Motorcycle Suspension: Master Sag, Preload, Damping for Bikes

Have you ever thought about how much your motorcycle suspension affects your ride? Probably not enough, right? Most riders just hop on their bikes and go, maybe adjusting a mirror or two. But trust me, understanding your suspension is a game-changer. It’s not just about comfort; it’s about safety, performance, and even saving some serious cash.

Here are three unconventional truths about your motorcycle suspension that you need to grasp right now:

1. Your stock suspension is probably better than you think. Before you rush out to buy expensive upgrades, give your current setup a chance. A proper setup of your existing suspension can make a world of difference.
2. Sag is everything. If you ignore sag, you’re missing the most fundamental aspect of suspension tuning. Seriously, if you don’t at least think about sag after reading this, I haven’t done my job.
3. Preload is your best friend (for free!). Forget complex adjustments for a moment. Just understanding and using preload correctly can dramatically improve your ride, especially when you load up your bike for a trip.

Think of it like this: your coffee machine is set up for some fancy barista, and your office chair is designed for someone else. Your bike’s suspension? It’s likely set up for a mythical “average” rider, who probably doesn’t exist. Just like you adjust your chair and coffee machine, you need to adjust your suspension. And no, unless you are a 75-kilo Dutch lady (which is who my T7 seemed to be set up for!), the factory settings probably aren’t perfect for you. So stick around, and let’s dive into the world of motorcycle suspension.

If you’d rather watch this guide, here’s my original video on the topic:

Building Suspension from Scratch

Let’s start simple, building a suspension system from the ground up. Imagine your motorcycle frame. Now, let’s add a wheel. If we just weld that wheel directly to the frame, we’re in for a very bumpy ride. Every imperfection in the road would be directly transmitted to you. Not ideal.

To improve this, we hinge the wheel to the frame using a swingarm. Now, the wheel can move up and down independently of the frame. Much better, right? But there’s still a problem.

If we put the bike on the ground now, the swingarm will just pivot, and the bike will collapse. We need something to support the bike and allow for controlled movement. That’s where the spring comes in.

The Spring: The Heart of the System

The spring is the first crucial component of our suspension. By placing a spring between the bike’s frame and the swingarm, we prevent the bike from collapsing and introduce the ability to absorb bumps.

Now, we need to consider sag. Sag is simply how much the suspension compresses when you sit on the bike. It’s a critical measurement because it dictates how much suspension travel is available for bump absorption and affects your bike’s handling.

Why Sag Matters

Too much sag, and you’ll use up too much suspension travel just sitting on the bike. This leaves less travel to absorb bumps, potentially leading to a harsh ride and bottoming out. On the other hand, too little sag (or no sag) means the wheel can’t extend downwards to follow dips and holes in the road. Remember, suspension isn’t just for comfort. It’s crucial for maintaining traction by keeping the wheel in contact with the road surface at all times. Suspension also heavily influences handling, affecting braking, cornering, and overall stability.

Most motorcycle manuals provide recommended sag values, both for the front and rear suspension. A general rule of thumb is around 30% of the total suspension travel as rider sag. This means that when the suspension is fully extended, and you sit on the bike, it should compress about 30% of its total travel.

This is why spring rate, or spring stiffness, is so important. It’s not just about comfort. Incorrect sag due to the wrong spring rate dramatically affects handling.

Too much rear sag, and your bike will feel stable at high speeds but sluggish in corners.

Too little sag, and the front end will be lower, making the bike turn in quickly in technical sections but feel unstable and wobbly at higher speeds.

Preload: Fine-Tuning for Weight

Okay, you’ve got your spring, and the sag is (hopefully) close to correct. But what happens when you decide to load up your bike for a trip, adding luggage and maybe a passenger? Suddenly, your carefully set sag is completely off. It’s sagging way too much.

Do you need to swap out your spring every time you change your load? Thankfully, no. That’s where preload comes to the rescue. Preload is an adjustment that compresses the spring before you even sit on the bike.

Think of it this way: a spring has a spring rate, often measured in Newtons per millimeter (N/mm) or kilograms per millimeter (kg/mm).

Let’s use kg/mm for simplicity. A spring rate of 1 kg/mm means that it compresses 1mm for every 1 kilogram of force applied. It’s linear, so 2kg compresses it 2mm, and so on.

Now, if you preload the spring by compressing it, say, 3mm using a preload adjustment, it will take 3 kilograms of force just to start moving the spring. Without preload, it would react to even the smallest weight. By adding preload, you essentially shift the spring’s working range, making it support more weight before compressing into the sag zone.

So, when you add luggage or a passenger, you can increase preload to compensate for the extra weight and bring your sag back to the correct range. This is why preload adjusters are often designed to be easily accessible and adjustable, sometimes even without tools.

Setting Sag: A Practical Approach

How do you actually set the correct sag? While there are fancy tools, a simple method works just fine. You need to measure the suspension travel in three states: fully extended, bike weight only (free sag), and with rider and gear (rider sag).

For my bike, I use a piece of cord with a screw and two markers. The screw goes into a hole in the axle. I mark a point on the rear fender with some tape. First, I lift the rear wheel off the ground to get the fully extended measurement. This is my starting point, the first marker on my cord.

Then, I measure down 6cm (60mm) from that point on the cord and make a second marker. Why 6cm? My bike, a Ténéré 700, has 200mm of rear suspension travel, and 30% of 200mm is 60mm. This 60mm represents my target rider sag.

Now, with all my riding gear on, I sit on the bike in my normal riding position. I check the position of the second marker on the cord relative to the mark on the fender. If the cord’s marker is above the fender mark, I have too much sag. If it’s below, I have too little.

On my Ténéré 700, the preload adjuster is a large, easily accessible knob. This is designed for frequent adjustments. You turn it to compress or release the spring, changing the preload and therefore the sag. There’s no single “magic” preload setting. It depends entirely on the weight on the bike. Adjust it as needed!

Spring Rate vs. Preload: Knowing the Difference

It’s tempting to think, “If my spring is too soft, can’t I just crank up the preload to get the right sag?” The answer is yes, to a degree, but it’s not ideal. A spring that is fundamentally too weak for your weight will have other negative characteristics beyond just sag. It might compress too easily through its travel, feel “mushy,” and not perform optimally.

If you use too much preload on a weak spring to achieve the correct rider sag, you might end up lifting the entire bike higher than intended. This can negatively affect handling and geometry. This leads us to the concept of free sag.

Rider sag (or race sag) is the sag measurement with you and your gear on the bike – the one we’ve been focusing on so far. Free sag is how much the bike sags under its own weight, without you on it. After setting rider sag with preload, you should check free sag. There should be a noticeable amount of free sag, indicating that the suspension is not completely topped out by excessive preload.

A small amount of free sag, around an inch or 2.5cm, suggests that the spring rate is reasonably well-matched to your weight and that the preload adjustment is within a good range. If there’s virtually no free sag, even with minimal preload, it’s a strong indication that your spring is too stiff. Conversely, if you need maximum preload to achieve correct rider sag and still have excessive free sag, your spring is likely too soft.

With the right spring rate and properly set sag, you’re halfway to a well-sorted suspension. But if we went riding now, we’d have another problem: a bouncy, uncontrolled ride. That’s where the damper comes in.

The Damper: Controlling Motion

The spring stores and releases energy, but on its own, it oscillates wildly. The damper’s job is to control this motion, preventing the “pogo stick” effect. Dampers use hydraulic resistance to slow down suspension movement, both during compression and rebound.

Imagine a syringe filled with oil. Pushing the plunger is easy with air, harder with water, and even harder with thicker oil. The resistance to movement depends on the fluid viscosity and the size of the opening the fluid is forced through. Motorcycle dampers work on the same principle. They consist of a cylinder filled with oil, a piston, and valves with adjustable orifices.

By adjusting the size of the valve openings, we control the speed at which oil can flow through the damper. Smaller openings create more resistance and slower movement; larger openings allow faster movement. There are two primary damper adjustments: compression and rebound.

Compression damping controls the speed at which the suspension compresses when encountering a bump. Rebound damping controls the speed at which the suspension extends back to its original position after compression. These adjustments are typically made using clickers or screws on the suspension components.

Adjusting Compression and Rebound

Unlike preload, which is easily measured and set based on sag, compression and rebound adjustments are more about feel and fine-tuning. Your bike likely came with factory settings for compression and rebound, usually listed in the owner’s manual.

These settings are a good starting point. They are often expressed in “clicks” from the fully closed position. For example, the manual might specify “9 clicks out” for rear compression damping. This means you turn the adjuster clockwise until it’s fully closed, then counter-clockwise 9 clicks.

Compression Damping: If your suspension bottoms out too easily on big bumps or feels too soft and dives excessively under braking or in corners, you might need to increase compression damping. Increasing compression damping makes it harder for the suspension to compress, providing more support.

Rebound Damping: Rebound damping is perhaps the trickier adjustment. Too little rebound damping can make the ride feel bouncy or shaky, as the suspension springs back too quickly after compression. Too much rebound damping, and the suspension can “pack down.” This happens when the suspension compresses on a bump but doesn’t extend back out quickly enough before encountering the next bump. Over time, the suspension effectively gets “stuck” lower in its travel, reducing available suspension and making the ride harsh.

Rebound is the adjustment I typically touch the least. Once I find a setting that works well, I usually leave it alone. Compression damping, however, I might adjust more frequently depending on the type of riding. For technical, rough terrain, I might increase compression damping for more support on bigger hits. For smoother gravel touring, I might soften the compression to improve small bump compliance and comfort.

Key Takeaways: Suspension Simplified

So, what are the main points to remember?

1. Prioritize Spring Rate and Sag: Get the correct spring rate for your weight and set your sag properly. This is the foundation of good suspension performance.
2. Utilize Preload: Use preload to fine-tune sag for varying loads. It’s a simple and effective adjustment.
3. Understand Compression and Rebound: Experiment with compression damping to control bottoming and dive. Adjust rebound damping cautiously to prevent a bouncy ride or packing down.

Before you consider expensive suspension upgrades, take the time to understand and adjust your stock suspension. You might be surprised at how much improvement you can achieve just by properly setting it up. For Ténéré 700 owners, especially pre-2023 models like mine, you can even try my personal suspension settings as a starting point. Just adjusting the clickers can unlock a lot of hidden potential in your stock suspension and demonstrate that you can achieve a much better feel without immediately spending money on aftermarket components – except perhaps for springs if needed.

Get your springs and sag sorted first. Then you can think about all the fancy suspension upgrades and bling for your bike. It’s all about getting the basics right first.

Thanks for reading! I hope this has demystified motorcycle suspension for you. Leave your questions and comments below, and feel free to correct any mistakes I’ve made in the comments. Let’s learn together!