6 over tubes

[Wildone385]

99 fxdwg i know the stock tubes hold 10.2 oz of fluid what do i need to add to 6 over tubes i figures 2.5 more but im getting alot of different answers including leave it at 10.2 thanks for any help

[Ohio HD]

Tube length shouldn't effect the fluid volume the dampeners need. Leave it as the manual calls for.

[Wildone385]

Thank you I will leave it at book level

[04 SE Deuce]

Ideally you want to maintain the same "air space" above the fluid level if you want the forks to have the same performance or total spring rate to include the air spring rate which effects the spring rate deep into the stroke prior to bottoming.  Air volume effects the progressiveness of the fork spring rate.

The forks springs being used and how well suited they are to your application and riding style effects tuning or oil level.  Also the added rake of the 6" over tubes makes the fork effectively stiffer.

In general if you want the fork to perform the same keep the air volume in the fork the same.  That would mean you need to add fluid for the additional 6" of tube minus the volume of 6" of preload spacer. 

Using a fork tube I.D. of 1.375 the volume of 6" is 4.93oz.  You need to reduce that by the volume of 6" of preload spacer which is approx. .5oz to 1oz depending on the wall thickness...don't know if your using thin metal or PVC.

4.9 (fluid to fill 1.375" by 6") - 1oz (for spacer volume) - .5oz (for added rake) = 3.4oz additional per leg.

Another simple way to do it is to measure the fluid level front top of tube to fluid level with springs removed, forks fully bottomed, after moving through stroke a few times slowly to purge any air.  Set at approx. 7".

[Wildone385]

Thank you