Why 3-puck clutch?

Why do modified cars use multi-puck clutch pads instead of full circle ones for more friction area? Has it got something to do with less surface area having more force?

One of the reasons is heat. Heat causes expansion and expansion causes things to crack and come apart, and most racers don't like to test their scatter shield to see if it's working or not. Multi disk's dissapate the heat better. Same thing holds true for flywheels. Plus with multi disks you get more clutch area for stronger lock-up.

Actualy more plates equals more surface area and more clamping force for less heat generated and more heat disapaited.

It also means more surface area can packed into a smaller diameter clutch which means less rotational mass which helps engine accleration.

Thanks for the replies, but I'm talking about single plate multi-puck ones, not multi plates.

I've read that for multi-plate ones u can have more grip without too much increase in clutch tension, is that so?

By 3 puck I assume you mean the 3 fingers or pucks on the clutch disc?

In which case its to reduce weight, and allow the use of very heavy duty materials on the disc surface all in the aid of allowing faster shifts and greater holding power with out increaseing pedal pressure.

Why do modified cars use multi-puck clutch pads instead of full circle ones for more friction area? Has it got something to do with less surface area having more force?

Those clutches are typically made of a metallic sintered material and are designed to be used with the stock pressure plate. Real racing clutches use the full circle.

The reason why the plates are so much smaller is because that the friction material is a little slippier than the organic friction materials usually used in clutches. But, the sintered clutch material can handle higher temperatures, and since we use the stock pressure plate we can only increase pressure on the pucks by reducing their area. In this way we can make the clutch handle more torque without too large costs.

http://www.apracing.com/pics/clutch/cp6174.jpg

The clutch on the picture above is a real racing clutch from a champ car, and it is of sintered type, has pull operation and 4 plates and its diameter is 115mm. With this type of clutch the full circle is used, and even though it size is small it can handle almost 1000 Nm of torque. The price of one of those is probably a few thousand dollars, but they also require a purpose built flywheel and a redesigned clutch operation.

In cases where money is no object carbon/carbon clutches are used instead, they are however very expensive. Another thing with those clutches that is a little different is that they don't use the flywheel as a friction surface (this also means that no flywheel is required, like in F1 where the engines do not have a flywheel), all friction surfaces are made from carbon/carbon and is in the form of plates. Prices around $10k is nothing strange, but they also last much longer than a sintered clutch.