April 13, 2023 2 min read
Increasing spring preload on a linear spring does not increase spring rate. Spring preload is not spring rate. Let’s get that out of the way first.
A linear spring is linear...meaning that the spring rate stays the same no matter how much it is compressed.*
Even popular tuners get this wrong. To change your spring rate, change your springs.
*No spring is perfectly linear, but most good quality coilover springs are linear enough. Swift, Hyperco, Eibach, and KW Race, are all good.
The progressive springs on the rear Bilstein coilovers above do change spring rate with increased preload.
The front linear springs on the coilover units above do NOT change spring rate with increased preload.
At “zero” preload, the spring perch is just barely touching the spring with the car in the air. Anything less than zero preload would mean the spring could potentially unseat from the perch when the shock extends.
Increasing preload raises the car. It will also increase your compression travel and reduce your droop (or extension) travel.
Reducing preload lowers the car and reduces compression travel. It also increases your droop travel.
Increasing spring preload here raises the car, increases compression travel, and reduces droop travel.
Dual height adjustable coilovers allow a user to adjust ride height separately from spring preload. This type of construction is usually the byproduct of a cost saving measure, but it can be useful.
Other coilovers use preload to adjust ride height. They often include helper springs, which are a low rate spring that keeps the main spring seated with minimal preload. They might have a narrower height range, but more total travel.
Dual-height adjustable coilovers like these Öhlins should be adjusted carefully. Even with a small drop from stock ride height, the car may have insufficient compression or droop travel.
Zero preload with very soft springs will result in limited compression travel.
Very stiff springs may require helper springs for adequate droop travel.