Fork Air

[Guest]

I know this has probably been covered somewhere, but I can't find it. A few of the manuals show a special setup in order to pump air into the front forks and then a valve to capture it, including a gauge. Apparently the tool kit came with a pressure gauge for this procedure. Does anyone have a spare they'd like to get rid of? The other thing I'm looking at is a fork & shock pump for a mountain bike. The only thing with these, they are high pressure, 3 to 4 hundred pounds. I would imagine it's user controlled. Just wondering if it would work.

Thanks,
Chris

[KGB]

There's 2 sides to this.
Some will say no air in the fork as it causes the oil to breakdown.
Air contains water and it doesn't mix with the oil causing it to faom and
break down viscosity.

I agree, in both my bikes, 15 weight oil, no air.


As to the small hand pump, try EMS, eastern Montain Sports or
my favorite store Brrokstone. The pressure guages are cheap, under $15.

[lukehan]

air bubble

In the past I have just used an air bubble. I just let out enough air until it is in the right pressure range and then air up both forks. No danger of over inflation and ensures that both sided are the same pressure. You may want to figure out a way to check the guage on the air bubble, but I figure they are accurate enough as long as each side gets the same pressure.

Luke

[Anonymous]

Some will say no air in the fork as it causes the oil to breakdown.
Air contains water and it doesn't mix with the oil causing it to faom and
break down viscosity.

Time to debunk this myth. Yes, the air and oil mix inside a conventional fork. However, adding or not adding air pressure makes no difference - there is always air inside your forks. Unless you filled them and assembled them in a vacuum, that is...

This is one reason why it is better to use fork oil than ATF or motor oil or whatever ever else is handy; it has an additive package specifically formulated to deal with the foaming issues. The real reason to not run air pressure is that it is hard on seals, causing them to wear prematurely and it adds to stiction. Air is really a crutch for springs that are too soft. The best solution is to put in springs of the correct rate and not have to run any air to prop them up. Whoever mentioned the 1" static sag was correct. The numbers to shoot for are 25mm static sag (bike with no rder on it) and 35mm laden sag (bike and rider together). Of the two, the laden sag is more important if you can't get them both to work at the same settings.

BTW, current MX forks and top level superbike forks now run pressurized bladders the same as shocks to eliminate the air/oil mixing that happens in our forks. This gives more consistent performance throughout a race and makes the oil last longer (not that racers care much about the longevity issues).

[Gary Lich]

If you choose to put air in your forks a simple way to ensure the pressure is equal is to use a cheap hand / syringe type pump. If you put the same # of strokes in each fork the pressure will be the same every time...no need to measure it once you deterime the right # of strokes (3 on my GK)...