Assist And Slipper Clutch: How It Works And Why It’s Important

Slipper Clutch is a feature which was once available only inexpensive motorcycles. Of late, however, the technology has started making its way into lower capacity, affordable motorcycles as well. So, what exactly does a slipper clutch do? How is a slipper clutch different from a regular clutch, and how exactly does it work? What are the advantages of a slipper clutch, and are there any disadvantages as well? In this article, we will try and answer all those questions in detail. Let’s get going then… and unravel the mysteries of this technology.

A regular clutch assembly, as we have explained in one of our previous articles, comprises an outer basket, an inner hub, friction plates, steel plates, a pressure plate and springs. Together, all these components allow a rider to engage or disengage drive to the rear wheel using a clutch lever. So, when you pull the clutch lever, the inner hub, connected to the rear wheels via a gearbox is disengaged from the crankshaft input, allowing for a free rotation of the rear wheel. This set-up works very well and doesn’t require a slip function as long as you are not engaging in overly aggressive, or wrong downshifts. You probably won’t need it as badly, if you know how to rev match and downshift at an optimal rpm to prevent the engine from over-revving and avoid rear wheel hop.

Now picture this – what if you somehow, mistakenly, managed to downshift at a time when the engine was already kissing the redline? The rear wheel speed at this point is way too high, and the engine doesn’t have any higher revs to accommodate the back torque from the wheels, which would force the pistons to rev faster. In such a scenario, the rear wheels would tend to lock up. This would create a rear-wheel hop, potentially a vicious skid, or even a crash. None of that, as you’d agree, is desirable.

This is where a slipper clutch steps in. It essentially prevents the rear wheel from locking and allows the clutch to slip for a limited time until the engine speed and the rear wheel speed match properly again. Apart from the safety aspect, a slipper clutch also allows a rider to downshift more aggressively, without worrying about engine over rev, and rear wheel chatter.

There are different types of slipper clutches available, however, the most common type is the ramp-type slipper clutch, which is the variety used in most of the motorcycles we use on the street. A slipper clutch assembly has ramps built into the inner basket as well as the pressure plate. These ramps have the ability to allow for a sliding or slipping motion in the direction of the rotation of the wheel. Now, with this kind of an arrangement, under heavy deceleration caused by a sloppy downshift, or shifting a gear more than intended, the rear wheel won’t be able to over rev the engine. Instead, the ramps designed within the basket and the pressure plate would slide, or slip over each other, pushing the pressure plate away from the clutch, release the frictional pressure that keeps the clutch pack together, thus allowing for a limited free movement of the rear wheel and avoiding engine over-revving, rear wheel locking or hop. This ‘slipping’ function within the clutch assembly allows a rider to downshift more aggressively, even brake late and enter a corner without the worry of going into a wild slide or rear wheel hop.

In essence, a slipper clutch would do the same action as pressing the clutch with finesse and rev matching like a seasoned rider, without you having to bother about it at all.

One issue that a lot of riders face, especially with higher capacity motorcycles which have a powerful spring pulling the pressure plate in, is that it requires a lot of force. The clutch lever in such cases is very stiff, and the rider has to use a lot of force, sometimes with all four fingers to release the clutch. If the compressive force or the number of springs needed in such assemblies could be reduced, it would spell more comfort and convenience for the rider, as he would require lesser effort while pressing the clutch lever.

A solution that automotive engineers have come up with is the ‘Assist’ clutch, which is also known as a ‘slip and grip’ clutch and works very well in tandem with a slipper clutch. Slipper clutch has ramps, which only allow slippage of the pressure plate and basket as the bike decelerates aggressively. It, however, doesn’t have any modifications made to the assembly for the time when the bike accelerates. In the case of Assist Clutch, there are reverse ramps too, which lock in, and pull the pressure plate in as the bike accelerates. Now, since the accelerating force of the bike itself is helping pull the pressure plate in, increasing friction between the plates, the goal of using lesser, or lighter springs could be achieved. As a result, a lesser force is required to be applied by the rider at the clutch lever. In essence, this type of clutch ‘assists’ a rider when he’s trying to decompress the clutch assembly, and thus the name.

Well, to start off, they are not as inexpensive as your regular clutch assembly to make and cost more. Economies of scale, however, have made them more inexpensive to make, and you can now see slipper clutch as a standard fitment even on relatively lower capacity, and less expensive motorcycles.

Also, some old school riders who pride themselves for their rev matching, and precise downshifting skills frown upon the idea of slipper clutches, as they think that they take a big part of skill and excitement away from sports riding. Finally, to an extent, slipper clutch also somewhat reduces engine braking, which can be useful for riders while going down steep slopes.

We hope this article managed to answer most of your questions about slipper clutch. If, however, you have any further questions, please shoot away, and we’ll be happy to answer your queries.