A beginner’s guide to motorbike suspension
Suspension for motorcycles can be hard to get your head around. With so many moving parts, you may wonder how it all works.
Motorbike suspension systems are crucial for the safety of your bike, and they have a great impact on its handling, comfort and maintaining tyre contact.
Here we go through everything you need to know about motorbike suspension to give you an initial understanding of how it all works.
What is a motorbike suspension system?
A motorcycle’s suspension system serves an important purpose. It maintains continuous contact between the tyres and the ground.
Without effective suspension, tyres would lose traction over bumps, dips, and other road imperfections. This is also vital when considering braking, acceleration, and cornering forces.
Without proper suspension, any impact between a motorcycle tyre and an uneven surface would range from an uncomfortable feeling to potentially leading to a dangerous incident.
How does motorcycle suspension work?
Motorcycle suspension systems use a spring and damper (shock absorber) combination to isolate the chassis and rider from uneven roads.
On-road setups mitigate the effects of potholes, bumps, cornering, and changes in speed, while off-road systems are built to handle roots, rocks, jumps, and ledges.
What’s the difference between basic and premium motorbike suspension?
The main difference is basic suspension lacks adjustability. You may question why you would need to tune your bike’s suspension, but it depends on what type of ride you have. Sport bikes and cruisers have different needs compared to your average two-wheeled machine.
If you have one of these types of bikes, having premium suspension will allow you to customise your ride based on your height, weight and intended riding style.
You can also adjust how quickly the springs compress and rebound as well as pre-loading spring tension, especially if you’re looking to carry luggage, or have someone ride pillion.
Advanced motorcycle suspensions allow for adjustments like preload, which controls the spring tension when the bike is stationary. This adjustment helps adapt the bike for riding solo, with a passenger, or with added luggage.
Do I need road or track suspension?
In general, there are two main types of suspension that riders use, and it’s worth considering the type of terrain you will be riding on, whether it’s road or off-track.
Those riding on the road will typically want smoother suspension due to travelling longer distances, and unfortunately, in the UK, you’ll come across plenty of potholes. You will also want to ensure you have a good static sag setting.
The best movement range for riding on-road is usually around 30-40mm for both the front and rear suspension. Starting with this range is recommended, as you can always make adjustments later if you feel you have too much, or not enough sag.
Off-road, or riding on tracks, usually focuses on optimum performance and how you can get the best out of your motorbike suspension setup, as opposed to how comfortable the ride is.
What are the key components of a motorcycle suspension system?
Most motorbike suspension systems involve a coil spring and a hydraulic damper setup.
Here are the components that make up a typical suspension setup.
Springs
Your wheels will need springs to move independently from your bike’s chassis and damper control (more on this later), managing the movement of the spring.
Motorcycle suspension relies on springs, typically made of coiled steel wire, which compress or stretch under external force. The ‘spring rate’ is the force needed to compress a spring a specific distance, usually measured in pounds-per-inch. This rate is influenced by the material’s thickness and the number of coils.
Critically, suspension components work independently from the chassis and damper control, managing spring movement. Without this damping, a motorcycle would dangerously and continuously bounce after every road impact.
Damper (shock absorbers)
A damper, also more commonly known as a shock absorber, is there to slow and control the spring action using hydraulic fluid.
Within the shock body, a precisely measured piston with a passage moves through hydraulic fluid. The piston’s travel speed is determined by the fluid’s weight and the passage’s size. When a motorcycle hits a bump, dampers slow down the spring’s compression and rebound as the fluid gradually moves through these passages.
The kinetic energy from the spring movement then turns into heat energy in the damper, whilst the hydraulic fluid dissipates from the heat.
Rebound damping and compression
Compression damping is when you are intentionally slowing down the spring compression for occasions such as hitting a bump in the road.
Rebound damping, on the other hand, is the intentional slowing of the spring expansion as it resumes to its normal configuration.
Motorcycles can feature both high and low-speed adjustments for both compression and rebound damping. Generally, sport and off-road motorcycles offer more adjustability than entry-level or cruiser models.
It’s important to note that high and low-speed damping relates to the speed at which the suspension travels, not the speed of the motorcycle itself.
High-speed damping will influence how the suspension reacts to sudden impacts, like hitting a pothole on the road or a single rock on a trail.
Low-speed damping affects behaviour such as the motorcycle’s dive during braking or changes in handling during cornering. Motorcycle damping is achieved through:
- Cartridge forks – fluid travels to control suspension movement; these are more adjustable and offer better damping from low to high speed.
- Damper rod – fluid travels to control compression and the rebound of the suspension. These are expensive to acquire.
Sag
Sag is the percentage of suspension travel used when your bike is stationary. Excessive sag can lead to the bike bottoming out over bumps, while insufficient sag results in a stiff and harsh ride.
Preload
Preload is simply the amount of tension on your bike’s springs when it is resting. Increasing this load will decrease the amount of sag, and vice versa when applying less.
Some bikes will come with suspension preload adjustability. Adjusting can allow for a degree of adaptability, especially as bikes can be used for multiple reasons such as solo riding, riding with luggage or having someone ride pillion.
Adjusting preload is not recommended, but for those who are experts in the field, adapting can lead to greater ground clearance for off-road travel.
What is rear motorcycle suspension?
Motorcycle rear suspension usually features a heavy-duty coil wrapped around a damper, often with external adjustments for preload and damping. Given the rear of the motorcycle bears more weight, robust springs are commonly used.
Some motorcycles employ dual rear shocks, mounted directly between the frame and the swingarm. Alternatively, other systems utilise a linkage and a single shock to manage the suspension.
What is front motorcycle suspension?
Motorcycles utilise suspension forks. These forks can either have both springs and dampers working in tandem within each leg, or they can be separate function forks where one leg houses the spring and the other contains the damper.
The front-wheel axle is attached to the lower part of the suspension fork, while the triple tree secures the upper part.
How long do dampers (shock absorbers) last for and what causes them to wear out?
Dampers (shock absorbers) are usually affected by oil that has not been changed regularly, which should be done when having regular service checks.
Piston bands and piston rod seals are also a cause for dampers to stop working over time, due to wear and tear from the number of miles your bike does.
For components to “wear out,” internal wear on the cylinder tube or scratches on the piston rod, among other things, must begin.
On average, dampers tend to last between 30,000 and 60,000 miles. Of course, this is an average and factors such as what terrain you ride on, your riding style and the quality of the components will be a key difference in how long they last.
How do I know if or when my front suspension needs oil?
A visible leak in your motorbike’s forks necessitates a service or repair, including an oil exchange. To increase bottom-out resistance and make the air spring more progressive, you can add oil.
Always refer to your user manual for the recommended and permissible oil quantities. While adding oil provides more support during specific scenarios like heavy track braking, it does not enhance overall support. Local dealers can perform fork servicing.
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