Why two different metals, colour in rear casette

k123456

Just curious

Bought a Stephens X8C yesterday
rear casette looks like it is made of two different metals , or is two tone in colour, see attached pic
The four largest sprokets are a ligher colour metal to the the remaining five



What is the reason for this, astechics, or is there a practical reason

Eamonnator

I would say, that the smaller sprockets are steel and the larger sprockets are
alloy. The smaller sprockets wear more quickly, therefore they are steel for longer life, and they make the larger ones from alloy to save weight.

Timmyboy

I'm guessing that there are two factors involved but both related to the number of teeth that are on the srpoket.

Firstly consider srpokets that have smaller numbers of teeth, for arguments sake let's choose that 20 teeth or less is "smaller". Due to the smaller number of teeth, then for the same distance travelled, these same teeth have to do more engagements with the chain than for a larget sprocket.
Along with other factors, this means that the teeth on the smaller sprokets get exposed to more wear. More wear means that ideally you may want to ensure that the wear capability of those smaller teeth is better. This may require a differt metal that can cope with that extra wear.

Secondly, in relation to torque application. If starting in a "high" gear, i.e where one of the smaller sprokets is used, then just about 1/2 of those teeth will be engaged in taking the tension from the chain (originating from rider effort/weight at the pedals and crank) and turning it into rotating torque.
Larger sprokets will be able to distribute this tension/force/torque load amongs more teeth so probably need to be less strong (so can be made of a cheaper/lighter material if economics of manufacture (or weight ) is being considered along with durability and survivability of the sprokets.

As such the smaller sprokets are generally made of the toughest/strongest material and a lighter but still sufficiently strong sproket can be used for the larger sprokets.

Hope that helps.

blorg

Is that an XT cassette? I think it is just the finish; chrome plating on the smaller cogs to improve their wear resistance. There wouldn't be any aluminium in the actual cogs, they are steel. Aluminium cogs wear very badly. The carrier the cogs are attached to on XT is aluminium. On XTR/Dura Ace the larger cogs are made of titanium (to save weight.) Ti wears worse than steel but not as bad as aluminium.