Technology: the operation of a slipper clutch
Motorsport is characterized by the constant development of technology. There were some revolutions in motocross, such as the switch from the four-stroke engine to the two-stroke in the mid-1960s. The introduction of mono suspension, liquid cooling, disc brakes and upside-down suspension were also major changes in existing technology. And let's not forget the return of the four-stroke just before the turn of the century. However, some parts such as the clutch remained virtually the same in design and operation all this time, but some manufacturers saw this as a challenge. The evolution of the clutch is one that deserves some explanation.
It has been several years since the slipper clutch was introduced in motocross. It was developed in racing and undeniably has some important advantages over a traditional clutch. Nowadays one can speak of three types of clutches: the standard clutch, the slipper clutch and the automatic clutch.
The slipper clutch
A slipper clutch – such as the Hinson BTL – disengages the clutch when the engine registers significant deceleration. This frees up the rear suspension by reducing chain torque. In human language: When you step on the rear brake when approaching a bend, you partly freeze the operation of the rear suspension due to the force you exert on the chain. With a slipper clutch, the clutch is only disengaged when the mass inertia of the engine falls below a certain point. When you release the throttle while braking, it pulls the link in so the rear shock can move freely.
However, a slipper clutch does not remain engaged. As soon as the deceleration and engine braking decrease, the clutch is reengaged. So the clutch must still be pulled in to prevent the engine from stalling. Basically, a slipper clutch is designed to limit wheel pressure when braking and downshifting in corners, but will still lock up like a fully manual clutch. You will especially experience the advantage of this coupling when passing brake clips just before a bend. The rear suspension will absorb this much better because it can move freely.
The automatic coupling
An automatic coupling – such as the Rekluse – is a fully automatic coupling. Not only does it disengage the clutch when it registers the deceleration, but the clutch remains disengaged until you accelerate again. With an automatic clutch, you don't have to pull in the clutch when you come to a stop, because it retracts itself. When you open the throttle and rotate the auto clutch to a preset RPM, the centrifugal weights in the clutch move outward to engage the drive discs and hold them until you drop the RPM to a level where the weights are reengaged. retracted to disengage the clutch.
In motocross, a slipper clutch is at its best when braking over bumps at the end of a long straight, when locking the rear wheel during hard braking or at the bottom of a steep hill. Why? Because by releasing the throttle you free the rear suspension from wheel pressure and chain force. However, you still have to pull in the clutch to start, shift or stop.
Conversely, an automatic clutch eliminates the need for the rider to touch the clutch lever. You can come to a complete stop, in gear, with an auto clutch and never have to worry about the engine stalling again. You can start from a standstill by simply opening the throttle - no need to release the clutch. Don't think that an automatic clutch will turn your five-speed gearbox into an automatic, you still have to shift from one gear to another. Most riders racing with the Rekluse automatic clutch don't have to worry about braking or manipulating the clutch lever, allowing more focus on choosing driving lines.
A few years ago, many motocross riders used slipper clutches, but as clutches have become more advanced, the tide has turned. Now automatic clutches are at an advantage and more useful in motocross. The benefits are also undeniable for a weekday enduro ride. On technical paths you will never have to worry about an engine stalling again. In the video below you can briefly see the advantage of an automatic connection explained.
Tekst: Danny Hermans
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