Clutches form the bond between getting the energy from all that internal combustion in the engine through to the transmission and then finally out to the driven wheels. And with countless combinations of engine and transmission types scattered all over the automotive world, many different denominations of clutch exist to adhere to the job required. Whether they’re dealing with 90bhp or 900bhp, there’s a clutch out there that - once engaged - will be able to help transmit as much torque as possible through to any transmission.

Before we get started, click here for a basic overview of how a clutch works!

Basic friction clutch

Most cars use a form of friction clutch which has all the normal components that you have probably seen or heard of before. Operated hydraulically or by a cable, a friction clutch uses a pressure plate, a clutch plate (or clutch disk) and a release bearing to engage and disengage the flywheel and the transmission. Most cars will use a simple single-plate clutch, with only higher powered engines needed a multiplate clutch to engage the transmission properly.

When the clutch pedal is depressed, the release bearing applies a pressure to diaphragm springs on the pressure plate which releases a clamping pressure on the clutch plate and disengages the transmission from the flywheel.

As the gear change is made and the clutch is released, the release bearing is sent back from the pressure plate and the clutch plate is again clamped and driven by the pressure plate, allowing drive through to the transmission.

Wet and dry clutches

Wet clutches in general have multiple clutch plates (in cars) and have a supply of oil to lubricate and cool the components. They are used in high torque situations where friction levels would be high and therefore clutch temperatures would soar without some form of coolant. Any powertrain over 250lb ft of torque should really be employing a wet clutch to avoid excessive wear on the rest of the transmission through overheating.

Dry clutches on the other hand have no oil supply and are generally single-plate. This means they can be more efficient as lubrication can lead to a lack of friction between the plates in a wet clutch as well as producing parasitic losses from the drivetrain as a pump is needed to supply the lubricating oil. The small coefficient of friction in a wet system is therefore the reason for having multiple plates for effective clutch performance.

Remote video URL

With multiple friction plates stacked on top of each other, obvious benefits are that the amount of friction generated within the clutch can be greatly amplified and therefore it can cope with much higher torque inputs. Used in many racing cars including Formula 1 and WRC, the amount of friction needed to stop the clutch slipping can be fitted into the same diameter as a single-plate clutch due to the neat stacking.

Dual-clutch systems

Dual-clutch transmissions now dominate the premium car market after their first general release through the VW Mk4 Golf R32. Using one large clutch for odd gears and a smaller clutch for even gears, this form of transmission is renowned for quick, smooth changes and is now found in every supercar worth its salt, as well as many hot hatches and saloons.

Used in automatic and semi-automatic setups, DCTs use two wet multiplate clutches which eradicate the need for a torque converter. The shifts are seamless due to the fact that the torque output to the driven wheels is not broken as it can be applied to one clutch while the other is disengaging, meaning no break in output.

Electromagnetic and electrohydraulic clutches

Electromagnetic clutches can be used when mechanical sympathy and timing of clutch operation is generally disregarded, with the clutch being actuated by a simple button press on the gearstick or even a proximity sensor when your hand is near the gearstick. When the clutch is actuated remotely, a DC current passes through an electromagnet which produces a magnetic field. The armature is then attracted to a rotor, creating a frictional force to engage the engine and transmission.

Electromechanical clutches are prominent in the automotive industry, used in virtually every paddle-shift system. By pulling on a paddle, an electrical signal is sent to a computer which engages a servo to disengage the clutch hydraulically.

This negates the need for any form of clutch pedal and when combined with a DCT transmission can become the most efficient form of gear changing on the market. In general, these systems are used alongside more powerful powertrains and therefore use multiple plates within the clutch.

There are a few other clutch types out there, but most of them are either extinct or are only used in much smaller factions of the automotive sector. For example, centrifugal clutches are widespread in the moped and biking industry, using shoes (like on a drum brake) to engage and disengage the clutch. Dog clutches are also used in non-synchromeshed transmissions but necessitate double de-clutching and were brushed under the mat once gearboxes evolved.

If you’re looking to get more power from your engine through modifications, thinking about your clutch is a must. As Alex experienced when turbocharging his MX-5, once torque reaches a level too high for your clutch, the plates begin to slip as they can’t handle the forces channeled through them. In this scenario, a clutch upgrade is needed, and numerous aftermarket specialists manufacture performance clutches for this reason. Most of us will only ever really encounter a standard friction clutch on our travels, but there are plenty options out there if an increase in power is on the cards.

I often get people asking me “What’s the best clutch?” It really is a more complicated question than a lot of people think. Everyone drives their car differently, and everyone has different expectations for how a clutch should feel, how long it should last, etc. First, let’s talk about the main different types of clutches that are out there.

Full-Faced Disc

This is the most common type of clutch, which virtually every manual car uses from the factory.

Generally, full-face clutches are going to be the easiest to drive and have the smoothest, quietest operation. However, when you start adding big power, it’s difficult to find a disc clutch that can support those power levels while maintaining a good pedal feel. You usually get increased pedal pressure, chatter, or both, depending on the design of the pressure plate and material of the disc.

Puck Clutches

Puck clutches are named so because instead of a full, circular disc, they have a “star” pattern disc with “pucks” of friction material at each point.

Puck clutches generally have much higher torque capacity than disc clutches, and because they don’t have a full disc, there is less rotating mass, which makes them lighter in weight. A lighter disc allows you to shift faster, as the synchros in the transmission have to do less work to match the speeds of the input and output shafts, since there’s less rotating mass on the input side. Plus, their higher torque capacity means they’re going to tolerate abuse better than “softer” clutches. So they’re great for competition use, in a case that’s going to see drag racing especially. But they do have a few drawbacks. Mainly, they tend to be extremely grabby and often noisy. People often describe them as feeling like they have very “on-off” engagement. They’re not as comfortable to drive on the street for this reason, and because there’s actually less friction material (just higher clamp loads), they won’t last as long as a full-faced disc.

Hybrid Clutches

These aren’t nearly as common, but hybrid clutches are similar to full-face clutches, just with slightly modified designs.

Hybrid clutches really need to be reviewed on a case-by-case basis, because they’re going to be designed for very specific applications or purposes. For example, the above is called the OFE (Organic-Feramic). Literally half of the disc is just like the Organic disc at the top of this page, and the other half is what you’d find on one of Southbends “FE” clutches. We’re seeing the Feramic side, the notches there show the Organic side showing through. Another popular clutch like this is the TZ disc. It’s the same on both sides, but uses a kevlar friction material and a unique design that sets it aside from a traditional full-faced disc.

Multi-Disc Clutches

Multi-Disc clutches are exactly what they sound like. There are multiple discs with friction material stacked up.

These are much less common than other clutch types, primarily due to their cost. They are most often used on motorcycles, where it’s necessary to use a clutch that has a high torque capacity but in a physically smaller space (build up, rather than out). Some multi-disc clutches for cars will employ a similar mentality, where the disc and cover (pressure plate assembly) are much smaller in diameter than the flywheel. In addition to their cost, multi-disc clutches chatter and make noise frequently. While they are known for having relatively light pedal pressure, most are also relatively grabby compared to single disc clutches.

Comparison Charts

So I put together a few diagrams to illustrate more clearly how some of the different clutches we sell compare to one another.

Here’s what each value means.

• Pedal Weight – This is how much pressure you have to exert to actuate the pedal. A lower value indicates a lighter pedal. A lighter pedal isn’t always better, though. Many find it difficult to modulate the clutch pedal carefully when it’s extremely light, but if you’re driving the car in traffic every day, you’re not going to want a heavier pedal. Additionally, TT Z32s originally came with clutch boosters to make the pedal lighter. So you may find that a clutch rated as being moderately heavy isn’t too bad in your car if you have it, or a clutch that most find someone light a bit heavier than expected.
• Torque Cap – Indicates how much torque capacity the clutch can handle before slipping. It’s important to note that a high torque capacity doesn’t necessarily mean it can take more abuse. For example, the SS-TZ has a very high torque cap despite how smooth it is, but it’s not recommended for drag racing, for which a puck or multi-disc clutch would be better suited. This is because when you drop the clutch, especially at high RPM, the disc is “shocked” with torque. So even if your engine only makes 300 ft-lbs of torque, if you’re clutch-kicking everywhere, you’re going to wear it out faster.
• Cost – How expensive the clutch is to purchase. Simple, right?
• Life Span – How long the clutch is expected to last. This is a combination of both the type of clutch (for example, puck clutches don’t last as long as full-faced discs) as well as perceived build quality, which is mostly from my own observations having sold these for a while. I should point out that clutches don’t just go bad. I’ve occasionally had someone install a clutch on a car making less power than the clutch is rated, and had the clutch start slipping after only a few months. It’s one thing if the pressure plate breaks physically, or a spring pops out of a disc, but other than that the only thing that can cause the clutch to fail is either incorrect installation or incorrect operation. Slipping the clutch, riding the pedal, launching/drag racing, clutch kicking, downshifting into the wrong gear (reverse torque damage), and improper pedal adjustment are all common/possible causes of clutch failure. On the rare occasion someone tells me they installed a (high quality) clutch in their car and it failed prematurely, I’m always tempted to ask: why are you replacing your old clutch to begin with?
• Comfort – How smooth and quiet the clutch is. The higher this value, the more “streetable” a clutch is. A clutch with a low value here may chatter, chirp, or be difficult to engage without bucking.

This list isn’t complete nor is it totally scientific, but hopefully it helps steer someone in the right direction!