Spring seats in twin chamber forks.
The spring seat in a twin chamber fork is located on the outside of the cartridge and retains the main spring in its position at the bottom of the fork. Its pivotal role is simply one of location, although some over imaginative tuners see the spring seat as a source of tune……hmmm.
There has been talk of spring seats in twin chamber forks being a source of harshness due to a restriction of oil flow. The restriction supposedly occurs as the fork compresses and the oil in the bottom of the outer chamber is forced past the seat and into the upper region. A simple measurement will show that the oil will have greater difficulty getting past the spring itself rather than the spring seat.
Changing the seat for a “high flow” unit will only change your bank balance.
Others have taken the opposite approach and produced spring seats that in fact are highly restrictive. This is done in an attempt to control bottoming. I question the validity of such a device. The oil in the outside chamber does not stay put at the bottom of the fork. Think “cocktail shaker”….. The oil is constantly moving up and down as the bike is in motion. The rougher the terrain, the greater the disturbance. The restrictive seat will only work when a reliable amount of oil is situated below it. Once this oil is forced past the spring seat the restriction works in reverse. In other words, what made it difficult for the oil to get to the upper region of the outer chamber is now preventing the clear passage for the oil to return to the bottom of the fork. This makes the spring seat an unreliable and totally inconsistent option for a tuner.
With so many areas of tune in the modern fork I question the need for this one. If you still find your fork bottoming after adjusting spring rate, compression valve, mid valve, oil height and clickers, perhaps your money is best invested in a new tuner.