RPS Performance Products has attacked these problems head on and created a patented solution. By segmenting the flywheel friction surface into four pucks, each puck can expand and contract in its own CNC machined pocket without affecting the other pucks. The steel pucks, unlike the one-piece hoop, have some room to grow.

Even though this RPS Cyn-R-G flywheel had obviously seen some heavy action, flatness measurements were still within specification.

This aluminum flywheel with a one-piece heat shield had seen some action, yet measurements showed the surface beyond specified limits. Look closely. The six-puck disc became so hot it fused to the heat shield in six spots. Tip: keep the clutch pedal depressed after a hot run.

Because the flywheel surface stays flatter it stays cooler, and this coolness helps the entire clutch last longer and perform more consistently. The steel pucks can be replaced for about the price of a flywheel resurfacing and RPS has even carried though the segmented design to their Pro MAX series pressure plates. Why replace the entire flywheel or pressure plate when the friction surface is the only thing that's worn?

HARD CORE

As it turns out being able to replace the flywheel and pressure plate friction surface is a good idea, as the problem of flywheel hot spots runs deep. RPS had one client with a mysterious clutch problem. In replacing strip and street-strip stock Mustang clutches with high performance setups, roughly half of the customers noted that their clutches chattered on engagement, despite the fact the flywheels were resurfaced according to specification.

RPS president Rob Smith mulled over the problem and asked the technician one question. Out of the customers that experience chatter how many are running with new flywheels? The answer was none. Rob managed to get one of the chattering flywheels in question back to Los Angeles for testing on a Rockwell hardness measuring device, and the results solved the mystery. Even though the machining was spot on perfect, the flywheel cast iron was harder in some spots than others. Excessive heat had created a flywheel with material of different densities despite being machined perfectly flat - the hot spots had gone deeper than could be machined away.

The result was that the clutch disc matrix grabbed the flywheel quicker in some spots than others and created chatter on engagement. The only solution in these cases was to start over and use a new flywheel – an expensive proposition at best. With a replaceable friction surface new flywheel performance can be attained for the cost of a stock flywheel resurfacing.

THE MATRIX

The matrix in this case has nothing to do with sci-fi, but instead refers to the collection of materials, resins, modifiers, fabric, and other top secret stuff that comprise the clutch disc friction material as a whole. How these friction materials grip to flywheel surfaces is part of the formula for clamping force. The clutch disc matrix literally plows into the microscopic texture of the flywheel and pressure plate surface and locks up to create grip. Think about trying to walk with a set of socks on a hard wood floor. Slip and slide guaranteed. Those same socks on carpet? Grip city and you're the Mayor.

These same ideas apply to clutch discs and how well they grip flywheel material. Chromoly, for instance, can be made into a flywheel that's thinner and lighter, but has drawbacks, as the material is also a lot harder. This hardness means it's smooth on a microscopic level, and requires more friction to create the same grip as cast iron or steel. The paradox is that the flywheel friction surface has to stand up to serious punishment, but also has to be made of the softest material possible in order to grab the clutch disc matrix.

"Let's say you have a six puck with a chromoly flywheel, vs. an organic with a cast iron flywheel, it's quite possible the organic with the cast iron will hold more than the six puck with the chromoly because the chromoly is particularly hard. You can't just jump off and say the six puck hands down holds more," said Rob.

Thus the flywheel material has a great influence on the overall holding capacity of a given clutch setup.