Progressive spring guys - lots of sag?

[robertob]

I've been riding my bike around with the progressive springs, and while the suspension seems pretty well sprung when I'm underway, there is a TON of static sag. By my measure total front travel is around 140mm, which means sag w/rider should be around 35mm (140mm/4). In fact, sag w/rider is like 65mm!

Sag w/o rider is nearly 30mm, so something is wrong. Maybe I should add some preload with spacers?

[tone]

Yep sounds like it needs a bit more preload :-D maybe even heavier oil

As a rule of thumb for the front end you should be aiming at around 25mm of sag with just the weight of the bike & another 25 or so with the rider sat on it :-D

[salty_monk]

Put a bigger spacer on top (or more washers or drill the top caps & make yourself some adjustable ones)....

Heavier oil wouldn't help static sag, but would stiffen up compression damping (the fork would resist big hits more than with a lighter oil) & also slow down rebound damping.

I use stock 15W with success but I'm only 165lb. I might go up to 20W if I was a bit porkier.

Dan

[trippivot]

up to 3" on the spacer size I've seen and used on various bikes. start at 1" and go 0.5" bigger until the static sag is to your liking.

the spring is active on the first half of travel. the fluid weight and volume is active on the last half of travel during compression. (active = most effecting)

heavier fliud will slow the rebound speed a little but getting the viscosity to your liking takes time and experimentation.

I like to mix 15 and 20 W oil I weigh 250# and my usual passenger is 170#

I use fork specific oil for the anti foaming quality needed for consistent suspension dampening.

atf and other oils just squish around foam up and suspend like a pogo stick.

[bwringer]

Just to give you an idea, here's where I ended up with my preload spacers and progressive springs. I'm about 280 pounds with my gear on, and I ride my GS850G like a bat outta you-know-where.

This is how far my preload spacer protrudes. It takes a lot of bad words, pain, and sweat to compress the spring and get the cap threaded in:




Static sag measurement. Excellent!


If you prefer a softer ride, you'll want a bit more sag.



The spacer it takes for me to get the correct preload. Yours will most likely be different. You have to experiment by making and installing longer spacers in 1/2 inch (12mm) increments until you're happy.






The happy results of all this trouble: a shaftie that handles.

[bwringer]

For fork oil, I use 15W with 10% "motor honey" mixed in.

Motor honey is a thick yellowish goop used to thicken motor oil in tired old car engines to help them leak a little less. (Whatever you do, don't put it in your GS engine -- it will destroy your clutch.)

In the forks, motor honey is a great way to fine-tune viscosity. I think it also helps reduce stiction -- I've noticed my front forks are more compliant over tiny bumps with the motor honey.

Most humans are a bit smaller than me and don't ride as aggressively, so plain 15W fork oil will work fine. Or you might try 10W fork oil with 5% to 10% motor honey.

Another very common mistake is to simply dump in the amount of fork oil in the book and button it up. This is not good enough, and will usually make the level uneven and too high, because of the unpredictable amount of oil remaining in the forks after draining.

The level of fork oil is what's important -- the actual amount is not important. You have to set the fork oil level precisely -- the specs in the manual call for these levels to be within 1mm, even on forks that use different amounts on the right and left. You have to dump in a bit too much fork oil to start, then slurp out the excess to the correct level with a fork oil level tool.

You can buy a tool to set fork oil levels, or make your own from a large syringe, some tubing, a coat hanger, and some zip ties. The manual has a diagram. There's a large syringe sold for measuring 2-stroke oil that's perfect for this.

[robertob]

Thanks for the tips. I have the forks set up with 15w fork oil and the level is to the FSM specs - 145mm, I think?


I've made preload spacers before so I guess that's what I've got to do in this case. I just wasn't sure if the Progressive springs are helping or hurting!

[Mark M]

Thanks for the tips. I have the forks set up with 15w fork oil and the level is to the FSM specs - 145mm, I think?


I've made preload spacers before so I guess that's what I've got to do in this case. I just wasn't sure if the Progressive springs are helping or hurting!

The Progressives are OK, but you do need to preload them to get your 35mm of sag (decent start number, BTW). Be careful that you do not preload the springs so much that they will coil bind at full bump before the forks hydraulically bottom. You will know if you do, because it will be HARSH when it hits solid on the spring.

I cut about 3" off my progressives and preloaded from there to get close to the spring rate I wanted for my 1100E. But I am also very close to coil bind at full bump, something like another 1/4" of preload or travel and it would bind. If anybody wants the specs I cut the springs to, let me know and I will dig out my 1100E notebook. It's still not as high a rate as I want, but it's as close as I can get with the spring envelope dimensions we have to work with in those skinny fork tubes.

Edit: Always use real fork oil instead of all the cheapo alternatives. It costs $2 more and then you have the correct item in your forks. Considering the cost of rebuilding forks, I just don't understand trying to save a a couple of $$ on oil. False economy IMO.
Mark

[robertob]

So after thinking about this a bit, I did some research on fork springs. The Progressive springs are "OK" but not very good - the progressive part of the spring basically collapses with my 175-lb ass on board meaning that I get lots of sag.

I could up the preload to get the sag back into the proper 35mm range, but then I'm basically disabling the "progressive" part of the fork spring.

The ideal spring would be a stiffer-than-stock straight-rate spring that I could install and tune for proper sag with nothing more than a little preload spacer.

Maybe I'll do what Mark says and just chop off the progressive part of the spring.

[gsgeezer]

Sounds like you need spacers. I use Racetech straight rate springs with cartridge emulators,now for my bikes and I am much happier. I just gave away a set of Progressives to a friend.

[Mark M]

Maybe I'll do what Mark says and just chop off the progressive part of the spring.

robertob,

I pulled out my GS1100E notebook tonight and looked up what I did.

The Progressive Suspension springs were 18" long x 27mm OD. I cut off the closely spaced end (the end that coil binds first) and left 41 turns. After cutting, closing and grinding the cut end flat I had an OAL of 14". This gave me a rate around 0.92kg/mm. I really wanted around 1.0kg/mm, but that is not achievable with the envelope dimensions the GS has to work with. I calculated an excess travel for the spring of 28mm more than the full suspension stroke and used 10mm of initial preload with the adjuster in the second position (#1 being full out). That left me two clicks of preload on the adjusters to JUST short of coil bind at full bump.

My notes do not show if I stayed in the 2nd adjuster position or went to the 3rd step, so I assume I am still at #2.

Hope this helps you some,
Mark

[robertob]

Yes it does, thanks.

By the way, I found an inexpensive source of GS Springs - any spring that will work in a Kawasaki EX500 will work for a GS.

In addition, sonic springs has reasonably priced springs:

http://www.sonicsprings.com/catalog/index.php?cPath=29_58&osCsid=031e0cbea422246020577b51f8ae5277

[82Shafty]

I wanted to add that I have an 82 1100GL that used a 6.5" spacer to set the sag at 1.125" out of my 5.4375 travel. I tip the scales at 160.

My dad will sit on the bike this weekend at 210lbs and see how much sag we get from him. I may need to do a 6.75 spacer to accomodate the 40 extra pounds. My bike will have had the springs in for about a week giving them a little time to settle in and to better dial in his for the additional weight.

I took my bike out with progressives and with the new set up (old stuff was low and dirty with no air) and it rode and handled awesome.

The 1107's are a few inches shorter than the stock fork springs hence the bigger spacer.


Bwringer: do you believe those no-air fork caps would fit my GS1100GL? Are they stock Suzi parts off of another model?

I had to use a 1" socket to fit on the air set up in order to get the top caps in the forks.

[robertob]

Well, in the end I added a 30mm spacer without cutting the springs, and while the sag is in the ballpark, the springs are way too soft.

I will eventually pull them out and cut them as Mark suggested. The brake dive drives me crazy!

[82Shafty]

Update:

I sat my Dad, Roadrash 210 #'s on my bike and it still only sag'd 1.125" so we set his spacers at 6.5" as well. 82GS1100GLZ.


Both bikes had no air left in the front forks and were in desparate need of some fresh lube.

After a thorough cleaning, new springs/seals and some much needed fresh lube; night and day difference.

With the progressives set up, the bike is so much more stable and handles a heck of a lot better.

I did a 2:1 ratio of 10W fork oil to Dextron 3.