6 THINGS YOU NEED TO KNOW…
Out on the road or at a trackday a slipper clutch’s standard set-up is just fine and they should need no more maintenance than conventional systems. But for racing they can be tuned to give different amounts of engine braking to suit various circuits. For example, Silverstone is fast-flowing and wide and it doesn’t have many slow corners, so there’s less need for slip. But take the same bike and settings to Snetterton 300 with its tight corners and hairpins and the bike would be chattering like a manic monkey. In that case you would fit ramps with a shallower gradient as that allows the plates to separate more easily. Riders coming from two-strokes with their minimal engine braking tend to prefer this softer setting.
Having the correct freeplay at the lever is essential, and it needs to be set when the bike is stone-cold, otherwise you’ll end up with permanent slip. The number of times I get rung up by riders complaining that their clutch is slipping though they haven’t changed anything “apart from the levers”.
This is the total thickness of the clutch plates. There is a mechanical limit to how far the plates can separate and if there is excessive wear the clutch will slip under drive. Conversely, if the pack is too thick to start with it will still drag when it is in ‘slip’ mode. The range here is very small, less than 1mm. On a ZX-10R it will be fine at 53mm, but slipping at 52.5mm, so you’ll often see race teams using a mix of old and new plates, and Moto2 and 3 guys put little spacers in bolts that run through pressure plate to allow for the wear from practice starts.
There are two types of springs in clutches; helicoil or diaphragm. The strength of the springs alters the nature of the slip. If you are a rider that likes to get it all sideways on the way into corners you’ll need lighter springs; if you want to keep it all in-line on a high-speed course like the TT, then those springs will be heavier. As you’ll only have two diaphragm springs compared to six or more helicoil, they are easier to swap in the paddock, and racers report that diaphragm springs make the bike easier to launch off the line because the lever ‘feel’ is better.