For most of us, the clutch in our performance car is comprised of a few components: the clutch master, slave cylinder, pressure plate, friction disc, throw-out bearing and the flywheel. However, the amount of horsepower and torque that a clutch can transmit is largely the responsibility of the pressure plate and clutch disc.

Essentially, your “holding power” is limited by what the clutch disc – which is sandwiched between the flywheel and the pressure plate – can transmit through the pressure plate, and ultimately, to the flywheel. The clutch disc is keyed onto the transmission input shaft via splines, while the pressure plate is bolted to the flywheel and spins with the crankshaft.

There are a number of different strategies available to increase holding power. The two most common ways are: (1) to increase pressure plate load and (2) to use a more aggressive clutch material. The former accomplishes the objective, but can translate into a heavier pedal that requires more leg effort. The latter involves using different types of friction materials and different disc designs (e.g., full face, 4-puck style, etc). However, in high horsepower applications, some very aggressive friction materials can cause clutch chatter and harsh clutch take-up.

A number of different companies in the industry have different opinions on clutch materials and design. Advanced Clutch Technology (ACT) chooses to use the same friction material on both sides of a given clutch disc. On their blog, ACT engineers explained their thoughts on the pros and cons of using two different friction materials on a clutch disc.

They’ve addressed the issue in their blog titled: What’s the story behind: Multi-friction clutch discs. In their blog, they bring up some interesting points about different materials and how those materials can react and wear differently based on a given material’s heating and cooling properties.

Just like a warped brake rotor is clearly evident when you apply the brakes, likewise, ACT explains that in their opinion, your drive train could experience similar vibration when the clutch surfaces are not flat or parallel.

According to the blog post, ACT engineers state that different clutch materials conduct heat at different rates, and the difference in the coefficient of friction could create those variances in temperature between the disc surfaces as the clutch heats up. “These temperature differences, combined with the unmatched thermal expansion properties, creates a condition where a clutch disc is vulnerable to deforming out of flat and, in some cases, out of parallel as well.”

Be sure to check out more entries on ACT’s blog for news, answers to common clutch technical questions and concerns about Advanced Clutch Technology. Visit their web site for product information and availability for your application.