6 THINGS YOU NEED TO KNOW…

Motorcycle News (UK) - - Garage -

Fine-tun­ing

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.

Freeplay

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”.

Pack thick­ness

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.

Spring choice

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.

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