Have I been screwed?

beans

I had some work done at a cycle-shop recently, during which my rear casette was replaced. Nice shiny-looking new shimano HG-50 was installed. All well and good until I got to cleaning my chain and sprockets last night after the rain...

I examined the teeth on the casette, and one tooth on each ring is 'shark-finned' as if it had been worn down through use.

Now I guess this is a design feature that I've never come across before... if so, what purpose does it serve? Or is this an old casette cleaned up and resold?

Trojan

HG is HyperGlide. It's a patented technique from Shimano which gets rid of the clunk-clunk as you shift when the chain jumps from ring to ring. What they've done is fin some of the teeth so that when you shift, the chain can occupy 2 different rings simultaneously (half and half). It makes shifting much smoother (gliding!). This isn't a great explanation, so google "sheldon brown hyperglide" and you should find his explanation.

You'll need to show us a picture to be sure, but it sounds like it's probably the normal HG cassette.

beans

Thanks for that, I thought it looked too machined and too new to be wear and tear, but I've neve heard of hyperglide technology before.

On an aside, it's amazing what new gear ratios can do to a bike, it's like cycling a new machine. It's an 11-23 casette and the difference over what went before is huge.