It’s rare to see a tuned car without an uprated clutch, and we show you why with our performance clutch guide…
The main purpose of an uprated clutch is to replace the standard item which can’t handle the level of torque the car is producing. It generally depends on the car and driver, as a hard used, but less powerful engine will wear its clutch out far faster than a more powerful engine driven gently. Clutch wear can be as extreme as slipping instantly under load, or it can occur when you use full power for short periods including drag racing, drifting, or during fast road use.
Standard clutches are designed so that even the least talented motorist can drive smoothly. But the payoff is a shorter life and inability to handle extra power. Many supercars for example struggle to launch hard more than a few times without destroying the clutch for this exact reason. But if the manufacturer had installed a clutch that could effectively handle the power under hard use, it would be too difficult for most owners to use.
Read on to see which clutches are available and which is best for you.
BREAKDOWN OF CLUTCH COMPONENTS
A clutch is fairly simple with three main components in a single plate example. It basically consists of two surfaces; one connected to the engine and one connected to the gearbox, and a central friction disc that transmits torque between the two.
This is the part that is bolted to the crankshaft of the engine and therefore spins at engine speed at all times. With the clutch engaged, the flywheel friction plate and the clutch plate are pressed together, sending torque from the flywheel to the gearbox. Different weights of flywheel are available, and although these are mostly used for other performance reasons, a lighter flywheel will also have an increased clamping effect. We’ll explain the effects of flywheel weight later on in this feature.
This is the part connected to the gearbox. When the clutch is engaged the clutch plate is pushed against the flywheel to transmit power between them. There are various materials and styles of clutch plate friction pads depending on the use of the car and the torque the clutch is expected to transmit, and this will be talked about in a separate section.
This is the part that pushes the clutch plate on to the flywheel when you engage the clutch. It has sprung metal fingers arranged in a circular fashion facing inwards that give the clamping force that helps stop the clutch plate and flywheel from slipping. An uprated clutch usually has an uprated cover which increases the clamping force of the clutch cover fingers. The downside of more clamping force is a stiffer clutch pedal, which can range from slightly stiffer to something barely useable on the road.
The majority of uprated clutches are actually what is known as a paddle clutch. A paddle clutch, rather than having 360 degrees of friction material like a standard clutch, is segmented into sections, usually four or six, but other combinations are available. These are commonly known as a four/six paddle clutch, or sometimes four/six puck in the USA. The reason for this segmented design is to help with heat dissipation. With increased power you are more likely to overheat the clutch, potentially warping it or simply ruining the friction material. Making it less effective.
SPRUNG PLATE OR NOT?
Almost all uprated clutch plates for road cars, even ones intended for enormous power levels, are ‘sprung’. This means they have springs between the centre plate and the friction pads to dampen the shock load as the clutch is engaged. This makes driving it on the road, where the clutch is constantly being engaged and disengaged, much smoother than without springs. On race cars smooth clutch operation isn’t so important so these are generally unsprung to give the most positive action possible, less weight, and less potential failure points.
Multi-plate clutches are commonplace these days on uned cars. They have more than one clutch plate with metal plates sandwiched between them. Using multiple plates spreads the load and increases heat dissipation, giving increased grip for the overall diameter of the clutch. This means a twin plate using friction materials that are more road-friendly can handle similar levels of torque to a single plate race-only sintered clutch for example. In race cars they use multi-plate clutches to save weight and rotating mass by using the smallest diameter clutch possible with a huge number of plates. Conversely, cars with very large diameter clutches as standard, V8s for example, tend to not need multi-plate clutches until a much higher power level than most four cylinder engines with smaller clutch diameters.
CLUTCH PLATE MATERIALS
There are various materials used on clutch plates, all with varying characteristics and torque handling. While the name can only give you a basic estimate of what the clutch is good for (especially as some component names can be misleading), here is a guide to the common clutch plate material names, advantages, and disadvantages.
These are generally part of standard and mildly uprated clutches. While smooth and easy to use, they have relatively low friction and are easily overheated. The friction material is usually a mix of sometimes up to fifteen components, depending on the characteristics and cost of the unit. Organic clutches often have metallic, Kevlar, and carbon components in them, just like more performance orientated clutches, but in lower levels, making them easier to use at the expense of friction.
This name stems from, unsurprisingly, the friction material generally being a mix of ceramic and metallic materials. This kind of clutch grips well hot or cold and is fairly userfriendly, though not as nice to drive as an organic clutch. The majority of performance clutches have a ceramic/carbon/Kevlar and metallic mix, and this is where a lot of confusion on clutch materials stems from. Many high performance clutches these days have a large amount of carbon/ ceramic/Kevlar in them with just a small amount of metal, but these are generally just called carbon/ ceramic/Kevlar clutches.
Although this suggests these are clutches with a pure carbon, ceramic, or Kevlar friction material, this is rarely the case, as there is normally some metallic substance in there too, though generally at a lower level than cerametallic. Clutches made with primarily carbon, ceramic, or Kevlar friction plates have a highcoefficient of friction and are very hard to overheat, but are far harder to live with in stop-start traffic than an organic clutch. Often, like carbon/ceramic brakes, they are far less grippy when cold, sometimes even less than a standard organic clutch, but once they have a little heat in them they are incredibly grippy. As a minor added bonus they are generally a little lighter, decreasing overall rotating mass.
This friction material is powdered iron and generally considered for race use only. They have incredible grip and are capable of huge torque, but can be incredibly harsh on the flywheel surface, wearing it out very quickly. Sintered clutches are very hard to use on the road and often feel like an on/off switch, much more so than other types of uprated clutches. Sintered clutches are quite rare these days aside from in extreme endurance racing, and most tend to go for a multi-plate carbon ceramic item if possible.
There’s a lot of talk about the effects of a lightweight flywheel, but to put it simply, on a high performance car there are many benefits. The first thing to remember is as it’s a rotating mass you are not simply removing 5kg. The effect is magnified by the speed of rotation and the gear ratios, meaning it can be the equivalent of a 150kg weight saving in a low gear, though in high gears it can be less than 10%. From a performance point of view it is why cars tend to rev faster and more freely with a lighter flywheel, especially in lower gears and of course out of gear. From a clutch point of view this lighter rotating mass makes it easier for the clutch plate to grip it, further increasing the clutches’ performance.
As ever with tuning, there is a downside, and that is a slight drop in drivability due to this decreased clutch mass as the revs drop more easily, making it harder to drive smoothly and easier to stall. Sometimes a slightly higher idle speed is used to stop a car with a very light flywheel from stalling when the clutch is disengaged.
HYDRAULIC OR CABLE OPERATED CLUTCH?
The vast majority of cars these days come with a hydraulically operated clutch. But there are still many popular cars with a cable clutch, Cosworths and Mk2 Golf GTIs for example, and this can cause problems when going for a high performance clutch. In a similar way to brakes without servo assistance need to be pushed harder to operate, a clutch with cable operation is much harder to use than the equivalent clutch with hydraulic assistance. With organic clutches and standard covers it isn’t an issue, but once the cover is stiffer you need a strong leg to operate the clutch. And once the plate material is uprated you need extra care to pull off smoothly. Single plate clutches can just about be driven on a cable clutch, but anything more will need a hydraulic clutch conversion to maintain any hope of road drivability.
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