I've been having some trouble with my 2009 Jamis Aurora, which I love.
It's been ghost-shifting (up to a higher gear) when I stand on the pedals going uphill. I like to be able to stand and stretch my legs sometimes on long climbs and increasingly the bike jumps to a smaller cog, at which point I MF the poor drivetrain out loud.
Here are some things I've ruled out:
1. Chain and cassette. Relatively new and properly installed.
2. Cable and housings. Recently replaced and properly installed.
3. Cable tension--oft-adjusted. Works fine on stand and when I'm not hammering.
Here's what the tech at my LBS (whom I trust) said:
There's a mismatch between the Tiagra shifters and the Deore derailleur, a road-mountain combo necessitated by the fact that Shimano makes no touring group. Jamis addressed this problem on more recent models of the Aurora and Aurora Elite by replacing the Tiagra STI shifters with bar-end shifters which would not have been a solution for me, as I don't much like bar-ends (no offense to them that do!).
I'm told there isn't much I can do about this other than switching to a Tiagra rear derailleur, but then I have to go from an 11-32 to an 11-28 cassette, and while that would probably be okay commuting (though I live in hilly Pittsburgh and certainly do spin in the granny gear from time to time), if I decided to do even a light loaded tour and hit some real hills, I could be unhappy. I'm not paying hundreds of dollars to replace my whole drivetrain with a Sram Apex--I don't know that I even could.
I like the triple crankset and the big range in the back. Anybody else encountered this problem and have any bright ideas, or do I just have to live with the occasional involuntary upshift until I decide to replace this otherwise worthy bike?
PS--I think the problem has been there off and on since I bought the bike, but has gotten worse of late. I've owned the bike for about a year and have probably put about 2500-3000 miles on it.