"Half" shifting -- what and why?

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!

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.

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.

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?

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.

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 :p).

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.

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!

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.

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".

Quote:

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Originally Posted by zia

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?

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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....

This is weird, I just logged on to ask the same question:eek:

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.

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).

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!

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. :p)

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?)

Quote:

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Originally Posted by OakLeaf

It's a 105 FD though. Maybe Ultegra would be easier (do they make those for triples?)

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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.

Thanks for posting this question - it clears things up for me, too.

Ultegra and 105 front shifting (as far as brifter action) will have no noticeable differences. Both are made to work with doubles or triples. The trim is only in the small ring (1/2 shift keeps you from cross-chaining when you are in the small ring/small cog combo). Dura Ace is double or triple specific (though I'm not sure that 7900 series has a triple option yet). However, DA7801 (for doubles) does have front derailleur trim when you are in both rings (there's a 1/2 shift either direction).

Many people seem to have a hard time with the harder, longer throw of the large lever for 105/Ultegra shifters (DA is an easier hand motion). So, people are maybe more likely to mis-shift and wind up trimming the FD by accident.