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Air in forks?

3 lbs seems a small amount to me for the application,

Boyle's Law: when the volume of a closed container is cut in half, the pressure of the gas inside doubles

On a fork with 8" of air column ,and no precharge, the air inside the fork is at atmospheric pressure (14.7psi absolute) when the fork is fully extended. If the fork has 8" of air at the top, the air pressure would be 29.4psi at half way through its travel (4"). At 6" of compression (3/4 of the way compressed), the pressure would be 58.8psi absolute). Acting on a 40mm fork end (about 2 1/2 square inches), the force would be 147 pounds minus the 2 1/2 sq in x 14.7 psi atmospheric pressure acting in the opposite direction (35.75) or 111 pounds PER FORK! The air in the two forks would be exerting 222 lbs of force trying to resist compression at 3/4 travel.

Now add 3 psi preload to the calculations. 17.7psi at full extension. 35.4 psi at 4". 70.8 psi at 6". Times 2 1/2 sq in. = 177 lbs. minus 35.75lbs = 141.25 lbs x2 = 282.5 lbs vs 222 lbs with no precharge.

60 lbs of force difference to the front of the bike from ONLY 3psi!!!!





I am also surprised that they make a gage that is that intricate that will properly show just 3 degrees

First, I know you meant to say precise instead of intricate and psi instead of degrees.

Precise low pressure tire gauges are EXTREMELY important for many forms of racing. A typical Top Fuel dragster will run about 6psi rear tire pressure. Swamp buggies, sand rails, and monster trucks all run very low tire pressure.

There are also innumerable industrial needs for low pressure air gauges.


:dance:dance:dance
 
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CC Products Air Forks Kit

Some of you may be interested is seeing one of those air fork kits that were around back in the 80's, this is a CC Products unit. They did indeed work, experimented a lot with them back then. The gauge was mounted on the handlebar so it could be easily monitored........................George
 

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Another Air Fork Kit

Here is another air fork kit, think it is for R65's....................George
 

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Wow! Now those are way fancier than the home jigged rig on that old R75/5 I had with air forks. While not willing to argue the reward/benefit or science side of the mod I can tell you from riding that old bike that the difference a few pounds of air in the tubes made to the ride was like night and day. The front end felt "stiffer" and better suspension when hitting potholes. Also less diving when grabbing a handful of front brakes (such as they were). I don't recall any issues with leaking seals but due to poor implementation it did leak air slowly.

There was no science applied by me though. Never measured a thing other than the fork oil itself. I would just stop by a gas station and pop it with the air hose very very briefly and that was that. You could feel the difference immediately.
 
Boyle's Law: when the volume of a closed container is cut in half, the pressure of the gas inside doubles


First, I know you meant to say precise instead of intricate and psi instead of degrees.

Precise low pressure tire gauges are EXTREMELY important for many forms of racing. A typical Top Fuel dragster will run about 6psi rear tire pressure. Swamp buggies, sand rails, and monster trucks all run very low tire pressure.

There are also innumerable industrial needs for low pressure air gauges.

:dance:dance:dance

I did mean to use the word "increment" rather than "intricate" but even that needed a restructured sentence. My meaning was that for normal bike riders, it would be very difficult to hold such a small amount of air pressure, and get it precise at all times. Incrementally, one could say that if 3 Lbs. would be deemed too hard, why not 2.5 lbs.? Why not 2.2? You see, to be able to set those increments would be very impractical, and a gage that would do so, would be very expensive, even if these forks could be trusted to maintain such an exacting pressure. The reason is that there is only a small amount of volume of air in there. It doesn't take much to "fill up" that space with more air and pressure would increase exponentially. The solution, would be to "plumb" some sort of tank to increase the volume, thus making it easier to maintain one's favorite pressure - whatever that may be. These forks simply weren't made for that sort of use.

I would suspect that is why this concept never really caught on. It was deemed impractical for the average rider. A novelty, yes, practical, no!

I would bet that those who make their living using these small pressure settings (as mentioned dragsters, etc.) don't use a $5.95 gage.


Using air pressure is, however, an interesting concept.
 
Jimmy,

The way to accurately fill them (or any thing for that matter), is to overfill and then bleed back to the desired pressure. Obviously, hooking up to a gas station air hose could blow out the fork seals in an instant, but hooking up to your home compressor THOROUGH A REGULATOR that is set for 5psi or using a bicycle pump, before bleeding back to 3psi with the gauge that I posted earlier, is easily doable.



:dance:dance:dance
 
I would bet that those who make their living using these small pressure settings (as mentioned dragsters, etc.) don't use a $5.95 gage.

If you need a higher quality gauge http://www.motosport.com/dirtbike/p...m_medium=cpc&gclid=CKWhsZ-clLoCFcs9QgodmRYA4g

accurate within 1.5%. That's 1/4 lb at 15psi or .044 lb at 3psi. Easily good enough.

Or you could use http://www.zorotools.com/g/00095563...kw={keyword}&gclid=CMGO4bielLoCFRDZQgoddC8A-A
same 1.5% accuracy, but .1 psi increments for VERY precise settings. Only $28.



:dance:dance:dance
 
Jimmy,

The way to accurately fill them (or any thing for that matter), is to overfill and then bleed back to the desired pressure. OTHOROUGH A REGULATOR that is set for 5psi or using a bicycle pump, before bleeding back to 3psi with the gauge that I posted earlier, is easily doable.



:dance:dance:dance


Hey.......FINALLY a valid use for the worthless self-flagelating piece of equipment supplied by the factory for what is called a tire pump........God bless........Dennis
 
If you need a higher quality gauge http://www.motosport.com/dirtbike/p...m_medium=cpc&gclid=CKWhsZ-clLoCFcs9QgodmRYA4g

accurate within 1.5%. That's 1/4 lb at 15psi or .044 lb at 3psi. Easily good enough.

Or you could use http://www.zorotools.com/g/00095563...kw={keyword}&gclid=CMGO4bielLoCFRDZQgoddC8A-A
same 1.5% accuracy, but .1 psi increments for VERY precise settings. Only $28.



:dance:dance:dance[/QUOTE

BOTH of the gages you show as being more than adequate, pose problems. In order to make anything usable, is to have the gage "plumbed" in so that the "air" can be overfilled and then bled down (as you describe). If 3 lbs. was the limit, and the volume in the shocks is so little, then simply checking with a standard gage like you would a tire would lose enough air in the checking process that it would be virtually impossible to maintain a setting as too much air would escape in the checking process.

Secondly, the percent of accuracy is +/-, Translation: to say it is 1/4% accuracy means 1/4% higher OR 1/4% lower, so with such a small pressure, and such a small volume I would suppose it would be virtually impossible to settle on a pressure. Then add the fact that the forks weren't made to hold pressure in this way, and probably leak constantly, holding an accurate pressure (even if it could be determined by a good gage) would be a nightmare.

If you would look at the pics of the kits that were used, I can see why this would be an undesirable and probably a waste to purchase and install on a bike t get minimal benefits. Iwould bet that this was one of the determining factors as to why this concept never really caught hold. Simply wasn't worth all the headaches!
 
If you would look at the pics of the kits that were used, I can see why this would be an undesirable and probably a waste to purchase and install on a bike t get minimal benefits. Iwould bet that this was one of the determining factors as to why this concept never really caught hold. Simply wasn't worth all the headaches!

IMO maybe, maybe not. I'm thinking one can dissect this all over the place but until it's been tried and dissproven, it might still something worth considering. One can evaluate the proposition objectively but utlimately it might just come down to giving it a try. In a simplistic fashion, one can very precisely overfill the forks with oil to change the air-over-oil effect. This in reality was the question posed by the original poster.

It seems that use of air can have an effect on the suspension. There may in fact reach a point of dimension returns along with a hassle factor that indeed makes it not worthwhile. But I wouldn't dismiss it out of hand.
 
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