Bicycle Mechanics - Gear ratio

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BikePHL
05-23-12, 02:33 PM
I am preparing for a very hilly 10 day bike trip. I have not had the opportunity to train as much as I had planned so I am considering switching cassettes to give me some different gear options. The current setup up on my bike is:

Crankset Shimano Ultegra SL HollowTech II w/7075 CNC 39/53T Chainrings
Bottom bracket Shimano Exterior Bearing System
Front derailleur Shimano Ultegra SL F-Type
Rear derailleur Shimano Ultegra SL
Shifters Shimano Ultrega SL STI shifter/brake, 20-speed Flight Deck compatible
Cassette Shimano 105 11-25T, 10-speed
Chain Shimano 105 10-speed

I would love recommendations for a rear cassette that will work well with this set up but will give me a couple easier gears.

Thank you!

HillRider
05-23-12, 02:43 PM
There are Shimano 10-speed road cassettes that will help a bit, a 12x27 and an 11x28 (and maybe the new 10-speed Tiagra 12x30) that should work with your current components. Beyond that you probably can't use your current rear derailleur since it won't (read probably won't) clear a larger cog. To go to a 32 or 34T cog you will likely need a MTB rear derailleur.
Andrew R Stewart
05-23-12, 02:44 PM
BikePHL- (How i dislike having to title responses with some fake name...) Shimano will tell you that the max rear cog size for the Ultegra SL is 27T. A 28T will likely fit well enough. Not much more without comprimises of performance or chain wrap capicity. Andy.

HillRider
05-23-12, 02:50 PM
BikePHL- (How i dislike having to title responses with some fake name...) Shimano will tell you that the max rear cog size for the Ultegra SL is 27T. A 28T will likely fit well enough. Not much more without comprimises of performance or chain wrap capicity. Andy.
That's correct which is why I qualified the Tiagra 12x30 recommendation. However, several posters have reported success with 30 and even 32T cogs with Ultegra rear derailleurs if the derailleur hanger geometry and b-screw cooperate. No guarantees, of course.
BikePHL
05-23-12, 04:45 PM
Thank you for all the advice. I have decided just to keep it simple with the 12-27. I am cutting things a little close with my trip so i don't have time for any surprises if things did not work properly.


Best regards,

Brian