This is one of the most common questions we hear when it comes to your suspension‘s springs. Many people insist to the last man that linear is the only way to go – but the reality is not black and white.There are a few basic things you should know about what each type of spring is good for. Think about the words, “Proven on the Racetrack”… while this is a phrase we’ve used ourselves, in the context of suspension, believe it or not, this could be a bad thing.
Why? Let’s look at what the real world driving situations are like: Racetracks are carefully paved and maintained, kept free of potholes, bumps and debris. Most consumers will base their opinions off of manufacturer research and development – and this explains the overwhelming preference of the internet, collectively, for linear rate springs. And even a normal road requires significant work to convert over to a proper racing course (see the Long Beach Grand Prix’ street circuit or Monaco and you’ll see what we mean) – normal streets just aren’t that smooth. God forbid you live somewhere gets “Frost Heaves”.
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Have you ever seen what happens if you try to use racing only tires on the street? They don’t work well, do they? Racing tires work great on a track because they’re within their “operating range” for temperature, but on the street they don’t get warm enough and as a result can have less grip than a standard commuter tire on surface roads. The best solution for a racetrack probably will not be the best solution for your local roads because what’s demanded of the suspension is totally different.
Straight Springs – aka Linear springs, have a spring rate that is consistent along the entire length of the spring as it is compressed. Progressive springs on the other hand, have a spring rate that increases or changes with the compression of the spring. An easy way to tell progressive rate from linear rate springs visually is that a with a progressive spring, the amount of space between every winding, or coil, of the spring is different. Springs are available in Linear and Progressive rates (though predominantly progressive) from such manufacturers as Eibach Springs, Vogtland, Swift Suspension, H&R Suspension, Hotchkis Springs, Whiteline and more.
What Are Linear Springs?
The key benefit of a linear rate spring is that it is easy to understand and set up for just about anyone, because there is only one variable to control, since the spring rate is consistent. Because of that consistency, it’s very easy to calculate out how the spring will behave under various conditions. This is what makes linear rate springs so advantageous in racing. On a road race course, you want to know exactly what the suspension is doing, when it’s doing it and where it’s doing it on the track. The only way to do this is when the spring behaves the same way under different conditions around the track to create a consistent handling pattern for the car. With that constant rate to work with, you can figure out exactly what spring rate you want under a very specific set of conditions to give you the best response, feel and traction.
However, since the spring has only one possible way to react, the ride is very stiff and responsive – Linear Rate springs are not really comfortable for street use, since the needs of a road car’s suspension vs a track car’s are very very different.
What are Progressive Springs?
The variable spring rate is what sets this apart – progressive springs react in more than one way, depending on what sort of demand is being made. Because there is more than one possible behavior for the spring, it’s harder to predict its behavior on any tarmac. When it comes to suspension, we have to look at what our desired outcome for the car is – we want it to handle well AND also dampen bumps in the road for a less bone-jarring ride. We want straight line comfort combined with sharp turn in with good feel and control – it’s impossible to have a suspension set up that does all three things perfectly, so the name of the game is compromise. As you tip the scale towards comfort, you lose out of handling – and vice versa. However, with a progressive rate spring, we can get close and can achieve a happy balance with a spring that’s at a low rate when least compressed and a high rate when most compressed. In a corner, the increased load on a progressive spring, causes the car to squat as the suspension is compressed, the comfortable rate for straightline cruising giving way to a stiffer rate that transmits feedback and creates a “planted” feel. The faster you drive, the most feedback and feel the spring will give you, but in a road car application.
So, Generally speaking, a progressive rate spring will be the better choice for a car that is going to see any time on surface street as it is better set up to deal with the demands of street driving, but if you’ve got a trackday-only toy, linear is a great way to go. As a result, most aftermarket springs – sport/lowering springs and coilovers – feature progressive rate springs unless you specify a specific linear rate spring.
Regardless of whether you want to go progressive or linear rate, it’s important that you choose a spring that’s correctly set up for your car – a badly set up straight spring is just as bad as a poorly set up progressive spring. So, does all this mean that all progressive springs are better than straight and that everyone else is just talking nonsense? Not at all – it’s got everything to do with the car you’re working on and the conditions you plan on using that car in.
Story by Nicholas Gregson