[Boogie Man]

I've got a 10 speed CS-7800 Dura Ace 12-25 cassette, but I'd like to swap out the last two cogs (23T and 25T) for a 24T and 27T, because I could use the extra gears in the mountains. I'm having trouble finding cogs in that range. Does shimano offer replacement cogs, or would I be stuck buying a whole new cassette?

 

[C-40]

21-24-27

The 21, 24 and 27 are all on one carrier. Click on the exploded view at the website linked, for the part number.

http://bike.shimano.com/catalog/cyc...<>ast_id=1408474395181419&bmUID=1144773478533

In theory, any LBS should be able to get the part, but whether it's cost effective is another question. Might be just as well to get a complete Ultegra or DA cassette.

 

[Boogie Man]

That's what I was afraid of. At $180, I guess I'd be better off suffering on the really steep climbs until my legs get stronger. Anyone wanna swap a 12-27 for a 12-25 cassette?

Edit: Found the part... http://www.bikecanada.com/detail.php?item=12-6452-0

With the exchange rate, I'm guessing that's about $110 + shipping. I'm not terribly worried about weight, so I guess I'd be better off just buying an Ultegra Cassette for $75.

 

[C-40]

don't suffer...

It's a lot smarter to gear as low as you need rather than suffer through long stretches of mountain. Unfortunately, the next step toward lower gears will also reduce your top gear. A 50/36 compact with the 12-27 will add one cog's worth of low gear and a 50/34 will add another.

I'm old, so I ride a triple in the Colorado mountains. My lowest gear is equivalent to a 39/35. I see a lot of folks who refuse to ride a triple but should, since they can't maintain a decent cadence and have to stand through the steep sections. I try to avoid dropping below 80 rpm if at all possible.

 

[Boogie Man]

I'm in the mountains in Colorado. Going to a triple isn't an option, but I may be able to switch out my small chainring on my crank from a 36T to a 34T. I'll have to check it out on sheldon brown's site and see if that would make a difference at all. I'm able to maintain a good cadence on most climbs, but there's the occasional grade over 12% that I need to stand up on that I wouldn't mind having an extra gear for.

 

[John844]

here is the three sprocket carrier for $40, but is ultegra.
http://www.bikemannetwork.com/biking/p/FW4716

 

[Boogie Man]

here is the three sprocket carrier for $40, but is ultegra.
http://www.bikemannetwork.com/biking/p/FW4716

Thanks. I found that one earlier, unfortunately, it's 9 speed not 10.

 

[Kerry Irons]

Don't do it!!!!

I've got a 10 speed CS-7800 Dura Ace 12-25 cassette, but I'd like to swap out the last two cogs (23T and 25T) for a 24T and 27T, because I could use the extra gears in the mountains. I'm having trouble finding cogs in that range. Does shimano offer replacement cogs, or would I be stuck buying a whole new cassette?

There's no reason on the planet for you to use a DA cassette. It saves a few grams, is outrageously expensive, and wears out fast because of the Ti cogs. Same story with Campy Record. These cassettes only offer value to those competing at the top level of the sport and whose livelihoods depend on those few seconds achievable in a long mountain ascent. For ALL of the rest of us, Ultegra or lower parts are the only rational choice. You can get an Ultegra cassette for less than the cost of the replacement cogs you're looking for.

 

[SC_clydesdale]

Ultegra cassettes

It's my understanding from the Cervelo website that CSC uses Ultegra cassettes on the 1/2 the race bikes and all the training wheelsets. Durability factor.

http://www.cervelo.com/bikes.aspx?bike=SLC2006#U under components.

 

[drewmcg]

very interesting

. . . to see Cervello spec'ing Ultegra cassettes *and* chains on their "Dura-Ace" team package. Thanks for the link!