• Today, we look at the hub centre steering front end.

  • In some ways, it’s better than forks.

  • But there are other compromises, too.

We had detailed about what happens to forks under load yesterday, so we shall continue with how hub centre steering works and their dynamics.

On paper, a hub centre steering (HCS) front end still carries out the functions of the conventional forks. But that’s where the similarities end. That’s because instead of combining steering, braking and suspension functions into a pair of the same items, each function is separate.

The basic layout of an HCS front end

First, think of a swingarm complete with suspension and brakes attached. Now turn it to face the direction of travel and add a steering mechanism to it. However, the steering mechanism is separate and not tied directly to the wheel. Conversely, the handlebar is connected to rods that pull the front wheel left or right.

How it works

As you ride along, the arm or arms move up and down. A spring and damper are mounted to arm to absorb the forces. Since the handlebar is isolated from these forces, you will enjoy a much smoother ride. Bump forces don’t shoot straight up into your palms and arms like they do with forks.

As you continue to ride, a sharp corner appears up ahead and you brake hard for it.

Weight is transferred forward to compress the suspension. Instead of being transferred onto a couple of bars, this transfer of weight is directed horizontally into the arm. It results in the motorcycle staying flatter, rather than attempting to stoppie.

With conventional forks, that dive will change the front end’s geometry. On a HCS front end, on the other hand, that dive does not affect the steering rods. Consequently, the rider can still turn the bike effectively. To him, steering may feel no different from when he was riding on a straight road.

The advantage here is that he can brake much later and harder into corners while still being able steer the bike through.

The swingarm could also be tuned for effective lateral flex when the bike is leaned way over. Stiffer forks cannot do so unless you want loss of feel or chatter to creep up, thus flex had to be built into the frame.

So why are bikes still using forks?

Forks may have many more complications compared to HCS but they have been refined over the years to where they are now. That means there is a wealth of knowledge and experience in working with forks.

But probably most of all, it’s that isolation of braking and bump forces from steering that will scare riders. It’s ironic that too much feel from forks also scare riders. However, riders brought up on forks have learned to compensate for their limitations. It’ll be interesting to see how a rider develops over time if he had been exposed to a HCS front end from when he first started riding.

Another disadvantage is weight. Having a chunky piece of metal up front will tip the scales more. Bimota compensated by making most parts out of expensive carbon fibre on the Tesi H2.


Building a motorcycle is all about compromises. The consideration that wins through is usually about cost and complexity. Unfortunately, the HCS is on the losing end of these two considerations. We could only hope that more manufacturers adopt the technology.


  • Besides the Bimota H2 Tesi, Kawasaki is now rumoured to be working on their own hub centre steering motorcycle.

  • What is hub centre steering (HCS)?

  • To understand HCS, we need to look at what forks go through first.

While we await the new Kawasaki Ninja H2 powered Bimota Tesi H2, Kawasaki themselves are rumored to be working on a hub centre steering (HCS) bike themselves.

It may be of no coincidence that Kawasaki bought out 49% of Bimota’s shares, after all. It now appears that the Japanese manufacturer needed Bimota’s extensive experience in building HCS motorcycles (besides superb frames).

We don’t see this sort of front end on many production bikes, truth be told. Those that did were just more than a handful: Yamaha GTS1000, four models from Vyrus, and of course, the Bimota Tesi 3D. Interestingly, Vyrus was working hand-in-hand with Bimota in developing the Tesi 3D but chose to split away to produce their own HCS bikes.

There were also HCS bikes in the 500cc World GP Championship in the late 80s. Powered first by Honda then ROC, they turned in some encouraging results.

What is actually HCS? How does it work? And why is it considered revolutionary?

But first, we have to understand how the front end of a motorcycle works, starting with the age-old telescopic forks. (The term “telescopic forks” applies to both conventional and upside-down forks.)

What are the functions of the forks?

We’ve described how forks work in a previous article. But let’s describe their functions.

The roles of the forks are to:
  1. Support the weights of the bike and rider through preloading the springs.
  2. Provide compression and rebound damping.
  3. Steer the front wheel, hence the bike.
  4. Hold the front wheel in place thereby “attaching” the front wheel to the bike.
  5. Carry the brake calipers.

That’s a lot, don’t you think?

What happens when the bike is moving?

When a bike is travelling straight up, the wheel is deflected upwards when it contacts a bump. The forks compress, the re-extend after passing the bump. Changing directions is also easy as no other forces are acting on the front end, except for the bump.

The suspension on this dirt bike has fully compressed during landing off a jump. Try to steer the bike when this happens – Credit Dirt Legal

Imagine the rider braking hard for a corner.

The decelerative forces from the brake calipers are pushed into the forks. Weight of the rider and motorcycle is shifted to the front due to inertia and compress the forks.

Now imagine the front tyre contacting a bump at this very moment. Much of the forks’ travel have been taken up due to braking and now more is requested by the bump.

The results are the bike will be difficult to turn as the tyre is hopping over the bump or worse, subsequent bumps. Also, more forces are being directed into the front tyre (as the suspension doesn’t have more travel) causing it to be squished out sideways. Consequently, the increased footprint makes turning the bike much harder.

Apart from that, provided that the front brake doesn’t lock up, all the weight will be shifted to the front and inertia forces the rear end to slide out.

Rear tyre sliding under braking. See how compressed is the front end – Credit Cycle World

In extreme cases of weight transfer will lift the rear end of the bike. As a result, the bike becomes squiggly, unsettled, unstable. This is also when rear brake becomes redundant, hence braking distance is increased. Worse, the rear end’s lifting while the front-end hops over bumps.

It’s spectacular to look at Marc Marquez  doing this and still make the corners, but it’s not a great idea on the road! What do most riders do in this situation? Answer: Let off the brake and run straight off the road.

Using a heavier (harder spring) or dialing in more low-speed compression damping helps but neither or both will eliminate the problem completely. Besides, the front end will become less compliant.

Additionally, extreme braking or sharp bumps or a combination of both can force the fork legs to bend backwards slightly, but enough to cause the sliders and legs to touch each other, thereby creating stiction. Stiction is the combination of two words, namely static and friction. It may also be influenced by the word stick. When stiction occurs, a large amount of force is needed to break the friction. The rider would feel as if the front suspension has stuck in its stroke. The solution is to make bigger diameter and stiffer forks but doing so creates their own set of problems. This is why high-end fork sliders are TiN (titanium nitrate) coated.

TiN coated fork slider – Credit reportmotori,it

Additionally, the length of the forks creates a leverage against the headstock (where the triple clamps are mounted to). Again, engineers respond by making larger forks, headstock and frame to compensate.

However, creating stiffer forks and headstock adds weight. But more critically, it will cause loss of feel of the front tyre especially when the bike is leaned over in a corner. In fact, extreme stiffness can induce front wheel chatter. When the rider losses feel or the tyre chatters, he’ll lose confidence, and loss of confidence forces him to slow down.

Check out the size of the headstock and centre spar of this Kawasaki Ninja ZX-10R frame. Some riders complain of lack of feel in corners. It’s due to lack to lateral flex

So, it’s a constant battle between fork, headstock and frame stiffness against stiction and leverage.

There are advantages of the forks, of course. However, these were brought on by the familiarity of how they feel and how we compensate. Other plus points are that forks require less complex architecture, are lighter and comparatively cheaper than HCS.

That’s it for now, we’ll look at how HCS functions, besides their pros and cons next time.

  • Hydraulic forks have been around since 1935.

  • The springs provide the preload function.

  • Damping works by forcing hydraulic fluid through orifices or shims.

The hydraulic fork has been with us since the BMW R12 in 1935. Since then, forks have been revised to no end in the pursuit of excellence, giving rise to electronically controlled suspension.

But how do they really work? What goes on in there?

Basic principles

The most basic principle involves inserting a spring in each fork. For many years, the spring was the only component to play the role of preload (keeping the suspension from bottoming out) and damping (absorbing shocks).

The earliest form of damping came in more… springs. Yup, you’ve got one with larger diameter, surrounding another with a smaller diameter. The former is longer than the latter, so as the fork compresses more due to a larger bump or shock, the shorter, more tightly wound spring comes into play to put up more resistance. This provides a rising rate suspension, in effect.

Hydraulic damper rod

Next to arrive was the hydraulic fork.

When the hydraulic damper appeared, fluid is pushed through orifices on a damper rod to create damping. The rod is inserted into each fork leg, on top of the spring. The damping rate – how the quickly the suspension reacts – depends on the size or sizes of the orifice or orifices.

Cartridge forks

Fork cartridge – Credit JBI

Instead of using damper with orifices, a cartridge consists of different sized shims. Oil is then forced through. A soft shock will bend the weakest shim to allow oil through. Harder shocks will bend more shims to allow the wheel to move up at a faster rate. This means damping is more precise. One of the biggest advantages of the cartridge fork is that you can replace certain shims for different damping characteristics.

Separate function forks

As the name suggests, one fork leg holds the spring or springs, while the other size holds the damper mechanisms. The one with the spring controls preload, while the other checks damping. This way, the forks could be made to cater to their specific purposes. They can also be lighter as the components are not duplicated. Having different functions on each side doesn’t give off different feedback when the bike is turned to either side as the forks are tied to the same triple clamps.

Electronic suspension

These systems can control preload and damping, or separately depending on the bike. Instead of having the rider adjusting the parameters with tools (plus sweat), it’s all done through a button on the handlebar.

However, the principles remain the same. What’s different is that sensors on the fork and swingram provide real-time ride height and damping data to the suspension ECU. The ECU then determines the correct strategy i.e. setting, depending on the selected mode. The ECU then sends signals to servos to alter the parameters.

Fork oil

Damping works by converting kinetic energy (moving fluid) to heat. This is why oil is commonly used as it could absorb the heat plus has low flow resistance. Changing the oil to difference viscosities or amount alters the damping characteristics.

But bear in mind that it must be replaced at every 20,000 km.

  • In this Suspension Explained series, we will unravel the “mysteries” of your bike’s suspension

  • Although the suspension is now very advanced, the basics remain the same

  • As the prologue, we touch on preload, compression damping and rebound damping

Suspension technology has progressed by leaps and bounds over the years. The motorcycle started out as a little more than an engine stuffed into a bicycle frame, hence the only suspension was the rider’s bum and his resolve to withstand the hammering.

Since then, motorcycle suspension evolved into simple underseat springs to sprung struts to hydraulic and gas damping to electronic self-adjusting marvels.

Regardless, the principles of the suspension remain the same. There are a number of parameters that govern how your bike behaves whether on the road, track or off-road. However, only three parameters are adjustable on a motorcycle (without further modification), namely preload, compression damping and rebound damping.

Adjusting the suspension best requires a bit of background knowledge, because whatever adjustments that may have you feeling right may not be exactly right for the bike’s dynamics. A wrong adjustment may mask itself as another problem, causing you to go around in circles. Oh yes, we’ve been there.

We’ll discuss one topic per week. We’ll also speak to the experts on aspects of suspension technology, adjustments and modifications, while dispelling some myths along the way.

Hope this series will be beneficial to all our readers.



Any discussion about suspension has to start with preload. Preload is of course related to spring rate, but since most riders don’t change the springs in their suspensions, we’ll just stick to preload.

To put it in simple terms, preload means the amount the springs are compressed when the suspension is fully extended.

Front preload adjuster – the blue bolt

For illustration purposes, take a valve spring and stand it on your desk. Now add some weight to the top so that it compresses a little. That’s preloading the spring. Adding more weight means adding more preload, while taking some off means reducing preload.

When you increase the preload by turning on the preload adjuster on the forks, or collar on the rear shock, suspension sag is reduced; and vice-versa. The spring pushes back against the adjuster collar, lifting that end of the bike up. So, if you increase (by turning clockwise) your rear suspension’s preload, the seat goes up higher, and similarly for the front.

Rear preload adjuster

Therefore, adjusting the preload DOES NOT change your spring rate. If someone comes up to me and say I’d make the spring stiffer by adjusting the preload… well, I’d tell him to go fly a kite. But that’s just me.

We’ll leave this subject here. More on this in latter instalments.


If a bike’s suspension depends on the spring along, it can leave itself prone to oscillations. A compressed spring stores kinetic energy. When it’s released, it may extend to more than its resting length. The load on top of the spring has now received this kinetic energy and unleashes it back downwards, compressing the spring. This goes back and forth until that kinetic energy is transformed to heat (absorbed in the shock absorber’s oil).

Courtesy of

Have you ridden on a bike that “pumped” up and down or wallowed like a sampan in stormy seas? (My bike does that.) Yes, it’s due to the lack of damping.

Damping is divided into two: Compression damping and rebound damping.


Compression damping (or just compression) determines how fast the wheel move upwards when it contacts a bump. Correct compression damping will allow the suspension to absorb bumps and road irregularities better.

The damping adjusters on the BPF fork are all on top. Compression is marked as COM

With more compression dialed in, the suspension, hence the wheel, is more resistant to moving upwards and vice-versa. Dialing in the correct amount will also deal with fork dive to a certain amount during hard braking, although that depends more on the spring rate and preload.

Compression damping is adjusted by the screw in the middle

Too much compression damping will cause the shock of the bump to be transferred directly to the chassis and rider. (That “BLAM” feeling when you hit a bump.) Consequently, the wheel will skip across the bumps, or cause the brakes to lock up easily as the suspension resists being compressed.

On the other hand, too little will have the wheel kicked up quickly, which will also cause it to lose touch with the road. Hitting corners at high speeds will cause the suspension to “squash” down, reducing ground clearance.


Rebound damping is the opposite of compression damping. Rebound determines how smoothly and controlled the suspension re-extends to its proper state, after it has been compressed.

Rebound damping is marked at TEN (for spring tension)

Without or too little rebound damping will cause the spring to re-extend quickly, or in simple terms, bounce back. The rider will feel as if he’s being kicked out of the seat after the initial bump has been absorbed. It’s like squeezing a spring between your fingers and letting it go abruptly, or like a Jack-in-a-Box.

Rebound adjuster on the rear shock is usually underneath the shock body. Here it is the screw surrounded by the red collar

Too much rebound damping will cause the wheel to “pack up.” That means the wheel will only come back down too slowly, causing the bike to feel “loose.”


That’s it for this week. This is just basic knowledge. We’ll touch on more next week, so stay tuned!

Whether it be conquering the track, the open-road, dirt, or acquiring a tailored setup for your custom machine, the UK’s K-Tech brand of suspension kits is one you can trust.


Renowned Italian motorcycle suspension brand Marzocchi faces imminent closure and will affect a number of bikes.



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