We have used two different types of clutches on a rider of 53kg.
The genuine Blata clutch lasted around 9 months and gripped very well, but did over heat the clutch bell.
The clutch bell showed no signs of wear in that nine months except for blueing of the bell.
Now we are using the Zocchi three shoe carbonium clutch.
It has been in for over one year.
The bell shows no signs of wear and does the clutch shows miminal wear.
The 79 mm bell still does not fit over the original clutch.
With the other compounds of clutches, we have not tested them yet.

Until I test further I won't be able to advise you further.

Well, where do you start...

First let's review the theory of operation of the centrifugal clutch and then add some variables.

The clutch operates by the centfigugal force generated by the spinning crank which 'throws' the clutch shoes when the force (remembering that f=ma) generated exceeds the 'holding' tension of the clutch springs. This a basic physics concept.

Add some variables...

Clutch shoes - mass. Increasing the mass of the shoes (i.e adding weights) will increase force, so the shoes will engage with more force and overcome the spring tension more easily for a given rpm (a). The trade-off is the impact damage to the clutch shoes.

Clutch shoes - acceleration (referring to the clutch spinning, not the bike moving!). Increase rpm and the shoes will again engage with more force.

Clutch shoes - force (equal to the spring tension). Increase spring tension and you need to generate more force to overcome the spring's tension i.e. increase (m)ass or increase (a)cceleration.

What happens when I ...

Install red springs -> you are increasing f. This effectively means that you are shifting the engagement rpm UP the power band.
Install blue or yellow springs -> you are decreasing f. This effectively means that you are shifting the engagement rpm DOWN the power band.

Wind in the springs -> you are increasing f. This effectively means that you are shifting the engagement rpm UP the power band.

Wind out the springs -> you are decreasing f. This effectively means that you are shifting the engagement rpm DOWN the power band.

Now let's review clutch material...

We are now familiar with the theory of operation of the centrifugal clutch, so let's look at the next concept - power transfer. In order to convert the kinetic energy of the spinning crankshaft to forward motion of the bike, we need some way to transfer that energy to the rear wheel. This whole process needs 'friction' to work. The net result of friction is heat.

The minimoto employs a friction system via a 'bell'. The bell is acted upon by the clutch shoes being thrown out by the centfigual force generated by the spinning crank. In order to 'engage' the clutch to the bell, a friction material is required between the two surfaces to provide (1) slip and (2) grip. Without a friction material, the two metal surfaces would not 'engage' and become one unit.

Slip - every clutch needs slip. This slip provides a smooth energy transfer and allows some heat build up (expands metal).
Grip - where the friction material no longer 'slips' but has engaged the bell (above the engagement rpm)

As mentioned earlier, heat is the by-product of friction. Too much slip means excessive heat is genarated and premature wear of the components.

Now, I can answer the question

Friction material - the compounds used are not necessarily soft, medium, hard. The friction material is useful for certain applications and offers the variation in 'slip' characteristic. Zocchi Special material is a low cost material for general use, whilst the Racing compound is suitable for racing applications (i.e. high heat build up) and Carbon is for high heat application too, but at a greater cost than Racing.

Bear in mind that the friction material is also 'bonded' to the clutch shoe with a glue. It is necessary to heat cycle the clutch shoes to be certain that the glue has 'cured' properly snd will not allow the friction material to seperate from the clutch shoe.

The clutch shoes will wear prematurely due to incorrect setting of the engagement rpm for the conditions including rider/bike mass, engine power characteristic and final drive ratio for the circuit.

Lightweight riders will have less effect on the wear of the shoes, since there is less total mass, so the force required is lower. Heavier riders need more force since mass is increased.

Final drive ratio is critical to ensure that the clutch is not overworked.

Finally, set your engagement rpm at the bottom of the power band. This setting is generally around 8000-8500rpm. During operation, it is advisable to keep the engine above this level so that the clutch remains engaged and is not slipping, hence maintaining a high corner speed is the key to both fast laps and good clutch wear.

Thanks heaps Johnny boi.
Some great info that answered and some little questions i had.

Thanks for the info guys should help me out wen setting up my NEXT clutch. i killed a Locchi(unsure wat compound it was) 2 shoe just running my motor in and destroyed a BZM 2 shoe at WCR last week(B5 compound)...maybe its just me ridding ill try out the B3 carbon at WCR tuesdy hope she holds up!