Fork air gap.

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   Fork oil change time on a Guzzi  Le Mans I've fitted cartridge type dampers from a VFR750 to the oem forks which originally used a sealed damper and only used a small amount of atf as a lubricant.When the forks were rebuilt with the cartridges I used the VFRs air gap as a guide and add an extra 30cc of fork oil. The original air gap used was approx 180mm. Since then I've changed the fork oil on various bikes and 180mm now appears quite a large air gap; I doubt the extra 30cc made more than a few mm difference. 
Is there a set ratio to determine the air gap for a specific fork i.e. set the air gap at a % ratio of the internal volume of the stanchion based on fork travel or am I best just experimenting. As built, the cartridge equipped forks never bottomed out and I'm using Silkolene RSF 5w oil as opposed the Motorex Racing 5w in the forks atm; the RSF has a very slightly higher cStk value than the Motorex.
Would value any input from those in the know.

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Stevex Members Profile Send Private Message Find Members Posts Add to Buddy List Moto GP Alien Joined: 05 Jul 2016 Location: UK Status: Offline Points: 1481	Post Options Post Reply Quote Stevex Report Post Thanks(0) Quote Reply Topic: Fork air gap. Posted: 16 Feb 2025 at 22:37
	Fork oil change time on a Guzzi Le Mans I've fitted cartridge type dampers from a VFR750 to the oem forks which originally used a sealed damper and only used a small amount of atf as a lubricant. When the forks were rebuilt with the cartridges I used the VFRs air gap as a guide and add an extra 30cc of fork oil. The original air gap used was approx 180mm. Since then I've changed the fork oil on various bikes and 180mm now appears quite a large air gap; I doubt the extra 30cc made more than a few mm difference. Is there a set ratio to determine the air gap for a specific fork i.e. set the air gap at a % ratio of the internal volume of the stanchion based on fork travel or am I best just experimenting. As built, the cartridge equipped forks never bottomed out and I'm using Silkolene RSF 5w oil as opposed the Motorex Racing 5w in the forks atm; the RSF has a very slightly higher cStk value than the Motorex. Would value any input from those in the know.
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Spoonz Members Profile Send Private Message Find Members Posts Add to Buddy List Admins Group Joined: 11 Feb 2008 Location: North Devon Status: Offline Points: 10957	Post Options Post Reply Quote Spoonz Report Post Thanks(0) Quote Reply Posted: 16 Feb 2025 at 23:24
	I’m not aware of any formula for oil volume to chamber capacity. If it doesn’t bottom but you are still able to use about 90% of the travel in general riding I would say you’re not far off. The amount of travel you are getting is the critical thing as that is the factor air gap influences most.