What are ASP "Aramid Sport Clutches" good for?
Why do I need an ASP modified clutch?
Simply put… Because eventually the standard one won’t do the job… but if you want a technical explanation, here we go.
At the standard Maxi top speed of 45 kph (28 mph) the engine and the clutch are spinning at around 6,500 rpm, it is all very happy and will last for many miles, the forces on the clutch are fine.
Our problem here is that the laws of Physics do not work in a linear fashion… We begin tuning, just a little at first, an exhaust for instance and we get up to 50 KPH (31mph) now our motor is having to spin at over 7,000 rpm. Although we have only increased the rpm by around 10% the forces on the clutch have increased by over 20%.
As we tune further our engine revs more and more… It is great, we go faster! The issue is that we are now starting to increase the forces through the clutch to a point where things might bend or break.
As an example, one of our test Maxis revs to 12,000 although this is below twice the standard revs, it puts nearly 350% more force though the clutch than at 6,500 rpm, with a standard clutch this is more than enough to start bending and breaking things. But, by changing to the lighter ASP clutch shoes we go a long way towards preventing this.
How does this work?
If we go back to the Physics lesson, we realise that the force produced is a combination of Mass (weight), Velocity (revs per minute) and the radius of the clutch bell.
We can not do anything about the radius of the clutch bell (it needs to fit!) and we don’t want to reduce the revs we achieve, so we only have one factor we can control, the Mass… Our clutch arms are lighter (they have less mass) so the forces acting are a little less. Here Physics begins to work with us, small changes in the mass of the components makes quite big changes to the forces involved.
Why do I need ASP clutch shoes?
When compared to the standard shoes the ASP Aramid lined versions offer several advantages.
1. The Large Aramid friction areas allows the clutch to slip smoothly up to the engagement point and then to grip efficiently when the engagement speed has been exceeded.
2. The shoes are lighter, reducing the need for very stiff springs if later engagement is needed, this protects the clutch pillars, helping to prevent them from bending or pulling out of the backing plate. (This can happen when the heavy standard shoes fight against very stiff springs in the more conventional set up)
3. These lighter shoes continue to reduce the bending forces put into the pivot pillars in high revolution applications, an ASP clutch brace should be specified when really very high revolutions are envisaged. (One of our test machines is often to over 12,000 rpm with such a brace)
4. In very extreme revolution applications, the forces can be so great that the shoes can begin to spread the clutch bell, opening it up like a flower, While ASP’s lighter shoes and increased contact area will not entirely prevent this, they can delay its onset until even higher rpm.
5. A lighter than standard clutch assembly helps the engine to accelerate and decelerate more freely, the engine uses its power to accelerate the machine not overcome the inertia from heavy assemblies.
In the clutch... What parts do we recommend?
1. Standard machine or mildly modified machine (for example just a sports exhaust) Our standard Surflex ‘repaired’ clutch shoes with the extra Kevlar re-lining, these live longer and allow some scope for tuning with stronger springs for later engagement.
2. More modified machine needing even later clutch engagement (for example 70cc with larger carburettor and exhaust pipe such as the mid-range power ‘circuit’ designs) … Our lightweight shoes with larger Aramid frictional area.
3. Modified and very high rpm application (for example 70cc with larger carburettor and when using very high rev exhaust pipes such as Homoet 6p/8p, Simoni or similar) … Our lightweight shoes with larger Aramid frictional area. PLUS, our additional brace.