25mm. This is an example of a relatively large motion ratio. On the other hand, a strut based front suspension system delivers a relatively small motion ratio, typically around 90%. That means that the spring will deflect 90% of the distance the wheel deflects for any given circumstances.
This motion ratio changes the leverage and effective rate of the spring at the wheel. Hence a 500lb front spring for a Miata can't be compared with a GTO 300lb front. stick with a companay that designs its replacement springs to deliver the optimum spring rate AT THE WHEEL, not at the spring.
The accompanying picture shows the only case where motion ratio is not an issue with spring travel matching wheel travel. But, there's more. This picture may represent a situation with no motion ratio issue but it shows a possible further complication if we consider the wheel is fitted with a pneumatic tyre. This has its own inherent spring rate, which will impact on the spring rate at the wheel vs the coils physical rate. Tyre pressure, compound and build structure will all affect the tyres effective rate. In fact, most race tyre manufacturers will recommend an optimum spring rate range for their particular tyre. So the tyre and spring relationship is particularly important.
I want "progressive springs", but can you tell me what they are first?
This is often the reality of customers requests for progressive springs. Marketing hype has convinced them that progressive springs "are good" but not necessarily why, where or in what way. For those of you that know the answer, now's the time to look elsewhere. If you don't know, or think you know, no one can see you so read on.
A progressive spring can be defined simply as one that does NOT have a linear rate. This means that it's rate changes depending on the amount of deflection in a way that can not be plotted via a linear relationship. Typical examples are coil springs in a conical shape, those using variable wire thickness and most commonly, those with irregular gaps between the individual coils. It is also possible and common to see all of the above used in the same design. An example of this is GTO IRS rear coils.
Progressive spring designs for lowering cars are used to (in order of relevance)
With lowered performance springs, we are more concerned with increasing the rate while lowering the ride height. Reducing the suspension travel creates its own complications but the last thing we need is a varying increased deflection rate that can not be matched by an appropriate damper or chassis mods to suit. In fact, performance applications are generally best served by a linear rate if possible.
Next time they try to sell you their " you-beaut lowered progressive" springs, ask them if they have some matching "progressive rate" shocks to suit. Also, ask the seller if the rate progression of the spring is designed to match the inherent rate progression of the vehicles chassis? For example, the EA-EL Falcon AND Honda Civic front suspension geometry has spring rate progression as part of its design. In fact, most suspension designs have sort of travel progression that leads to rate progression because the wheel moves in an arc. Adding progression to progression creates all sorts of problems so be wary of some manufacturers claims.
Good Springs are only progressive where and if they need to be.
Why don't I just cut my existing springs?
1. Many aftermarket lowered springs are designed to be just captive (held in place) with the wheel at full droop. This is a legal requirement throughout many countries. Cutting off a portion of the coil will reduce the free height (length of the spring out of the car), possibly to the point making the spring loose at droop. This can also happen with OEM springs but is more often a problem with aftermarket product.
2.Most springs are designed to a fairly tight tolerance of material volume to load carrying capacity. That is, the amount of steel used in the spring is hopefully just enough to hold up the car over the life of the vehicle with normal use. Chop off some coils and you've dramatically reduced the amount of material, which almost always will lead to an overstressed coil that will sag prematurely.
3.A reduction in ride height is normally coupled with a proportionate increase in rate to
offset the reduced bump travel. We need to slow down the compression of the spring enough to make sure we don't punch through to the shock at high velocity. A properly designed lowered spring will have a rate increase sufficient to offset this bump travel reduction.
4.The cutting method can also be a problem. Generating heat is not so much a problem as reduction in the heat afterwards. That is, heating the material beyond its temper and then rapidly cooling it will affect the composition of the material. A hack saw would be preferable but, irrespective of what tools you use, its not good practice overall.
How low should I go?
There are a couple of important points to note here. Firstly, that MAny "superlow" do deliver a greater "cosmetic" look compared to street versions. This is because the degree of lowering is generally in excess of what is optimum with standard dimension or configuration struts, shocks and suspension geometry. Once you get down to these sorts of changes from standard, there are a whole range of issues that need attention like significantly modified shock dimensions for increased bump travel, relocation of key suspension pickup points to counter roll center changes and many others.
All in all, at extra low heights, standard components cannot possibly deliver good objective handling outcomes particularly on the road where suspension travel is SOO important. The second issue is that most extra low springs in any brand are the same rate (sometimes actually softer) as low springs because of physical design constraints to meet the competing objectives.
The lower the spring ride height, the higher the rate needs to be to compensate for the reduced bump travel. The weight of the vehicle presumably stays the same so we need some more spring rate to compensate for the reduced compression travel available so we don't either crash through the shock or pogo up into the atmosphere after bouncing off the bump stop. (Even after we've shortened it).
Now, in the case of a strut equipped car like the WRX, the lower you go from standard, the more the front roll centre and roll couple geometry starts working against you. This leads to the effective wheel spring rate reducing in roll even though the physical rate at the spring is the same. Under bump the rate may be the same but there is a compounding reduction in rate as the car corners with the roll centre migrating well below ground.
Some brands do manage to increase the spring rate for extra low but only by using an increased number of "Dead" progressive coils that simply close up and remain ineffective once fitted. This is OK in theory but not unless the remaining "active" coils are up to the task of supporting the weight of the vehicle 24/7 let alone dealing with high impact performance loads. In our case, we will not reccomend a spring design unless it meets key design criteria and simulated life cycle tests.
I'm sure many people know of performance springs that have sagged prematurely and generally this is because of the conflicting design goals and the very fine tolerance involved. One vehicle with extra low springs may simply do boulevard cruising while another may get involved in spirited driving, its not hard to work out which is more likely will suffer "automatic lowering" as we call it.
we know what happens in terms of grip and handling with "lowering" springs and
standard shocks. On a nearly perfect surface using near new stock shocks, the "street" springs are “grippier” in terms of lateral G’s and faster than stock. We have also tested this result on the track with the same outcome but we know that even partially worn shocks or poor road surface changes the result dramatically. There is no point testing same with Race springs because we know from experience that it’s a backward step with out other modifications like shock upgrade or significant geometry changes.
The preload issue is therefore a consequence of the design constraints. major springs are designed to have some preload on full extension when using standard dimension shocks at worst. Sufficient preload to keep the spring in place and stop it from relocating so I would be confident that though you may be able to move the spring a little, you could not move it to the point that it can incorrectly seat on the shock.
I’m not sure about the comment of “working with standard shocks” being fine though. We do not quote that anywhere, as it’s too much of an open statement. Yes, our springs will physically fit in the space as determined by the shock and suspension geometry but they are not designed to work with standard dampers, NO aftermarket lowered or heavier rate spring is. The street springs are less likely to cause problems where as using race springs with stock shocks is asking for trouble.
Coil overs and height adjustable suspension.
What are they?
Often referred to as simply "adjustable" suspension but specifically refers to height adjustable suspension. Also known as "coil-overs", "height adjustable struts". Like many other trends, the technology is derived from motor racing with a variety of different kits now being sold for road use. And, like many other trends that a lot of people jump onto, there are a lot of factors that need to be considered before spending money on what is considered to be the top end solution for performance suspension.
Main reasons for use on road vehicles (in general order of actual use.)
How do they work?
Most height adjustable systems use a threaded sleeve on the outside of the strut or shock body to lower or raise the base height of the coil. Because the other end of the spring is held by the shock or strut, changing the height of the spring seat acts to increase or decrease the pre-load on the spring. Because the weight of the car remains the same, this has the effect of changing the ride height. To try to make it a little clearer, suggest you look at our Whiteline web site FAQ on spring rate
The important point to note is that you don't change the actual rate of the spring by changing the seat height position. In the case of raising the springs seat, we simply force it higher up its rate curve, which means the weight of the car will not deflect the spring as far resulting in a higher ride height.
What are the Pro's and Con's?
Apart from height adjustability, a major benefit of these systems stems from the fact that they use a "race coil" with reasonably standard dimensions. There are a number of common inside diameters like 50/53/57/60/63/65mm which are a conversion from Imperial measurements. The most commonly used sizes are 60, 63 and 65mm with a few companies offering off the shelf units in a variety of lengths and rates with a standard inside diameter. This allows serious chassis and suspension tuners to change the spring rate and style for different tracks and environments, but this is only relevant if the shock rate is also adjustable.
These relatively small diameters do come with several down sides. The first is a restriction as to the maximum spring rate that can be used while maintaining captive spring height. In fact this is contradictory to the main use of the system such as high spring rates for racing applications. As the designed spring rate goes up, the "free" or fully extended height of the spring must become shorter to maintain the same relative ride height. This means a greater need for "progressive" or other design solutions to avoid severely restricting suspension travel. VERY relevant for rear of front wheel drives.
The other problem resulting from small springs and heavy rates is the restriction of total suspension travel, which is a problem for all road cars. Given a billiard table smooth surface, we really wouldn't need springs at all but even the best racetrack has bumps and undulations, let alone the corner kerbing and ripple strips. The best suburban roads require at least 100mm of total suspension travel to ensure contact between tyre and road. The solution lies in either using a single progressive design spring as seen in picture 1, or a helper tender spring as shown in picture 2.
This same design constraint leads to potential problems for the coil's longevity. The smaller diameter severely restricts the amount of material that can be used in the coil. Hence given a coil-over race spring and a lowered road spring for the same application, the road spring will almost always outlast a coil-over or race spring by a significant amount. Adding progressive or "dead" coils to the spring can also dramatically shorten the life span, as round spring steel bar does not like repeatedly hammering onto itself. This is not such a problem with a large road spring with lots of wire but it is a problem with a small race type spring.
Despite large budgets and clever technical solutions, it is not uncommon for top end race teams to plan for a life span of 1 spring set per race as they fatigue very quickly due to a relatively short life cycle compared with road springs. They also try to use as little material as possible to keep weight down. That's fine if winning is everything and money doesn't matter but this could mean your adjustable height road system may become automatically height adjustable as the spring sags with use.
Unfortunately this market is still young so it's too early to tell how long the name brand stuff is going to last but it would pay to ask some questions and seek some assurances from the manufacturer when shopping around. Go for a long warranty, as this would imply that the manufacturer has at least calculated the life cycles of the spring to make sure they suit road use.
The ideal solution is the helper spring system as it uses a special flat wire tender spring that is designed to collapse completely without stressing the material. These are used extensively by anyone serious about race performance. The tender spring rates also vary giving the chassis tuner a huge range of tailoring solutions for different tracks and drivers. These tender springs are typically fully collapsed at normal ride height so as not to deliver a progressive spring rate during compression or bump. Otherwise the shock absorber would need elaborate rate progression relative to travel to properly control the spring.
The last thing is that coil-overs are generally very noisy compared with the OE suspension because the components are often connected with out elaborate spring pads or insulators. The first problem is much higher levels of NVH but the second is that this can also result in premature cracking of body and chassis near the mounting points. The worst example is early subaru front strut towers, which often need strengthening and re-welding after prolonged use of coil-over systems but this problem is also common in many small 4 cylinder cars as the bodies were never designed for this type of use.
Though the noise issue is not really relevant for motor sport enthusiasts, it should be considered when looking at road use as the suburban "race track" unlike a real racetrack, is often poorly surfaced with big holes. Again, it would pay to ask questions about warranty and potential chassis problems.
Tender vs Helper springs
Helper and tender springs are both made from a flat wire spring that are designed to completely compress. In Whiteline's view, the difference is mainly in the application of the spring and at what point they close in the chosen application. This is obviously dependant on spring load, where a helper spring is generally known to close BEFORE normal load is applied, and a tender spring is generally known to close AFTER normal load is applied.
So, a helper spring in one application may be used as a tender spring in another application. For the same application, a helper spring generally will be softer then a tender spring.
uses of helper springs.
What about the shocks?
"Adjustable suspension" with ride height adjustment does NOT automatically mean adjustable shocks. Two separate things.
For a more detailed explanation of adjustable shocks, have a read of the Adjustable Shock section FAQ
As you could probably imagine, adjustable shocks would be particularly useful for a coil-over application. In fact, more positive suspension tuning results are generally achieved from adjustable shocks than adjustable height springs. An inappropriate spring rate can by masked by a good quality adjustable shock, but you can't change the spring rate or height to overcome a poor or inappropriate shock.
The most important thing therefore is to ensure that the shock supplied with the kit matches the springs, both in rate and performance characteristics. This is difficult enough to do for a suspension specialist armed with a shock dyno let alone the average customer so it pays to ask some specific questions and stick to known brands.
So what's available?
What is currently available on the market and how well they apply to American or other normal road conditions? Fortunately, the answer here is often quite simple, they don't. our road and driving conditions ARE the most diverse in the world. We have very good roads and we have some very bad ones and it is normal for the average enthusiast to experience both within a short period. Hence suspension designs have to cope with these diverse conditions and you can say with pride that the result is that we have some of the best handling products in the world. The same can also be found in almost any country in the world. Having a wonderful freeway system does not fix the problem of poor suburban and secondary roads. The problem lies in the expensive imports being largely (in our experience) unsuitable for road use on anything but smooth freeways.
Part of this is due to products being designed for racetrack use but sold for road cars. These are either imported from Asia as kits or arrive already fitted to performance grey imports. You would be surprised the number of times we remove these systems in response to customer complaints of poor ride AND handling. Unfortunately this stuff is sold largely for looks, both on and off the car, with the promise of race car handling but this is only possible if driving on the track at speeds high enough to require the high spring and shock rates. The outcome on suburban roads is crashing and banging of the undercarriage, skittish unpredictable cornering, terrible ride and almost non-existent suspension travel.
Locally developed solutions may be manufactured off shore but they should at least reflect a closer fit to your roads and conditions if they've done their homework. I would not like to suggest that the high-end imported name brand solutions are poor quality, just that they are rarely suitable for road use. As for the lower priced imports, watch out for cheap looking components because if it looks cheap, it probably is. Remember that there is more value in what you can't see like what's inside the shock, than what you can see like the coil springs. Also, watch out for simple external adjustment knobs for the shocks as these can be totally ineffectual and designed to con the consumer into paying a lot more for something, which is only marginally better.
So what should I buy?
Before you go out and buy one of these top end solutions, make sure you or the seller can adequately answer these questions:
So, if you need height adjustment, be ready for the pro's and con's. Ask yourself if you also need adjustable shocks and be prepared to ask a lot of questions because you are buying from the top shelf. Make sure there is a warranty involved and check how comprehensive it is. Be wary of imported solutions, particularly second hand ones as there is probably a good reason why they're for sale in the first place.
This is by no means the definitive guide as each sub section alone can justify a volume of books let alone all the components we have not covered yet. So, if you're interested in finding out more, let us know and we can recommend some other texts for you to read. Naturally this FAQ will be expanded as more questions are asked and we get round to answering them.
Springs
What Aftermarket Springs will and won't do?
Will Aftermarket springs lower my car 1 1/2" or 37.5 mm?
Will my tires scrub after fitting lowered springs?
What is "spring rate" and why should I know about it?
Motion Ratio, what are we talking about?
I want "progressive springs", but can you tell me what they are first?
Why don't I just cut my existing springs?
How low should I go – Control vs Flatout?
Bumpstops - are they important?
Coil-Overs and Height Adjustable suspension
What are they?
How do they work?
What are the Pro's and Con's?
What about the shocks?
So what's available?
What should I buy?
A Tender spring or a Helper spring?
What Aftermarket Springs will and won't do?
Springs models recommended WILL make your car handle better if matched with appropriate shocks and they WILL deliver a lower sporting look however I DO NOT condone cosmetic lowering solutions.
That is, rates and heights are calculated to try to deliver the optimum ride/handling outcome. I would not try to "even out" front to rear fender gaps as these are generally different for a reason. To do so would be to disproportionately lower one end more than another which could result in poor handling and ride through unwanted changes to weight and geometry.
We do sometimes change the front/rear height balance on some vehicles as part of an overall handling strategy but again, improved handling is the main target. Fender gaps are a misleading way to asses "rake" (the amount of angle rear to front). The only way to measure this accurately is at the bottom of the sill or rail under the doors. If a car looks even at the fenders, it will almost always have a VERY significant downward rake to the front.
Having said that though, I often refer to separate ranges of springs for popular vehicles. Street range springs are designed to deliver an optimum ride and handling compromise with an increase in spring rate coupled with a moderate decrease in ride height. This will vary between 25-40 mm depending on model as some cars are quite low from the factory. Also, factory sports options may already have a significant height reduction so the spring may not lower more than 15 mm but will have an increased rate tuned for sharper response.
If low is the goal I usually say go with a "race" spring. Though still acceptable for controlled road use, they are more suitable for track use where the surface is smooth and predictable. However, they offer the lowest ride height available in the range, up to 60 mm for some applications
Will X brand springs springs lower my car 1 1/2" or 37.5 mm?
Probably neither!
Irrespective of brand, it is impossible to confirm or guarantee how much a pair of springs will lower because of the variable starting point. That is, any cars standard height can vary enormously start including accessories and other modifications to the equation and we have a very complicated problem.
Add a few years or km’s of use (or mistreatment) and an absolute starting point becomes impossible to predict
Therefore, claims that any pair of lowered springs lower a vehicle a fixed or precise amount are wrong and misleading. However, there is some data that we can provide and that is the resultant fitted heights using Known Springs with a tolerance of +/- 5 mm. Note that this can only relate to a relatively standard vehicle as even mono-tube gas shocks can have an effect on the final height. Add sub-woofers or aftermarket strut top camber adjusters and this height can vary by 25 mm.
These fitted height measurements are taken from the centre of the wheel to the lip of the guard (fender) cut-out, measured at all 4 corners with the car parked on level ground.
These measurements are published in our kit Fact Sheets where available. We always encourage our customers to use these measurements to compare their existing heights with the proposed lowered height prior to purchase. This way there is no misunderstandings about the outcome.
Firstly, they are used to hold the weight of the car and secondly to deflect when required at a specified rate i.e. when the vehicle hits a bump or starts to pitch forward and back. In reality they work as an energy store. The spring is there to minimize the transfer of loads from the unsprung mass to the sprung mass. Or, to absorb as much of the shock, bump and pitch load the car is subjected to with out influencing or affecting the body and occupants. The damper or "shock absorber" then dissipates this stored energy. This process is also critical in maintaining tyre contact with the road. With out springs the car would simply bounce from bump to bump.
Springs should not be designed to limit body roll. When the vehicle is in roll the spring needs to be soft enough to absorb bumps. If the spring is stiff enough to control roll then it will be far too stiff when you have roll and a bump at the same time. The result again would be a car that jumps around requiring constant steering adjustments. Unlike many other springs, our Whiteline Springs range is designed to be as soft as possible for this very reason.
Will my tires scrub after fitting lowered springs?
Provided standard wheels and tyres are used and the manufacturer had provided clearance between the tyre, suspension and body work at FULL suspension travel, then lowering the ride height will not cause tyre-to-body interference or "scrubbing". That is, if you follow manufacturers maximum recommended options etc, everything should be fine. Lowering the vehicle simply relocates the wheel and tyre to a different point of its travel arc, it does not change the travel arc.
However, when fitting bigger wheels and tires it is important to keep within the original overall outside diameter and width relative to wheel offset. That is, fitting larger diameter tyres which dramatically increased overall diameter will probably lead to scrubbing problems. As will increasing width excessively or using the wrong offset. Simplest rule of thumb is that if it scrub now when loaded, it will scrub even more if you lower it but that's not the springs fault.
What is "Spring Rate" and why should I know about it?
A spring will be compressed when a load is applied. The distance it is compressed (deflected) for that given load is referred to as the spring rate. Spring rate is specified in terms of force applied per distance of deflection. Typically, the units of spring rate are pounds force per Inch or using the metric Sl system - Newton's per millimeter. We can just as easily convert the pounds into kilograms and measure the deflection in millimeters.
If a load of 1 kg deflects a spring 1-mm, each additional 1-kg will deflect it another mm. For each kg removed from the load the spring will return one mm toward its original state. The spring may be loaded at the rate of 1 kg per mm until it is deflected beyond its capacity. This means the spring will become damaged and will not resume its original characteristics when the load is removed. This point is called the elastic limit. A spring loaded beyond the elastic limit is deformed permanently.
In this example using linear design coils, both springs have 125 kg's of force applied to them. The standard spring has deflected 150mm from its original height. It therefore has a spring rate of 125 kg's per 150 mm, or 0.833 kg's/mm.
The replacement coil however with the same force only deflects 100 mm. Its rate is therefore 125 kg's per 100 mm or, 1.25 kg's/mm. It is a heavier spring.
Even though the replacement spring is 50 mm shorter, given the same weight, the ride height will be the same. However, because the spring is of a heavier rate, it will sag less, handle greater loads and often perform better in performance applications. A lowered heavier rate spring may be shorter again to deliver a lowered ride height with a heavier rate.
Motion ratio, what are we talking about?
Probably the most misunderstood component of the spring design function. The effective spring rate at the wheel is the only relevant number when discussing spring "rates". The actual rate of the spring itself is irrelevant without the knowledge of the effect of the motion ratio on that rate.
That is, it is rare that the spring moves up and do over the same distance as the actual wheel. For example, a HQ Holden front wheel may move up 50mm when hitting a bump but the spring will only move (compress) around 25mm. This is an example of a relatively large motion ratio. On the other hand, a strut based front suspension system delivers a relatively small motion ratio, typically around 90%. That means that the spring will deflect 90% of the distance the wheel deflects for any given circumstances.
This motion ratio changes the leverage and effective rate of the spring at the wheel. Hence a 500lb front spring for a Miata can't be compared with a GTO 300lb front. stick with a companay that designs its replacement springs to deliver the optimum spring rate AT THE WHEEL, not at the spring.
The accompanying picture shows the only case where motion ratio is not an issue with spring travel matching wheel travel. But, there's more. This picture may represent a situation with no motion ratio issue but it shows a possible further complication if we consider the wheel is fitted with a pneumatic tyre. This has its own inherent spring rate, which will impact on the spring rate at the wheel vs the coils physical rate. Tyre pressure, compound and build structure will all affect the tyres effective rate. In fact, most race tyre manufacturers will recommend an optimum spring rate range for their particular tyre. So the tyre and spring relationship is particularly important.
I want "progressive springs", but can you tell me what they are first?
This is often the reality of customers requests for progressive springs. Marketing hype has convinced them that progressive springs "are good" but not necessarily why, where or in what way. For those of you that know the answer, now's the time to look elsewhere. If you don't know, or think you know, no one can see you so read on.
A progressive spring can be defined simply as one that does NOT have a linear rate. This means that it's rate changes depending on the amount of deflection in a way that can not be plotted via a linear relationship. Typical examples are coil springs in a conical shape, those using variable wire thickness and most commonly, those with irregular gaps between the individual coils. It is also possible and common to see all of the above used in the same design. An example of this is GTO IRS rear coils.
Progressive spring designs for lowering cars are used to (in order of relevance)
- keep the spring trapped (legal requirement)
- sell to the customer (this is better just because it is progressive)
- easy solution for the designer
- duplicating the OE progression (e.g.; conical shape is progressive)
- actually is better for the vehicle to have progressive rate (rarely happens)
With lowered performance springs, we are more concerned with increasing the rate while lowering the ride height. Reducing the suspension travel creates its own complications but the last thing we need is a varying increased deflection rate that can not be matched by an appropriate damper or chassis mods to suit. In fact, performance applications are generally best served by a linear rate if possible.
Next time they try to sell you their " you-beaut lowered progressive" springs, ask them if they have some matching "progressive rate" shocks to suit. Also, ask the seller if the rate progression of the spring is designed to match the inherent rate progression of the vehicles chassis? For example, the EA-EL Falcon AND Honda Civic front suspension geometry has spring rate progression as part of its design. In fact, most suspension designs have sort of travel progression that leads to rate progression because the wheel moves in an arc. Adding progression to progression creates all sorts of problems so be wary of some manufacturers claims.
Good Springs are only progressive where and if they need to be.
Why don't I just cut my existing springs?
1. Many aftermarket lowered springs are designed to be just captive (held in place) with the wheel at full droop. This is a legal requirement throughout many countries. Cutting off a portion of the coil will reduce the free height (length of the spring out of the car), possibly to the point making the spring loose at droop. This can also happen with OEM springs but is more often a problem with aftermarket product.
2.Most springs are designed to a fairly tight tolerance of material volume to load carrying capacity. That is, the amount of steel used in the spring is hopefully just enough to hold up the car over the life of the vehicle with normal use. Chop off some coils and you've dramatically reduced the amount of material, which almost always will lead to an overstressed coil that will sag prematurely.
3.A reduction in ride height is normally coupled with a proportionate increase in rate to
offset the reduced bump travel. We need to slow down the compression of the spring enough to make sure we don't punch through to the shock at high velocity. A properly designed lowered spring will have a rate increase sufficient to offset this bump travel reduction.
4.The cutting method can also be a problem. Generating heat is not so much a problem as reduction in the heat afterwards. That is, heating the material beyond its temper and then rapidly cooling it will affect the composition of the material. A hack saw would be preferable but, irrespective of what tools you use, its not good practice overall.
How low should I go?
There are a couple of important points to note here. Firstly, that MAny "superlow" do deliver a greater "cosmetic" look compared to street versions. This is because the degree of lowering is generally in excess of what is optimum with standard dimension or configuration struts, shocks and suspension geometry. Once you get down to these sorts of changes from standard, there are a whole range of issues that need attention like significantly modified shock dimensions for increased bump travel, relocation of key suspension pickup points to counter roll center changes and many others.
All in all, at extra low heights, standard components cannot possibly deliver good objective handling outcomes particularly on the road where suspension travel is SOO important. The second issue is that most extra low springs in any brand are the same rate (sometimes actually softer) as low springs because of physical design constraints to meet the competing objectives.
The lower the spring ride height, the higher the rate needs to be to compensate for the reduced bump travel. The weight of the vehicle presumably stays the same so we need some more spring rate to compensate for the reduced compression travel available so we don't either crash through the shock or pogo up into the atmosphere after bouncing off the bump stop. (Even after we've shortened it).
Now, in the case of a strut equipped car like the WRX, the lower you go from standard, the more the front roll centre and roll couple geometry starts working against you. This leads to the effective wheel spring rate reducing in roll even though the physical rate at the spring is the same. Under bump the rate may be the same but there is a compounding reduction in rate as the car corners with the roll centre migrating well below ground.
Some brands do manage to increase the spring rate for extra low but only by using an increased number of "Dead" progressive coils that simply close up and remain ineffective once fitted. This is OK in theory but not unless the remaining "active" coils are up to the task of supporting the weight of the vehicle 24/7 let alone dealing with high impact performance loads. In our case, we will not reccomend a spring design unless it meets key design criteria and simulated life cycle tests.
I'm sure many people know of performance springs that have sagged prematurely and generally this is because of the conflicting design goals and the very fine tolerance involved. One vehicle with extra low springs may simply do boulevard cruising while another may get involved in spirited driving, its not hard to work out which is more likely will suffer "automatic lowering" as we call it.
we know what happens in terms of grip and handling with "lowering" springs and
standard shocks. On a nearly perfect surface using near new stock shocks, the "street" springs are “grippier” in terms of lateral G’s and faster than stock. We have also tested this result on the track with the same outcome but we know that even partially worn shocks or poor road surface changes the result dramatically. There is no point testing same with Race springs because we know from experience that it’s a backward step with out other modifications like shock upgrade or significant geometry changes.
The preload issue is therefore a consequence of the design constraints. major springs are designed to have some preload on full extension when using standard dimension shocks at worst. Sufficient preload to keep the spring in place and stop it from relocating so I would be confident that though you may be able to move the spring a little, you could not move it to the point that it can incorrectly seat on the shock.
I’m not sure about the comment of “working with standard shocks” being fine though. We do not quote that anywhere, as it’s too much of an open statement. Yes, our springs will physically fit in the space as determined by the shock and suspension geometry but they are not designed to work with standard dampers, NO aftermarket lowered or heavier rate spring is. The street springs are less likely to cause problems where as using race springs with stock shocks is asking for trouble.
Coil overs and height adjustable suspension.
What are they?
Often referred to as simply "adjustable" suspension but specifically refers to height adjustable suspension. Also known as "coil-overs", "height adjustable struts". Like many other trends, the technology is derived from motor racing with a variety of different kits now being sold for road use. And, like many other trends that a lot of people jump onto, there are a lot of factors that need to be considered before spending money on what is considered to be the top end solution for performance suspension.
Main reasons for use on road vehicles (in general order of actual use.)
- pose/style value - "trinket" factor
- ability to achieve much lower ride height legally (if used in conjunction with shorter shocks) than available through conventional means.
- flexibility to change overall height for car shows etc.
- flexibility to change overall height for mid-week road vs weekend track use
- flexibility to use a suite of various rate coils for different track conditions.
- flexibility to change overall and/or specific corner heights and rates for optimum chassis tunning.
How do they work?
Most height adjustable systems use a threaded sleeve on the outside of the strut or shock body to lower or raise the base height of the coil. Because the other end of the spring is held by the shock or strut, changing the height of the spring seat acts to increase or decrease the pre-load on the spring. Because the weight of the car remains the same, this has the effect of changing the ride height. To try to make it a little clearer, suggest you look at our Whiteline web site FAQ on spring rate
The important point to note is that you don't change the actual rate of the spring by changing the seat height position. In the case of raising the springs seat, we simply force it higher up its rate curve, which means the weight of the car will not deflect the spring as far resulting in a higher ride height.
What are the Pro's and Con's?
Apart from height adjustability, a major benefit of these systems stems from the fact that they use a "race coil" with reasonably standard dimensions. There are a number of common inside diameters like 50/53/57/60/63/65mm which are a conversion from Imperial measurements. The most commonly used sizes are 60, 63 and 65mm with a few companies offering off the shelf units in a variety of lengths and rates with a standard inside diameter. This allows serious chassis and suspension tuners to change the spring rate and style for different tracks and environments, but this is only relevant if the shock rate is also adjustable.
These relatively small diameters do come with several down sides. The first is a restriction as to the maximum spring rate that can be used while maintaining captive spring height. In fact this is contradictory to the main use of the system such as high spring rates for racing applications. As the designed spring rate goes up, the "free" or fully extended height of the spring must become shorter to maintain the same relative ride height. This means a greater need for "progressive" or other design solutions to avoid severely restricting suspension travel. VERY relevant for rear of front wheel drives.
The other problem resulting from small springs and heavy rates is the restriction of total suspension travel, which is a problem for all road cars. Given a billiard table smooth surface, we really wouldn't need springs at all but even the best racetrack has bumps and undulations, let alone the corner kerbing and ripple strips. The best suburban roads require at least 100mm of total suspension travel to ensure contact between tyre and road. The solution lies in either using a single progressive design spring as seen in picture 1, or a helper tender spring as shown in picture 2.
This same design constraint leads to potential problems for the coil's longevity. The smaller diameter severely restricts the amount of material that can be used in the coil. Hence given a coil-over race spring and a lowered road spring for the same application, the road spring will almost always outlast a coil-over or race spring by a significant amount. Adding progressive or "dead" coils to the spring can also dramatically shorten the life span, as round spring steel bar does not like repeatedly hammering onto itself. This is not such a problem with a large road spring with lots of wire but it is a problem with a small race type spring.
Despite large budgets and clever technical solutions, it is not uncommon for top end race teams to plan for a life span of 1 spring set per race as they fatigue very quickly due to a relatively short life cycle compared with road springs. They also try to use as little material as possible to keep weight down. That's fine if winning is everything and money doesn't matter but this could mean your adjustable height road system may become automatically height adjustable as the spring sags with use.
Unfortunately this market is still young so it's too early to tell how long the name brand stuff is going to last but it would pay to ask some questions and seek some assurances from the manufacturer when shopping around. Go for a long warranty, as this would imply that the manufacturer has at least calculated the life cycles of the spring to make sure they suit road use.
The ideal solution is the helper spring system as it uses a special flat wire tender spring that is designed to collapse completely without stressing the material. These are used extensively by anyone serious about race performance. The tender spring rates also vary giving the chassis tuner a huge range of tailoring solutions for different tracks and drivers. These tender springs are typically fully collapsed at normal ride height so as not to deliver a progressive spring rate during compression or bump. Otherwise the shock absorber would need elaborate rate progression relative to travel to properly control the spring.
The last thing is that coil-overs are generally very noisy compared with the OE suspension because the components are often connected with out elaborate spring pads or insulators. The first problem is much higher levels of NVH but the second is that this can also result in premature cracking of body and chassis near the mounting points. The worst example is early subaru front strut towers, which often need strengthening and re-welding after prolonged use of coil-over systems but this problem is also common in many small 4 cylinder cars as the bodies were never designed for this type of use.
Though the noise issue is not really relevant for motor sport enthusiasts, it should be considered when looking at road use as the suburban "race track" unlike a real racetrack, is often poorly surfaced with big holes. Again, it would pay to ask questions about warranty and potential chassis problems.
Tender vs Helper springs
Helper and tender springs are both made from a flat wire spring that are designed to completely compress. In Whiteline's view, the difference is mainly in the application of the spring and at what point they close in the chosen application. This is obviously dependant on spring load, where a helper spring is generally known to close BEFORE normal load is applied, and a tender spring is generally known to close AFTER normal load is applied.
So, a helper spring in one application may be used as a tender spring in another application. For the same application, a helper spring generally will be softer then a tender spring.
uses of helper springs.
- Simplicity. In a tender spring system, the specifications of both main spring and tender springs are absolutely critical for the system to work properly.
- Noise. In a helper spring system, as the helper is closed at normal ride height, there is minimal spring noise. In a tender spring system, the tender is designed to close during suspension compression potentially creating noise
- Spring rate tuning. In a helper spring system, it is very easy to change springs for tuning purposes. In a tender spring system it is a much more complicated process, and will require both new main and tender springs.
- Vehicle corner weight tuning. In a helper spring system, adjusting the height of the spring platform directly effects the height of the main spring. In a tender spring system, platform adjustment compresses the tender spring and main spring at the same time.
What about the shocks?
"Adjustable suspension" with ride height adjustment does NOT automatically mean adjustable shocks. Two separate things.
For a more detailed explanation of adjustable shocks, have a read of the Adjustable Shock section FAQ
As you could probably imagine, adjustable shocks would be particularly useful for a coil-over application. In fact, more positive suspension tuning results are generally achieved from adjustable shocks than adjustable height springs. An inappropriate spring rate can by masked by a good quality adjustable shock, but you can't change the spring rate or height to overcome a poor or inappropriate shock.
The most important thing therefore is to ensure that the shock supplied with the kit matches the springs, both in rate and performance characteristics. This is difficult enough to do for a suspension specialist armed with a shock dyno let alone the average customer so it pays to ask some specific questions and stick to known brands.
So what's available?
What is currently available on the market and how well they apply to American or other normal road conditions? Fortunately, the answer here is often quite simple, they don't. our road and driving conditions ARE the most diverse in the world. We have very good roads and we have some very bad ones and it is normal for the average enthusiast to experience both within a short period. Hence suspension designs have to cope with these diverse conditions and you can say with pride that the result is that we have some of the best handling products in the world. The same can also be found in almost any country in the world. Having a wonderful freeway system does not fix the problem of poor suburban and secondary roads. The problem lies in the expensive imports being largely (in our experience) unsuitable for road use on anything but smooth freeways.
Part of this is due to products being designed for racetrack use but sold for road cars. These are either imported from Asia as kits or arrive already fitted to performance grey imports. You would be surprised the number of times we remove these systems in response to customer complaints of poor ride AND handling. Unfortunately this stuff is sold largely for looks, both on and off the car, with the promise of race car handling but this is only possible if driving on the track at speeds high enough to require the high spring and shock rates. The outcome on suburban roads is crashing and banging of the undercarriage, skittish unpredictable cornering, terrible ride and almost non-existent suspension travel.
Locally developed solutions may be manufactured off shore but they should at least reflect a closer fit to your roads and conditions if they've done their homework. I would not like to suggest that the high-end imported name brand solutions are poor quality, just that they are rarely suitable for road use. As for the lower priced imports, watch out for cheap looking components because if it looks cheap, it probably is. Remember that there is more value in what you can't see like what's inside the shock, than what you can see like the coil springs. Also, watch out for simple external adjustment knobs for the shocks as these can be totally ineffectual and designed to con the consumer into paying a lot more for something, which is only marginally better.
So what should I buy?
Before you go out and buy one of these top end solutions, make sure you or the seller can adequately answer these questions:
- What am I going to use it for and do I really need it?
- Is it just ride height adjustable or are the shocks adjustable as well?
- What is the total available suspension travel of the system compared with the original? That is, how much has it been restricted?
- Does it use adequate bump stops?
- Are the spring rates designed for road or race use?
- Are the coils designed for road or race use, from a longevity point of view?
So, if you need height adjustment, be ready for the pro's and con's. Ask yourself if you also need adjustable shocks and be prepared to ask a lot of questions because you are buying from the top shelf. Make sure there is a warranty involved and check how comprehensive it is. Be wary of imported solutions, particularly second hand ones as there is probably a good reason why they're for sale in the first place.
Last edited by treekiller; 06-10-2009 at 12:12 PM.
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