Bicycle Mechanics - Cassette compatibility

I just got this (http://www.giant-bicycles.com/en-CA/bikes/road/1739/30696/) bike and so far I think the 11-28T cassette is a little too wide of a range and would like something with closer steps. The problem certainly could be (probably is) me and not the cassette as I'm not in shape yet but I also like to tinker and fix things that don't need fixing.

Now according to the spec sheet on my bike I have a Shimano shifter and chain, SRAM cassette, and Xero hubs. There obviously must be some sort of standard in place for all these parts from different manufacturers to work together, but I'm assuming there must be limitations to these standards as well.

Based on suggestions I've gotten from another thread I think I'd like to try a 12-25T cassette. It would appear according to this (http://sheldonbrown.com/k7.html#9cassettes) site that I happened across that my stock SRAM is compatible with most Shimano equipment. The c-c spacing is the same but the cogs on the Shimano are 0.02mm thinner which sounds like a very small difference to me plus already having a Shimano chain I don't anticipate any compatibility issues in that respect.

At this point I'm eyeing a Ultegra 6500 12-25T and aside from the mentioned compatibility worries, I'm also unsure about quality. These apparently have something called "Hyperglide" which says it provides smoother shifting. Does my SRAM have the same "technology" but by a different buzz term or is the Ultegra better? My SRAM from time to time (not sure if it's specific to some combination but usually when shifting down) tends to jump and gives me a little jerk. Not a big issue but I'm really trying to baby my knees as I've had problems in the past so anything smoother would be welcome.

Thanks,
Ryan

hyperglide is just shimanos way of stamping the chainrings to provide better shifting. SRAM has their own way of doing it too. The Ultegra cassette will work just fine for you.

However, most people who arent in great shape perfer a cassette with a wider range, so that they can spin up the climbs a little more, and prevent from mashing up them so much. Just something to think about.

Before you change anything, why not count the teeth on your existing sprockets? You may find that the 2nd or 3rd sprocket is already 25 teeth and the next to top is 12. If so, save yourself the effort and expense and just don't use all the current ones!

The SRAM c-c overall spacing from the smallest cog to the largest cog should be the same as the Shimano, so if there is a difference in cog thickness it seems there should be an offsetting difference in spacer thickness. Any 9-speed Shimano cassette should work well on your bike. I can appreciate your interest in a closer ratio cassette, I like them that way too. As you probably know, the main advantage of close ratio spacing is in being able to maintain an ideal cadence in various riding situations. A fast pace group ride where you are trying to draft and match speeds with others is a prime example. A wide spaced cassette often puts you "between gears", one gear is too low and the next is too high. On the other hand you wouldn't want to give up your lowest gear, in this case the 28 cog if you think you may need it for climbing. You'll want a gear that will get you up your toughest hill when your tired. This is why I like for my cassettes to start with a 13, this way I can have closer ratios and low enough gearing for climbing. I don't know what your overall gearing is but if you have a 50 or larger big ring you may not need an 11t. My big ring is a 53 and I have one cassette that starts with a 12 that I use for racing, the others start with a 13.

Al

Shimano & SRAM are interchangeable. Any difference in cog thickness is compensated by a difference in spacer thickness.
The OP has an 11-28 & 30-42-52 rings.
He (like myself) wants a close spaced cassette to keep cadence in a narrow range because of knee issues.
He doesn't use the 11T cog. (Not sure about the 12T either)

See thread-
http://www.bikeforums.net/showthread.php?t=449777

Shimano makes 12x25 and 12x27 cassettes in both 9 and 10-speed configurations and the only differences are in the two biggest cogs (....23,25 or ...24,27) The first 7 or 8 cogs are identical.