The debate over whether a dry or wet clutch is better has been pretty much won by the proponents of wet clutches.
For both motorcycles and automatic cars, the wet clutch provides many benefits lacking in a dry clutch.
However, dry clutches are much cheaper and easier to repair.
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What Are the Benefits of a Wet vs a Dry Clutch?
Wet clutches are covered in oil. This oil acts as a coolant, allowing more aggressive use of the clutch while dissipating heat. This is in contrast to dry clutches that heat up and slip when abused. Wet clutches are smoother and quieter to use, requiring less effort to engage in heavy traffic.
While motorcycles benefit from wet clutches due to their smaller size and ability to dissipate heat very quickly, performance cars and hot hatches adopt wet clutches for their smoothness and performance benefits.
What Exactly is a Wet Clutch?
A wet clutch does the same thing that a dry clutch does, it transmits torque from the engine to the gearbox. It also helps the gearbox to shift gears by reducing the force on the gears, making it easier to slip them to the next ratio.
The wet clutch is a mechanical linkage in the same way that a dry clutch is. They both perform the same function, albeit in a slightly different way.
To understand the benefits of a wet clutch, you need to have a basic understanding of how it works.
Whereas a dry clutch normally has a single clutch plate and pressure plate located inside the bell housing, a wet clutch is made up of numerous friction and steel plates.
The wet clutch has a fluid coupling which means that the friction plates and steel plates are drenched constantly in engine oil.
This keeps down the temperature as the multi-plate system is constantly exchanging oil with the rest of the engine.
Where Are Wet Clutches Used
Wet clutches are most usually found on motorbikes and cars with automatic transmissions.
They are long-lasting, much more so than standard dry clutches that tend to wear out more quickly due to high temperatures and constant friction.
With motor vehicles that have high-output engines, wet clutches are preferred due to their ability to withstand the heat generated.
When compared to dry clutches that will quickly overheat, wet clutches have lower wear and tear and much lower operating temperatures.
Wet clutches are not suitable for some smaller engine cars as they contribute to a loss of power due to energy being lost to the oil’s greater drag.
The use of multiplate systems was introduced to combat this problem.
Wet clutches are preferred for everyday road bikes as well as offroad bikes as they are much quieter and are better able to meet the stringent noise levels mandated by the government.
What are the Benefits of a Wet Clutch?
Greater Durability
The biggest benefit conferred by wet clutches is that they last longer than dry clutches.
As they are constantly drenched in oil, they effectively resist wear and tear. This is particularly apparent when they are subject to intense use and abuse.
A dry clutch will start to overheat after it has been used hard, especially in racing. Without oil to dissipate heat, the dry clutch wears out the friction material much faster and its ability to resist the rotational forces becomes less and less until the clutch is no longer able to function.
With lower operating temperatures, the wet clutch is less likely than the dry clutch to require repair or adjustment. The long-term repair and replacement costs of wet clutches are lower than dry clutches.
Removal of Dust and Debris
When the wet clutch engages, the friction causes particles to break free from the surface of the clutch. These metallic particles as well as other contaminants are suspended in the oil.
The oil then transports these particles and debris to the oil filter where they are captured. This keeps the whole system running smoothly and efficiently.
Allows for Higher Torque
With the higher torque generated by modern engines, wet clutches are better able to handle it than dry clutches.
A maximum rating of about 250-pound feet of torque is all the dry clutches can effectively control.
Wet clutches make it possible to enjoy the sportier models generating higher torque. With the multi-plate design having a greater area over which to stretch the friction, more torque is easily handled.
Quieter Cars and Motorbikes
The change over to wet clutches used in motorbike design was driven to a large degree by noise reduction and better efficiency.
Now that car makers have seen the benefits of wet clutch multiplate design, adding them to automatic transmissions has resulted in noise levels dropping significantly.
The Downside of a Wet Clutch
While the upside of a wet clutch design is a powerful motivator in getting them into as many cars as possible, there is one major drawback.
And that is a loss of power.
Despite the use of the multiplate design, the oil generates a significant drag which saps engine power.
The loss of power is more evident with less powerful engines. This is the one significant advantage of a dry clutch.
Once it has engaged, there is virtually no loss of power through the action of the clutch.
Basic Friction Clutches
Friction clutches are activated either with a cable or via hydraulic pressure.
The design is quite simple with a pressure plate, clutch plate or disk, and a release bearing. The release bearing engages and disengages the flywheel so that the torque from the engine is transferred to the transmission.
On more powerful engines, the manufacturers overcome the additional torque by using a multi-plate dry clutch.
As you depress the clutch pedal, the release bearing puts pressure on the diaphragm springs located in the pressure plate. This releases the pressure and disengages the gearbox from the flywheel.
After the gear change, and as you release the clutch, the springs clamp the pressure plate and clutch plate together, transferring the engine’s force back through the transmission.
Dual-Clutch Systems
A variety of high-performance, premium vehicles such as the Golf R32 pioneered the use of dual-clutch systems to handle the ever-increasing torque of their new-era engines.
Through the use of a large clutch for odd-numbered gears and a smaller clutch for even-numbered gears, the transmissions enjoyed very slick gear changes.
These pioneering clutches are now commonplace on supercars and high-end saloons and hot hatchbacks.
The semi-automatic and automatic transmissions are designed to incorporate a dual-clutch setup with two wet multi-plate clutches.
This innovative design does away with the need for a torque converter.
Shifting gears is incredibly smooth as the torque output is delivered via one of the clutches while the other one is disengaging. The power curve is thus uninterrupted.
Frequently Asked Questions About the Benefits of a Wet vs a Dry Clutch
Is a CVT a wet clutch?
A CVT is a continuously variable transmission that moves through an almost infinite number of gears as it adjusts for the torque and road speed and is not a wet clutch. Wet clutches are typically fitted to automatic and semi-automatic transmissions and motorbikes.
Can you burn a wet clutch?
A wet clutch can burn, but not in the traditional sense of a dry clutch burning out. The wet clutch will wear down to the point that the friction pads no longer function and it fails to work. The engine oil that circulates around the wet clutch keeps it remarkably cool.
Is a dry clutch reliable?
Dry clutches have been around for a very long time and are still fitted in vehicles today. The design is tried and tested and very reliable. They may not last quite as long as wet clutches, but they cost a lot less to replace and are of a simpler design.
Conclusion On What Are the Benefits of a Wet vs. a Dry Clutch
While there is still a place for dry clutches in today’s cars, wet clutches are a new technology that meets the demand of consumers for higher torque engines.
It will be some time before automobile manufacturers completely replace dry clutches with wet clutches, as they have mostly done in the motorcycle world.