TECH: SUSPENSION 101
BY CHAD DE ALVA
Motorcycle suspension is something that seems to have a limitless ability to be misunderstood and perplexing to riders both new and old. Yet the suspension on your bike makes all the difference in how your bike rides, so it’s something that all riders need to understand. When set up and adjusted correctly, your bike is fun to ride, confidence inspiring, and able to handle most anything you point your bike towards. Suspension that isn’t set up properly, on the other hand, can be dangerous. It can significantly impact the bike’s handling, its ability to handle obstacles, and it makes the motorcycle much less fun to ride. To ensure that your suspension is properly set up for you as a rider, de-mystify suspension terms, and help you make the correct adjustments for what you are experiencing while riding, here is Upshift’s suspension 101.
Before we get started, we need to get one thing straight: suspension DAMPS. It does not DAMPEN. Suspension does not make things wet, which is what the word dampen means. It’s compression damping and rebound damping. Proper grammar matters.
Suspension is a system that’s carefully designed to work in concert with the rest of your bike to make the bike fun to ride, handle well, and do a good job absorbing all of the bumps on the various surfaces that you ride over. If one or more of these other components in the system is not properly set up, it could cause other problems that no amount of suspension tuning can solve. So before we start nerding out on preload and clickers, we need to make sure our bike is in good mechanical order. Whether you’re working with a brand new bike, or a new to you bike, it’s always a good idea to make sure that the following bike checks have been completed.
The first thing to check is tire pressure. Make sure that your tires are correctly inflated if you’re running tubes or Tubliss. A tire that’s overinflated will want to bounce off of everything, and a tire that’s underinflated is going to feel mushy and create other handling issues. Tire pressure is absolutely something that should be tailored to the surface that you’re riding on, but it’s important to keep it constant while testing suspension settings.
Next you need to ensure that your front wheel is properly installed in your forks, as an incorrectly installed wheel can cause fork binding. Follow the procedure in your manual and use a torque wrench. With your front wheel properly installed, ensure that the bolts on your bike’s triple clamps are properly torqued to their respective specs as well. If these bolts are too tight, they can cause problems with fork operation.
Setting sag is critical to proper suspension performance and bike handling. There are two types of sag: Rider Sag and Static Sag. Rider sag refers to how much suspension travel is used when the rider wearing all of their riding gear and any luggage are on the bike. Static sag refers to how much suspension travel is used by the weight of the motorcycle while it’s standing upright on a level surface. To set your rider sag, you first need to put on ALL of your riding gear. If you wear any sort of pack, load it up with water and anything else just like you were about to leave on a ride. Now go hop on a scale and record your weight.
Most owner’s manuals cover how to set sag on a bike, but here is the general idea: first, measure the suspension fully extended
(bike on a stand) from the rear axle to directly above it on the plastics. Then, pull the bike off the stand, park it on a level surface and have the rider hop on with all of their gear and any luggage. Next, support the bike so it’s perfectly upright (trackstand or get a friend to hold the bike upright) and bounce the suspension a couple of times to let it settle, then measure again to see how much suspension travel is used up.
Your owner’s manual should provide a specific target, but a general target is 1/3 of the travel. If you’re off by a few mm, adjusting the spring preload should be sufficient to reach your target sag. If it’s significantly off, you will need to look into different springs. Cranking your preload up too far can lead to coil bind and other problems, so don’t do it. Some owner’s manuals will have charts that list a spring rate for a certain rider weight (you did record your rider weight, right?), but if your manual doesn’t, a suspension tuner or your dealer can get you sorted out. For a deep dive on sag and chassis tuning, check out Chassis Set-Up in Upshift 44.
It’s important to check your sag from time to time to make sure that you’re still on target. If you’re going to add luggage for a trip, you’ll need to add some additional preload into the mix, which is why many adventure bikes have hand adjusters for their shock preload. Keeping your bike set at the correct sag will enable the chassis to perform at its best, so it’s critical to have your sag set properly before starting to play with other suspension adjustments.
If you’re working with a used bike that was set up for a different rider, it’s important to determine if the setup will work for you as well. If your rider weight and the previous owner’s rider weight are within a few pounds, you may be okay, but don’t assume – take the time to check. If there is a significant difference in rider weight or skill level, expect to change springs, and/or valving. To get the most out of your suspension, it needs to be set up for your weight and rider ability level.
The best way to tune suspension is to identify a test track, such as a section of trail that you can ride again and again to evaluate how changes impact performance. The idea is that with a consistent test track, you’ll be able to really understand what difference a setting change makes. If you try and adjust more than one setting at a time, it can be very hard to pinpoint exactly what each change is doing, so take your time and play with one setting at a time.
Before you start sessioning a test track and turning clickers, it’s important to record what your starting settings are. To measure this, turn each one of your adjusters in (clockwise) until they stop (GENTLE – don’t force ANYTHING) while counting the number of clicks or turns. Then, count the number of clicks or turns back out (turning counterclockwise) to return to where you started. Settings are expressed in clicks or turns out. If you end up at the end of an adjuster’s range of travel, it’s time to look into a valving change.
Depending on your particular motorcycle, you may have some or all of the adjustments covered here, and you may have other settings that aren’t covered. The goal of this article is to provide baseline knowledge, not a master class in tuning your particular suspension setup.
Compression damping adjusts the shock’s ability to absorb energy while the shock is getting compressed. On many bikes, there are two compression damping circuits: High Speed and Low Speed. High speed compression damping comes into play when your rear tire smacks into an exposed root, embedded rock, whoop, or other obstacle on the trail that causes the shock to compress at a high rate of speed. The shock doesn’t care how fast the motorcycle is moving, it only cares how quickly it’s being compressed. Low speed compression comes into play when the shock is compressing at a slower rate, like when you’re loading the bike up in a bermed corner or going through a dip in the road.
Rebound damping controls how quickly the shock can extend after being compressed. If a shock has too much rebound damping (shock extends slowly) the shock will not be able to extend between bumps, and this leads to suspension packing up where the shock is stuck in a compressed state. Too little rebound damping (shock extends quickly) will cause the rear wheel to want to jump off the ground or the bike will feel like it wants to throw you off when the rear suspension extends. The ideal amount of rebound damping is as quick as possible without causing the rear wheel to bounce or leave the ground.
A common misconception with shock settings is when the rear end kicks back after running into a large obstacle like a big root or embedded rock. Many riders assume that this is their rebound damping being set too fast / soft (shock extending too quickly), but it’s commonly a symptom of the shock not having enough high speed compression damping. What’s really happening is that the shock is unable to absorb the hit, so it’s blowing through all of its travel and bottoming out, causing the rear end to kick out. To diagnose this, find an obstacle that causes the problem, then try adding more high speed compression damping and hit the obstacle again in the same manner. Remember, suspension tuning is all about balance, so don’t pursue ultimate big hit absorption performance at the cost of performance everywhere else. If at any point you reach the end of an adjuster’s travel, you need to consult with a suspension tuner about suspension re-valving. There is also nothing wrong with bottoming out your suspension on occasion – you want to use all of the travel that you’re carrying around after all.
Depending on the motorcycle that you’re working on, your front suspension can have a number of different adjustments. It’s a great idea to dive into your bike’s manual to understand exactly what can be externally adjusted. There are many tuning changes that can be accomplished internally, but for the purposes of this article, we will focus on what can be adjusted without cracking your forks open.
If your bike has external spring preload adjusters, know that they are helpful for maintaining chassis geometry when loading additional weight on the front of the motorcycle. For example, I routinely carry a chainsaw in a fork mount on one of my bikes, which adds 22 pounds to the front of the bike. By clicking in some extra preload, I can maintain the same suspension geometry (my fork isn’t sagging too much) when carrying this extra weight.
If your bike has an air fork, like the WP AER forks, adjusting the air pressure is essentially the same as changing the spring rate. More air pressure is like having a stiffer spring in a coil-spring fork. Your bike’s owner’s manual will explain how to set your fork’s air pressure, and guess what, you’ll need to know your rider weight to do this properly.
Compression damping on your fork determines how your fork absorbs impacts. Less compression damping will cause your fork to use more of its stroke (travel) when hitting a given obstacle, and more compression damping will have the opposite effect. As with every other adjustment, there is a balance here. You want the forks to be able to hold up to big hits and remain compliant on the little bumps and trail chatter. If your front suspension feels harsh, or deflects off of obstacles, try reducing your compression damping by a few clicks. If the fork feels mushy, or is bottoming out, try increasing the compression by a few clicks. Again, clicker adjustments are measured by turning the adjuster all the way in, and counting the number of clicks back out.
Rebound damping works exactly the same on your forks as it does on your shock. This adjustment controls how quickly your forks can extend after being compressed. If your rebound is too fast (too little rebound damping) your bike’s front end will feel like it’s trying to pogo stick off of every obstacle. Too much rebound damping will present as your fork packing up, where once you start hitting obstacles, your fork will never have a chance to fully extend. Try adjusting your rebound damping to the point that it’s just short of pogoing or costing you traction; this will allow it to extend as quickly as possible so that your forks have as much travel available as possible for the next obstacle without causing the front wheel to lose traction. Again, the name of the game is to test, tune, and test again.
PUTTING IT ALL TOGETHER
Suspension tuning is a process that takes time, so don’t expect to find your best settings in five minutes in the parking lot before your next ride. To really find the settings that work best for you as a unique rider, you need to put the work in at home and out on the trail. Start by ensuring that your bike is set up correctly with the right springs for your rider weight, and that your bike has the forks, front wheel, and its tires set up correctly. Get your sag set correctly. Record your starting settings. Then find a section you can ride again and again, and make one change at a time to see how it changes things. Don’t be afraid to experiment either – this will only improve your understanding of how things work. Once you get your head around what all of your adjusters do, it becomes an easy process to make adjustments as needed on the fly for different riding surfaces. If you ever get stuck or need help, a good suspension tuner can help get you sorted out and get the most out of your motorcycle’s suspension.