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Swift Coilover Springs

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Nearly 10 years ago Swift began selling coilover replacement springs in Japan to tuner shops and performance auto retailers. Most of the time these shops were puzzled why anyone would sell “replacement springs"* for coilover systems since they all came with springs already. Now Swift springs are regularly sold in shops. Once people saw replacing springs can improve the comfort of the ride, coilovers on the street became more and more popular.

Swift Springs are a Linear Spring as opposed to Progressive, here is what the means to you:

Well linear spring theoretically keep the same spring rate regardless of stroke.
If you have a 6kg/mm linear spring, if you compress it 10mm it should only take an additional 6kg to compress another mm. Therefore, if you compress a linear 6kg/mm spring with 60kgs of force, it will compress 10mm.

Linear Spring Characteristics
The benefit of a linear spring is consistency, meaning the weights transferring from side to side should be very smooth and consistent. After getting use to the car dynamics, drivers can anticipate weight transfers and body roll more accurately. While exiting a corner, a linear spring will return the body in a smooth manner because both sides are compressing and rebounding at the same rate, which keeps one mm of expansion to one mm of compression throughout the traction of the springs. This reduces the demand for excessive counter steering, which can result in fish tailing. For winding roads driving, this has great benefit and allows for more confident use of weight transferring because the driver won't experience unpredictable weight shifts.

Progressive springs are springs that gradually increase spring rate as the spring compresses. So, if the spring starts out with a 6kg/mm spring rate after 50mm of compression it may then measure 17.75kg/mm.
Using the above example a 6kg/mm linear spring will take 300kg to compress 50mm while it will take 594kg to compress the progressive spring.

Progressive Characteristics
Say you are cornering with these progressive springs, you have compressed your outside spring by 50mm (a little over 2"). While you are exiting the corner the centrifugal channeled inertia (the force that causes body roll during cornering), reduces, allowing the body roll to stabilize. You now have an outside spring that has stored 17.75kg/mm of force. As the centrifugal inertia reduces, it throws the outer side of the chassis up with 17.75 kilograms per/mm of force, roughly 950lbs/ inch of force.

Since suspensions are designed to keep the vehicle level that force throwing the outside of the chassis up will be partially transferred to the opposite side. But the outside spring has not compressed during cornering so it will absorb the transferred energy at 6kg/mm of compression so for the first mm the outside releases, will translate to almost 3mm of compression on the inside. As the outside spring releases the excess energy and the inner springs absorb it, the ratios gets closer to 1:1, it may even change back and forth. This is excessive body roll requiring more attention and finesse to effectively control. While negotiating chicanes it can make steering extremely complex and demanding compared to what linear spring would produce. Please use the chart below to see the differences in the linear and progressive spring characteristics.


Swift offers a variety of widths (60mm, 65mm, 70mm), lengths (5"-11") and rates (4kg-34kg).  In addition they offer Helper/Assist springs as well.  Please review the Swift Coilover .pdf document below for available coilover springs, then contact us for details before ordering.

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