Air assist for forks - thoughts
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HDF Community Team
Joined: Nov 2012
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From: USA
Air assist for forks - thoughts
I've an 04 road king, lowered in the rear with so air shocks. Winter project likely is to lower the front forks as well.
My rumination is on the notion of drilling the caps and installing the same fittings as the rear air shocks have, so I can easily adjust the front. I've already got the fittings and lines from the so shocks.
I've used air assist forks before on other bikes, and liked it. I understand harley did have it before, but discontinued it for some reason.
I can't see any real downside to this. Other than blowing seals if I ran silly high pressures. Would also make changing fork oil a whole lot easier.
Thought and comments?
My rumination is on the notion of drilling the caps and installing the same fittings as the rear air shocks have, so I can easily adjust the front. I've already got the fittings and lines from the so shocks.
I've used air assist forks before on other bikes, and liked it. I understand harley did have it before, but discontinued it for some reason.
I can't see any real downside to this. Other than blowing seals if I ran silly high pressures. Would also make changing fork oil a whole lot easier.
Thought and comments?
Club Member
Joined: Jun 2007
Posts: 45,429
Likes: 2,898
From: Bedford UK
Harley used air forks for a very long time, although I'm not sure when they stopped using them. They also used an external air reservoir with the forks, which on early models was the front crashbar, on later models was the handlebars. The air added extra springing to the steel springs installed, so was not the main spring medium, whereas air is the main spring for stock rear shocks. In other words the front and rear suspension used air in different ways.
You can retrofit the older Harley parts to your bike with a little effort, but I am not sure using the same hardware as the rear shocks would do much good. You can achieve improved ride quality by using dedicated springs, such as from Race Tech.
You can retrofit the older Harley parts to your bike with a little effort, but I am not sure using the same hardware as the rear shocks would do much good. You can achieve improved ride quality by using dedicated springs, such as from Race Tech.
Road Captain
Joined: Apr 2006
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From: Erhard, MN
Had air assist frontend on a 2001 flhtc. I liked it. If I remember correctly, it fed from a seperate valve on the year [there were 2 valves on 1 bracket - 1 for rear shocks/1 for front]. Feed to front was the same black plastic line that goes into rear shocks; then fed into front through a fitting in the cap.
Road Master
Joined: Oct 2006
Posts: 832
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From: Vermont
My '89 had air adjustable forks. The air reservoir was in the crash bar and it was charged with a valve behind a screw off cap on the left hand grip. It had an anti-dive feature where a valve between the reservoir and the front fork would close on hard breaking. Very good system that was trouble free for 18 years for me.
I remember asking where the front shock schrader valve was relocated when doing the walk around with the tech on my new '07. He had no idea what I was talking about. Gone... like the standard fork air baffle and passenger grab rails...
I remember asking where the front shock schrader valve was relocated when doing the walk around with the tech on my new '07. He had no idea what I was talking about. Gone... like the standard fork air baffle and passenger grab rails...
Former Sponsor
Joined: Apr 2007
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From: Davie, FL
Air Assist
When you add air to a closed calender it is like adding fork oil to a fork to reduce the air cavity from the oil level to the fork cap. The reason why it was not used any more is because customers were having problems with the air leaking. The majority of HD mechanics may not be trained well enough to find or understand why the air is leaking and how to find it. That is my guess only. It works very well. Of course you must have good fork seals.
Here is a graph that has always been on my site demonstration the change by adding 10mm of oil to a cartridge fork. Adding pressurized air does the dame effect. KYB is now making a new cartridge for motorcross that used very little oil and pressurixed air. Changing the air changes how the front end responds.
Here is a graph that has always been on my site demonstration the change by adding 10mm of oil to a cartridge fork. Adding pressurized air does the dame effect. KYB is now making a new cartridge for motorcross that used very little oil and pressurixed air. Changing the air changes how the front end responds.
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HDF Community Team
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From: USA
Yep, that's what I'm looking to exploit as I ruminate this. That and the ability to quickly and easily change fork oil types and levels.
I'm thinking of increasing the progressive spring rate so I can keep the sort base ride, but have a rapidly rising spring rate as the wheel travels, so I hopefully won't bottom out so abruptly or frequently.
I'm thinking of increasing the progressive spring rate so I can keep the sort base ride, but have a rapidly rising spring rate as the wheel travels, so I hopefully won't bottom out so abruptly or frequently.
Club Member
Joined: Jun 2007
Posts: 45,429
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From: Bedford UK
Yep, that's what I'm looking to exploit as I ruminate this. That and the ability to quickly and easily change fork oil types and levels.
I'm thinking of increasing the progressive spring rate so I can keep the sort base ride, but have a rapidly rising spring rate as the wheel travels, so I hopefully won't bottom out so abruptly or frequently.
I'm thinking of increasing the progressive spring rate so I can keep the sort base ride, but have a rapidly rising spring rate as the wheel travels, so I hopefully won't bottom out so abruptly or frequently.
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HDF Community Team
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From: USA
Poor wording on my part. The air cushion in the fork tube above the oil is what I was referring to as being the progressive spring that I can adjust. Both in rate change from the height of the fork oil, and static pressure from adding air pressure from a pump.
I didn't know harley used a pressure tank on the earlier forks. I was not planning on that myself, as it negates the progressive aspect I'm interested in with air pressure.
I didn't know harley used a pressure tank on the earlier forks. I was not planning on that myself, as it negates the progressive aspect I'm interested in with air pressure.
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