danbert

Hello,

I recently purchased a Giant comfort bike from a local shop. I live in Findlay, OH and if you are not familiar, there is maybe a 20' elevation difference between the high point and low point in the county. As such, my bike has way too many low gears, and not nearly enough high gears. Out of the 21 possible combinations, I use the top 3 gears on a normal basis, and even the top gear feels too low when I am moving at speed on flat ground.

Here is a picture of my current rear cassette (according to site it is a Shimano TZ37): http://picasaweb.google.com/lh/photo...eat=directlink

So for my birthday, my mother wanted to upgrade my gears so I could have a more comfortable ride and hopefully get a better useful range out of my bike. The local bike shop where I purchased my bicycle told me that there was no way to change the gears without spending more than the bike was worth. I didn't believe him and so I looked online and found this cassette (figuring I'd go from 14 to 11 teeth on the highest gear): http://www.amazon.com/gp/product/B00...ef=oss_product

I also ordered this accompanying tool: http://www.amazon.com/gp/product/B00...ef=oss_product

Well I now have all the stuff laid out (see additional pictures) and come to find that the locking tool does not fit my current cassette (it is very close, but it will not fit), but it does fit the new one.

http://picasaweb.google.com/lh/photo...eat=directlink
http://picasaweb.google.com/lh/photo...eat=directlink
http://picasaweb.google.com/lh/photo...eat=directlink

So finally my questions:
What is the meaning of the letters (TZ vs HG) and numbers (37 vs 30)?
Are these cassettes not compatible?
How do I find a cassette that is compatible with my current one?
Why would someone design two similar looking cassettes of the same brand that are just a tiny bit off on the locking mechanism size?
Any other suggestions?

Thank you in advance!