"What is the difference in progressive and linear springs?"
Well linear springs 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.
The Swift Spec-R Sport Springs are engineered with redesigned lowered ride height to maximize the suspension performance, allowing the vehicle to fully absorb road condition for maximum traction and increased spring rate (based on the vehicle's factory valve settings) to further enhance cornering speed through entry & exit.
2008-2013 E9X M3 (Front -1.0" drop, 279lbs/in; Rear -0.7" drop, 670lbs/in)
Please contact myself or joe@trinityautosport for any orders and inquiries.