Basic Suspension Tuning

This article is not about advanced techniques for race-preping suspension, nor is it a beginner's step-by-step guide. The intent of this article is to provide a small amount of insight into the process of tuning bike suspension for people that have some basic mechanical skills.

First, some terms:

Spring rate is how strong the springs are. Stronger springs take more force to compress a given amount. Heavier or more aggressive riders can benefit from stronger springs, but they also reduce the ability to absorb smaller bumps. Springs, being springs, take more force to compress as they go, thus we have spring "rate." Any force will start to compress a spring, it's how much the force needs to increase per amount of travel that determines the rate.

Progressive springs have variable spring rates and usually appear to have the spring coils closer together over part of the spring length. The spring coils that are closer together are designed to be weaker than the rest. When a bump comes along, they collapse first, until the spring coils bind against each other, and then the rest of the spring coils, which are stiffer, begin to compress. Thus, the springs can be stiff enough for more aggressive riding while still being able to absorb smaller bumps smoothly.

Preload is how much spring force the suspension has to keep the bike and rider up. Rear shocks usually have an external preload adjustment; forks are usually adjusted with spacers on top of the springs. Without preload, the bike would just sag down, collapsing the suspension. Too much preload and the suspension will be fully extended, even with the rider sitting on the bike. Basically, preload should be set such that there is some sag but not too much. Note that preload does not increase spring rate, it just preloads the initial force on the spring to shift where the bike sits on the "rate" scale.

Sag is a measure of how much the suspension settles down when the rider is sitting on the bike. When going over dips, the wheels need to extend downwards to stay connected to the ground. Without sag, even going over small bumps would let the wheels fly off the ground. This kills traction. Some sag is good. Sag also consumes your suspension travel and this will reduce the ability to take bigger bumps without bottoming. Too much sag is bad. How much is right? Lots of people will give you exact numbers but the truth is that it has to be right for you and, unless you are a serious racer, this isn't going to get reduced to a formula. You just have to try different amounts until it feels right.

Damping is the rate at which the suspension can move in and out. It is either controlled by valving or by the weight (viscosity) of the oil. Too much damping and the suspension will be too slow to absorb the bumps. Too little damping and the bike will collapse onto and spring off bumps like a pogo stick. Sometimes, you will be able to adjust compression and rebound dampening separately - this can be a good thing. Like everything else, the right amount of damping depends very much on where, how, and what you ride.

Oil height is a measure of how far down the oil level is in the fork tubes with the springs out and the fork fully collapsed. Oil height matters because forks are sealed. As they collapse, the air pressure in them increases; increasing air pressure effectively adds to the spring rate. Thus, as forks collapse, the air in them acts sort of like progressive springs. The higher the oil in the tube, the more pronounces this effect is. Oil height allows you to fine-tune how your suspension behaves in the bigger hits.

Air pressure in front forks can be adjusted with the tire-style valves at the top of the forks. Honestly, the manufactures installed these valves so you can take air pressure out, not put it in. As you ride, your forks will warm up; as they warm up, the air pressure will increase. Increasing pressure will add to the effects of your preload and oil height settings. Also, over time, forks tend to "pump up" just by riding. Serious riders with well-tuned suspension will take this extra air pressure out. However, some people use these valves to add air pressure. Now, if you are attempting to temporarily tune your suspension to some unusual set of conditions, this is fine - so long as you don't add too much. Most manufactures recommend against this. Too much air pressure is very hard on fork seals; you may start leaking fork oil. Besides, if you are using air pressure all the time, then you might want to properly tune your suspension in the first place. Air pressure changes too much as you ride and this will change how your bike handles, making it less predictable. Predictable is good; it allows you to ride closer to the edge.

Bottoming is what happens when you hit a bump so hard that the suspension collapses to its limits. If you are bottoming often while riding around then you either have too soft of a spring rate, too little preload, too much sag, not enough fork oil, too little damping, or you don't know how to ride very well. Hey, I never said suspension tuning was easy.

Lock up or binding is what happens when you screw up your suspension tuning. If you add too much preload, the spring coils will bind up before the suspension bottoms. This is a bad thing as it puts way too much force on the wrong parts of your suspension. If you have too much fork oil then you will bottom out on the oil before the suspension is finished. While this isn't quite as bad and coil bind, it's still really hard on your fork seals. Bike manufacturers usually specify limits on preload and fork oil height; it is wise to stay within these limits. If you need more - start thinking about buying new springs.


Why bother with all of this?

The object of suspension tuning is to maximise traction and control. If your suspension is too soft, and you regularly bottom out, then you will have a hard time controlling the bike. If your suspension is too hard, then the bike will stutter on small bumps and you will loose traction, and probably control. If everything is just right, you will be able to maintain control while traveling quickly over smaller bumps and still be able to absorb the bigger hits without having to slow down too much. Riding a well tuned bike makes a huge difference in a rider's ability to go fast over varying terrain. And, let's face it, if you're not going fast, your suspension doesn't really matter - just about anything will work well enough.


So, how do you do manage all those combinations in suspension tuning?

Basically, very basically, here's the order I recommend:

1. Get the preload right. Once you get the preload right, move on to the next step. If you need longer spacers than the maximum allowed, then you need stiffer springs.
   
2. Get the front damping right. Typically, this means changing fork oil weights, but your bike may be adjustable. It doesn't really matter, just get it right. The heavier the oil, the less your forks will collapse on a big hit and the less they will absorb the stutter-bumps (= loss of traction). Then, when this feels about right, go on.
   
3. Get the fork oil height right. The higher the oil is in the tub, the faster your air pressure will increase and the stiffer your forks will get before bottoming. If the above is right, and you still bottom a lot in the front, add more oil - being aware of the maximum for your bike. Then...
   
4. Adjust the compression and rebound dampening for you back shock. On my KLR, there is only one adjustment, so I do what I can.

So, what's right?

Riders will note that I've spent a lot of time describing what can be adjusted, and the order to adjust them, but nothing about what they should be adjusted to. This is because I can't tell you. Suspension tuning is not really about specific measurements or right and wrong, it's about the best compromise you can get for YOUR riding style. Suspension is not perfect, it's always about trading off one thing for another... you want soft suspension for traction but stiff suspension for the bigger hits. In fact, the settings you use as a learner will usually be way too soft once you really know what you're doing. On the other hand, I've also seen inexperienced riders way over-stiffen their suspension. Basically, they're hitting the larger bumps all wrong, hammering the suspension until it bottoms out. To compensate, they stiffen the suspension to avoid the bottoming, but in doing so they sacrifice traction. Without the control from decent traction, they can't ride that fast.

What I'm trying to get at is that the suspension needs to be tuned to the rider. There are just too many variables: height, weight, terrain, bike, ability, etc.. There are a lot of people out there offering specific advice. If you can find someone with the same variables as you, you might get some decent information on where to start. This is especially true if you are riding a bike outside of its intended terrain, a motocross bike on tight-woods trails for example. Generic advice for all makes, terrain, and riders, will probably be less useful than the stock manufacturer's settings. What this article is attempting to do is just provide some insight into what the terms mean and some ideas about what each setting will do. You get to take it from there.

Chance Favours the Well Prepared

I ride my KLR650 - away - from civilisation at every opportunity. I also like riding nasty single track where extra weight, even on a monster like the 650, is an issue. Besides that, I frequently ride alone. So, I make sure to carry what I need to fix my bike, but not so much that I can't ride where I want. Over the years, I've fine-tuned my gear to match my bike, my riding style, and my capabilities. The following list may not be right for you, but I hope it will at least give you a few ideas about where to start.

The list:

1. Poor Man's Batman Utility Belt: Bailing wire, black tape, zip ties,
   and duct tape. I don't carry rolls of each, but rather, I take lengths
   and wrap them around other things. For example, my spark-plug wrench
   has a length of black tape wrapped around it, my axle spanner has bailing
   wire, and my water bottle has duct tape. Not a lot, but just enough to
   make an emergency repair. I also replace these lengths as they get
   ratty.
   


2. Everything I need to fix a flat tire. This includes an air pump
   strapped to my handlebars, tire levers zip-tied to my down-tube - just above
   my skid-plate, and an over-stuffed patch kit with extra glue tubes.
   Also, I replace one of my valve cover caps with one that can remove valve
   stems.
   


3. Better tools. I always replace the standard wrench sizes from the
   original bike toolkit with better quality wrenches. I only keep the
   specialty stuff, like plug wrenches and axle spanners. I also augment
   the kit with a pair of needle nose Visegrips - in place of the original junk
   pliers, a 1/4" extension with the head filed down to fit a 10m wrench and a
   few sockets, some allen keys, a master link for my chain, and a few nuts and
   bolts of various sizes. To lighten the load, I've drilled and filed
   the centres out of the larger tools, including the tire leavers.
   


4. My emergency pouch. This pouch contains the bare minimum I need to
   survive a night in the bush. It includes a pair of nylon jogging pants
   (in case I'm out in jeans and get soaked in the cold), a couple of
   Powerbars, a large garbage bag (very useful for lots of things, including
   emergency shelters), candles and matches (to make a fire), and a space
   blanket. It also has a cable saw (just in case there's no way around,
   under, or over a fallen tree - I've never needed it but it's light).
   


5. First Aid kit. My first aid kit is admittedly small - it's actually in
   a plastic travel-soap container. It contains Steri-strips, band-aids,
   gauze pads, a razor blade, Imodium, anti-histamine, and a shoe lace - just
   in case I have to tie something off. I figure I can use the tape from
   my toolkit or water bottle if things get rough. First aid kits are one
   of those things that will never really be enough; there's no end of things
   you can carry. Where you draw the line is pretty personal. I
   figure that if I'm alone and need more than what I usually carry, I'd pass
   out long before I got to apply the stuff anyway. If you're alone,
   carrying shell dressings for sucking chest wounds seems pretty pointless.
   


6. Pack stuff. Besides my emergency pouch, I usually also carry a
   Thinsulate vest, Gortex over-pants, and x-large rubber gloves - for when the
   weather gets nasty, water, extra food, and a map and compass - in case my
   GPS dies. If the weather is likely to get cold, I may also carry some
   fleece pants to zip under my Gortex.
   


7. Pockets and belt. I carry a neoprene face mask and scarf in my jacket
   pockets. In another pocket, I carry a little gas money, just in case I
   lose my wallet. On my belt I carry a Leatherman Crunch (locking
   pliers) and a cell phone. I'm often out of cell phone range, but you
   never know.
   
   

Things other people recommend you carry, that I don't bother with:

A spare tube. There is always the possibility that a tube will shred beyond being patchable. For those instances, some riders will carry an extra front tube - the theory being that a front tube can always be stuffed into a back tire if absolutely necessary. It's a good idea, but I don't bother. What I do bring is lots of extra tire cement and patches. I also make no attempt at riding on a flat tire, which will shred a tube quickly. I figure that, with sufficient time and glue, I could probably get a fairly damaged tube to hold air for at least a little while. Another point against carrying an extra tube is that they are big and hard to pack. Maybe someday I'll be cursing my decision but, for now, I just don't bother with a spare tube.

Clutch and brake leavers. These things stick out from the bike and can, when things go wrong, snap off. At that point, braking or shifting can become quite difficult. Some people carry spares; I don't. I do recommend taking a simple preventative measure: keep your hand levers loose enough such that you can, just barely, move them by hand. That way, when you fall down, they will move rather than break. Most people tighten them right up, and they break right off when falling over. Even if you carried spare hand levers, odds are the mount will break instead. Reduce the strain on both by keeping them slightly loose. Besides, for the most part - if the trail isn't too challenging - I can ride without a clutch or front break. It's not easy, but I can do it. As for the rear brake, no one I've ever met carries a spare rear brake lever. Riding without a rear brake is no big deal, annoying but not critical.

Shift lever. Some people swear by carrying a spare shift lever as well. I've bent mine around until it's hit the foot peg, but I've never broken one. KLR650 shift levers are prone to cracking; rather than carrying a spare, I make sure mine is okay by inspecting it once in a while. A little weld here and there is all it takes to make the stock shifter strong enough. If I did snap the shifter off, then I suppose I could make due with Vicegrips clamped on the stub. On a side note, before you go out and purchase that super-strong aftermarket shift lever, think about what you would rather have bend, the shifter on the outside or the shaft on the inside? If you hit a rock at speed, something is going to bend; I happen to think it should be the cheapest thing there is to replace. Sometimes weaker is better, like a fuse.

Clutch cables. Some people even carry spare clutch cables, I don't. It would be rather silly of me as my clutch is now hydraulic anyway. Besides, like a broken clutch lever or mount, all I have to do is get the bike started in first gear and I can make it out - at least until I get into traffic, and then it's not life threatening.

Some people always ride with a buddy. Well, that's a really good idea, but I don't bother much. There are problems with the buddy system: First, they always have the bike that breaks, which I wind up fixing for them - or worse, towing them out. Oh yea, tow rope; I don't carry one of those either. Second, if said buddies ride out front, I have to eat their dust. Third, if they ride behind, I either have to wait or they get lost and I have to go find them. Fourth, they wimp out and want to go home just when the trails are starting to get fun. And finally, I hate waiting around in the emergency ward after they've tried to keep up. So, I tend to ride alone, just wandering wherever the wind blows me. This is why I carry the stuff I do. I also acknowledge that I'm taking a risk and, if I screw up, I could die. No one will be there to save me, and I'm okay with that. I do take it easy while riding alone, and this is also the main reason I like racing.


Racing gives the best of both worlds. Like riding alone, I can go at my own pace. Unlike riding alone, if I screw up, I know someone will eventually be sweeping the course for people in trouble. Because of this, I can cut loose and ride as hard as I want, without that nagging thought that I could wind up in a ball on the trail, gasping for breath for a week, while slowly starving to death. I might die quick during a race but there's no lingering demise - thanks to the sweeps. Also, while I'm riding with a bunch of other people, I don't really have to look after them. Sure, if someone is hurt or broken down, I'll stop to help. But, I don't have to worry about the guy behind me when climbing a nasty hill, or going through some tough section. That's the job for the sweeps; escorting people out that get in over their heads.

And yes, I still carry all my emergency gear and tools, even when I race.