'81-'83 Fork Blowup '84 And Up Fork Blow Up Damper Tube Retaining Tool
For those of you who like the way your bike rides, your task is easy. Do your maintenance--which consists mainly of changing your fork oil periodically and checking your rear shocks for blown out rubber bushings and general function. Also, you really don't need to read this article. But for those of you who have a deeper interest in Virago suspension systems, or have a problem such as leaking fork seals, you may want to read on--at least until you find the point you are looking for, or fall asleep, whichever comes first.
In the world of motorcycles we have front suspension (typically forks) and rear suspension ( a rear shock or shocks) We'll talk about forks first.
As we go through this it will be helpful here to have a manual handy with a blow-up of the parts of a fork. Or download one of the blow-ups linked above. The damper tube ("conventional") fork is used on all Viragos. These forks have five main parts:
1. The fork tubes mount to the bike by means of the triple tree clamps at the top and bottom of the steering head tube. While they do turn, they move with the frame, and are essentially part of the bike.
2. The lower legs (what Yamaha calls the "outer fork tube") slide on the fork tubes, and move up and down against the spring as the wheel hits bumps and the suspension does its work.
3. The fork springs (inside the fork tube) hold the lower legs in position and allow them to move upward when a bump is encountered, or downward in the case of a depression.
4. The damper rods control the motion of the lower legs and prevent them from going up or down too far or too fast as the lower legs move. The control goes both ways; that is, you have a certain amount of compression damping when a bump is encountered and the lower leg is coming up against the spring, and you have rebound damping as the spring pushes the lower leg back down again to its normal or "static" position. As we'll see , the damper rod teams up with fork oil to provide the needed damping.
5. And then there is fork oil (we'll call this a "part"), which has two main functions. It provides lubrication between the lower leg, and the fork tube, so that the leg can slide freely up and down. And it is also the means by which the forks are damped. As the lower leg moves it forces this non-compressible fluid through holes in the damper rod, and in that way the motion of the lower leg is slowed somewhat and controlled.
In addition to the big 5, there are several other parts that you will see on your blowup that are of interest.
---One is a little spring which goes around the damper tube and buffers the impact when the fork goes to full extension, as in dropping into a pot hole.
---Then there is a piece called the taper spindle which fits on the bottom of the damper rod, and by progressively trapping oil, buffers the impact of the lower leg as it goes to full compression under a severe bump. That is, it acts like a rubber bumper.
---Also we find a piece inside the bottom of the fork tube (which I will call the "foot valve" and is not shown on the blowups) that works the damping. It directs the fork fluid through the bigger holes in the damper tube on the "bump" or compression stroke, and through the smaller holes on the down or rebound stroke.
---There are the fork seals which hold the air and the fork fluid inside the fork. These do wear over time, and may start to leak. When this occurs they must be replaced, and this involves removing the forks from the bike and disassembling them, which we will touch on later. The main cause of fork seal wear is dirt that gets onto the exposed fork tubes and finds its way past the dust covers ("scrapers") and on down into the seals.
---Finally, there are caps at the top of the fork tubes which keep the springs, air, and oil inside those tubes.
So these parts are, to my knowledge, what you will find inside the Virago fork.
Now Let's talk Viragos
'81-'83 MODELS (Except the 1982 Virago 920 J)
Forks on these models are pretty simple and have components as described above. They came with straight wound springs. (More on springs later).
Most of these early forks are "air forks", and allow for air to be added to the space above the fork oil. Unlike fork oil, air is compressible and can act as an additional "spring". Air forks were popular in the seventies and eighties and the idea was that you would start with a fairly soft spring and then let the rider add air to the fork for a firmer ride, to suit the rider's preference. A common question I get is: How much air should I add?
The manual says that the permissible range is 0 to 17 psi, with the 'standard' amount of air being about 6 psi. As long as you don't exceed the maximum you can run the amount that gives you the best ride. Over the max you run the risk of blowing air and oil out past your fork seals and maybe hurting them.
Note, however, that even though you don't add air, you still have air in the fork above the fork oil, and this is definitely an "air spring" since it compresses as the fork compresses. The strength of this "air spring" can be varied by how much oil you put in the fork.
NOTE: Be careful how you add air to these forks. The space inside is small, and a little puff goes a long way. To be accurate about it, you ought to find an air gauge that can handle these small psi pressures. They are out there and not that hard to find. Later forks had a "balance tube" so that you can fill both forks at once from one filler stem. Early fork had to be filled individually.
It is generally felt that using a lot of air makes forks stick (adds "stiction" or binding), and if you want to get off the air, you can install a set of Progressive Suspension (or similar) fork springs. These are beefier than stock, and give a firmer but still comfortable ride, in my opinion. (Sometime in the late eighties or early nineties Yamaha dropped the air feature from Virago forks, and air forks are a thing of the past today.)
Fork tubes on these bikes measure 36mm. These were considered a little spindly for hard riding and some riders added fork braces to cut down on the flexing under hard cornering. I'm not aware of anyone offering fork braces today.
A weakness in the design of these forks is the lack of slider bushings. The lower legs slide directly against the fork tubes and if much wear occurs, the legs can cock on the tubes, thereby reducing the bearing surface and causing stiction. When stiction occurs, the lower legs fail to track small bumps and the impact of these bumps is telegraphed up through the fork tubes and into the frame, where the rider feels it. It is therefore important for owners of these early models to change their fork fluid and flush their forks periodically, and to use good quality fork fluid. Also, anyone considering buying one of these bikes would do well to see how free and how well the forks work.
I am not going to cover the complete topic. Consult your manual(s). Here we'll talk about some of the practical things you get into when working on these forks.
To get to the springs (or service the forks in any way) you have to remove the fork caps on the top of the tubes. The fork caps on these early models are held in place with a steel retaining ring. To remove the cap, you push it down (against the spring inside the fork), and pick out the retaining ring. The cap then comes (pops?) out pushed up by the spring. These caps are prone to rust and corrosion and sometimes need a little coaxing to get them out. WD40 can help.
Once the caps are off, you can change fork oil (and springs), without removing the forks from the bike. Drain screws on the lower legs allow you to drain the fork oil and you can also flush the forks with a mild solvent (such as kerosene) if you want to. With the caps out you can move the wheel and lower legs up and down as a unit to expel all the old fork fluid and help in the flushing. You'll want to figure out a suitable method to catch the fork oil, as it will squirt out quite forcefully when you compress those lower legs. This is easier with the wheel removed in which case a can may be placed around the bottom of the fork leg(s) and wired in place.
The manual specifies 10 weight fork oil, and this seems to be about right. What brand to use? I can't really recommend any specific brand and would say any "quality" brand your dealer is carrying would be O.K. There is some very expensive trick stuff out there these days which is claimed to be superior.. Check out RACE TECH. However, beware of oils that claim to solve all your "stiction" problems. They are not going to cure a worn out fork. Some mechanics advocate going to slightly heavier oil as forks get older and "blow by" starts to occur around the damper rods. If you suspect weak damping, you might try 15 weight oil, or a 10-15 weight blend..
Fork seal replacement gets you into deeper disassembly procedures and here you have a couple of ways to go. A simple and good way is to remove the forks from the bike yourself and then take them to a competent shop or dealer and have them do the work--thereby saving about half your labor costs. Or you can tackle the job yourself. Note: fork seals are installed with the numbers up.
Complete disassembly of the fork is pretty straightforward stuff, but there is one roadblock that often presents itself. The lower leg is held on by an Allen bolt which goes up through the bottom of the lower leg and screws into the bottom of the damper tube. Often, when this bolt is loosened a bit, the damper tube starts turning inside the lower leg, and the bolt won't come out. Yamaha has a special tool which you stick down the fork tube from the top and fits into the top of the damper tube to hold it so it can't turn. Without this special tool you have a couple of options. First, you can take an old broom handle and taper one end. Shove that end down the fork tube into the top of the damper tube and tap it in as tight as possible. Have your friend (if you don't have a friend, you'll have to make one of those also) hold the broom handle tightly so it stays in and doesn't turn. This may secure the damper rod enough to get the Allen bolt out.
The top of the damper tube is fashioned like a 19mm socket, so if the broom handle doesn't do it, head over to your local nuts and bolts store and pick up a metric bolt with a 19mm hex head on it. If in doubt take along a 19mm socket and find a bolt that will fit it. Then go to ACE hardware and get yourself a 24 inch length of iron pipe that will accept the shaft part of your bolt. Back home again, stick the bolt shaft into the pipe, drill a hole through both of them, and pin the bolt into the pipe. Now you have your special tool which can be inserted down into the fork tube to hold the damper tube. Drill a hole through the top of the pipe if you want to so that you can put a screwdriver or other rod through it to hold it. Without a hole you can use a stout vice grip.
The rest of the disassembly is pretty easy. The factory manual explains it and Haynes is good also. Clymer maybe O.K. too.
1982 Virago 920J
I think at some point Yamaha decided to take on Honda by offering a wide array of models, and by doing some fancy engineering. In any event, in 1982 we got the Virago 920 J, sporting (among other things) its weird and wonderful CYCOM instrument cluster and front forks which were a strange size (37mm),
and included slider bushings, and adjustable rebound damping.
Slider bushings are Teflon coated bushings. The lower (inner) one resides on the bottom of the fork tube, and the upper (outer) one sits in the lower leg at the top, just below the fork seal. With these bushings, the fork tubes and the lower legs never actually touch one another, since the sliding is done on these bushings. In theory the Teflon coating is softer than the metals of the fork tubes and lower legs, so that the bushings now take most of the wear. Since they are replaceable, excessive wear in the forks can now be remedied by replacing these bushings rather than buying new fork tube or lower legs. More on this, later.
Disassembly of these "J" forks is more complicated and I think a thorough reading of the factory manual and Haynes would be in order before attempting it. I have taken a set of these forks apart and can remember no major difficulties, but it has been a while and I don't recall the details. I don't remember using heat on the lower legs as is described in Haynes, and I certainly don't think you have to force the seals out under Hydraulic pressure as described in the factory manual. I think the final disassembly (pulling the forks apart) is similar to the process described below for later models--you just yank 'em apart. The 37mm slider bushings are of a strange size and are probably not available in the after market today. And new factory fork tubes and lower legs are almost surely n/a as well. Retaining the damper tubes requires a different technique, and the "special tool" described above doesn't apply.
1984 AND UP--ALL MODELS
At this point several things happened:
--The forks became bigger (38mm)
--Forks caps became threaded caps
--Slider bushings became standard
--Fork Braces were added as a standard feature
--Air was continued, but was dropped in 90's (don't know
--Fork oil drain screws were dropped in the late 90's, which
means that the forks have to be removed from the frame to do a decent job
of changing the fork oil and flushing them.
--The damper tube tool now needs a 22mm hex bolt head. Procedure is the same.
Disassembly is the same as with the earlier forks, except that the slider bushings prevent the forks from just sliding apart once the damper tube bolts are out. What you do is remove the dust seals from the tops of the lower legs, then pick out the fork seal retaining ring. At this point a few sharp tugs will separate the forks. The top slider bushing hooks into the fork seal and pops it out, and the lower leg and fork tube now separate.
If you intend replace slider bushings, note this strange thing: Yamaha will sell you the upper bushing as a piece, but the lower bushing is shown on the parts blowup as part of the fork tube, and is not sold separately. A few guys have actually paid for a new fork tube just to get this bushing. Luckily, these bushings are almost surely still available in the after market, Try RACE TECH. The dimensions are:
Lower (inner) Bushings (the ones at the bottom of the fork tubes)
Upper (outer) Bushings (the ones that reside in the top of the lower leg)
Fork caps now screw into the fork tubes on very fine threads. When removing these caps, the fork spring will want to pop them out. To prevent the possibility of damaging the lowest threads, I like to maintain counter pressure on these caps as I unscrew them. I do this by putting downward pressure on my ratchet wrench as I work it back and forth. If I do this right, the cap eventually clears the last thread and lifts out cleanly without any pressure on that last thread.
I install them the same way. The critical part is positioning them straight into the tube with good counterpressure to seat them, and then carefully turning them so that the threads catch cleanly. If you cross thread a cap, you'll likely have to buy a new one, or maybe worse. So if you feel resistance or have any doubt about whether you are threaded up correctly, don't continue. Back off and start over.
Fork braces deserve a comment. They need to be flat and true relative to the mounting surfaces on the lower legs where they bolt on. If they don't lie perfectly flat, bolting them down can place torque on the lower legs which, in turn, can cause "stiction". If you chose to check this when you have the brace off and find that it is not quite true, consider pacing shims in the area that does not touch (typically one out of the four bolt holes areas) to the stress off the lower legs..
Aftermarket Fork Springs
The most common complaint with Virago forks is that they are too soft, with excessive dive on sharp braking. Once air was gone, the only good solution to this was to consider a stronger set of springs. The most common solution to this is to install a set of Progressive Suspension fork springs, and this is a pretty good thing to do in my opinion. There are many satisfied Virago owners riding around with them. They come with good directions. And in my experience the Progressive guys are good to work with in the event any problems present themselves or the customer has questions.
At this point we will take a moment out of our busy schedule to note that fork springs for Viragos come in two different types: straight wound and progressive wound. With straight wound springs, the coils are all the same distance from each other. With progressive wound springs the coils at one end are closer together. As a general rule, the closer the coils, the softer the spring. So the idea of progressive wound springs is to give you a soft ride around the "static" position--where the forks normally sit with you on the bike riding on a smooth road. But when you hit a hard bump, the softer (close together) coils fully compress and touch each other (go into "coil bind") and the stiffer (farther apart) coils then come into play to soak up the bump with more resistance.
There are several spring options out there and I have tried a couple, but the Progressive springs are reasonably priced and do the job pretty well as I've said. Beware of springs offered by sport bike-oriented suppliers such as RACE TECH. Following their guides may get you springs that are too stiff. Note that most sport bikes have a fairly even weight distribution at both ends of the bike, whereas the Virago plants only about 40% of its weight on the front wheel, and 60% on the back wheel. When riding two up, most of the passenger's weight lands on the back wheel as well, making the difference between the front and back wheels even more pronounced.
Here are some measurements (in pounds) I took on a 1991 Virago 750 (will hold true for most any '84 and up 750 and 1100)
Total Front Rear
Bare bike 520 235 285
With 190 lb rider 710 280 430
Two up (130 lb pas.) 840 300 540
Bent Fork Tubes And Lower Legs
So you bad girls and boys ran into something and bent your forks, did you? The book will say it is unsafe to straighten them and will tell you to buy new ones. I will tell you that a seriously skilled and professional "bending" shop can often straighten them. And this applies to both the tubes and lower legs. One test is this: if the fork tube(s) are "creased" (typically happens where they join the triple clamps) then they are goners. But if the bend is smooth, it would be worthwhile to find a really good
shop (such as the Frame Man in Sacramento, California) and have them tell you whether it is safe to straighten the forks or not. Same for the lower legs.
Finally, Frank's Engineering (Forking By Frank) claims they can duplicate most any fork tube, so in the event you have the problem it might be worth a call to see what they've got. Ask them how they handle the "foot valve" in the fork. Yamaha is a source for later model fork tubes, but as expected, pricey.
Extended Fork Tubes
I get questions about extended forks from a few guys building choppers. The only source I know of for these is Frank's Maintenance and Engineering noted above. Extending forks will radically change
the handling of the bike and give much slower turning. I am not a chopper expert.
Remember that little spring sitting around the damper tube to cushion the fork on full extension? Well, by lengthening that spring and shortening the main spring a lowering effect can be achieved, and this is what "lowering kits" are all about. But what you give up here is fork travel. A simpler way to get your lowering (if that's what you are after) and retain all your travel is simply to move the forks up a tad in the triple trees. Up to an inch might work. You need to test the forks at full compression to make sure the fender doesn't hit the exhaust header. This means removing the fork caps and completely collapsing the forks to make sure the clearance is there. AIR FORKS: For those with air forks, you may have to discard the air filler and balance tube to achieve this. You may want to plug the air holes in the tubes and just go without air. Yamaha dropped air forks in later models, and you can do without air, particularly if you install Progressive fork springs. As I recall, I plugged my air forks with a toothpick held in by JB Weld. But how you do it is up to you.
Few Viragos that I have seen run boots on their front fork tubes. I do because I like to keep rocks from hitting/pitting the tubes, and road grime from attacking the fork seals. Of course, that's what the scrapers are for, but they don't catch everything. Kawasaki KLR's have 38mm forks and boots for these bikes could probably be adapted. Some work at the bottoms of the boots will no doubt be required, particularly with later models that have the fork brace. I figured out a way to make boots work, so if you want to try them, shoot me an e-mail.
As we noted above, aftermarket fork braces were available for the early models, and one might be found on e-bay or elsewhere. Later models come with them as standard equipment.
Well, that's all on the forks for now. You may want to take a ride and clear you head before we get into
The general principles of springing and damping apply in the rear as well, but here there are no damper tubes. Damping is handled with hydraulics (fluid through holes) but here spring loaded valves or "shim stacks" which bend under pressure, vary the oil flow on compression damping and allow more flow as velocity increases. I have never had a virago rear shock apart (they are not rebuildable like many of the more expensive aftermarket shocks) but I would assume they use shim stacks.
As for springs, most OEM Virago shocks appear have straight wound springs although some of the dual shocks look a little progressive. But the springs in aftermarket shocks are usually progressive. You can verify this by looking at them to see if the coils are uniform for the length of the spring.
'81 to'83 Viragos
In these years Viragos came with monoshocks, that is, one shock attached to the swing arm in the middle. These shocks have an air feature and also provide for rebound damping. How much air? The manual says a minimum of 7 and a maximum of 57 psi, with a "standard" setting of 14 psi. It warns you not go below 7 and certainly not above the maximum allowed. The amount of air is really set by your
preference, with the higher psi air settings used primarily for two up riding.
The monoshock also has an adjustable rebound damping feature which is necessary in that adding air effectively makes a stronger spring, which will rebound faster, and therefore needs more control. The adjustment has five setting as I recall, from light to heavy damping. The whole range can be moved up or down but I'm not getting into this in this article. If you want to do this, have a look at the damping mechanism then e-mail. me.
The main problem with these units is that after a long and happy life, they may quit holding air.
Here again Progressive Suspension comes to the rescue with a beefed up spring for these shocks (a nice red one), which pretty much gets you off additional air, since it supports the bike and rider all by itself. A little extra air can be used for two up. If your shock quits holding air and/or is too soft for you, this maybe the solution to be able to continue riding.
Works Performance has also been known to make rear shocks for these models. They aren't cheap, and I have not had great luck with WP on their street bike offerings, mainly in respect to getting the right spring rates.
'84 And Up Models
In 1984 the Virago style changed in a major way. Gone was the "standard look", and in was the "cruiser look". And with it came dual shocks on the rear. The 700's and 750's received basic shocks with preload adjustment only. Preload sets ride height, and you might want to use this adjustment when you are riding two-up, or if you are on the "heavyset" side. I talk a lot about preload later in this article, if you are interested.
Back in the early 90's the complaint in respect to 700/750's was "too much spring, not enough damping". However, I think these shocks have been improved over the years.
The 1000's and 1100's got (in my opinion) a better shock which was more compliant, and had both the preload adjustment and a rebound damping adjustment.
What can happen to these shocks? They can just wear out internally and quit working well, in which case it is time to replace them. Under tough use or heavy loads, the hard rubber bushings in the eyes of the shocks can start to break down and oval out, in which case, if it gets bad enough, the shocks
should be replaced. Yamaha won't sell you these hard rubber bushings, and I don't know a source. You might try Progressive.
So much for the OEM equipment.
The stock shock length is 11 3/4 inches. In the after market you can find 11.5 inch shocks and 12 inch shocks. While in theory different length shocks will change the geometry of the bike somewhat, my view is that .5 inches one way or the other isn't going to make a whole lot of difference in the handling or feel of the bike, particularly for cruising type riding. Personally I'd go for the 12 inchers, which won't have the effect of "kicking the fork out" and slowing the steering (by a very tiny bit, as I said.)
Progressive Suspension offers shocks for Virago, as do other suppliers. Koni used to sell a really good shock for the Virago with preload and rebound damping adjustments, but alas, they have gone out of the motorcycle shock business. There is a rumor that an Australian firm bought all the equipment and will be offering these shocks again. This company is called Icon, I believe, but is a different Icon from the one seen in motorcycle magazines these days dealing in clothing and helmets. Anyone with experience regarding good aftermarket shocks for Viragos is hereby invited to contribute that knowledge.
The main problem with buying aftermarket shocks is getting the right springing. You are looking for springs that will support you and the bike correctly with no preload dialed in. The preload adjustments are then available for use when you carry a passenger or luggage, or both. In theory, suppliers have done some testing (R&D) work, and when they specify a shock for a Virago, the damping and spring rates should be ball park. In cases where the spring rates are wrong, the supplier can usually substitute lighter or heavier springs, there maybe some "cut and try" to get things right..
In general, you are safe to follow instructions in your manual relative to fork disassembly/assembly amount of fork oil, etc. For firmer front forks I think Progressive Suspension springs are a clear improvement. there maybe other good alternatives. For rear shock replacements, I have no slam dunk recommendation. Progressive makes them, as do several others.
This concludes my basic discussion on Virago suspension. For those readers who just can't get enough of this stuff, I've included some additional material of a more advanced nature which you are welcome to have a look at, if you want to.
MORE TECHNICAL STUFF
The role of springs is to store energy on compression, and spit it back out on rebound. As we have said, there are two kinds of springs typically used in Viragos. The first are straight wound springs. The coils in these springs are the same from one end to the other. The force needed to compress these springs stays the same. That is, if 100 lbs. of pressure will compress the spring one inch, and additional 100 lbs. will compress it another inch, and on so. I haven't see 'em all, but my recollection is that most OEM (original) Virago fork springs are straight wound.
The second type of spring is called a progressive spring. Here typically the coils at one end are closer together than those found in the rest of the spring. These coils give the spring a softer character at first. For example it may only take 50 lbs of pressure to compress the spring the first inch. But once these close-together coils touch each other and go into "coil bind"), then we are into the stiffer coils that are farther apart. The next inch of compression may require more pressure, say a 100 lbs., and from then on. The progressive feature makes the spring softer and more compliant when it encounters small bumps , but stiffer when compressed further by bigger bumps. This also has implications as to preload and damping as we shall see.
Note that the pressure numbers presented here don't relate to the real world and are used for example purposes only.
Spring preload and ride height
We don't just throw a spring into a fork tube and let it rattle around. Some initial pressure is put on the spring to compress it a little, even when the fork is fully extended. This is called 'preload' and one of its main purposes is to set ride height. For example, let's say that the total travel of the lower leg is 5 inches up and down. With the rider sitting on the bike, a ballpark goal is to have the fork compress to about one third of this travel That gives the lower leg plenty of travel left to soak up bumps, but also allows it a little reverse travel to drop into depressions it may encounter. So we try to set preload to achieve this "1/3 of travel" rule with the rider sitting on the bike.
Preload is changed by varying the length of spacers which go between the top of the spring and the bottom of the fork cap, taking into account the depth of the cap as it screws in..
Progressive Suspension says "most motorcycles need between 3/4" and 1" (20mm-25mm) of preload".
RACE TECH says: "Typical preload for street bikes is 5/8" to 1 1/4" (15mm-30mm)".
The springs you buy will probably come with instruction and preload suggestions.
NOTE that in regard to straight wound springs increasing preload does not "stiffen the spring up", that is to say, change the spring rate in any way. The straight wound spring will still require the same amount of additional pressure to compress it an additional inch.
However, the situation is a little different with progressive wound springs since the preload will mainly influence the softer coils. In this case adding preload does slightly stiffen the spring by taking up some of the initial softness.
Another way of looking at "ride height" is called "sag". That is, how far do the forks compress (sag) under the weight of the bike alone, and the bike and the rider together. Here is the way this is measured.
First, while the springs are out of the bike we fully compress the fork. We then place a plastic tie around the fork, tighten it, and slide it down to the wiper. Then we install the springs and any preload spacers required, throw the bike on the center stand, and make sure the forks are fully extended. We then measure the distance between the wiper lip and the plastic tie. This is the total fork travel.
Second with the help of the friend you made earlier in this article, take the bike off the centerstand and hold it upright. The weight of the bike should cause a small amount of compression in the forks To measure this sag the professional way, with the bike upright, lift the front of the bike to achieve full fork extension and then let it down slowly. Measure the distance from the point where the wiper stops to the plastic tie, and note it. Then push the bike down to compress the forks, and let it up slowly. Then measure that distance and note it. The difference between those points is caused by fork "stiction". (Hopefully, that distance is not too great.) The point midway between those two points is considered the accurate measure of FREE SAG.
Third, we now want to measure what we call STATIC SAG, which is the more critical one. This is the distance the forks compress with the rider on the bike, and is the same as "ride height". Take your measurements the same way you did for free sag. Static sag is the one we want to see at roughly 1/3 of total fork travel.
What is the "Right" spring ?
Springs come in different weights--that is, some are softer and some are stiffer. Here's my definition for what it's worth. The right spring is one that (with preload set within the ranges described above) supports the bike and rider at about one third travel, and provides a "good" ride. This last bit is highly subjective since some riders like a "plush" ride, and others like a firmer ride. As noted, most aftermarket springs come with instructions which suggest preload settings to achieve this. And when you order aftermarket springs you assume that the supplier has done the R&D and that the springs are the right weight for you plus your bike. But, again, beware of springs from sportbike people. They are not always tuned to cruiser fork needs and are likely to be on the stiff side. Sportbikes typically have more weight on their front ends (e.g. 50%) than do Viragos.
When playing with spring weights, note that you can achieve proper ride height/static sag (i.e. 1/3 of total travel) with a spring which is too stiff, by setting a small amount of preload On the other hand, by cranking up preload you can achieve the 1/3 figure with a spring that is too soft. But even though the static sag will look good, your springing will still be too soft or hard, and your ride will be affected accordingly. Finally, note that if things are right, you should see a little free sag, and more static sag as the rider weight is added. Assuming roughly 1/3 static sag, too little or too much free sag may indicate that your springs are too soft or too hard. You can recheck your preload numbers but you maybe looking at different weight springs.
Note that the principles discussed above apply to rear shocks as well. But here we don't have spacers to play with, and with Virago shocks our ability to change things is limited. Preload adjustments are available on the shocks, but these should be used to mainly to accommodate additional weight (luggage, passenger) and not to set initial ride height. If static sag is too great with the spring provided, you probably need a stronger spring. The technique for measuring travel on rear shocks is a little different. Total travel is harder to come by, and I generally use the specs given for the bike, i.e. 2.8" (50mm) for Viragos. Note that this translates into greater wheel travel since the shocks attach well ahead of the axle. I have made some special tools to measure total travel, free sag, and static sag on the rear of my bikes--mainly for tuning sport bike suspensions. I think we must accept stock Virago shocks "as is", but usually have some spring options with after market shocks.
Unsprung Weight, Inertia and the need for Damping
Unsprung weight is that weight which is not supported by the spring. Wheels, tires, brakes, lower legs are all unsprung weight. When a bump is encountered, this unsprung weight has to respond directly, that is moved an equal distance out of the way. If the bump is one inch high, the unsprung weight has to move one inch up (although actually the 'give' in the tire provides a slight bit of "spring") The whole bike doesn't have to move up an inch, however, because as the fork spring soaks up the bump, and the bike can stay pretty much level.
When a baseball sits on the ground it doesn't want to go anywhere. When a pitcher picks it up and throws it, that same ball takes on a life of its own and wants keep moving. It will go its way forever until something (catcher, bat etc.) stops it, or until the force of gravity finally pulls it to earth. This phenomenon is called inertia--which is the tendency of an object to keep still when no force is applied to it, and to keep moving once some force gets it moving
When usprung weight (wheel etc.) gets moved sharply up by a bump, it takes on momentum and wants to keep moving. The spring provides most of the slowing action, but some compression damping control is also needed to assure that the momentum is checked before the forks compress too far. The springs should be doing most of the work here, with a small assist from the compression damping.
On the way back down, it is now the spring that provides the force, and rebound damping is needed to see that the weight below the spring doesn't travel too fast too far and over-extend the forks.
Some Thoughts On Fork Oil
Yamaha designed Virago damper rods to use 10 wt. oil--to provide what they consider to be optimum damping with stock springs. Damping will be increased by going to heavier weight fork oil This is because it is harder to force thicker oil through the holes in the damper rods. The reverse is also true. Damping is diminished by going to lighter oil.
Yamaha also specifies the amount of fork oil which goes into each fork, and this can vary somewhat by model so consult your manual for the correct amount.
Another way to measure the amount of oil in a fork is to find how high the oil level is in the fork tube. This measurement is typically taken with the forks fully compressed (springs out, bike on centerstand) and after you have pumped the forks a few time to make sure the oil has filled all the cavities in the lower leg. This measurement will give you a benchmark which maybe useful if you ever decide to vary the amount of fork oil up or down a little, based on different springs or other considerations.
Dirt riders often vary their oil levels based on track conditions, and some road riders tune their forks this wa as well. Why do they do this? We must remember that that the air above the oil in the fork tube, being compressible, acts as a air spring. The higher the oil level in the fork, the smaller the amount of air, and the stronger the air spring.
Another reason you may be interested in oil level is this: Oil is not the only thing in that fork which displaces air. Your spring itself also does so. Progressive springs, for example, have heavier, thicker coils than stock Virago springs. If you pour in the stock amount of oil recommended in your manual and then fit Progressive springs, your oil level in your fork tube is going to be higher than it was with stock springs. To achieve the "stock amount of air spring" you would want to use a little less oil.
Measurements can be taken with any kind of simple "dip stick" you care to make. One mark always need to line up with the top lip of the fork tube. A measuring cup is a must for your initial full. You can easily add oil. To remove some, however, is harder. I use a turkey baster with a long pipe attached to it. To check oil levels with different springs in, simply jack up the bike under the engine to where the forks are fully extended, and measure the oil height with the different springs installed. Pull springs out slowly, or you'll drag half the oil out with them.
The big compromise inherent in damper tube forks
Damper tube forks can do a very good job and have been the standard approach to damping from the beginning of time. They are still fitted to many new bikes built today, including most cruiser bikes. For cruising type riding they are more than adequate. The problem they have is this:
Fluid passes through a hole very easily when the fluid is moving slowly. As you attempt to force it through faster resistance at the hole goes up by roughly the square of the fluid velocity and it gets progressively harder and harder to push the fluid through the hole.
For example, we will say that if a slow movement of the fork produces a velocity of 2 and gives a resistance through a damper hole of 4 , then faster movement of the fork giving fluid velocity of 3 will increase the resistance through the hole to 9. Increase the velocity to 4 and the resistance goes to 16, and so on. So if the hole stays the same size we start to approach a hydraulic bind situation where the movement of the fork is restricted now by the damping, and the spring doesn't get to do its job of soaking up the bump. The bottom line is that as the fork moves quicker and fluid velocity increases along with this, we really need a bigger hole to maintain a steady damping rate and allow the spring provide most of the resistance to the bump.
But if we make the holes big enough to give us the right amount of damping on big fast bumps where the velocity is high, then on slower bumps and braking where the velocities are lower the fork fluid will flow too easily through those big holes and won't provide enough damping. So that is the dilemma of the damper tube approach to fork damping. The nature of this damping method is that it just can't do everything well.
How to solve this dilemma? The answer is you compromise. Engineers set the size of the damping holes to achieve the overall best results, giving away a little performance at each end of the spectrum. And for cruising type riding they can get the forks to do a pretty decent job.
But there is a better, more complex, and more expensive way. For performance bikes, the engineers go to so-called "cartridge forks" which do solve this problem by means of spring loaded valves which open up the holes in response to different levels of velocity. This technique is said to be "velocity sensitive" since the amount of damping will adjust to compensate for different velocities of the fork and fork fluid, and provide the "right" amount of damping for both slow and fast movements.
Note that this problem is mostly a "compression stroke" problem, since on the rebound stroke things get easier. On the compression stroke we are looking at a wide range of different velocities-from slow, easy movements, to very big, harsh, fast ones. But on the rebound, the spring sends the lower leg back down at pretty much the same velocity each time. That's because the spring is the spring. It only knows how far it has been compressed, and how much energy (e.g. 100 lbs per inch of compression) it has stored up. It could care less how slow or fast it got compressed. When the pressure goes off it, it will simply want to rebound based on its stored energy and it will do this at the same speed rate (velocity) every time. To illustrate this, if you slowly compress a spring and then suddenly release the pressure, do you think the spring will return out to its full length as slowly as it was compressed? Given this steady velocity on the rebound stroke, damping holes can be sized to take care of rebound damping quite well, since they have basically only one fluid velocity to deal with.
I must add that this explanation is somewhat oversimplified since there are some other forces working in the rebound situation. So we do find adjustable rebound damping, particularly on sport bikes. But in general, it is an easier problem than the "bump stroke" for the reasons cited. Also note that in respect to progressive springs the fluid velocity does slow down slightly as the spring approaches full extension and gets into the softer coils.
Solving the Damper Tube Dilemma-- Gold Valve Emulators
As we have said, sport bike engineers go to cartridge forks which self-adjust to different velocities and also have sophisticated adjustments to dial in both compression and rebound damping to meet various track and road conditions.
But what about our Viragos? Could such an approach be applied to the Virago? The answer is, well sort of. RACE TECH offers something called an "emulator" which emulates the action of the cartridge fork on compression damping only. But as we have said, that is tougher of the two to control. To use this device (which sits on top of the damper tube, below the spring) you first drill out the compression holes in the damper tube to allow more than enough fluid flow for the highest velocities that the fork is likely to encounter. The emulator is then installed to take over control the fluid flow on the compression stoke and provides better damping over the wide range of velocities that the fork is likely to see on the compression stroke. It does this by means of a spring loaded valve which is "velocity sensitive" and allows more fluid to flow on the hard pumps, and less on the slower movements, such as braking. If you want to vary rebound damping you can do this by varying the weight of the fork fluid. The emulator does not affect rebound damping at all.
No doubt, a higher tech approach to Virago fork damping. But there are some problems with this.
First, the little springs on the emulator which control its action are not adjustable from outside the fork, like on sportbikes. To change spring tension you have to remove the fork cap and fork spring. You then fish the emulator out, change the spring pressure and put it all back together.
The second problem is that RACE TECH is basically a high performance oriented company, and in my opinion has not really done the R&D on cruiser bikes to where they can tell you specifically where to set the spring tension for the best results. They will say things like "it's a matter of personal preference".
And the final problem is that us cruiser types don't often really have a finely tuned idea of what our "personal preferences" Really are Most of us don't go out scraping pegs every weekend, or do track days. If our suspension is providing a "good ride" we're happy. And most of us are.
So my advice would be to relax and not install emulators unless you would enjoy spending the money and experimenting with them. I must confess that I tend to fall into that latter group, and so do have a pair in my forks. But I must say that my discussion with RACE TECH about the right adjustments have been less than inspiring, with at least one major change in the adjustment spring used. I still don't know whether I'm totally "dialed in" or not. The suspension works O.K., and maybe someday I'll ride a little harder and try to develop a better feel for the damping.
In the mean time, I'm following my plumber's advice., "Fuget abot it an enjoy da ride!" (a heavy New York accent helps to fully appreciate this).
Finally, note that suspension science is one deep mutha, particularly when you consider the forces at work as the tires get close to the limit of adhesion-- as in racing and serious sport riding. This article just scratches the surface.
As always, comments, corrections, questions are encouraged.