About Motorcycle Clutches

About Motorcycle Clutches.


A Motorcycle Clutch is the tool that connects or disconnects power made by the engine to the transmission. The clutch is how a rider isolates the transmission from the rear wheel to stop the bike from driving forward. The clutch is a series of spring-loaded FRICTION PLATES that, when pressed together (engaged), act as one to connect the crankshaft to the transmission (and rear wheel). To change gear, a rider uses the clutch to isolate the crankshaft from the transmission, selects a new gear and releases the clutch so power resumes to the rear wheel.

So the Clutch is very important, you rely on the Clutch Friction Plates to connect the Engine power to the rear wheel and drive the bike forward.

Clutch Friction Plate basics.

Clutch Friction Plate materials are graded according to the grip they provide, this measure is called 'The Coefficient of Friction' and it gives an indication of the slip resistance of a surface. The coefficient of friction value is a calculation expressed as a number between 0.0 and 1.0. The closer the number is to 1.0 the greater the resistance to slip provided (ie: higher numbers give more grip). Surfaces with high coefficients of friction (COF 0.6 or higher) have greater texture, provide more grip and last longer. ...and grip and long life is what you want from Clutch Friction Plates.

So what's in there now: Usually Rubber Impregnated Cork - co efficient of about 0.03.

The standard material on most Japanese and some late Model European Motorcycles with wet clutches is a rubber impregnated cork (co efficient of about 0.03). This rubber impregnated cork material does not grip well (low Coefficient) and slips so it is prone to glazing. Once glazed, it will continue to slip until the Clutch Plates are replaced. This slipping may not be noticable and yet it will cause excess heat which can cause damage. Unfortunately, Cork is not known to handle heat well and the cork may de-laminate from the plate it is bonded to. Heat may also cause hot spots and warping of the intermediate (steel drive plates). Not to mention the damage the heat does to the oil the clutch, gearbox and Motor runs in.

The bottom line is this; Rubber impregnated cork is not the best material to use, it does not grip well, it does not last, it does not offer optimum performance. It is a compromise material and when Original Plates require replacing far superior materials are available.

So how do you choose...


Option 1: Replace with Rubber and Cork.
Rubber Impregnated Cork - co efficient of about 0.03.

Just replace the Clutch with the same old from your Dealer. It will improve nothing so you can not expect a different or better result. You will not get longer plate life or help lower running costs.

Option 2: Kevlar.
Kevlar - co efficient of about 0.13.

Kevlar blended composite Plates are goldy green in colour, it is the same type of material used in bulletproof vests. It is very strong, durable and abrasion resistent, Kevlar has a co efficient of about 0.13 (433% more grip than some Rubber Impregnated Cork). The Kevlar used is designed to run only in oil. If Kevlar is pushed hard and does happen to slip it will not glaze, it will form a small amount of carbonization and wear through and it will still last longer than Rubber Impregnated Cork.

Plates Resurfaced with Kevlar will increase Clutch Plate working life compared to the Rubber Impregnated Cork. Kevlar will usually handle temperatures of up to 300 deg Cecius and the resin used to bond the friction material to the plate has a sheer point of 350deg Celcius. Kevlar resurfaced Clutch Plates have been used in drag racing / road racing / street riding and off road use with great success.

Option 3: Carbon.
Carbon - co efficient of about 0.13.

Carbon fibre blended composite Plates are black in color and have similar technical qualities and co efficient to Kevlar. Carbon friction material is suited to a more high energy application, so it is mainly used where high RPM or sustained periods are experienced. Although Carbon can run in a dry clutch, it is only recommended in low hp applications like vintage bike dry clutches. Carbon is mostly used in very high RPM motors and by riders and teams in long races, however it is dearer than Kevlar and doesn't last as long.

RE SURFACING IS EASY...
simply send us your old friction plates and we will resurface them.
It is simple, affordable and it works.
Email: info@mrclutch.com.au or Phone: 02 9836 0774