Can you give me the basics on which knob is which (black and silver I think)? I got one of these and it came with no useful instructions and I don't want to flatten my shock like an idiotDuck! wrote:I use a Giant pump which has a funky head attachment that enables you to close off the valve before removing the pump from the shock, so you don't lose any air.
The outer, silver knob is to connect the pump head to the valve stem, the smaller, darker knob opens and closes the valve core. To attach the pump to the shock, first wind the smaller knob out as far as it will go, then screw the pump head onto the valve. Wind the core knob down to open the valve. Reverse to remove the pump; unwind the core knob to close the valve first, then remove the pump.Mububban wrote:Can you give me the basics on which knob is which (black and silver I think)? I got one of these and it came with no useful instructions and I don't want to flatten my shock like an idiotDuck! wrote:I use a Giant pump which has a funky head attachment that enables you to close off the valve before removing the pump from the shock, so you don't lose any air.
Thanks for the link - interesting read. Not really conclusive one way or another. I suppose a big factor with analogue might be the quality of the gauge - I have seen analogue gauges that were way out compared a proper calibrated process gauge, and also some of them have very poor scale printing/layout, so it makes it harder to actually read with reasonable accuracy.
DuckDuck! wrote: ↑Thu Jun 17, 2021 10:41 pmThe Giant-branded pumps are the only ones I've seen with the two-step head, but there may be others.
For a fork you don't need a super high pressure capability; you're unlikely to need much more than 100psi, even for a short-travel, smallish spring chamber volume with a heavy rider.
The high pressures really only come into play with rear shocks, which have much smaller air chambers; the really high, 300+psi is only when you get into the servicing side of things.
For general use, absolute accuracy isn't super critical, as long as you have a consistent reference to work to. Fork (and where applicable, rear shock) setup is based around "sag", which is the compression of the fork (or shock) when the rider is on the bike. For a fork, this is typically 15-20% of the total travel (for 63mm, in round figures 9-13mm). So tweak the pressure to suit, and the pump says what it says. As long as you're using the same pump you'll have a consistent reference. For a short-travel, low-volume, a rough starting reference pressure is 60% of body weight expressed in pounds; multiply kg by 2.2 for conversion, and go for 60% of the result. Fine tune from there to get the sag right.
Most air forks have an O-ring around one of the upper tubes, specifically for setting sag. If there isn't one, wrap a cable tie around one of the tubes. On the bike in your riding position, push the O-ring or cable tie down against the dirt wiper. Gently step off the bike (so you don't over-squish the fork), and measure the gap between the top of the dirt wiper and bottom of setup ring. Adjust pressure as necessary.
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