Need Advice Concerning Gearing on Compact Double

[indysteel]

Well, switching from a 12-27 to an 11-28 isn't going to be much of an improvement for hill climbing purposes. So, that more or less leaves you with mountain gearing. I, personally, would opt for the 32, but that's because I currently hate the wide jumps I have to deal with on the flats with my own compact road set up. If that's not an issue for you, then go with a 34 or 36.

I'm no expert on road/mountian compatibility. Is your current group Shimano? Just make sure that whatever mountain set up you get is compatible with your road shifters. I vaguely remember reading that 10-speed Shimano road shifters are (or at least once were) only compatible with a 9-speed mountain cassette. I think SRAM also offers an Apex 12-32 10-speed road cassette that would be compatible with a Shimano 10-speed drivetrain--if that's what you have.

[Crankin]

I have the mountain derailleur on the back of my bike with a compact (11-34). It's a Deore XT with an Ultegra front derailleur. It's a lot of low gears, although the range in the middle of the cogs feels widely spaced compared to my triple with an 11-28. However, i am now used to the feel and it's fine. The combo works perfectly and I ride up steep grades (10-18%) on a regular basis.

[Hi Ho Silver]

As others have said, changing to a 28 in the rear isn't going to provide you with much relief. My bike has a compact crank (50, 34) and a 12-32 cogset in the rear. The lowest gear is more than sufficient to allow me to get up any of the nasty hills here in the Texas "hill country". In my experience with mountain bikes and road bikes, a low gear ratio of about 1-to-1 (e.g., 34 chainring to 32 cog) is low enough to get me up any incline.

[tzvia]

It's basically what SRAM calls 'WiFli'; it's nothing new but they put all the pieces together for the road and are doing a good marketing job with it.

You basically need a longer chain to be able to wrap around the larger cogs. That would require a medium or long cage derailleur to take up the slack of that longer chain when you are in the smaller gears. Then you could add a wider range cassette that goes to 32 or 34 (that would require a long cage).

I can't tell the difference between 26 and 27 in back so I just use a 26 on the road bike (I am a fan of the SRAM Red Cassette). On the commuter, which is 12 lbs heavier than the road bike before I put my stuff in the pack, I set it up with a long cage X5 mtn rear derailleur with a 26~39 up front and a 11-28 cassette as the route only has a slight incline at each end. But with that rear derailleur, I can lengthen the chain and put a MTB cassette that goes to 34 if I needed it.

[Cyclesome]

Thanks for all the advice. I went to my LBS who suggested I not switch to an 11 -28 nor change to a mountain bike derailleur, but instead keep the same derailleur and switch to a 12 - 30 rear cassette. Lower grade however, Shimano does not make a 12 - 30 in Dura-Ace. Hopefully, I will have a few more gears when I need them for the hills Thanks again.

[tiva]

Thanks for all the advice. I went to my LBS who suggested I not switch to an 11 -28 nor change to a mountain bike derailleur, but instead keep the same derailleur and switch to a 12 - 30 rear cassette. Lower grade however, Shimano does not make a 12 - 30 in Dura-Ace. Hopefully, I will have a few more gears when I need them for the hills Thanks again.

Let us know how you like it! I have the same issue with my compact double on my Cannondale synapse and the steep hills here in the driftless area of WI, but I haven't yet talked with my LBS to figure out my options. It was a shock the first time I flailed on a hill I'd gone up dozens of times on my old bike. My rear derailleur is 11-26, so hopefully there's some room for improvement.

[OakLeaf]

Just be prepared that you might need to replace your RD after all. DA7900 specs for a maximum 28T rear cog. It's not uncommon for people to successfully put on a cog one tooth bigger than recommended, but two seems to be pushing it. And if the RD is the one that originally came on your bike, it's probably an earlier series - I don't know when Shimano came out with each series, but DA7800 specs for a maximum 27T. Since your mechanic suggested it, try it, see if it shifts okay and doesn't drop the chain, but be prepared.