Breaking the difference between the two clutch styles
If you’ve ever been pulled over at a stoplight and heard the noise of a sports bike as if it were about to explode, then you are familiar with the iconic sound of a dry clutch. Dry clutches used to be quite common –
Ducati used them for decades – but today the vast majority of motorcycles made use wet clutches. What’s the difference, why would a manufacturer or rider choose one over the other, and why are dry clutches going out of style?
What is a wet clutch?
For starters, let’s talk about wet clutches. They are known as wet because they are bathed in motor oil. The main purpose of oil is to cool the clutch plates, and because of this cooling effect, wet clutches can withstand a lot of abuse, such as that encountered in braking and running traffic.
Wet clutches generally have a nice, wide friction zone that makes them quite easy to use. They also tend to last a long time and are quieter than dry clutches. And did we mention that they can take a lot of abuse?
That’s a nice feature, especially if you’re just learning to ride or don’t want to replace your motorcycle’s clutch every 10,000 miles.
On the other hand, wet clutches dirty the engine oil faster, as all the dust that is created as the clutch wears out remains inside the engine. Fortunately, the oil filter takes care of that.
The other downside is that wet clutches are more difficult to work with. Also, because the clutch rotates in oil, there is fluid drag that saps the engine’s power a bit.
What is a dry clutch?
Avoiding that fluid drag is the biggest benefit of a dry clutch. Dry claws, as you may have already guessed, are not bathed in oil. That means less drag and more power to the rear wheel, as well as cleaner motor oil, but it also means less cooling for the clutch pack. With no oil to cool things down and wet the hitch, dry clutches will perform poorly if you hammer them and tend to be more grippy and harder to modulate.
They also wear out faster and are much louder, especially if you run an open clutch cover, which many motorcycles do to help keep the clutch cool.
The rattle of a dry clutch idling is a legendary sound, especially for Ducatis, but it’s all that noise that put the dry clutch on the endangered species list. As noise regulations get tighter, every decibel counts, and switching to a quieter wet clutch means more noise on the budget for other things, like a sweeter-sounding exhaust.
Two places where you still see dry clutches are in Moto Guzzis and MotoGP. Moto Guzzi still uses them because that’s what they’re used to and, to be fair, Guzzi’s chosen engine design, the longitudinal V-twin, encourages the use of a large diameter single disc clutch – and if not it it’s broke, don’t fix it. They are used in MotoGP because in racing every little advantage helps and, as we mentioned before, the dry clutch exerts less resistance to the engine.
Ultimately, it’s ease of use, durability, and quiet that has made the wet clutch the configuration of choice for the vast majority of motorcycles.