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-   -   Air Assist on Front Forks, VL800 (https://www.volusiariders.com/47-custom-mods/283433-air-assist-front-forks-vl800.html)

dfinitlydisturbd 10-02-2013 02:40 PM

Air Assist on Front Forks, VL800
 
3 Attachment(s)
Finally just went ahead and tried it after years of debate with myself as to whether it was a good idea or not.

So far I've had it aired up for 24 hours and emptied a full tank of fuel testing it. Handles bumps and cracks better, even a couple nasty ones around here that used to bottom out the fork and get the rear airborne (now I need to figure out how to improve the rear suspension). All in all the front is much smoother. A side effect is an increase in front ride height of .75" @20PSI slightly more at higher pressure. Personally I like the height increase and the extra 3/4" inch of available wheel travel. While it doesn't seem like much I noticed it immediately when I got on, it does seem to improve the steering geometry (there is a noticeable improvement in cornering that I suspect is a combination of the change in rake and trail as well as the more progressive behavior of the fork). At 30PSI the fork does not feel stiffer as one would expect, in fact it takes bumps far more smoothly than stock.

I will post any issues should there be any, but so far there are none. This seems like a winner for folks unhappy with the stock fork's shortcomings.

This is a very easy and cheap mod, no special tools required, and the parts are available at most auto parts stores.

Step 1. Purchase bolt in valve stems for alloy wheels.

http://static.speedwaymotors.com/RS/...91058500_R.jpg
Step 2. Remove the fork caps. (easy enough eh?)
Step 3. Select a drill bit the same size or slightly smaller than the bushings in the stem kit.
Step 4. Set the caps upside down on a hard surface, locate the center and drill them.
Step 5. Remove any rough edges.
Step 6. Install the stem kits in the caps. (A dab of gasket adhesive couldn't hurt.)
Step 7. Reinstall the fork caps.
Step 8. inflate to 10 PSI (after a test ride you can increase or decrease pressure as desired. I have mine at 30PSI.)
Step 9. Take a test ride Adjust pressure as needed.

https://www.volusiariders.com/attachm...1&d=1380741287
https://www.volusiariders.com/attachm...1&d=1380741604
As you can see by the less weathered area the front forks extend a bit when the pressure is upped. This is at 30PSI at 60 they extend fully at lower pressures they extend a little less.
https://www.volusiariders.com/attachm...1&d=1380741604

CoolC50 10-02-2013 02:50 PM

Did you feel any difference? How does it feel riding the bike now??

dfinitlydisturbd 10-02-2013 03:10 PM

Yes, Immediately.
Awesome. The bike has never handled or rode better. As I said above now i need to sort out a cure for the lousy rear suspension. As far as I'm concerned the front is as perfect as a cruiser suspension can get. In the works is sorting out plumbing to add a compressor and a deflate valve in my fairing. For the compressor I'm going with a cheapy $10 dollar store unit as it only takes 10 seconds at most to inflate the forks to 60PSI (way overkill). Stripped of it's case it would easily fit where the Suzuki tool box is. So far the trick seems to be finding the airshock fittings like Gabriel uses.

Apologies to all for no pics yet, the stupid uploader keeps crashing. I will get some up just as soon as I figure out why they won't upload.

EDIT: Pics added to the opening post.

PV458 10-02-2013 03:23 PM

Wow!! I'm impressed....You've got my undivided attention!

OzriderC50T 10-02-2013 07:55 PM

Great job, I would never have thought of doing this on these bikes.

This was standard on my old V45 Sabre, be careful not to run too high pressures as you may blow fork seals, compressors or service station pumps may overinflate very quickly.

I would use a small bicycle pump like this Tioga Alloy Dual Head Bike Bicycle Pump Gauge Schrader Presta Road MTB 120PSI | eBay

In the end I replaced the springs with aftermarket progressive springs and done away with the air altogether.

As for the rear, mine was terrible, it felt like the rear was bottoming out and therefore bucking on big potholes. The more I increased the preload the worst it got.

I eventually fixed it by reducing the preload on the rear coil to let it soak up the bumps, it hasn't bottomed out once.

1954rider 10-02-2013 08:23 PM

I'm getting a pretty well balanced ride in the rear on notch 3 with the hard Commander II tires.

I'm still mulling over the air system for the front. If I understand the system correctly the aspects to consider are:

1. Spring - rate, and whether intentionally progressive or not
2. Preload of the spring - adjustable by putting in shims on our machines, or a special mod
3. Hydraulic Damping - our adjustment is oil kinematic viscosity
4. Compression preload / damping - air.

I'm just trying to work this out. Based on racetech discussions, a linear rate spring does nicely for bikes, a softer one than stock on touring type bikes to soak up little stuff. I'm not convinced that a heavier bike doesn't like progressively wound springs.

I'm convinced that we have too much damping in the stock system, primarily in the oil. Without replacing the system, less viscous fluid in combination with progressive springs might well give a great ride quality, but offer very poor progression under load, allowing bottoming.

That's where I suspect the air adjustment might be great to have. Now we have the option of less headspace (higher oil level) for greater compression resistance. With an active air pressure control system, a more compliant suspension could be adjusted nicely to give a highly progressive response, providing very comfy level ride, but rapid stiffening up under load (braking - cornering).

I could see something like a progressive spring with somewhat shorter than standard spacer (say 1"), slightly lighter oil than standard (perhaps 10 cSt), plus air. The optimum oil level and air pressure would have to be figured out (past me) or experimentally determined (That I could do).

Seems like a really fun project!!

dfinitlydisturbd 10-02-2013 08:37 PM

Quote:

Originally Posted by OzriderC50T (Post 2631489)
Great job, I would never have thought of doing this on these bikes.

This was standard on my old V45 Sabre, be careful not to run too high pressures as you may blow fork seals, compressors or service station pumps may overinflate very quickly.

I would use a small bicycle pump like this Tioga Alloy Dual Head Bike Bicycle Pump Gauge Schrader Presta Road MTB 120PSI | eBay

In the end I replaced the springs with aftermarket progressive springs and done away with the air altogether.

As for the rear, mine was terrible, it felt like the rear was bottoming out and therefore bucking on big potholes. The more I increased the preload the worst it got.

I eventually fixed it by reducing the preload on the rear coil to let it soak up the bumps, it hasn't bottomed out once.

I'm using a cheapy 12V compressor, it's quick but not so quick that I can't dial in the pressure right where I want it.

It's worries about the fork seals and only worry about the seals that's keeping me from plucking the springs entirely. I suspect that air pressure alone would be adequate, BUT the pressure required might very well blow out the seals...doing my homework and investigating the differences between our forks and air pistons....if I like what I see them springs are coming out for further experimentation....our forkseals aren't too expensive right? (I hope)

1954rider 10-02-2013 08:55 PM

Might try taking out just one spring first . . . .

OzriderC50T 10-02-2013 09:25 PM

Quote:

Originally Posted by dfinitlydisturbd (Post 2631609)
I'm using a cheapy 12V compressor, it's quick but not so quick that I can't dial in the pressure right where I want it.

It's worries about the fork seals and only worry about the seals that's keeping me from plucking the springs entirely. I suspect that air pressure alone would be adequate, BUT the pressure required might very well blow out the seals...doing my homework and investigating the differences between our forks and air pistons....if I like what I see them springs are coming out for further experimentation....our forkseals aren't too expensive right? (I hope)

Every air suspension system I have ever seen is based on a sealed bladder system, I have serious doubts that a seal designed to hold back fork oil that is not under any pressure would come close to supporting the forces required for an air suspension system.

dajogejr 10-03-2013 09:12 AM

I myself am very curious to see how long and if there are any problems with the fork seals, short or long term, due to adding extra pressure in the system.
Please keep us informed, very, very interesting.


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