YellowDuck

I agree with khp that getting the spring rate "correct" is about the most fundamental thing you can do to alter the feel and performance of your suspension. I say "correct" in quotes because there is some element of personal preference in this as well. One rider may prefer to have a more rigid suspension under all conditions and so might like a higher spring rate. That setup promotes stability without having to use excessive rebound damping, and helps ensure that travel is always adequate. The compromise is that the suspension may not be sufficiently compliant over positive deflections (bumps) so that traction might suffer in certain scenarios such as accelerating over rough pavement exiting a corner. Another rider might like a lot of compliance and so uses a lower spring rate but increases the preload to prevent bottoming; the tradeoff there is that the suspension will more often be topped out, under acceleration for the forks and under braking for the rear, which can create harshness and chatter under those conditions. Spring rate and compression damping work together to determine the suspension position at any given moment as cornering forces are applied or positive deflections occur, so some will say that they prefer a soft spring but "hold the bike up with compression damping". There is some truth in this but for sustained (more than a second or two) cornering or braking loads it is pretty much all spring rate and preload that determine the maximum suspension compression; as khp explained, under a steady-state (static) condition that is long enough, the spring is eventually going to compress to the point where it supports the load; compression damping just determines how long it takes to get there. Factor in separate high-speed and low-speed compression damping adjustments as found on many modern sportbikes, and you can get pretty lost in all of this... In my experience, compression damping is the most difficult thing to get right because it is pretty hard to make the adjustment and then clearly see the effect of the change on a stationary bike. You can feel it by bouncing the suspension, but not to the same extent that you can see the effect of a rebound damping change on the rate of suspension extension, or measure how a preload change affects sag. Fortunately, the compression damping setting also tends to be the least critical. Setting the sag (preload) is easy - do it once and forget it, at least until your braking intensity or cornering speeds increase to the point that you need more travel. Set the preload, then set the compression damping to some kind of middling best-guess setting, and then by only tuning rebound damping you can get most of the way to a setup that is sufficiently optimized for all but the highest rider skill levels. This is why when a suspension component only offers one damping adjustment, it will pretty much always be rebound damping - it just has a much more profound effect on how the bike handles.

I suspect your experience with bicycle suspension may have affected your view of how preload works. I don't know much about bicycles, but I can tell you for sure that much of what you wrote here does not apply to motorcycles. For example, you found that adding preload made the spring shorter, and removing it made it longer. This will happen on a motorcycle too, but only if there is little or no weight on the suspension (e.g., bike on the rear stand with the wheel in the air and the swingarm fully extended). But once you put the bike back on the ground, as long as there is ***any*** sag at all in the suspension under the weight of the bike and rider (and normally, there should be sag even with just the bike weight), then the spring length will be exactly the same regardless of the amount of preload you added. The only difference will be the amount that the suspension had to sag to get to that spring length. When you added preload, the spring got shorter with the suspension fully extended, but ***only*** with the suspension fully extended. In use (i.e., with sag), the spring length will be the same, and therefore the tension in the spring will be the same. Because the tension in the spring is the same, the "stiffness" of the suspension will not be affected by preload. Again, your bicycle experience may have given you the wrong impression. It is quite possible (I don't know for sure) that cranking in preload on a bicycle can result in a suspension that is fully extended under normal use - i.e., it is acting like a bicycle with no suspension at all. When you put enough load on it (e.g., by landing jump, or hitting a big bump at speed), only then would you get suspension movement. On a properly set up motorcycle, this is not the situation at all. Since there is always static sag, and since the spring rate does not change, any given force always produces the same amount of movement - stiffness is the same. The above applies almost exactly to forks, since they don't change much in terms of mechanical advantage. For a modern rear suspension, the above is not strictly true, because of the progressive linkage ratio - the amount the shock compresses for any change in swingarm angle actually changes with the swingarm angle. But in that case, adding preload usually has the *opposite* effect of what you described. That is, when you add preload, you extend the swingarm, and the resulting change in the linkage ratio makes the rear suspension *softer*, not stiffer. Try to get your head around these basic ideas about preload and what it does. There is another subtlety related to topout springs that I hope we can cover before talking about damping adjustments. I know some of this is counter-intuitive, and your current ideas about spring preload are shared by a majority of riders.

Here's a trick related to measuring sag and setting preload... Just about every article about measuring static sag reminds you that stiction in the system messes with the measurements, so that you need to measure sag based on the average of "stuck up" and "stuck down" measurements. I won't repeat all of those instructions here, but here is an example article of that type, from Andrew Trevitt: http://www.sportrider.com/ask-geek-set-your-static-sag This is especially important when making measurements on the forks, where the effect of stiction can be 10 mm or more (quite a big fraction of the 35 mm sag we might be targeting). With the rear suspension it tends to be much less important, since the spring force tends to be very large compared to the stiction in the shock and swingarm bearings. "Stuck up" and "stuck down" sag tend to be very similar at the rear. Anyway, here is the not-so-commonly-known tip I wanted to share: Most people assume that stiction in the forks is due to friction between the tubes and the bushings and seals. This is true, but a significant amount of fork stiction can also derive from the hydraulics of the damping system. If you wind your rebound and compression damping adjustments completely out before making your sag measurements, you will reduce apparent stiction substantially and your stuck up and stuck down measurements will be much closer to one another. (If you don't have notes on your damping settings, remember to first turn them both full in, counting the clicks or turns, so you can put them back where you found them once you are done with your sag measurements.)

Once installed, the spring is exerting 15 kg of force inside the fork tube, because the tube when fully extended is shorter than the spring free-length. That is, the spring is squished inside the tube even when the tube is fully extended to the stop. That tension in the spring is enough to support 15 kg. If you add more weight than that, it starts to compress the spring further and the tube halves can start to move relative to one another. It will compress until the additional tension in the spring is enough to support the additional weight. Does that help?

Thanks Laura - I love hearing that other people enjoy the blog posts. It's not hard at all to make them interesting because every single race weekend really is an adventure. Wes asking his mom if it is okay for him to keep racing - you can't make stuff like that up. My team mates are also a riot. The reason I throw Allen under the bus almost every post is because he always spends the whole weekend teasing everyone else mercilessly. We are in stitches every evening.

I am quite certain that you are the Prairie Dogs' biggest (read: only) fan. Nonetheless the support is much appreciated! If we get another batch of T-shirts made up I am totally sending you one. Oh, by the way....last SOAR round I ran into Brodie and told him he had something of a reputation around the CSS forum. He found that hilarious.

Ha! Nice one. I hope more folks post stuff like that. Believe it or not I have at least three more topics related to springing and preload that I want to post about. One of them (the last one - it is the most advanced) relates exactly to the example you gave.

That's not a thread jack at all - I was really hoping that we would start some discussion here where we could all share our experience and ask each other questions. It wasn't my intention to write a textbook! Two thoughts on your question. The first thing I would do is monitor suspension travel with a a zip tie around the fork leg. If it is bottoming out, then there is your answer - you ran out of travel and bottomed the forks, so any additional bumps were delivered right up through the forks to the bike and rider. The question is, why? A common cause of this is too much rebound damping relative to the spring rate + compression damping. If the forks compress much more readily than they expand (because the spring rate is too light, the compression damping is too light, or the rebound damping is too heavy), then as you go over a series of bumps during heavy braking the forks will "pack down" progressively until you are out of travel. That's the most common cause of what you describe. Second thought - this is a story from personal experience. I was experiencing a hammering through the front suspension in the braking zone at the end of the front straight at my local track. Yet my front suspension data acquisition system (zip tie) indicated that I had a good 20 mm of travel left. Big head scratcher. I fiddled with a bunch of adjustments to no avail. Phoned Traxxion Dynamics who had sold me my fork internals. Their first question: "Are you sure it is the forks?" Of course I was - what did they think I was, an idiot? Second question: "Are you using the rear brake?". I reminded them my question was about the forks. They politely suggested increasing the air gap (i.e., dropping the oil level). I was convinced that the fork positive travel must be somehow internally limited with the cartridges they sold me, so I had the forks off the bike and the springs out. Nope - they compressed right down to the dust seals; my "data acquisition" was giving correct information about available travel. So, I increased the air gap and reassembled. Next track day, same problem, same place. I couldn't brake hard at all without getting that wicked front end chatter. Total despair. Then I started paying attention and realized, much to my surprise, that I was indeed (unconsciously) applying rear brake! I stopped doing that. Problem gone. Instantly. 100% fixed. What I had been experiencing was violent rear wheel hop under hard braking, not front chatter. I couldn't tell the difference! Morals of the story: 1. I am an idiot. 2. Take advice from experienced people seriously. 3. Sometimes it is not the solution that evades us, it is identifying the problem.

For those who like visuals, here is a diagram I made some years ago to explain how preload adjustments work. There is something very similar in Trevitt's book. The parts of the figure A - E are as follows: A. Spring is 600 mm long, and has a rate of 1 kg / mm. That is, it compresses 1 mm for each kg of force applied. B. Spring has been installed. Preload adjuster is wound all the way out. With fork fully extended, the spring is compressed by 15 mm. This is the “installed preload”. Thus, it will take 15 kg of force to start compressing the fork. After that it will compress by 1 mm for each additional kg of force applied. C. There is now 65 kg of bike + rider weight bearing down on the fork leg (130 kg across both legs). This causes the fork to compress by 50 mm from its fully extended length. That is, the first 15 kg is supported by the 15 mm spring preload, then the additional 50 kg compresses the spring 50 mm. Thus, with this load, the total “sag” in the fork is 50 mm. D. Since 50 mm is too much sag, the preload adjuster has been wound in 10 mm. This extends the fork by 10 mm, so the sag is now 40 mm. Note that the length of the spring has not changed. Adding preload does not compress the spring, it just extends the fork. This is always true, except if the fork is topped out. E. With the same preload setting as in D, the weight has been removed from the suspension. Now, there is 25 mm of preload (the 15 mm installed preload shown in B, plus the 10 mm preload added in D). Thus, it will take 25 kg of force to start compressing the fork. After that, it will compress 1 mm for each additional kg of force applied, as always. Summary: Adding preload does not result in a spring that is more compressed in use, and therefore does not make the suspension feel “stiffer”. The suspension will still compress by the same amount per unit force applied, regardless of the preload setting. Adding preload merely extends the fork so that it has more positive travel available before bottoming.

Nope. If you have 1.0 kg / mm springs in the forks (2.0 kg / mm for the two forks together), they will compress 1 mm for each additional 2 kg of force you apply, regardless of the preload setting. The exception to this is if there is not enough weight on the forks to compress them at all (zero sag), and then you try to compress them from fully extended. For example, let's say you have one of the fork legs off the bike. It is fully extended, since the 1.0 / mm spring inside had to be compressed 20 mm to install the spring (that is the "installed preload"). There is 20 kg of tension in the spring , so you will have to apply 20 kg force to the fork leg to get it to start compressing at all. But once you do that, it will compress an additional 1 mm for every additional kg of force you apply. Now turn in the preload adjuster 3 mm. The preload on the spring now totals 23 mm with the fork leg fully extended. You will have to apply 23 kg of force to get it to start moving, but after that each additional 1 kg of force compresses the fork leg an additional 1 mm, same as before. With the forks on the bike, they will compress whatever distance they need to to support the weight that is on them - the fraction of rider + bike weight that bears on the front wheel. (I am ignoring the effect of geometry of rake here to keep it simple - the forks here are straight up and down). Let's say there is 90 kg weight on the front suspension, and there is no extra preload dialed in. Both springs were compressed 20 mm to install them in the forks, so with the forks fully extended they exert 40 kg of force. With the wheel on the ground and the rider aboard they must support an additional 50 kg, so the fork compresses 25 mm (1.0 kg / mm x 25 mm x 2 fork legs = 50 kg). Now all of the weight is supported and the "sag" is 25 mm. Now you turn the preload adjusters in 2 mm. Fully extended the forks could now support 44 kg before they start to compress, so they only need to compress an additional 23 mm to support the remaining 46 kg. So what happened? You added to 2 mm preload, and the sag was reduced by 2 mm (went from 25 mm to 23 mm). That is, the forks just extended by 2 mm. Total compression in the springs is the same (22 mm preload + 23 mm sag = 45 mm total - enough to support 90 kg). The spring rate has not changed and you will still get 1 mm of fork compression for every additional 2 kg of force on the forks.

Hmmph....I guess I was hoping to generate some kind of reply.... This place is awfully slow lately. I hope that is because everyone is too busy riding!

As requested...here you go. I have so much to post here - this really is my favorite topic by far. Can we start with preload? This is truly my pet peeve. It is so poorly understood by 75% of riders, and you can always find someone who completely misunderstands it but will argue until they are blue in the face that their view of it is correct. The big misconception is that, when you add preload (turn the preload adjuster in), you somehow compress the spring and make the suspension firmer. A huge fraction of riders labor under this misunderstanding. What really happens is that, when you add preload (say, 3 mm), the suspension simply extends by exactly that amount. So, your starting sag position is 3 mm higher, and you will have 3 mm more positive travel before it bottoms out. The spring compression does not change. The only condition under which the suspension is made "stiffer" with added preload is the situation where the suspension is fully extended (e.g., full extension of the forks when the front wheel is off the ground). It will take more weight on the suspension to get it moving from the fully topped-out postion, but once it has any compression the spring rate is the same as it ever was (e.g., it will compress 1 mm for each 10 N (1 kg) of weight, if it is a 1.0 kg / mm spring). Obviously we don't spend too much time with the suspension topped out, so suspension stiffness under that scenario is not terribly important. So, what preload really does is set the initial ride height and sag - it determines the ratio between available positive travel (compression) and negative travel (extension). That's it. It does not make the suspension firmer. When you start talking about rear suspension, the average rider's understanding of this is even more incorrect. Because of the rising rate linkage ratios on most bikes, adding rear preload (and therefore extending the rear shock and increasing the swingarm angle) will actually make the rear suspension action *softer*. Yes, softer. Even some well-known suspension tuners speak incorrectly about this issue, saying, for example, that when you add fork preload you also should increase rebound damping to help control the "extra energy stored in the spring". What's really happening is that you probably needed the extra preload because your corner speed was increasing and you were running out of positive travel. It was *you* and your high-G cornering putting the "extra energy in the spring", not the preload adjuster. If anyone would like further explanation of preload and how it works, I have links I can share. There are some complicated exceptions to the basic picture above, especially when dealing with suspension where the topout springs are regularly engaged...but that is not Preload 101, that is the Master Class.

+1 on a suspension thread. Should we just start one?

Great - it will be fun to have another suspension geek a round here to talk to!

Am I misreading this, or are some posters arguing that "locking the rear is not as bad as locking the front, so you should use the rear brake"? If that is the argument, I strongly disagree. I think I already explained why. Why not just use the front as effectively as possible, and not have to worry about the back of the bike coming around on you because you locked the rear? If you were braking properly with the front, the rear wasn't helping you significantly anyway. If the bike gets sideways your braking effectiveness is going to be reduced substantially. Rear brake, bad. Threshold front braking with massive weight transfer and the front tire squirming and squealing, good.

I watched the video. For a novice rider my advice is to avoid the rear brake altogether, except in a few odd circumstances where too much front brake use is dangerous. The only two I can think of are travelling downhill on a sketchy surface (e.g., asphalt strewn with sand or gravel), or if you find yourself off the pavement and onto the grass on a track (or anywhere else you end up on grass!). Other than that, using the rear is just a bad habit that can bite you. Sure, under normal braking you can use the front and rear together just fine, but then what happens when you have your first panic stop? You apply both brakes hard and skid the rear tire (for sure). Startled, you likely release both brakes, and now your stopping distance is increased substantially. You would have been much better off with effective application of the front only. EVERY rider should regularly practice hard, front only braking, with a progressive squeeze on the lever over about 0.5 s to let the front suspension compress and weight transfer to the front tire to occur, and then hard braking to the point of nearly lifting the rear tire, with increasing brake pressure as the bike slows right up until the point where it stops. This should be practiced often enough that it is second nature in an emergency situation. The rear brake has NO place in this, since there is so little weight on the rear tire anyway. On a bike like your wife's, you have a linked braking system that changes all of the above, plus ABS to possibly protect you from amateurish use of the rear brake. Personally, I would still recommend avoiding the rear brake, unless the rider never plans to ride any bike that doesn't have ABS and linked brakes. When you get to the point of running expert pace on the track and are seeking to shave those last few tenths, then maybe the rear brake starts to come back into the equation, as pointed out in that video. I don't use the rear at all, ever (except on the grass....), and I am fast enough to be a reasonably competitive amateur racer. But I am still seconds away from an expert race pace, not tenths of seconds. I know opinions will vary on this. My opinion is based on 25 years of street riding and 5 years of track riding and racing, and only applies to sportbikes and standards, one-up. Cruisers, touring bikes, two-up riding...I think my opinion would be different.

Not to mention needing a bigger vehicle to pack all that stuff. I currently pull my bike on an open trailer, but my Dodge Journey can't handle all the other stuff needed for a race weekend, even with the back two rows of seats down. I think I need a 5 x 8 (at least) enclosed trailer.

Here is the blog post for Round 1. By far my most enjoyable race weekend yet. http://prairiedogracing282.blogspot.ca/2015/05/round-one-2015-so-far-so-good.html

Oooh! Round 1 was awesome. Blog post coming soon...

Yeah, that does look unnerving!

I still think this is an awareness / confidence issue. I am not trying to be rude here. You *are* countersteering, you are just not countersteering very hard (quick flick). Here's what I would do. With the tires warmed up (i.e., not first lap if you are not using warmers), pick a corner where you have a long braking area. Don't charge the corner at all - get your braking done very early and be off the brakes completely by the turn point so the the bike is almost level on the chassis (maybe just a bit of engine braking) , with your body already in position on the inside. When you get to your turn point sight the apex and *consciously pay attention* to what your inside hand is doing. Feel your self press the bar, and press it as hard as you dare. You will not break the front loose under these conditions (assuming warm tires, decent asphalt, etc). Next time, same corner, do it again but harder this time. You will be turning it hard in no time, and convince yourself that the front tire is not going to let you down. You just need to get comfortable again with turning the bike hard. I strongly doubt it is a matter of strength, leverage, etc. if you feel like you are not countersteering at all. It is simply confidence.

This *really* depends on the person. Honestly, "getting into the motor" isn't the most important thing for racing. Most novice racers change the pipe and maybe the intake, get a fuel map made, and maybe add a quickshifter. Or just run the motor totally stock... What really makes the difference is learning about chassis tuning - brakes to some extent, but even more so suspension, ride height etc. This is where racers really differ. Some will take the bike to a professional suspension tuner, have them set it up, then never touch an adjuster again all season. To me, that's crazy. I have done more reading about suspension tuning than any other motorcycle-related topic, and I am always making adjustments and, in the off-season, even hardware changes (springs, valves). At the very least a rider should be comfortable monitoring travel and adding or removing preload. Experimenting with ride height and attitude (either directly or via preload changes) can also be really useful. I am actually always a bit surprised how little understanding many riders have about suspension adjustment. Check out Andrew Trevitt's book on Sportbike Suspension Tuning as an excellent starting point.

In our series you are provisional novice (amateur) for the first weekend, and you need to get through it with no more than one at-fault crash. Then you have your full novice license. Many riders will stay novice forever. If you compete in the premier classes (supersport, superbike, open) and consistently finish high and show pro pace, you get promoted to pro. This can happen even against your will. Because I don't compete in those classes I will never have black (pro) numbers on my bike. Which is just fine with me. Those guys really are at another level, and you also have to spend a lot of money to compete in that pack.

2015 Racing Blog, first post... http://prairiedogracing282.blogspot.ca/2015/05/here-we-go-againseason-2.html

Thanks for sharing that Nic and I really look forward to reading about your experience. I wouldn't worry about being too heavy for a 600 at 189 lbs. At the novice level rider weight really doesn't seem to come into it much. Our rookie 600 championship was won last year by a guy who I am sure is heavier than that...and he was riding a CBR old enough to qualify for our "lost era" class - a 2003 I think. Just shows you that skill is a much bigger part of the equation. Lots of guys over 200 compete very effectively on the 600s. When you get signed with a WSBK team they may ask you to hire a trainer and create your Troy Baylis body... My test and tune day is this Thursday. Pulled the bike out of the basement workshop Monday, and it is now fully assembled in the garage with fresh oil, etc. So excited! I found it funny reading on the other thread about people claiming they get super rusty after a 3-month layoff. In this part of the world *everyone* is off the bikes for 6 months or more. It really builds the sense of anticipation.