Why I dread changing fork oil

[bwringer]

My bike is a 1983 GS850GD, and is wearing Progressive fork springs. I thought it might be valuable to someone to see what it takes get the proper fork spring preload. Please keep in mind that the preload spacer length you see here may not apply to your bike's forks.

The proper spacer -- I don't remember what the initial recommendation from Progressive was, but this is at least 25mm - 35mm longer (now 86mm). The spacer is made from thin wall aluminum tubing, which I believe was originally a clothes hanging rod in a closet:


With fork spring, washer, spacer, and cap installed, here's how far I had to compress the spring and thread in the fork cap. Urk. :


After a painful struggle involving blasphemous language, bruises on my chest and hands, and an unseemly amount of sweat, here's the first sag measurement:


Actually, sag usually measures out a bit more than this -- usually 30mm or so. You have to measure several times to get a good average.

[mlaalm]

Thanks for the play-by-play
Did you take the load off the springs by jacking up the front a little
I use a small phunmatic jack towards the front of the oil pan and lift it up just enough to take the compression
off the springs; especially when removing the caps - I've almost lost an eye before doing it this way
Kinda helps me out when I'm messing around with the springs

Nice pics . . . . its a labor of LoVE
-Mike

[bwringer]

Yes, you have to get the front wheel off the ground when reinstalling fork caps. I have a small set of jack stands that fit perfectly under the #1 and #4 pipes with a rag for padding on top.

Most people won't need this much preload, but I'm XXL and I like to ride fast.

[Billy Ricks]

Thanks for the play-by-play
Did you take the load off the springs by jacking up the front a little
I use a small phunmatic jack towards the front of the oil pan and lift it up just enough to take the compression
off the springs; especially when removing the caps - I've almost lost an eye before doing it this way
Kinda helps me out when I'm messing around with the springs

Nice pics . . . . its a labor of LoVE
-Mike

You can't properly set sag without the first reading being with the fork being fully extended.

[bwringer]

On my bike, the forks are fully extended when the bike is on the centerstand. There's a bit of weight on the front wheel, but nowhere near enough to start compressing the monster preload on the springs.

[Clone]

That's a lot of preload, thank god I am only 150lbs, my spacer isn't that big. I don't mind changing fork oil.:-D

[Pharkmeh]

Thanks for the play-by-play
Nice pics . . . . its a labor of LoVE
-Mike

ditto & excellent pics - thats the sort of stuff will help me understand:-D

[Hoomgar]

After a painful struggle involving blasphemous language, bruises on my chest and hands, and an unseemly amount of sweat,

LOL! Brian, I can picture the whole thing while your saying it :?

Thanks for sharing. This is another one I will need eventually because you and I are very much alike in the area you described (as your reason for all the extra preload).

This is also another one that should be made sticky or go in the new area. I really think we should create a new tips area of the forum that is for threads like this. The author can recreate it there and no replies allowed. The threads get locked. That way it will start a catalog of GS related fixes and procedures for the masses that come here looking for that info.

Also, to anyone new who came here looking for info, make sure you visit Brian's web site that he has linked in his signature line (actually here --> http://bwringer.com/gs/index.html ). There is a wealth of tech info like this and more there to be found.

[Hoomgar]

I installed my new Progressive springs in the front forks last night. Man oh man what a difference! It still is not 100% of what I would like it to be but it is a 300% improvement over what I had. The stock springs in this thing were sloshed completely out and with the fork top caps having their damping adjustments frozen in the lightest setting, I would bottom my forks constantly on even the smallest bumps. I had set the preload on the rear shock up to adjust for my weight but that combined with the front the way it was it felt like a wobbling Elephant in the turns and was a bit scary at times. Very unstable. I took it for a 2 hour burn last night to test it out and after killing about a half million bugs I have to say it is waaaaay better. It needed this upgrade really bad!

Now I need to find new fork caps to replace the ones I have but it really seems a lot better already.

Brian, do you have a guide on your web site that goes over setting the sag on the front forks? I want to tune these for my weight and riding style but am not 100% sure what I should be looking for?

Thanks for all your tips BTW!

[bwringer]

As a rule of thumb, proper static sag is 1/4 to 1/3 of total suspension travel with the bike held straight up and down, both wheels on the ground (not on the center stand) and the rider's weight on the bike. You would set sag closer to 1/4 total travel for aggressive riding or short travel suspension, closer to 1/3 total travel for a cushier ride (as long as you don't bottom out.)

On most GS models (and most streetbikes, for that matter), suspension travel is about 100 - 125mm (4-5 inches), so 25-30mm of sag (1 - 1.25 in) is a good all-purpose number.

For most rear shocks, changing preload is as simple as turning the preload collar. For forks, you have to experiment with different spacers unless you're lucky enough to have a model with preload adjusters.

To measure fork sag, I simply place a zip-tie around the fork tube, carefully get on the bike with my full weight without bouncing, and then carefully climb off. With the forks fully extended again, measure the distance the zip tie traveled. You do need to do this several times and take an average -- stiction (the drag of the seals and various sliding parts) makes this measurement a little random.

One thing that's nice about progressive springs is that the spring rate goes up as you compress the spring. With my monster preload, I'm actually using a higher spring rate than I would with a shorter spacer. The air trapped in the forks (you should not use air pressure with aftermarket fork springs) also acts as a spring as the fork compresses. Unfortunately, fork springs in different spring rates are difficult or impossible to find (unless you find a different brand has a different rate), so your flexibility in this area is limited.

Once you've set static sag to an intelligent guess, go for a few rides and decide whether you like the results. It's a subjective thing that depends on your riding style, weight, and personal preferences. If you brake heavily, you may want to increase preload and/or spring rate to ensure you'll never bottom out. If the roads in your area are in bad shape, you may want to go a bit softer so that the front tire stays in better contact with the road instead of chattering over bumps. This fine tuning would involve spacer length adjustments of maybe 6-12mm (1/4 - 1/2 inch).

Once static sag is set properly to create the proper foundation for suspension tuning, then it's time to start experimenting with different weights of fork oil to get the best damping action possible out of ancient, tired GS forks. As noted above, I use 15W, which is already pretty thick, plus about 10% motor honey goo to make it even thicker. Most riders with fewer miles on their GS and less weight would start with 10W or 15W and experiment from there. You can add up to 10% motor honey to make the oil thicker, or mix fork oils of the same brand if you want something in between. This is an even more subjective process

The next topic is dynamic sag and what it can tell you about your riding...

[Billyboy]

Here's a dumb question... Maybe Mark can help.

On my GS1000, there is no obvious nut ion the top of the forks, just the air valve. So how do you take 'em apart? My fork seals just came in.

[steely]

Here's a dumb question... Maybe Mark can help.

On my GS1000, there is no obvious nut ion the top of the forks, just the air valve. So how do you take 'em apart? My fork seals just came in.

I used a big crescent wrench slid on from the side opposite the schrader (air) valve.

[Hoomgar]

Here's a dumb question... Maybe Mark can help.

On my GS1000, there is no obvious nut ion the top of the forks, just the air valve. So how do you take 'em apart? My fork seals just came in.

The nub that the air valve screws into turns out. Use a piece of bike inner tube rubber or a good thick rag and an adjustable wrench and just turn them out. Be sure to remove the air valve first.

I'm talking about part number 20 in this pic:

[Billyboy]

You guys rock!

[Hoomgar]

The next topic is dynamic sag and what it can tell you about your riding...

Thanks for all that Brian. Now as for this quoted statement? What is that?