Organic clutches are the OEM standard. As the name suggests their base is of organic origin, usually a phenolic resin or compounded rubber together with cellulose as an organic friction material. When they’re well made organic clutches offer many advantages, which explains why they have been the OEM clutch disk material of choice for many decades. They offer very smooth and gradual engagement which means they are easy to operate and comfortable for daily use and stop and go traffic. They generate adequate friction over a a broad range of temperatures and have a minimal or no break in period. So let’s step things up by borrowing something from bulletproof vests and integrating it into our clutch. Kevlar! When in tensions, Kevlar is 5 times stronger than most steel alloys. This is how it stops bullets. But it can also make your clutch extremely durable and dramatically increase its lifespan. Kevlar clutch discs can withstand higher temps than most organics and will take a lot of hard usage, for example hard driving on the race track, but they absolutely hate stop and go traffic. Kevlar has good burst strength and great wear resistance if used correctly but it also has a low coefficient of friction, which means it doesn’t actually grab very hard. The upside to this is that it usually enables very smooth engagement, just like an organic, the downside is that it needs a very strong pressure plate with lots of clamping force to grab the flywheel without slipping. The final downside of Kevlar discs is that they must be carefully broken in before they can be used hard. Depending on the disc the break in period can be relatively long and ranges from 100 to 500 miles. A metal clutch disc is also often called a ceramic clutch. Ironically, ceramic clutches actually contain very little ceramic in them, many don’t have any ceramic in them at all. Instead the base material is usually copper or bronze or a mixture of both and then iron, steel, silicon, graphite, ceramic or any mix thereof added into in to further increase friction. Copper and many other metals are excellent heat conductors which means that all metal clutch discs can tolerate extreme heats. It takes some very very extreme abuse to be able to fry a sintered metal clutch, which means you can let loose on the track with them. Unlike Kevlar, metal discs have a very high coefficient of friction, which means they can hold massive power even without a very strong pressure plate, but the downside is that you can forget smooth engagement. High friction means that sintered metal clutch discs grab strongly and abruptly, often with chattering and shuddering sounds and sensations accompanying engagement and disengagement. But what if even a ceramic clutch isn’t enough for you? Let’s say you need to transfer something like 1000 hp and god knows how much torque onto your transmission. In that case you need sintered Iron! The easiest way to understand sintered iron clutch discs is to think of them as ceramic clutches on steroids. They are extremely abrasive which means they will destroy most conventional freewheels. They can hold incredible amounts of power without slipping but their engagement is so sudden they’re like a switch. On and off. This means it’s next to impossible to use them on the street. On the upside they can take incredible amounts of abuse and it’s nearly impossible to fry a sintered iron clutch. When it comes to twin plate and multi plate clutch kits, they can do something single plate clutches can’t and that is to increase the total surface area of the clutch disc. Multi plate clutch kits can do this by using more than one disc. By increasing the surface area multi plate clutches can retain a relatively low clamping force and abrasiveness, which means they can hold more power and torque while retaining OEM like driveability. Another important distinction is sprung and unsprung clutches and clutches with and without a marcel spring. In general a sprung clutch with a marcel will be tolerable for street driving regardless of material, while a fully rigid clutch will be much better suited for racing only applications.
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