Air Pressurized Forks?

[Flywheel]

While doing research on streetbikes from the 80s, I noticed many of them featured forks (and occasionally rear shocks) that could be pressurized with air. Was it a gimmick to cover for cheap components, or a decent concept that couldn't be reliably engineered at the time? I gather it was supposed to allow the rider to "fine tune" the suspension for a passenger, crummy roads or more aggressive riding (strange considering many were cruisers).

It couldn't be totally bogus, as some 2013 MX bikes feature springless forks ("air" forks).

 

[TwistedKestrel]

It had two effects. One was that it provided a form of progressive damping, as the air compressed at a different rate than the spring in the fork. The other was that it provided a form of adjustability. My VF500F had them as state of the art technology, and combined with the anti-dive system I think they actually worked pretty good. The shock on it was also air pressurized.

I think that combined with anti-dive, it's a superior setup than just plain damping rod forks, but inferior to modern cartridge forks.

Edit: if you're buying a bike with this type of suspension, you might want to check if it still works with a pressure gauge and a hand pump before you buy it. It was not hard to blow out the air seals on them if an air compressor was ever attached.

 

[kneedragger88]

Dumbest idea EVER. All they were really good at doing is blowing out fork seals. By adjusting oil level you create the same effect. Oil doesnt compress. Air does. Worse part is IF people use the air in the forks 99% of the time they do it Waaaaaaaaaay to much. It should be no more than 4psi. Most manuals will tell you 6 but in my experience thats too much. Its also almost impossible to get that low of a pressure using a high pressure air line. Best to use a hand pump or the local gas station compressor.
Better yet adjust the oil level and dont use it all. Just my opinion

 

[GreyGhost]

Many MTB forks use air as it saves some weight and allows a lot of adjustability. The system is relatively high maintenance (you have to check the pressure occasionally as it can leak, unlike springs which last for years and years with no maintenance).

 

[Flywheel]

Dumbest idea EVER. All they were really good at doing is blowing out fork seals. By adjusting oil level you create the same effect. Oil doesnt compress. Air does. Worse part is IF people use the air in the forks 99% of the time they do it Waaaaaaaaaay to much. It should be no more than 4psi. Most manuals will tell you 6 but in my experience thats too much. Its also almost impossible to get that low of a pressure using a high pressure air line. Best to use a hand pump or the local gas station compressor.
Better yet adjust the oil level and dont use it all. Just my opinion

Considering what you do for a living, it's probably spot on. I'm not sure my bicycle pump could accurately pump 4psi, much less an actual compressor. The 80's must have been good for fork seal vendors since I keep seeing 8-10 psi as acceptable ratings.

After the CB1100 sticker shock and reading about Yamaha's JDM SR400 (looks great, likely overpriced like the TU250 if it comes to NA), I've decided a real vintage mullet could be the way to go. Cafe racers/Honda CBs have been done to death, so I'm leaning towards the quirkier models (xs750/850, v30/45 Magnas & Sabres). Nothing concrete yet until I learn more--I want a manageable money pit.

 

[Rob]

The new 2013 CRF450R uses air in their new design front suspension.



Air Fork = The Future.
The CRF450R’s new 48mm inverted KYB PSF® (Pneumatic Spring Fork) air fork is a cannon shot in the suspension revolution. It’s almost two pounds lighter than a conventional-spring fork, is super easy to tune (all you need is an air pump—no special tool needed) and totally eliminates internal spring-to-forkleg friction.

 

[dricked]

The new 2013 CRF450R uses air in their new design front suspension.



Air Fork = The Future.
The CRF450R’s new 48mm inverted KYB PSF® (Pneumatic Spring Fork) air fork is a cannon shot in the suspension revolution. It’s almost two pounds lighter than a conventional-spring fork, is super easy to tune (all you need is an air pump—no special tool needed) and totally eliminates internal spring-to-forkleg friction.

Kawasaki is going the same way, didn't know Honda was too.

 

[Flywheel]

Air Fork = The Future.(all you need is an air pump—no special tool needed) and totally eliminates internal spring-to-forkleg friction.

Maybe. Fournales offers pneumatic shocks for the Burgman (and other models). They are the most expensive option for an uprgrade, very finicky to get adjusted correctly and have a tendency to leak, turning the bike into a hardtail. The anecdotal evidence posted by riders wasn't encouraging--and the streetbikes involved weren't MX or even dual sports. Another kick at the can with better boots, I guess.

 

[Charlie-brm]

. . . I'm leaning towards the quirkier models (xs750/850, v30/45 Magnas & Sabres). Nothing concrete yet until I learn more--I want a manageable money pit.

I've got your xs750 for sale right here with a collection of spare bits, Haynes, etc.. It's a 79 Special and yup they are quirky like anything when you're looking back 33 years.
OT - it has the fork caps with the air valves but on everyone else's advice I ignored using that feature and treated the forks like normal units.

 

[N3WMAN]

Best to use a hand pump or the local gas station compressor.

Best to use the tool designed for the job. A shock pump.

When 1psi will significantly affect preload a hand pump wont do. Just disconnecting a normal pump will lose you 10-20psi. Shock pumps have a locking collar so you can set the desired pressure and remove the pump without any air loss.

I use it mainly for Mountain Bike forks/shocks, but have used it occasionally for old MX air forks and shocks.

 

[Venom01]

OK, so my bike is an old 81 cb750f and it has the air/oil forks. Min pressure is 12psi while it recommends 16 psi for a full load or track days. I've had the seals blow out once but replaced them with better then OEM ones from all balls. Its not so bad. I just had a hell of a time finding a bike tire pump with a quick release and a gauge built on to it. I think the problems most people had with these forks is putting too much air in while never replacing the oil because other then that for street riding I've had no problems at all. The 900f and 1100f forks had an anti dive mechinisim on them that I would love to try. Anyone know if 900f forks would fit a 750f of the same year?

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