fork oil weight/air combination on GK?

[fanman]

New to the board and very green mechanic on my recently aquired GK. I'm replacing fork seals and wondering what you GK owners are running for fork oil weight and air pressure. The Clymer recommends 10, 15 or 20 fork oil and 10 psi air. I'd like a very plush ride for the bumpy roads in my area. We have no wide sweeper curves mainly straight-ahead pavement. I don't know what the previous owner was running. So I'm thinking maybe 10 wt. oil and 7 psi air. Is this a good start? What are others running? Also wanted to say I'v learned more about the GK on this site than the manual could ever teach me. Great site.

Chip

[bwringer]

I would immediately replace the old, sacked stock fork springs with Progressives, fiddle with preload spacer length according to your weight and riding style, and use no air pressure.

From there, you can experiment with fork oil weight and mixtures. You don't want to go too light with fork oil, or you'll end up with a very bouncy, hard-to-control front end.

I'd start out in the middle with 10W fork oil (flush well with kerosene and let the forks air out for a while).

Your manual will have instructions for a simple device using a large syringe and a length of tubing that you can use to set the fork oil level. The important measurement is the level of the fork oil, not the amount.

If you want more controlled damping, you can mix in "motor honey" with the fork oil. You can also mix in 1/2 ATF (it's about 7W) if you want less damping.

[Poot]

I was convinced by another previous GS owner to use 20w fork oil, and im putting in about ....10psi .

[Rico]

bwringer cut right to the chase. ALL good advice!

poot, how does that front end feel with so much air in it?
Don't you have new springs in there? I know if I put 10lbs in my front end your 150lbs wouldn't compress it to much.

anyway, after using a nonfoaming hydrolic jack oil, I think I'm gping with some real 15wt fork oil this time.

Ric

[Poot]

bwringer cut right to the chase. ALL good advice!

poot, how does that front end feel with so much air in it?
Don't you have new springs in there? I know if I put 10lbs in my front end your 150lbs wouldn't compress it to much.

anyway, after using a nonfoaming hydrolic jack oil, I think I'm gping with some real 15wt fork oil this time.

Ric

Still got the stock springs. maybe a tad under 10psi then?

[pidgey]

I'm gonna flush my forks on the weekend and am using 10w oil. I don't know what's in there at the moment, but the ride is a bit choppy for my liking. Hopefully this will soften up the front end a bit. Will keep y'all posted.

[fanman]

Thanks for the input guys. Been reading past post's on the progressive springs and people seem to prefer them over stock. So I just made the leap and ordered a set from bikebandit.com. Actually I'v been wanting them but feared the wife's reaction to yet another got-to-have motorcycle part. Caught her in a good mood and gave her the ol 'how much safer I would be for it' So progressive springs on the way, 10wt. fork oil and forget about the air.

Chip

[Jethro]

I highly recommend the Progressives. I use them with 20 wt oil and no air pressure. Awesome ride quality, a big improvement.

[Poot]

what is the difference between stock and progressive springs? not that im buying them now (broke) but for future reference.

[pidgey]

These look good http://www.bikebandit.com/partsbandi...id~1069356.asp

[bwringer]

For starters, new Progressive springs are stronger, and aren't sacked out from being under load for 25 years. The original springs in older Japanese bikes are also quite soft because they based suspension setup on feedback from their 100 - 130 pound Japanese test riders. Americans, (and Aussies, Brits, and other westerners in general) are at least 40 to 50 pounds heavier on average, with some samples going much heavier...

They've gotten better about this in recent years, but forks on new Japanese bikes are still almost universally far too soft in the land of the Big Mac (and the lands of vegemite, bangers and mash, etc.).

Secondly, Progressive fork springs are also, well, progressive. In a normal spring, you get pretty much the same spring rate all through its useful travel. For example, a 100 pound spring would deflect one inch for every 100 pounds of load. 200 pounds=2 inches, and so on.

With a progressive spring, the spring rate goes up as deflection goes up. In a hypothetical example, it might start out at 100 pounds = one inch of travel, but require 250 pounds to deflect 2 inches, and 450 pounds to deflect three inches.

Therefore, a progressive spring gives a smooth ride on small irregularities, but increased resistance to bottoming on larger bumps. From a performance standpoint, the flexibility over small irregularities helps the tire track the pavement better and increases traction, while the higher spring rates over larger bumps help keep the wheel under control.

As far as air pressure in the forks, you can continue to use air pressure after installing new fork springs. However, I think there are some compelling reasons for using spacers to set preload and using no added air pressure.

Air pressure in the forks contributes to seal wear and failure, and increases seal stiction. If a seal fails, even just a little (quite common on older bikes), you're suddenly left with sagging forks and bottoming out if you have to use the brakes hard, which is quite dangerous.

Properly set up with the right amount of preload and the right fork oil for the rider's weight and riding style, the forks on our machines can be quite comfortable yet very well-controlled.

The biggest mistake I see is not enough preload -- a lot of people mistakenly think that flaccid, uncontrolled suspension will be more comfortable somehow. However, if your machine is using up 3/4 of its fork travel just sitting at a stoplight, very little is left to cushion bumps.

Even if you're not a fast rider, squishy suspension is quite dangerous, since it badly compromises the bike's stability in corners along with your ability to control the bike during emergency maneuvers.

Once preload is set correctly by measuring sag (about 1/4 of total suspension travel sitting on the bike), selecting fork oil is a matter of experimentation and taste. My bike has over 60,000 miles and I am a rather aggressive rider, so I use 20W fork oil with about 10% "motor honey" added to make it a bit thicker. (The internal oil passages wear over time, so you need slightly thicker fork oil to keep the same damping action.) This combination gives me plenty of comfort over small bumps, yet keeps the front wheel planted and in control when leaned way over on bumpy roads.

On a bike with less wear, or a more comfort-oriented or lighter rider, a different fork oil might be perfectly appropriate. You really have to start in the middle and experiment to figure out what's right for you and your bike.

In a nutshell:

1) Install new fork springs. Follow the directions on the package for making preload spacers. Make sure you drain and flush the old fork oil.

1a) Set the fork oil level as specified in the shop manual -- the specified amount will be too much, since the new, thicker springs take up more space. (The fork oil LEVEL is what's important, not the amount of fork oil!)

2) Measure static sag -- how far the fork compresses from fully extended to when you're sitting on it. If this is more than about 1.5 inches, install longer preload spacers.

3) Make an educated guess as to the fork oil you want to try, then experiment from there.

[bwringer]

Oh, and make sure you attend to the rear suspension too. Worn-out stock shocks can lead to some far-too-interesting wobbles and weaves.

I use and enjoy Progressive shocks with extra-extra-heavy duty springs, but I dream of dropping $500 or $800 or more one day for a set of fully adjustable IKONs or Ohlins... The Progressives are way, way better than stock, and a pretty good performance/dollar deal.

The Emgo shocks you might find for about for $80 or so are probably a little better than stock, but not by much. They're mostly useful if the stock shocks are totally blown or missing and you don't have much money to spend.

[Poot]

Thanks for the info.

I cant wait to see what it feels like with non-25 year old fork oil in it. The 20wt. should do fine.

My suspension was never to soft before, and the only time it bottomed out, was when I jammed on the fronts with a 200+lb passenger on the back. :x


Also, I cant wait to feel the new front i just put on . My old ones date code was 252. either '92 or '82... 8O 8O either way its horrible. but I got a new one on, so I'm safe now!