Are Progressive Springs what my Vanagon really needs?
- A progressive spring is simply one that does not have a linear rate. This means that it's compression rate changes depending on the amount of deflection. This can be accomplished by a few different designs:
- variable diameter (like a stock Vanagon rear spring) coil thickness
- irregular gaps between the individual coils. The original Vanagon front springs are not progressive, while the rears are.
- They can be wrong for a vehicle that was not designed for them. They are softer under small displacements and get stiffer as the spring compresses. This is supposed to make the ride more comfortable, but matching a damper to them is tricky, so the damper may only be properly matched during part of the suspension travel. Generally it will have to be soft, so it doesn't overdamp the lower displacement part of the spring, which makes it too soft for the high displacement rate of the spring. Basically, they're good for a smooth ride with properly designed light or variable damping.
- Some original equipment manufacturers use progressive designs to allow for some suppleness during initial spring deflection. This allows for a heavier rate to be used once the lighter rate coils go "dead" or bind making them ineffectual. These clever designs are carefully matched to the dampers, swaybars, bushes and chassis design to create a tuned solution.
- For those that sell progressive springs for a vehicle that didn't originally come with them, ask them if they have some matching progressive rate shocks to match. Also, ask the seller if the rate progression of the spring is designed to match the actual rate progression of the vehicles chassis? Most front suspension geometry has spring rate progression as part of its design, a travel progression that leads to a rate increase because the wheel moves in an arc. Adding progression to this type of suspension creates all sorts of problems so be wary of manufacturers claims.