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  1. #1
    Join Date
    Aug 2009
    Posts
    127

    Question "Half" shifting -- what and why?

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    Excuse my beginner terminology as I work my way up the road biking learning curve...

    I have a Shimano 105/Ultragra mix on my bike. To shift the front derailer, I have to push in twice. (But not for the rear.) My husband says this is for "half" shifting... or somethinglikethat. I barely notice it anymore, but I don't understand why. Why would I only want to shift halfway?

    When I first got the bike, I get doing it *incorrectly* (only pushing in once) and kept dropping the chain. I thought something was wrong with the derailer!

  2. #2
    Join Date
    Mar 2008
    Location
    Atlanta, GA
    Posts
    715
    I used to have this problem sporadically on my 105/Ultegra setup on my old bike. My DH says this happens to him about 1/3 of the time. I'm definitely not a component guru and know very little about the mechanics of the bike, but I know it's not a "half shift". It's something to do with the position of the chainring when you shift. Your LBS might be able to tune it up for you. I don't think it's a bad thing, but I also don't think it should happen all the time.

    On my new bike with all Ultegra, it doesn't happen at all... one tap and I move into the large or small ring.
    ----------------------------------------------------
    "I never made "Who's Who"- but sure as hell I made "What's That??..."

  3. #3
    Join Date
    Dec 2005
    Location
    WA State
    Posts
    4,389
    It's not a problem - its for "trimming" your front derailleur. While you don't want to cross chain, sometimes you can be in a gear combination that is perfectly fine, but the chain is still rubbing - you can use the "1/2 shift" to move the derailleur just enough to stop the rubbing, but not shift to a different ring.
    "Sharing the road means getting along, not getting ahead" - 1994 Washington State Driver's Guide

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  4. #4
    Join Date
    Mar 2008
    Location
    Atlanta, GA
    Posts
    715
    Should you have to shift twice all the time? I could see if it was sometimes, but OP is stating it is all the time?
    ----------------------------------------------------
    "I never made "Who's Who"- but sure as hell I made "What's That??..."

  5. #5
    Join Date
    Sep 2007
    Location
    Uncanny Valley
    Posts
    14,645
    You just need to give it a harder, longer shove (longer in distance, not time), similar to shifting two or three cogs at once with the RD. It will always trim ("half shift") if you stop at that first stop, and it will then be possible to do it again to accomplish the shift, as she's doing now.
    Speed comes from what you put behind you. - Judi Ketteler

  6. #6
    Join Date
    Aug 2006
    Location
    Vermont
    Posts
    1,414
    This is actually a really nice feature. My new bike (ultegra) has it but my older bike (older ultegra) didn't -- and I find it really helpful. I have a bad habit of riding in 39-12, and if I couldn't trim the derailleur I really couldn't use that combination on the new bike without serious chain rub. I actually have to trim around 39-14 I think.

    (I know somebody's gonna tell me I shouldn't be riding in that combination anyway ).

    Are your shifters/fd 105 or Ultegra? I find it's quite easy to do a full shift all at once on my bike (2007 Ultegra, I think). I have another bike with older 105 that requires a serious, hard shove to shift into the big ring that I think would be difficult for those with small hands (it's pre-"double shifting", no trim available), but I've heard newer 105 is better in that regard.
    Last edited by VeloVT; 09-20-2009 at 04:11 PM.

  7. #7
    Join Date
    Aug 2009
    Posts
    127
    Ah, I'm learning so much... but still have far to go!

    Eden, doe "cross chain" mean when you have the chain on a biggest/smallest combo? I think I know what you are describing in general -- when you shift, and the chain makes that *rubbing* noise?

    OakLeaf, I did not know it was possible to shift 2-3 cogs at once! I will have to try it...

    Lisa, my shifters are 2007 FD 105. In an effort to figure this out, I've tried pushing very, very hard, all at once, but my hands simply can't do it without steering into the bushes... and once I accidentally threw on my front brake in the effort!

    This is very interesting. *Trimming* is something that never even crossed my mind!

  8. #8
    Join Date
    Sep 2006
    Location
    MS
    Posts
    221

    Trim

    I have a 2009 Fuji with Ultegra, I find it very easy to shift to the big ring. I'm surprised the LBS did not explain this to you when buying the bike, mine did. Also you can use the "large" FD shifter to trim the other way if you get chain rub as you shift to a smaller ring in the rear.
    "Only those who dare to fail greatly can ever achieve greatly" (Robert F. Kennedy)

  9. #9
    Join Date
    Sep 2006
    Location
    MS
    Posts
    221
    If you are having trouble doing it in one motion you may need short reach shifters.

    To shift multiple gears at once you push the large shifter for the RD over "hard".
    "Only those who dare to fail greatly can ever achieve greatly" (Robert F. Kennedy)

  10. #10
    Join Date
    Dec 2005
    Location
    WA State
    Posts
    4,389
    Quote Originally Posted by zia View Post
    Eden, doe "cross chain" mean when you have the chain on a biggest/smallest combo? I think I know what you are describing in general -- when you shift, and the chain makes that *rubbing* noise?
    Not exactly. What you want to avoid is using biggest-biggest or smallest-smallest (physical size that is). What you are looking to avoid doing is making your chain go diagonal.

    It gets a big confusing because your biggest rings on the back are the easiest gears, but on the front your smallest ring(s) are your easiest. The biggest rings are closest to your hub on the back (inside) - smallest rings are on the outside. On the front your big ring is on the outside, small ring(s) inside. So trying to use the extreme ends together makes your chain stretch diagonally. It will usually rub against the derailleur and it tends to wear your rings and chain faster.

    Hopefully I don't have you terribly confused now....
    "Sharing the road means getting along, not getting ahead" - 1994 Washington State Driver's Guide

    visit my flickr stream http://flic.kr/ps/MMu5N

  11. #11
    Join Date
    May 2009
    Location
    CA
    Posts
    8
    This is weird, I just logged on to ask the same question

    I haven't really used my front derailleur yet but today I decided to mess around with it and was terrified that I needed to clicks to shift it. Kept thinking my hands sucked or something.

  12. #12
    Join Date
    Aug 2006
    Location
    Vermont
    Posts
    1,414
    You might try softpedaling for a few revolutions as you're executing a FD shift. There is more chain tension in the front of the chain than in the back, and if you are whaling on the pedals while you try to shift you may overwhelm your FD, resulting in either a dropped chain (usually if you are shifting into the small ring) or a failed shift (usually if you are shifting into the big ring).

  13. #13
    Join Date
    Aug 2009
    Posts
    127
    Nope, not confused. That makes sense.

    I bought the bike used and spent 20 miles of a 30 mile ride in frustration trying to figure out how to shift -- realized I had everything backwards. Relieved. I had a nagging worry the derailer was broken!

  14. #14
    Join Date
    Sep 2007
    Location
    Uncanny Valley
    Posts
    14,645
    I think maybe this is one of those triple vs. compact things. Although since I've only ever ridden with a compact double once, when I'd just returned to road cycling, I don't actually know. (I'll still defend my triple to the death, though, especially now that I've put on shorter gearing on my cassette. )

    I've got R700 shifters (short reach Ultegra grade shifters) and a triple, my hands aren't super small but small enough to need those shifters, and it's pretty much as far as I can reach to upshift the FD. I do have to be careful I don't inadvertently steer while shifting.

    Downshifting is easier, so it probably has more to do with the amount of tension I'm exerting on the cable, than the actual distance of travel.

    It's a 105 FD though. Maybe Ultegra would be easier (do they make those for triples?)
    Last edited by OakLeaf; 09-21-2009 at 03:56 AM.
    Speed comes from what you put behind you. - Judi Ketteler

  15. #15
    Join Date
    May 2008
    Location
    northern Virginia
    Posts
    5,823
    Quote Originally Posted by OakLeaf View Post
    It's a 105 FD though. Maybe Ultegra would be easier (do they make those for triples?)

    I have an Ultegra FD for my triple. I got it last year, when I brought the bike to the shop for the umpteenth adjustment to the Tiagra FD that came on the bike, and it broke while the tech was working on it. The only one they had in stock was an Ultegra so they gave it to me for free. It was a big improvement over the Tiagra.

    I've been having an issue this summer that I never had before. I mostly ride in the middle chain ring and largest-middle cogs. I've always had to do the extra half-shift when shifting back to the middle from either the small or large ring to stop the chain from rattling. But lately when the road flattens out and I shift from the bigger cogs to the middle, the chain rattles and the only way to stop it is to shift into the big chain ring, then shift back to the middle but not follow that with a half-shift. But then at the next hill when I shift to a bigger cog it starts rattling again. It's very annoying.

 

 

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