Linear rate coil: A linear rate coil has a constant  rate throghout its movment. For example if a linear coil has a spring rate of 100lbs/in then for every 100lbs placed on the coil it will compress one inch, the next 100 lbs will compress it another inch and so on.

Progressive coil: A progressive coil will increse spring rate at a certian designed point in its compression cycle.

We use linear rate coil springs over a progressive or multi rate coils as we have found they offer the best perfromance and durability for our application.

While multi rate coils have there place and can provide excellent perfromance in the right applications there is simply not enough up travel from ride height on the HD Ram platform before the coil progresses into the higher spring rate to work properly. Once the coil has gotten into the higher spring rate not only does the compression force rise but so does the rebound force and this can lead to a harsh ride compared to linear rate coil.