Suspension questions

[Shaun]

Well this is the first bike I've had with adjustable suspension so I have some questions. What I first noticed when I rode my bike (90 fj) was that when I got into a corner the back end felt kind of sketchy like it wanted to skip out. So I started reading through the manual, it suggests that front and rear suspension should be set com-pairable front and back. So I had a look at the bike, rear suspension set to 4 1/2 and front appears to be at 1 softest. Okay soften up rear to two as suggested in repair manual. Take bike for a ride feels much better, but soft I think it needs to stiffen up the front to medium( I think) I like getting into corners but the bike doesn't instill confidence in me when it gets in there. Now comes the question, the repair manual says the marks should line up on the forks outer ring has three marks indicating setting, soft, medium, hard, special nut has line apparently to move to? next there is a slotted screw head with a red punch mark that should also line up with the fore mentioned red marks? So what I get from the repair manual is that all three marks should line up to be at a correct setting? Also to adjust the forks can I just use a 12mm hex socket in that "special nut" and turn it to the next setting and turn the screw so the punch mark aligns with everything? Now when I look at the setting and read the manual it says that you should not leave any adjustment half way in between any settings, however when I rotate the slotted screw in one fork it does not match up to any mark it notches in between, it will not line up with anything, suggestions? I also need to understand spring pre-load and damping better so as to better understand because the feel of seat of the pants thing get get pretty dicey pretty quick. Any good suggested reading out there on suspension that will help understanding the concept better?
Thanks for looking.
Shaun

[rktmanfj]

Some good articles here:

http://www.sportrider.com/tech/motorcycle_suspension/index.html 

http://www.gostar-racing.com/club/motorcycle_suspension_set-up.htm

Randy T
Indy

[the fan]

Not FJ specific, but something I put together for a YZF forum I moderate..

Since you are dealing with less than perfect pavement, set your sag at 1/3 of overall travel at both ends. This will be 40mm of ride sag out back and 44mm on the forks.

This will get you in the ballpark. On smoother roads and tracks I prefer to run 32mm up front and 30 in the back (appx 1/4 overall travel), but thats a bit harsh on rough pavement.

Its important to check the "free sag" once the Ride sag is set. You suspension should sag 10-15% (13-19mm front, and 12-18mm rear) to determine if you need stiffer/softer springs. if free sag is LESS than 10% you need a stiffer spring, MORE than 15%, softer.

RIDE SAG.) Difference in legnth of suspension loaded with weight of bike, rider and gear and completely unloaded (fully extended) Measured from the axle to a fixed point on the chassis in line with the suspension movement.

FREE SAG.) Difference in legnth of suspension loaded with weight of bike only,and completely unloaded (fully extended). Measured from the axle to a fixed point on the chassis in line with the suspension movement.

Once the springs are dialed in move on to the rebound and compression damping.

Set the rebound first. To do this first turn both the compression and rebound clickers (not an option on first year models (95 US 94 rest of the world) fully out from the seat. Count the "clicks" out from seat as you go. This is the softest possible setting and serves only as a baseline.

Start with the fork rebound. Holding the brake lever firmly, quickly compress the forks and let them rebound on thier own. Note that at the lowest setting (fully out) your forks will top out and bounce like a Lincoln Continental with bad shocks. this is bad.
Turn both rebound clickers in 2-3 clicks at a time until the forks extend to the top of the travel and come to rest. I like rebound damping to be fairly soft, so I will play around with the clickers until I find the point hat the forks top out on extension an settle to a rest.

Repeat this with the rear shock.

Once both the spring rates and rebound are set its time to mess with compression.

I like to use a Zip Tie to set fork compression. To do this I first set the compression clicker to appx 1/3 of overall "clicks" out from the seat as a baseline. Place a zip tie around the front fork leg snugly and just above the lip of the dust seal.
Extend the fork leg and measure the distance from the top of the zip tie as i rests against the dust seal and the bottom of the lower triple clamp. Record this measurement.

Now take the bike out and ride it in the manner that you normally ride, on the roads you normally ride. The dust seal will push the zip tie up to the point that you have compressed the forks the most. Pull over every so often and measure the distance from the top of the tie to the bottom of the clamp. You want to use 75-80% of your travel riding in your usual manner. Simply divide the distance measured at each check by the number recorded with the forks fully unloaded. this is the percentage of travel used.

For track use you will want to go as much as 70-75%, really rough roads 80-85%.
I generally set the rear shock by feel as its a pain in the butt to measure otherwise.

Simply, once you have set all the other adjustments, hold the front brake and usung your foot, shove down on the footpegs several times the suspension should compress and rebound at equal rates front an rear, if not adjust the shock compression (and possibly rebound) until they do. It works best if you have a friend watch from a few meters away and give feedback.

Once you finish all the tests above, take the bike out and ride it for an hour or so. Pull to the side of the road and recheck the Rebound settings. Both the compression clickers and the oil temp have an effect on the rebound damping. make sure it it still where you want it.

the numbers and settings advice are for a 96+ YZF600 but the theory is the same for pretty much all bikes.

[FJ Flyer]

Thanks, Bill.  I'll have to try this on the FJR.  Or get my ass to a rally and have your expert skillz assist.   

[Shaun]

Thanks for the set up info folks, I had a read through the links that Rktmanfj posted, I found the second one most useful. and Thefan posted a useful tip from his forum which for the first time two or three people have said the same comparable things. So I now know a lot more than yesterday. however the one thing that still bothers me is the indicators on the forks for damping. They do not match up, and will not no matter how much you try and turn them. Does this mean that they can not be setup the same (is one fork working more or less than the other one)? Will the damping rates be different enough to cause any issues? Is the best plan to tear down the forks and insure they are put back together equally?

[the fan]

I am not completely familiar with the early FJ forks, but one basic rule when working with suspension components is that if there are detents, then use them and ignore the punch marks. the punch marks are often easily misaligned or misleading.

I always suggest disassembling your suspension components and cleaning / serviceing them at least once every year.  Especially if you ride a lot.  If this has not been done for a while, you might be amazed at the results.

when adjusting the suspension you should always set things up in the following order.

1. Fork Ride and free sag; To find a good baseline setting I look for sag numbers of 1/3 of overall travel for basic street riding and 1/4 overall travel for agressive sport riding. On the FJ this works out to 50mm for general street riding or 37mm for more agressive riding.  (based on assumption that my service manual is correct listing 150mm overall travel) . While this is fairly easy to achieve by adding preload with adjusters and spacers, you still want to make sure that you have somewhere between 10-15% (15-22mm) of overall travel in free sag. If you are unable to reach both the ride and free sag numbers you need new springs.

2. Shock ride and free sag; You want to use the same sag percentages at the shock as you do the forks. On the FJ this works out to 40mm for general street riding  and 30mm for the more agressive.  Again you want to check the Free sag to ensure that it is in the acceptable range (12-18mm). (based on assumption that my service manual is correct listing 119mm overall travel)

NOTE: Running excessive preload or heavier oil is NOT the same as running the proper rate springs and can result in a loss of compliance and/or control when riding. I'm no Jeff Hoffman, but I have tuned a bike or two...

3. Fork rebound damping; Possibly the most important suspension adjustment you can make. Without rebound control, you have no control. The problem is that the FJ has little or no adjustment depending on the model (someone correct me if I am wrong bur the damping adjustment found on some models is for rebound, correct?) If you are unable to find an acceptable setting with the the stock 10 wt oil you can fine tune the system by altering the oil weight.  One way to do this is to use a syringe and tube to draw a measured ammount of oil out of the forks and replacing it with either thicker or thinner oil. Record the changes you make as well as the ammount of oil you started with when you serviced the forks. This will help in getting it righ the next time.

EXAMPLE;  you start with 450cc of 10wt oil and find the damping to be too soft. You then remove 100cc of oil and replace it with 20wt, arriving at appx 12.25 wt oil.

4. Rear shock rebound damping; On later model bikes there is a rebound adjuster located at the bottom of the shock. the adjustment range is from 3 clicks out from seat to 12 clicks out with 3 being the stiffest setting. Earlier models have a cable operated damping adjuster that I know very little about, but assume controls rebound. (somebody help the guy out here)
   With any luck you can find an acceptable setting with the available adjustments, otherwise start saving for an aftermarket shock. If you like the FJ its worth every penny.

5. Fork compression setting. As far as I know none of the FJ forks have provisions for this adjustment, but all is not lost. Compression damping is controled largely by oil viscosity, but if you make big changes here, you will often have very negative effects on the rebound. in other words DON'T DO IT! There are however a few options.
  The first is the race Tech Emulator. It works reasonably well to control  both HSD and LSD and at the same time allows you to run heavier oil for more rebound control if needed.
  The second is an old tuning trick that actually works pretty well. Raising and lowering the fork oil. BY raising the fork oil level 5-10 mm from the stock setting you decrease the volume of air in the fork. Remember that while fluids do not compress, Gasses do. What happens when the forks collapse is that the air trapped in the system compresses adding a spring effect which slows the compression of the fork. If you decrease the volume of air by raising the fluid level, you also increase the air pressure making your forks seem progressively stiffer as they travet through the stroke. Lower the oil height and decrease the effect. Neat hunh.

6. Shock Compression adjustment. If you are running the stock shock, move on. If you are running an aftermarket shock or a shock with compression adjustment refer to my earlier post.

NOTE TO ALL THE MODDERS, The above assumes you are running stock or near stock components. If you change something, say switched to a YZF fork, or adding a Penske, you need to know how this affects the overall suspension of your bike. You really need to find the overall wheel travel of the bike at both ends and take it into consideration.

In the example listed above switching the YZF fork is fairly common. but be awarw that the YZF fork only has 130mm of travel as opposed to the FJ's 150mm. With the forks adjusted to the proper sag for the riders needs the YZF fork will be compressed nearly 7 mm less than the FJ fork it replaced. Assuming it was installet with the same legnth from the top of the triple clamp to the centerline of the axle as the FJ fork, your bike will be riding 7mm higher up front, with a shallower rake and longer trail (think chopper...) To correct this you need to either run the forks with a 7mm shorter legnth from the top of the triple clamp to the axle centerline, run a shorter (60 series?) tire, or raise the rear to correct (I dont have the measurements in front of me to do the math).
likewise the shock.
My manual shows the stock FJ shock with 48mm shaft travel and 119 wheel travel with the stock swingarm and linkage. This works out to a 2.48 ratio. If the aftermarket shock has a longer shaft travel than stock, say 52mm, this equates to an overall rear wheel travel of appx 129mm, 10 more than stock and adjusts the sag numbers accordingly....

And I'm just getting started....

[RichBaker]

Thanks for the set up info folks, I had a read through the links that Rktmanfj posted, I found the second one most useful. and Thefan posted a useful tip from his forum which for the first time two or three people have said the same comparable things. So I now know a lot more than yesterday. however the one thing that still bothers me is the indicators on the forks for damping. They do not match up, and will not no matter how much you try and turn them. Does this mean that they can not be setup the same (is one fork working more or less than the other one)? Will the damping rates be different enough to cause any issues? Is the best plan to tear down the forks and insure they are put back together equally?

Sounds to me like whomever did the fork seals last did NOT install the damper rod correctly.....it would appear that they didn't get the cut-out in the bottom of the rod set over the positioning screw. Therefore, the detents don't line up with the marks on top of the fork cap....
The only way to know is take the fork apart and check.

[Shaun]

To the Fan WOW! thank you, now with that explanation I feel that I can set up my suspension to behave relatively well and understand what is actually going on and what it is I am really changing. Yes the bike is pretty much all stock, and a rear shock shall be added to the want list as I do like my FJ very much. I have printed of your reply on suspension setting and will use it as reference material. As for emulators? what's is their purpose, I will have to research these and look into them further. I'm not a road racer by any means but out here on the west coast of Vancouver Island we do have some great roads and most of them not straight, I'll let you know how the setup progresses.

RichBaker, after reading through the manual more I found what you speak of, I would say you are right.

As for taking apart and redoing my forks, it sounds like the right thing to do as I do not know the history of the bike or how it was looked after. What I do know is that it sat over on the mainland at an auto dealership for about a year untouched, until it came up in an auction and I bought it. And so to all of you thank you for the input, I will let you know how it all works out. I believe understanding what your bike is doing and why is key to having the most fun possible.
Cheers.
Shaun

[the fan]

This should tell you everything you ever wanted to know about suspension..

brought to you with love, straight from the mind of Jeff Hoffman and the FJ yahoo group files...

http://tinyurl.com/Jeffs-fork-info

Some day the slacker who volunteered to copy all the files over to here will quit making excuses and post them up....

[FJ Flyer]

Mr. Slacker,
Your linkie no workie.

Is that Jeff's suspension explanation article?

[Shaun]

Some one said it first, the link takes me too some search engine and gets lost in the ether net, somewhere.

[the fan]

Odd, It works perfectly from here... and Chris thats the file I wanted.

lets see if this works....

[FJ Flyer]

Bill,
Cool, you can embed a pdf file in the post.  And yes, that's what I thought you were referencing.

[Shaun]

So I got into my forks on the weekend, and yes they came apart easily enough. What I found was a lot of sludge and crud. Mechanically I found a couple of things; I found that the last person who was into the forks made some errors when reassembling, when the bottom screw was put in the notch in the damper rod was not aligned properly, so the screw is beat and bent and flattened out, I will have to replace with a new one and washer. Second apparent error, at the bottom of the fork tube there is an aluminum piece called a oil lock? (I don't have the manual in front of me) Anyway it was installed up side down according to the picture showing the orientation in the manual. Now that creates the question being each fork was different, is the picture showing the fork break down in the clymer manual correct? As I see it the oil lock piece should sit inside the fork tube, inserted so to speak. The largest diameter of the oil lock piece should sit even with the bottom of the fork tube with the the rest of the oil lock inside the tube, not pointed down into the lower leg?

Thanks for looking.
Shaun

[racerman_27410]

So I got into my forks on the weekend, and yes they came apart easily enough. What I found was a lot of sludge and crud. Mechanically I found a couple of things; I found that the last person who was into the forks made some errors when reassembling, when the bottom screw was put in the notch in the damper rod was not aligned properly, so the screw is beat and bent and flattened out, I will have to replace with a new one and washer. Second apparent error, at the bottom of the fork tube there is an aluminum piece called a oil lock? (I don't have the manual in front of me) Anyway it was installed up side down according to the picture showing the orientation in the manual. Now that creates the question being each fork was different, is the picture showing the fork break down in the clymer manual correct? As I see it the oil lock piece should sit inside the fork tube, inserted so to speak. The largest diameter of the oil lock piece should sit even with the bottom of the fork tube with the the rest of the oil lock inside the tube, not pointed down into the lower leg?

the oil lock... which looks kind of like a flower pot should be oriented so that the flower pot is upside down... larger diameter facing down..... small diameter facing up to the damper rod with two spring washers and one flat washer sandwiched in between


KOokaloo!

Frank

Thanks for looking.
Shaun