Wear on Cog teeth - Normal or Not

youtheman

Just been bitten by the cycling bug. Bought a new Cube Peleton about 3 weeks ago and I estimate I have about 200 km done so far (Shiman Tiagra gear).

Had it 'up side down' last night giving it a good clean. Was cleaning the front gears when I noticed that some of the cog teeth seems to have flat tips, and others were round. Seemed to be random so I thought "5hit, it's wearing already". But then I was looking up Chain Reactions web site and if you look closely you'll see that some of the teeth seem to be flat, and others rounded (http://www.chainreactioncycles.com/Models.aspx?ModelID=50447 ). So maybe it's suposed to be that way.

Any reason why?.

Morgan

The teeth are profiled to make the chain shift over the cogs better.

youtheman

But what I don't get is why all the teeth don't have the same profile. If you look at the link there are two teeth at the 9 o' clock and 11 o'clock position that have flat tips, and the majority of the other are round. Still don't get it (sorry if I appear thick).

niceonetom

Chainrings have areas where the teeth are different shapes to facilitate shifting from one ring to the other. They work in concert with the 'pins' you see protruding on the inside surface of the big ring.

In short, it's supposed to be like that.

seamus

This is the reason why if you look at it properly, shifts don't always occur instantly. If they all had the flatter profile, you'd shift much easier, but you'd also be more prone to having the chain pop off or shift randomly at the wrong time. If they were all pointy, it would be harder to shift and your chain and chainring would wear much faster.

Holyboy

If you look at the inner ring whether its a double or triple it will be flat and all the teeth will be uniform,this is because it doesnt need to grab the chain to help it shift up.

youtheman

Thanks folks. Nice to know it's normal. I've a good engineering head on myself (I like to think), but I've never have guessed the logic behind it, especially the 'pins' on the big ring. As they say, you learn something every day.