Front fork air pressure


Information and questions on GL1100 Goldwings (1980-1983)
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beantricks
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Joined: Fri Oct 08, 2010 9:29 pm
Location: Phoenixville, Pennsylvania
Motorcycle: 1983 GL1100 Interstate

Front fork air pressure

Post by beantricks »



I'm adding a pressure gauge to front forks on my 83 GL1100 Interstate. Have bought the OEM fork cap with valve and will replace with the gauge. Still using crossover hose. My question is what does the pressure peak at when fork compresses in bumps? If I'm running 20 psi does it bounce to 60 or higher? Will be using a glycerin filled gauge to deaden the pressure chatter while riding, but it's mainly for changing pressure between solo and two up riding and being sure no leaks. I have options of 0-30 psi, 0-60 psi, 0-100 psi, and 0-160 psi. At those two higher ranges the gauge scale gets to small to accurately set correct pressure. I'm afreaid at 0-30 psi I might peg the gauge just in normal riding, must less hitting a bump. Anyone ridden with a guage mounted?


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Re: Front fork air pressure

Post by WingAdmin »

beantricks wrote: Thu Apr 16, 2020 3:37 pm I'm adding a pressure gauge to front forks on my 83 GL1100 Interstate. Have bought the OEM fork cap with valve and will replace with the gauge. Still using crossover hose. My question is what does the pressure peak at when fork compresses in bumps? If I'm running 20 psi does it bounce to 60 or higher? Will be using a glycerin filled gauge to deaden the pressure chatter while riding, but it's mainly for changing pressure between solo and two up riding and being sure no leaks. I have options of 0-30 psi, 0-60 psi, 0-100 psi, and 0-160 psi. At those two higher ranges the gauge scale gets to small to accurately set correct pressure. I'm afreaid at 0-30 psi I might peg the gauge just in normal riding, must less hitting a bump. Anyone ridden with a guage mounted?
You have a space inside the fork that is filled with air. You pressurize that space, to say 20 psi.

When the fork compresses, that space is compressed. If it compresses to 1/4 the original area, then the pressure will quadruple to 80 psi. Very large bumps causing large fork excursion will cause very high peak pressures. That's why the fork caps have long threaded necks, they have to hold in against tremendous pressure.

This is also why overfilling with fork oil is so bad - it replaces the compressible air with non-compressible fluid, so when you hit a big bump, the tiny air space that is in there gets compressed so much that the resultant pressure blows out the fork seals.

Your problem is that you want a pressure gauge that has a small enough scale to be accurate for setting pressures, but that doesn't go past full scale deflection during massive spikes. I don't know that such a pressure gauge exists. This is why the OEM Honda pressure gauge on the bikes that have them are only connected to the suspension when you press a button. You press the button while stopped (and on the center stand), read the pressure. The pressure is not displayed when riding.
beantricks
Posts: 3
Joined: Fri Oct 08, 2010 9:29 pm
Location: Phoenixville, Pennsylvania
Motorcycle: 1983 GL1100 Interstate

Re: Front fork air pressure

Post by beantricks »

Thanks for the explanation. Sorry my reply was a few years late. Now retired and still riding. More time to dig through the forums. Might consider a gauge with a on/off valve.

On to new question. Want to add tube extensions. Found what I was looking for in 39mm but seller says threads are for Harleys.

Anyone know supplier or thread info for GL1100I?

I already know moving forks down (longer) makes a difference in steering tension. I had the forks slid shorter when bike was two wheels so my short legs reached ground. Moving them back after riding for a few months after installing sidecar made a noticeable difference. Figure another couple of more inches will make steering a little lighter.

Ideally would get a leading link. Unfortunately not readily available for 40 year old bike. Will keep looking.
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Re: Front fork air pressure

Post by Rambozo »

There are digital pressure gauges that have good resolution and can handle high pressure. Not sure if there are small ones, I've only used larger versions.
A machine shop could make up some fork extensions for you, just give them the ID, OD, and a cap to measure the thread.
What you might be able to find is an EZ-Steer triple clamp. They change the fork angle. They were very common for sidecars and trikes. Hunt the forums, post that you are looking, and check salvage yards. Be sure to hit the trike forums.
That will be a lot easier to find than a leading link setup.
Looks like they are still being made for other bikes. Maybe you can special order one?
https://championtrikesaz.com/ez-steer-kits/


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