WORKSHOP
sprockets wear less quickly and can typically do more road kilometres in bad weather than alloy. Quality steel sprockets should be heat-treated( to improve the hardness), but this must be done correctly otherwise the sprocket can become brittle. Induction hardening, that is, heating an electrically-conducting object by electromagnetic induction, can be used to control this process. Tempering is next, to produce the correct level of hardness required, chiefly for efficient power delivery and durability. To sort out any distortion that might have occurred, the sprockets are then put through a machine to flatten them uniformly. Machining involves the sprocket’ s teeth and outside diameter being cut at the same time, which ensures the teeth are concentric to the sprocket’ s centre. Normal OE maximum run-out is around 0.5mm.
WHAT ABOUT ALLOY SPROCKETS? Aftermarket aluminium alloy road sprockets are used mostly for their weight-saving properties as they can be up to a third lighter than steel. Alloy sprockets are normally made from heattreated 7075-T6 aircraft grade aluminium. They can be hard anodised for corrosion resistance and durability, especially important for extensive road use- even if the sprocket is surface anodised, the subsurface still has to carry load and deforms faster than steel. There are some sprockets on the market which mate an alloy
inner with an outer steel ring with the teeth, giving the‘ best of both worlds’.
REPLACEMENT The two most common causes of premature chain wear are an improperly aligned rear wheel and worn sprockets. Misalignment is indicated by wear on the side of sprocket teeth, which will lead to reduced chain life( chains could develop tight joints because the sprocket teeth are forcing the inside plates outward on the bushings, and then binding the joint). It also increases drive noise levels. Another common indicator of sprocket teeth wear is curvature( the teeth look like waves). If you can afford it, try to replace both the chain and sprockets together. The chain-rollers and sprocket teeth wear together so, for example, if you use a new chain with old sprockets, it can wear your new chain more quickly- shortening the life of your new purchase.
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