Most Important Differences Between the Wet and Dry Clutch
If you’re buying a new car — or a motorcycle — then you might see words like “wet clutch” and “dry clutch” when it’s talking about the transmission. What does this mean? Is the wet clutch under water? Is the dry clutch not lubricated at all? It can be confusing when you don’t have the appropriate know-how.
In today’s blog, we’ll be discussing what the actual difference is between a wet and dry clutch. Let’s start with the basics:
What is a Clutch?
Most of us in the UK are familiar with clutches since we are still, by and large, a nation of manual transmission drivers, though that picture is quickly changing as we start to transition more toward electric cars. In any event, a clutch is a mechanical device that links the engine and your transmission. It separates the engine from the transmission system, which allows the driver to change gears smoothly and without causing awful grinding noises.
In a manual transmission car, as you know, the clutch is the left-hand pedal in your typical set of three pedals in the vehicle’s footwell on the driver’s side. For an automatic car, the clutch is still there but operates without driver input. Automatic transmissions use either a torque converter or a CVT-style variable transmission that shifts gears automatically.
What is a Wet Clutch?
Wet clutches work on a multi-plate design when used in cars and make use of an oil supply to keep the moving parts both lubricated and cooled. This kind of clutch is favoured on vehicles that generate high levels of torque where only the presence of a liquid coolant can prevent potentially catastrophic rises in temperature.
It is therefore quite standard to use a wet clutch in any vehicle that outputs more than 250lb-ft of torque. If not, then the excess heat would possibly cause a lot of additional wear and tear to the transmission.
What is a Dry Clutch?
Unlike the wet clutch which gets its liquid bath, the dry clutch operates using friction. It is made using a single-plate design, and the lack of lubrication, some argue, makes them more dependable for efficiency because the presence of liquid in a wet clutch can create losses in power from the drivetrain. Not only does the liquid create a parasitic loss in itself, but it also has to be supplied via a pump, which needs power.
What are the Pros and Cons of a Wet Clutch?
The first pro for wet clutches is their lifespan. The presence of lubrication helps to keep the moving parts from prematurely wearing down. The reduced friction that comes from lubrication doesn’t overly diminish power, but better secures the mechanics of the drivetrain from harm.
Another advantage is that wet clutches can be used for high-torque engines. With many engines now much more powerful than they were years ago, and demand for more powerful engines and high-torque engines increasing, wet clutches are there to deal with the higher temperatures that come with the additional torque.
Wet clutches use multi-plate design to maintain high levels of friction. Though there is some diminishing effect of the lubricant when it comes to friction and power, the multi-plate design of the wet clutch is designed to compensate for that, providing a wider friction zone overall.
The multi-plate design is complex, making maintenance more complex. The inevitable result of having more moving parts is that there is more to look after and more to possibly repair when things go wrong.
The lubrication using oil just means oil gets contaminated faster. Needing additional oil in your clutch means there is more dust and other contaminants getting into the oil, which ultimately means your oil wears out faster.
Lubricant does create resistance which can create small power loss. There is some compensation from the multi-plate design, but overall power output is lower than a dry clutch.
What are the Pros and Cons of a Dry Clutch?
The first advantage comes in transmission efficiency. Without the lubricant in place, the overall transmission efficiency in a dry clutch is much greater. It minimises any power loss because the clutch plate and drive shaft have direct contact.
On a motorcycle, a dry clutch can be cooled by the air. On motorcycles, because the dry clutch has its clutch plate outside the engine casing, it can be easily air cooled without any need for additional coolant.
Their single-plate design and lack of lubrication make them simpler. Their simpler construction makes them easier to manage in terms of repairs and maintenance, but there are downsides to this, too.
No oil needed on the clutch means your oil can be cleaner, longer. If oil is not needed to lubricate the clutch, then the clutch operation won’t be able to get the oil dirty and contaminated. One less way for your oil to get contaminated is good news.
First, they only work well in low-torque vehicles. If the vehicle has fewer than 250lb-ft of torque, then the dry clutch is a viable option. For anything above that number, however, then it just creates more problems.
Second, they wear out faster. One of the benefits of lubrication is that it keeps the moving parts from wearing away too fast. A dry clutch will inevitably cost more in maintenance because it will wear down faster and potentially have more issues.
Third, a dry clutch is often noisier.The friction created in dry clutches makes them louder when things go wrong. That can be a negative aspect, especially when riding on a motorcycle where all sound is in the open air.
Conclusion: Wet, Dry, What’s the Difference?
Ultimately, the type of clutch that is used in your vehicle, be it a car or a motorcycle, is mostly determined by the OEM. For you, it’s still advantageous to know about the different types and what it says about the car. For example, if you’re looking at a vehicle with a wet clutch, then you know that it likely has a higher torque rating. That’s useful knowledge, any day of the week.