As dirt bikes get more and more complex with their suspensions, it’s easy to think that the complexity behind your suspension on is almost too much to understand. But understanding how your dirt bike’s suspension works and what effect the various adjustments have will help you get the best out of your bike’s suspension based on your riding style and the terrain. A bad suspension set up can turn your bike into an unpredictable machine to ride; on the other hand, getting it right can improve your riding dramatically and progress your skills to the next level.
Your dirt bike suspension can be broken down into two essential functions – they are the spring and the damper. Both have very different functions but are really useless without each other. The spring holds the weight of the dirt bike and serves to absorb impacts from the ground through riding. However, just absorbing impact alone would not be of any use, as the bike would continue to bounce up and down like a ball. Damping on-the-other-hand is used to slow both the compression of the spring as it squeezes together – this is called the compression damping. How fast it returns to the original dimensions – the rebound damping. Most modern bikes will have adjustment available for the spring and both compression and rebound damping, and it’s getting the balance between these factors right that will make your bike handle well.
At the rear of the machine, most off-road bikes will run an external spring on a single centrally mounted shock absorber, commonly actuated through a linkage system. Damping is inside the structure of the unit, and there is an external reservoir to the damping system.
At the front, the springs are held internally and up to recently, within both legs. However, the development of SFF systems – Separate Fork Function – for motocross bikes has allowed manufacturers to split the springing and damping function between the two side, one leg holding the spring, the other handling the damping. For enduro and trail machines, this is less common and most will have both springs and damping systems held internally within each fork leg.
For both front and rear suspension, manufacturers have been developing suspension systems that use air rather than conventional springs, backed up with oil damping. While the rear systems are still very much restricted to the top tear race teams, air forks are very much in evidence in the motocross market, although customer response has variesbtween riders
Getting your suspension set up is essential to making your bike handle well, but it’s certainly not a simple process. The main factors are how heavy you are and how aggressive a rider you are, but after that, there is all manner of other factors to take into account from terrain to weather conditions.
Most new bikes are set up for an average rider who weighs around 150 to 170 pounds, so if you are vastly outside this predetermined set-up, then you will need to change springs and in some cases, the valving. Don’t assume that the setting is correct for you even if you are that weight – you still need to check it and adjust accordingly whether your bike is brand new or used.
The best way to get settings for the forks and the shock that is right for most of the conditions you ride and your style of riding, then look to tweak things slightly to cope with the conditions and terrain.
DIRT BIKE SAG: It all starts with SAG
The first stop on setting the suspension up for your bike is to set the sag. If you don’t know what this is, sag is the amount the suspension goes down under the weight of the bike alone and under the weight of you sat on the machine. This forms a baseline from which you can adjust everything else. I not going into how to set the sag on your dirt bike, there are many great videos on YouTube that will walk you through the process. The main point is, SAG is the first step in the process of getting your suspension dialed in.
When it comes to the front of the bike, the process can be very challenging. Most conventional forks don’t have any way to adjust the preload on the springs, so the same level of tuning is not possible. That being said, enduro bikes will sometimes have pre-load adjustable via a nut on the top of the fork and the modern breed of air forks have almost infinite adjustments, all of which are possible with nothing more complex than a pump. You do however need to make the adjustments in the correct order, or you risk reducing the travel and totally messing up the suspension!
As a rule of thumb, your sag and free sag should be roughly the same as the figures you used for the rear, otherwise, the bike is going to be unbalanced. Setting up your forks is best done by a suspension specialist who will be able to identify whether you need pre-load spacers or totally new springs to get the bike to behave correctly.
COMPRESSION AND REBOUND DAMPING
Now that you have the right spring, we need to look at the damping. Compression damping, particularly in the case of rear suspension, is commonly split into low speed and high-speed damping. But the terms relate to how fast the shaft of the shock is moving, rather than the actual speed of the bike. Small bumps or rocky trails will mean the shock is moving up and down quickly, whereas whooped-out sand tracks will mean the shock is moving more slowly.
Low-speed compression damping adjustment is usually by turning the adjuster at the top of the shock absorber reservoir with a flat head screwdriver by the required amount of clicks. High-speed compression damping is adjusted using a spanner on the outer nut at the top of the shock reservoir
Either way, you want enough compression damping to ensure that you don’t smash through the shock’s movement when you hit bumps and enough rebound damping that the bike isn’t bouncing like an excited puppy, but not so slow that the shock hasn’t returned for the next bump.
The rebound damping adjuster will be located at the bottom of the shock absorber and can be adjusted with a flat head screwdriver again.
At the front of the bike, the compression an rebound damping adjusters are in different positions, with rebound damping adjusted using a flat head screwdriver at the bottom of the fork. Or on some models it may be an easy-turn adjuster at the top of the fork unit.
Make sure you let out any trapped air using the air-bleed screws before any changes are made, this should be done before each ride– you can see it on the image below, along with the rebound adjuster.
So what happens if you decrease the rebound? Well, the ride will feel particularly plush and smooth as the wheel will move quickly move back, but if you take it too far and the handling will become very loose. As you increase the rebound damping, the ride moves from plush and to harsh.
But if less rebound makes the ride nice and plush, why would you want to increase it? The answer is because having too little rebound reduces traction – the wheel pushes back down in a relatively uncontrolled way that can lead to bouncing and will cause loss of forward drive.
COMPRESSION DAMPING ADJUSTMENTS
TOO MUCH: The action of the shock is harsh with far too much resistance to movement and the full suspension travel can’t be used.
TOO LITTLE: The bike feels unstable and uncontrollable with the suspension traveling through the full stroke, breaking traction as it pogos across the ground.
REBOUND DAMPING ADJUSTMENTS
TOO MUCH: The bike sits low and returns to the correct height very slowly resulting in poor traction and loss of drive and a harsh ride.
TOO LITTLE: The bike feels nervous and unsettled as the suspension jumps around with every bump.
As you may be gathering by now, it’s a delicate balance to getting it all right and the answer is going to be trial end error if you are going to do it yourself rather than using a suspension specialist. But you can do it, start at the manufacturer’s OEM settings from your manual and make adjustments in really small increments, marking down what you are changing. keep in mind that if you do change the springs or increase the preload, then this will feel like the compression takes longer as the suspension will be generally stiffer, so in this case you may need to back off the suspension damping.
Add a fact that if you make changes to the rear suspension, it will affect the way the front suspension works and vice versa. Now you can see that this is complicated stuff – perhaps why so many riders never touch the stock settings!
GETTING THE RIGHT SET-UP FOR YOU
GENERAL HANDLING PROBLEMS AND SOLUTIONS
Suspension feels too hard, ride is harsh and FULL travel not being used
Rear – reduce compression damping, reduce spring preload or change spring /spring rate.
Front – reduce compression damping and change springs / spring rate.
Suspension feels too soft, bike is unstable and bike bottoms out
Rear – increase the compression damping, increase spring preload or change spring / spring rate
Front – Increase compression damping or change springs /spring rate
Bike loses traction and breaks away
Rear – back off the rebound, reduce spring rate
Front – back off rebound, raise forks through the clamps to reduce steering angle
Rear of bike squats under acceleration
Increase rear compression damping. Increase spring pre-load or spring rate
Bike dives in corners
Increase fork rebound, fork oil level or compression damping
Bike turns too swiftly
Increase both rebound or compression, drop forks through clamps to increase steering angle
Bike bottoms out on larger bumps
Rear – Increase compression, increase preload or spring rate
Front – Increase compression, increase spring rate or oil level
Rear of bike kicks around and refuses to stay in line
Reduce rear spring rate / change spring, increase rebound damping
Handlebar / head shake
Increase fork compression damping, change springs / lower spring rate.
Bike sits low in suspension travel
Rear – Increase spring rate, reduce rebound compression
Front – Increase spring rate, reduce rebound compression
DROP -OFFS & JUMPS
Bike bottoms out on landing
Rear – increase compression damping, increase spring rate
Front – Increase compression damping or oil level
Suspension rebounds too quickly, bouncing the bike back up
Rear – Increase rebound damping
Front – Increase rebound damping, reduce compression damping, reduce spring rate.
So hopefully my simple guide has given you enough information to dial in your suspension. Start with the sag and then take the bike to your favourite track or trail and start experimenting – at worst it will make your bike easier to ride, at best it might even make you a better rider.
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