Air Expansion Tanks.... Something Good??

[woodsracer250]

Hi everyone,

I was wondering if Air Expansion tanks for a fork are the "Hot Ticket" and are sure to be the next greatest thing or are they just someone's hopeful idea??

It's something that you remove the bleeder screw at the top of the fork and replace it with a fitting that has a hose attached which then goes to a cylindrical tank behind the front number plate for each leg with the two "tanks" connected by a crossover tube.

Is this a hot setup or one of those things that the inventor will likely end up with a garage full of parts for life??

Just wondering...

 

[whenfoxforks-ruled]

Do they have a brand name? They are all older forks can get, some can change valving? I have a pair from the mid 70's. Vintage Bob

 

[RM_guy]

You are talking about fork sub-tanks and they have been around for years. In a nut shell they add extra air into the system with adjustable valving that makes them speed sensitive so they react softly on slow speed hits but are stiffer on high speed hits. They work amazingly well. I have a set of Enzo sub-tanks on my bike and they work great.

For the Enzo tanks you have to drill out the air bleed screw and add a fitting for the tank hoses. This is what you want. The other brands just screw into the bleed screw. The problem with that is the air bleed hole is too small to let enough air through and the hole becomes an orifice that restricts the air flow too much. The tanks have valving in them to adjust the ride but the small bleed hole renders the adjustable valving ineffective and you loose the speed sensitivity.

The other brands work OK but if you really want adjustability and the full affect of what the tanks can do, get the Enzo sub-tanks.

 

[whenfoxforks-ruled]

The tanks I have, there would be no benefit from drilling the cap hole larger, all the rest of the fittings are 1/4" flare fittings, connector lines, and some compression also. I will try and ask Jeremy about that. I am really hoping they do something to help bottoming shock. No pressure on the inside schrader, and 140 or so on the outside? Race Tech is pretty good for marketing a lot of bolt ons, I might as well have their valves in both ends. A lot of people swear by them, and anything will help! 81 showa started with compression adjusters, 83 they added rebound. 84 and on for any resemblance of a decent shock or fork. After market was making serious stuff around the late 70's!

 

[RM_guy]

...there would be no benefit from drilling the cap hole larger...

Not true. Do your homework.

 

[whenfoxforks-ruled]

Care to explain?

 

[RM_guy]

...The problem with that is the air bleed hole is too small to let enough air through and the hole becomes an orifice that restricts the air flow too much. The tanks have valving in them to adjust the ride but the small bleed hole renders the adjustable valving ineffective and you loose the speed sensitivity...

The fitting that screws into the air bleed hole makes it even smaller.

 

[whenfoxforks-ruled]

It is all the same size fittings. 1/4" into the fork cap, and 1/4" going into the sub tank. They make a few different styles and brands over the years, mine are from Ottow's Works, circa 1975. Enzo and Race Tech swear by these contraptions, some do not, they swear at them. If the tank has a larger fitting, on yours, then yes, a larger hole in the air cap would be required. There is also emulators available. They copy valving and actually go inside some models of forks. I have heard tell they do emulate rebound dampening.