Bike Cassette and gearing Questions.

If you were going to get a 10spd cassette for the rear you would also need: a 10 speed chain - (the chains are thinner so they can slip the extra gear in and not change the wheel size) - a 10 speed rear deraileur and a matching 10 speed shifter. In short - you can't.

12-25t could have any number of gearing options, but probably you have 12,13,14,15,17,19,21,23,25, the "t" stands for "tooth" or "teeth". If you remove the cassette (and this is something you should learn how to do for proper maintenance), you will notice the individual cogs have their tooth count on them. You may be able to see them while still assembled.

Shifting should be equally smooth between each of the adjacent gears. Shifting becomes less smooth when the chain moves towards the outside or inside most gears - and you won't have access to all 9 gears in either your small or your large chainrings. The largest cogs in the rear will only work WELL (they will technically work, but they're noisy and shift lousy) in the small front chainring, and the smallest cogs in the rear will work well only in the large front chainring.

Sometimes it is only one or two clicks of the rear der. adjuster that makes all the difference in shifting. It is a little barrel shaped device at the junction of the cable housing and the rear derailuer itself. If the shifting is problematic going into an easier gear, a click or two counter clockwise often helps. If it is more troublesome shifting into an easier gear - the opposite. Lots of bikes have in line adjusters on the shift cables themselves.

Also - 105 does not shift as smoothly as Ultegra or Dura Ace.

Edited by Schwingding 2005-06-16 11:19 AM

Hoo boy. That's a lot of questions, dude.

First, the "t" just means "teeth" ... for a standard 105 9-speed 12x25 you've got 12-13-14-15-17-19-21-23-25. The "A" (or "S") on the chainring sizes usually indicates whether it's "Aluminum" or "Steel" ...

You've got the same bike as me, IIRC, and I too have an Ultegra derailleur. The cassette is indeed 105.

You can get the gearing ratios (and speeds at a given RPM) from Sheldon Brown's website:

http://sheldonbrown.com/gears/

there's a lot of other useful cycling info there, though it's geared toward custom build stuff somewhat.

Even on a properly adjusted bike, you may have some shifting issues when the chain is crossed (i.e. 53x25 or 53x23, or 39x12 or 39x13). If there's a particular shift that it doesn't want to make and it's NOT cross-chained, turning the little 'barrel adjuster' at the end of the shift cable housing 1/4 to 1/2 turn in the direction you want it to shift better may help. That is, if it doesn't want to shift "down" to the next bigger cog, turn the barrell adjuster counterclockwise - toward the wheel. If it doesn't want to shift "up" to the next smaller cog, turn it clockwise - away from the wheel. SMALL adjustments only!!

With a bike as new as yours (you just got it this season didn't you?), any shifting issues are likely due to cable stretch, so the above adjustment should help a lot.

A 10-speed cassette could be done... places like Colorado Cyclist sell upgrade kits that include a new cassette, rear derailleur, shift levers, and chain. The DuraAce upgrade kit is over $700, so I don't see that being an economical idea. You'd be better off buying a new bike.

As usual, I'll defer to the Bear on any of this I've gotten wrong...

woo hoo..

lots of info to read.. thanks all..

also.. to clarify.. the shifting is pretty smooth... what i was referring to (sorry to be confusing) was really the difference in pedal RPMs between gears.. the shift could be smooth but the jolt or increase in RPMs from the previous gear I could do without. On the gears with only 1 tooth difference.. it's fine.. but the ones with larger jumps in teeth numbers.. could be better..

Since the 10-speed gives you one less two-tooth jump, it would fix this in one place.

Strictly IMHO and generally speaking, but your cadence should be the same regardless of your gear. If you upshift and can't put forth the effort to maintain your cadence, then you shouldn't have. If you downshift to where you're spinning too fast, then get back up a gear. Of course climbing is different...

I'll keep that in mind next time out and see if it improves my riding..

I'm pretty sure that I won't be doing any upgrading just cause i think my bike could be easier to ride.. I've only got about 300 miles on it.. so I'm assuming for now that anything wrong with the bike.. is actually wrong with me

Thanks for the help everyone.. I learned a lot on this one..

ws

I'm not sure of the tooth counts or ratios on my mtn.bike but I have been watching the cadence display on the computer. I've also noticed the bigger gearing jumps. I've gotten comfortable spinning in the low 90's but to shift up to, or down from, a pedal rpm of 90 to 95, I've found that I'll sometimes have to turn 105 rpm or more. Now, I'm trying to extend the range where I'm comfortable by forcing myself to pedal that fast regularly. I think the "ride lots" principle may apply here. Maybe something like that would save you from having to change cassettes?

I was recently debating replacing my Sora cranksetand shifters and Tiagra rear derailler - yeah yeah I know but the frame is nice - with 105's.  I didn't for a couple of reasons, but while i was looking I noticed that the Shimano 105 rear derailler said it was "10 speed capable".  Does that mean you could use it with either a nine OR ten speed cassette? 

Yeah, you could. A derailleur is essentially an "analog" device. if pulled (or released) the right amount by the cable, it can stop at any location within its full range of travel with precision. Theoretically, you could get an old 5-speed derailleur to work with a 10-speed cassette... you'd have more trouble getting the narrow 10-spd chain to run smoothly through the pulleys than anything else.

What makes things 8- 9- or 10-speed compatible is really the SHIFT LEVERS. The levers are the things that pull or release the shift cable by just the right amount to stop the derailleur precisely over each cog.

The other main thing that matters is the difference in # of teeth between the smallest and largest cogs on a cassette... this affects how much chain slack the derailleur must take up, and therefore how long the cage must be. But there wouldn't be any difference in this respect between a 9-spd and a 10-speed cog if both were, say, 12-27 range.

So yeah, you could use your 105 9-speed rear derailleur with a 10-speed cassette, but you'd have to upgrade your shift levers to Ultegra-10 or DuraAce 10 to get it to stop in all the right places...



** Not to say there aren't various OTHER improvements in the derailleur design that would make a newer, fancier RD work better than an older or lower-spec model... just that the fundamental design of a derailleur doesn't care how many cogs there are... only how wide the cassette is and what the largets/smallest cog ration are...