Increasingly these days, bikes are being produced with adjustable suspension. For as long as probably most of us can remember, most bikes have had preload adjustment on the rear suspension, but increasingly now, bikes offer multiple adjustments that allow you to tailor the characteristics of how the suspension operates to suit your riding style and personal preference. Or, alternatively, it allows you to totally bugger it up! Sadly, that can be the result for some people who fiddle with these adjustments without knowing what they’re doing. Hopefully this article will help you achieve the former, instead of the latter! To some people, having multiple suspension adjustments might seem like just more bling added to the package; but it’s much more than just bling, it can take out the bang and the boing! It can, as I said above, allow you to tailor the characteristics of how the suspension operates to suit your riding style and personal preference. For example, when I was looking for my present bike, one of the things I particularly wanted was a bike that had fully adjustable suspension. I was after a comfortable ride, so I wanted to be able to adjust the suspension to deliver that. Others might want sportier handling, so prefer to sacrifice a bit of ride comfort to give them better performance in corners. As I said, it’s a matter of adjusting the suspension to suit your riding style and personal preference. This article is intended for bikes that have fully-adjustable suspensions, but if your bike doesn’t have these adjustments, there are some things you can do. See the section down the bottom called “Adjusting The Non-Adjustable”. Okay, first I should give a list of terminology used, and what the words mean.
Preload. You’ll probably know this one. Preload is an adjustment that squashes the spring a bit before any further load – like the rider getting on – is placed on it. Basically it places a “load” on the spring. Depending on how much preload is placed on the spring, the spring will compress more or less with the weight of the rider.
Static Sag. This describes how much the suspension compresses when the weight of the bike is placed on it, compared to it’s natural unladen state.
Rider Sag. This describes how much further the suspension compresses when the rider sits on the bike. (Note: Various other terms are used for types of sag, but these are the most common).
Compression. Pretty logical, really; when a spring is compressed it becomes shorter, squashed down. This compression is usually caused by placing a load or force on the spring. In simple terms, that load or force can be the rider sitting on it, but it can also be the effect of heavy acceleration and braking, or hitting a bump.
Rebound. When a spring is compressed (see previous word), after the load or force that caused that compression is removed the spring returns to its normal length. And that motion of returning to its normal length is called rebound.
Damping. The word “damping”, in automotive usage, means to limit movement, or the speed of movement. The dictionary describes it in these words: “To make a strong feeling be felt less strongly.” It’s actually referring to emotions, but the description applies equally well to automotive things. Now we get to combine these terms.
Compression Damping. This lessens the amount and speed of the spring’s compression when a load or force is applied to it. The greater the damping, the less the spring will compress, and the slower it gets there. Note: Some bikes, especially sports bikes, will have a separate adjustment for “high-speed damping”. This refers to the speed of the suspension movement, not the speed of the bike. For example, a sharp bump or a sudden application of the brakes will tend to make the suspension compress quickly. A softer bump, or more gentle easing of the throttle, will cause it to move more slowly. Separate “high-speed” and “low-speed” adjustments allow you to control how the suspension behaves in both of these scenarios, rather than having one adjustment to control both.
Rebound Damping. This controls how quickly the spring returns to its normal length after that load or force has been removed from it.
Okay, so now you’re familiar with the terms, we can have a look at what each of these adjustments does, and how to go about making the adjustments. But first, some basic rules, some “Dos” and “Don’ts”.
Do remember that you have these adjustments available. Many riders just leave the suspension set as it was when it left the factory. But unless you are the same weight, and have the exact same riding style and chassis-performance preferences as the “average rider” the factory would have set it up for, your riding experience will benefit from taking advantage of the adjustments the factory provided.
Do refer to your owner’s handbook to find out how to make these adjustments, and what the standard settings are. If you don’t have a handbook, you can probably download one from the manufacturer’s web-site or even some other third-party site.
Do make sure you start from having the suspension set to standard factory settings. And it’s probably best to check the factory set it to standard, not just assume they did it correctly.
Do make sure that, in the case of front forks and twin rear units, you adjust each side equally.
Do make notes. Write down each adjustment you make so you know where you are, compared to standard.
Do use the same section of road – preferably one that provides a good indication of both ride and handling – to test how your adjustments are working. If you make an adjustment and then test it on a different section of road you’re not getting a true comparison.
Do make only one adjustment at a time. If you adjust a couple of things and then test-ride it, you won’t know which adjustment is responsible for whatever change you notice.
Do make small adjustments only, and then check what difference it makes.
Do remember that the suspension will soften up over time – especially if the bike is new. Some people will tell you not to adjust the suspension at all until the bike has done a few thousand kilometres. I don’t agree; why not set it up to suit you right from the start? But remember that you will need to re-adjust it as the suspension loosens up. That means that, generally, you’ll need to increase damping and preload etc over time.
Do analyse how the suspension is performing from time to time. As I just explained, the suspension will change over time; but so might your riding preferences too. So from time to time, analyse what the bike is doing and check if that is what you want it to be doing. Another thing that can alter how your bike works is tyres; if you change the brand (or construction / compound) of tyre, that will often have an effect on handling and ride comfort; and you might need to re-adjust the suspension to suit.
Don’t assume that what a previous owner or salesman tells you is correct. If they say “It’s set to standard”, don’t assume that it is – always check it yourself first before you start adjusting.
Don’t bother doing any of this if your tyres are badly worn. Worn tyres – especially rear tyres – can upset the handling quite dramatically. A worn tyre will also ride differently to one in good condition. Replace any worn tyre and then start adjusting.
Don’t adjust it to the same settings your mate has; even on the same bike. Not unless your mate is exactly the same weight as you, and has exactly the same preferences in riding style! There isn’t a one-setting-suits-all; otherwise the factory would set it to that and not provide the adjustments to cater for individual differences.
Don’t adjust it to settings you find recommended on some internet site. This is the same principle as the one above, but people are often more willing to follow what seems to be an authoritative recommendation on the internet. But what you read on the internet is not necessarily right! And as I said above, the right setting will be the one that works best for you, not your mate, or someone on an internet site.
Don’t make big adjustments; adjust each setting in gradual steps and repeat the adjustments until you’re happy with the result.
Don’t adjust more than one thing at a time. (Yes, I know I wrote the opposite of these in the “Do” section above, but these are important principles and deserve a mention here too).
Don’t rush your assessment. It might be necessary to try the new settings over a couple of different rides to see if it is doing what you want it to do.
Okay, so now you know what to do and not to do, let’s get to the actual adjustments. And the first adjustment you need to make is to preload.
I read an article that claimed that preload did not alter how the suspension performed; it existed purely to maintain correct ride-height for different weight riders. The writer provided some complex mathematical equations to back-up his theory, but I’m not sure I agree. Perhaps on single-rate springs this might be true, but on progressive-rate springs, which most bikes have, it stands to reason that as you apply load (preload) to the spring, it will compress the softer section first; thereby making the spring stiffer. So the more preload the stiffer the spring. Having said that though, the weight of the rider is the most significant factor when it comes to adjusting the preload. As an example of how important this is, when Harley Davidson released its 2011 range to some Australian magazine journalists, there was an engineer from the Harley headquarters in the U.S. on hand to adjust the rear preload according to each journalist’s weight. It makes sense. Obviously a bike is going to sink further on its suspension when Fat Albert sits on it than it will when Feather-weight Frank climbs aboard. And as the manufacturer intends the bike to operate at a particular ride-height at the back, it is important to adjust the preload to position the bike where it should be. One reason for this is that if the back sinks down it alters the steering geometry, which effects the handling.
I’m going to start with this because it’s logical to start with compression before rebound. Although, of the two types of damping adjustment, compression is the less common to have. Many bikes will have adjustment for rebound but not compression. But, as I said, it’s logical to start with compression – because before a spring rebounds, first it has to be compressed. The suspension compresses by hitting a bump, or braking (front) or acceleration (back). So you need to ride it and hit a few bumps, give it a handful of throttle, and also hit the brakes. If you’re after the best ride comfort, you'll want to soften the compression damping. Adjust it so that the suspension absorbs bumps smoothly and gives a plush feeling. You’ll be looking to eliminate (or reduce) any jarring or thumps through the bars or seat when you hit bumps. If you’re after the best handling, you'll want to increase the compression damping. Adjust it so that the bike feels solid and firmly-planted on the road. You’re after that “running-on-rails” feeling. You’ll also be looking to reduce the amount of dive under brakes and squat under acceleration. Remember I said it was a compromise though. If you get a nice smooth ride, you’re also going to get more dive under brakes and squat under acceleration. That will make it feel not quite as solidly-planted on the road. It’s going to feel slightly less stable. Conversely, if you get it feeling really solid and planted-on-the-road, that ultimate running-on-rails feeling, you’re also going get more bangs through the bars and seat when you hit bumps. As I said, it depends where your preference lies in this ride / handling balance. The trick is to get a good compromise; a ride that feels comfortable without making the bike bob around like a dingy on a choppy sea; or handling that eats up the twisties without having every bump bouncing you off the seat. So you want ride without the “boing”, and handling without the “bang”. One final point. If you’re after the best handling you might think that the least amount of dive you get under brakes the better. But that’s not the case; you actually want some dive. When the bike dips down at the front it changes the geometry of the front-end; in effect, it makes the forks more vertical, which will make it steer quicker and turn into the corner better. So some dive is good; but too much is not! Also, if the suspension is too stiff bumps will bounce the wheels off the ground; and bikes don’t handle well if the wheels are up in the air!
This is very closely related to compression-damping. Compression damping controls how quickly the spring compresses, and rebound damping controls how quickly it returns to normal again. There is a rough, in-the-shed method of setting this. Push down as hard as you can on the front of the bike, and then release it. Do the same at the back. Time how long it takes for the bike to return from its compressed state to its normal level. It should be about 1 second. If it takes longer than that, the rebound damping is probably too hard. If it takes less than a second, and especially if it shoots up past the normal level and then bounces a bit before it settles, then the damping is too soft. But you need to take it out on the road to test it properly. Let’s take ride first. Imagine the wheel hitting a decent sized bump. If you have the compression damping set up for a smooth ride, when the wheel hits the bump it will travel upwards compressing the suspension, and leaving the bike at a constant level. When the wheel rolls over the bump and down the other side, the suspension has to rebound to its normal length. If the damping is too hard the suspension won’t spring back quick enough and the bike will effectively drop down, which makes for an uncomfortable ride. So you want it fairly soft. Go too soft, however, and you’ll find the bike bucking up like a pogo-stick, which is not something you want if you’re looking for the most comfortable ride! If it’s the best handling you’re after, you need the rebound set fairly hard. You’ll get maximum traction, and maximum feel, if the bike follows the contour of the road, maintaining a constant weight on the tyre. At the front, you don’t want it shooting back up, lightening the load on the tyre, which reduces your feel through the bars. At the back, if it bounces back too quickly it will, again, lighten the weight on the tyre and lessen traction. If the rebound damping is too soft you’ll tend to get a see-sawing type motion through corners; which is definitely not going to give you the best possible handling.
GETTING IT EQUAL
One final thing. It’s important to get the damping roughly equal at both ends. You’ll need your assistant again for this. With the bike off the stand, push down as hard and quickly as you can on the foot-peg. Then take your foot off. What you want is for both ends of the bike to move down and back up again at the same rate. It’ll be hard for you to see what’s happening if you try to do this on your own, but your assistant should be able to see what’s going on. If you don’t trust your assistant to judge this, have them do the pushing down bit (remind them again not to let the bike fall over!) while you watch what the bike does. In fact, some people recommend setting the front to achieve the desired level of ride or handling that you want, then set the back by matching it to the front. However I think that, especially with the back damping being so critical to ride quality, you should adjust the back according to on-road performance. But keep this balance aspect in mind though, and try not to get it too far out.
Okay, here is a list of symptoms and what you should do to fix the problem. Most are handling / stability related, but a couple are ride-related. If it’s handling you’re after, you’ll want the suspension set fairly stiff, but remember if you get it too stiff it will make the handling worse. So you’ll want to go through this list and make sure none of this stuff is happening. If ride quality is your aim, you’ll have it set fairly soft. Many handling problems can be caused by going too soft on these settings, but some are caused by having them too hard. Again, make the adjustments to get the ride you want, but keep checking that you haven’t introduced some of these problems in doing so.
Suspension bottoms out. The suspension is too soft. Increase preload and / or compression damping.
Front dives excessively under brakes. Increase front compression damping
Front feels light and shoots up too quickly after braking. Increase front rebound damping.
Back squats under acceleration. Increase rear compression damping.
Back shoots up under braking. Increase rear rebound damping.
Front jars harshly on bumps. Reduce front compression damping.
Bike skips around on bumps. Reduce rear compression damping.
Front judders under braking. Reduce front compression damping, and / or front rebound damping.
Front shakes exiting corners. Reduce front compression damping.
Rear squats over bumpy roads. Reduce rear rebound damping.
Front shakes in corners. Increase front rebound damping.
Bike runs wide on entry to corners. Decrease front compression damping.
Bike drops into corners too quickly. Increase front compression damping.
Bike wallows around corners. Increase rear rebound damping.
Bike runs wide in the middle of corners, especially after releasing brakes. Increase front rebound damping.
Bike runs wide accelerating out of corners. Increase rear compression damping.
ADJUSTING THE NON-ADJUSTABLE
Many bikes will not have all these adjustments available. Some provide only preload adjustment on the back. Some have preload adjustment at both ends but nothing else. Well, there’s not much you can do about the lack of adjustment at the back (without up-grading the suspension!), but there are a couple of tricks with the front. If the forks aren’t adjustable and you’d like more preload, you can achieve this by fitting spacers on top of the springs. You don’t need special factory items for this, washers of the appropriate size will do fine. Just unscrew the fork caps and place the washers on top of the springs. (Just don’t unscrew both at the same time – as I stupidly did many years ago!). If you want to change the damping of the front – stiffer or softer – you can do this by changing the fork-oil. Heavier oil will, of course, increase the damping, lighter oil will reduce it. Well, there it is; a bit of a marathon, but I hope you found it helpful. When I got my current bike I knew the basic principles of what each adjustment did, but I needed more information to know what to do to achieve the suspension performance I wanted. So I went searching on the net and reading books etc. This article is the result of that research; added to the things I already knew. I know I appreciated the detailed articles I read at the time, so I hope you find it useful. P.S. Peter, who has had a lot of experience in the motorcycle servicing industry, wrote in with some comments on the article. Here is what he wrote.
“While it is a very common misconception adding preload makes the spring stiffer this is not correct. (Sorry, science guy is correct, adjusting preload just lifts the bike up and down). I agree that adding preload may make the suspension ‘feel’ stiffer as it becomes harder to bottom out because the spring has been compressed further. However the spring rate always remains the same.” I suppose there’s no arguing with science – and the mathematics I mentioned seemed logical when I looked through it – but I think there is also no arguing with the fact that, as Peter says, “adding preload may make the suspension feel stiffer.” My seat-of-the-pants tells me that increasing the preload makes the suspension feel harder, decreasing the preload makes it feel softer. He went on to say that, “Most people do not have the correct rate springs installed and this is the first step to getting any suspension system correctly set up. Trail, road or race does not matter; and while most often suspension on touring bikes is ignored, they are usually the most in need of fitting correct rate springs.” Yes, this is an important issue. And if you take your bike to a suspension specialist to set up for you, it’s probably the first thing they’d look at. But probably the last thing the DIY home-mechanic would look at. Peter puts it very simply: “As you have gone to the trouble of measuring static and rider sag you can now easily tell if a softer or harder spring is required. At the correct rider sag if the static sag is less than 5-10mm you will need a heaver spring. Then the reverse is also true: If you have the correct rider sag and get too much static sag then the spring rate is too high and you need a softer spring.” A final and very worthwhile tip. “The rear rebound control is the most important control by far; and once preload is set it is the first control newer fiddlers should play around with.” That is probably why many bikes just have rear rebound adjustment, in addition to preload front and back. Thanks for the info, Peter.