Front suspension expiriment results

[jimfj]

I have read about the many people who have switched to Progressive springs on the 850. I thought I would so a little expiriment on my bike before I took the plunge.

I have the original fork springs in my 82 850.
I am also currently using a Vetter Windjammer fairing on the bike, about 20 pounds maybe.

It has the air adjustable preload. I have been noticing that the front end would start to really get stiff and bounce over every little ripple in the road after riding a short time on the highway.
I have a tool from Progressive to adjust the air pressure in the forks down to the nat's ass. Basically, I can dial in the pressure to the half pound. I set the pressure at 10 psi in each fork a month ago. I checked it last night and it was still at 10 psi. I took a ride from my house, about 8 miles and got off the highway. I stopped and because I had the tool with me, I checked the pressure. It had the needle pegged at 15 psi. I bled the pressure down to 4.5 psi.
I rode back home and checked it in the driveway, it had climbed to just over 6 psi again.
Okay no wonder that everybody says to go to Progressive fork springs and no air. I know that if you heat air it will expand and I can't remeber my physics, but does the fluid expand too? I am runnig a mix of 15wt fork oil and ATF in the forks.
With the pressure backed down to 5-6psi it was much more comfortable but I could still feel alot of the road undulations.

Any suggestions or comments

Jim

 

[Steve]

My first suggestion would be to get rid of the "mix" and go with the proper quantity of a known viscosity. With the 'Jammer, a straight 15w fork oil will probably do well. While you are experimenting, you might also want to try making some spacers to add some preload to your existing springs. You may find that you do not need any additional air. Note that ALL forks are also 'air assisted' forks, it's just that on some forks (like yours), you can add air for more assist.

.

 

[Don-lo]

I always run 15 psi in my GS1000 (bought new in 1980), and have never seen rising pressures like that. How did you measure your "mix": by cc or by oil level? Too much oil would mean less space for the air, and more compression would mean more heat. Your "mix" could also be foaming. I would suggest trying straight 10 or 15 fork oil.

 

[Sandy]

When measuring the air you also have to make sure it's measured with the fork at exactly the same compression height. Any higher or lower than where you first checked it will alter the readings a lot, not to mention any heat built up from aggressive riding. Progressives, no air, no hassle.

 

[jimfj]

I measured the level by cc using a large syringe. I didn't think about the positioning of the bike. When I first did it the bike was on the centerstand. The times I measured after the bike was on the side stand.

I will drain the mix and go with a 15wt fork oil and see what happens. I guess the only way to get to where I need to be on this using the air is to have someone do it for me while I'm sitting on the bike with no stand of any kind involved.

Or just bite the bullet and go for the Progressives and get it in the middle with no further adjustment available. I kind of get hung up on losing something that was designed with adjustability in mind.

Anyone know if the fork caps off of an 1150E with the 4 detent adjusters will fit an 850? I like the idea of going with a new set of springs, but still being able to adjust the preload without changing spacers.

Jim

 

[salty_monk]

You could try cutting 3 or 4 coils off your original springs & replacing with a spacer of the same length. It increases the spring rate (adding just a spacer will only increase pre-load). Poor man's progressives... I've done it on a bike & it worked great.

Progressives aren't that expensive though at about $65.

This is one reason I don't like air forks. Stiction (from tighter seals needed) & also pump up. A lot of mountain bikes use air (race models anyway). The fork diameter is nearly the same as that on our GS & the air pocket is about the same size & they get pump up (without 500lbs pushing it).

Dan

 

[Sandy]

Just measure it on the centerstand, as long as you do it the same each time then you will have a stable reference point.

I measured the level by cc using a large syringe. I didn't think about the positioning of the bike. When I first did it the bike was on the centerstand. The times I measured after the bike was on the side stand.
Jim

 

[DMorris]

It's my understanding that the oil should be measured by the distance from the top of the fork leg and not by volume added unless you can be sure that ALL of the oil has been drained.

For what it's worth....

 

[salty_monk]

140mm from top for my bikes. I fill with oil then cut a hose of a spray bottle to the right length & pump out any excess onto a rag.

Dan

 

[Steve]

I guess the only way to get to where I need to be on this using the air is to have someone do it for me while I'm sitting on the bike with no stand of any kind involved.

No, the BEST way is to use the centerstand ONLY. You need to have repeatable fork-length settings and the only way to do that is to have them totally extended. The easiest way to do that is to put the bike on the centerstand. If you did not have the 'Jammer on there, you could use the side stand, but then you would have to pick up on the bars to make sure the forks are fully extended. Much easier to simlply put the bike on the center stand.

It's my understanding that the oil should be measured by the distance from the top of the fork leg and not by volume added unless you can be sure that ALL of the oil has been drained.....

Even then, it's better to check the level. Some bikes, like my Wing, have extra hardware in one fork leg that's not in the other, so the amount of oil to be added is different. If the proper amount is added, the level will be the same. The reason you need the level the same on both legs is because of the trapped air. When the forks compress, the air that's in there will also compress, adding to the spring rate. If the oil level is different, one side will get higher pressures than the other, which can affect handling.

Overall, your best results will be when you have no more than 1/4 of your suspension travel taken up by you sitting on the bike. For most of our bikes, we have about 6 inces of travel in the front forks. This means that when you are on the bike, ready to roll, you don't want it to 'sag' any more than 1 to 1 1/2 inches, leaving 4 1/2 to 5 inches to absorb bumps. You need to start with a spring of the proper tension that also has enough travel available. Next, you adjust the preload to acheive your proper ride height. In the case of forks, that's about it. If you have air shocks, you can then play with additional air in the shocks to compensate for the additional loads of passenger and/or luggage.

.

 

[bonanzadave]

Any suggestions or comments

Try it with Nitrogen instead of air and let us know if there is a difference.

 

[jimfj]

Next, you adjust the preload to acheive your proper ride height. In the case of forks, that's about it.

Is this done with spacer that is supposed to go with the progressive springs?

No, the BEST way is to use the centerstand ONLY. You need to have repeatable fork-length settings and the only way to do that is to have them totally extended. The easiest way to do that is to put the bike on the centerstand.

I have prevously done everything to the forks with the bike on the centerstand. For everyone's reference here, I am just fine tuning what I think is already a pretty good ride. I know many of us want to replace the rear shocks along with the front springs but mine arn't sagging and I can definatly tell the difference between dampening settings when I change them.

My goal for the setup is to have a comfortable ride on the highway...65-75 mph and still be able to carve a decent line in the corners now and then. I think I'm pretty close and I have no problem going with new springs up front to get what I'm looking for. I just like knowing that before I go there I fully understand what the manufacturer intended for the hardware that was on it when it came out of the factory. I can't and just don't want to solve the "challenge" by throwing new parts...ie money at it.

I appreciate all who have contributed to the discussion, I am learning alot.

jim

 

[salty_monk]

Then cut a couple of coils off the springs, add spacer of length of coils + preload spacer to suit & don't worry about adding air... Total cost $0 apart from time.

The result is a maintenance (apart from oil change) free system that rides much nicer than an air spring.

Dan

 

[Pacman]

FYI, Jim has a Vetter Quicksilver fairing on the bike which is quite a bit smaller than a Windjammer.

Jim, take the fork springs I have from when I put in the progressives and cut them down then add the preload bushing to make up the difference. This way you can go back to stock.

Or just suck it up and buy the Progressive springs.:dancing:

Chris

 

[Guest]

clip 1 1/2 inches off the springs.....