Air gap when using fork sub-tanks

[tankslapper]

I normally set the air gap on say KYB forks for an average rider at about 100mm, I have heard when using sub-tanks that the air gap should be set smaller (higher oil level), is this true? I would have thought that setting a higher oil level when using sub-tanks would defeat the object of fitting the tanks!

If this is correct then what would be a typical air gap with the tanks fitted on KYB forks for an average rider?

 

[KTM-Lew]

I believe 80mm is the spec. The sub-tank adds about 100mm of air-space to the system with the adjuster all the way out. (generalized explanation)

The idea is that on small, slower speed impacts, the air travels into the sub-tank easily. The line that connects to the cap has an adjustable orfice so you can adjust the "response time" of the air flow. As the adjuster is closed the "response time" is delayed and the effect is like having a much higher oil level when the susp is compressed quickly and deeply into the travel.

 

[marcusgunby]

I thought you halved the normal airgap-so 100mm becomes 50mm??

 

[tankslapper]

I understand the principle of how the tanks work but I cannot see why we still need to raise the oil level. It kinda defeats the object in my mind. We are trying to make the forks softer on the small choppy stuff but then we raise the oil height which will surely lose what we have gained in plushness.

 

[Jaybird]

If you understood it, you'd see it.
If you had no extra air space with a higher oil level, then yes it would stiffen it up...but you have added airspace wich allows for the softer feel during short strokes, as if you had a lower level. When the suspension is stroked hard and fast, the restriction at the air flow controls keeps the air from moving into the chambers quickly, and allows the higher oil level to do it's job.
Sorta the best of both worlds. It's a speed and volume thingy.

Not trying to be smart, just stating facts.
It's actually an ingenious design.

 

[tankslapper]

ok i know what you mean but I recently tested a pair of sub tanks on a 03 KTM125SX, I left the air space standad at 100mm and after experimenting with the restrictor position we found the tanks worked well on small stuff but was still ok on big hits with no sign of bottoming the forks. In this case would you still add the extra oil?

 

[KTM-Lew]

Did you modify the bottoming cones to allow full travel? The WP are known to have too long a bottoming cone, usually you can't get the last 30-35mm travel, even on a big hit. Makes it kinda hard to know if they are "bottoming"!

I'm in the process of trying them for off-road use (GNCC type). Just got to get the time! :(

 

[tankslapper]

Lew, no I did not modify the bottoming cones, what work does that involve?