Princess_Allez

Is it ok to shift the front and rear derailleur at the same time? I've tried it twice now and the first time was with good result, but the second time the chain came off the front. If it matters, I'm using the current Shimano 105 groupset.

79pmooney

It's problematic and very dependent on the exact details of the setup. (not just the components but little details like the exact rotation of the front derailleur, distance between the real derailleur pulleys and the cogs, what gears you are starting in and shifting to, your speed, the grade....) One thing you can do which will prevent the chain falling off to the inside is install a Chain Watcher. (Chain Watcher is made by 3rd Eye. Deda makes another with a different name but does the same thing. There are probably others.)

When you do a double shift, basically coast while pedaling. In other words, keep the pedals turning but do no work at all until you know everything is in place. Best done while you still have plenty of speed.

Pay attention while you do it. There's a learning curve. And when you ride a different bike, it will be different. But ride one bike long enough and it becomes part of you. Those double shifts will be easy and you will know well when they won't work. Keep shifting!

Ben

Princess_Allez

Thanks for the quick reply. It sounds like it can/should be used as a technique then, not to be avoided. I was pedaling downhill when the chain fell off. I attempted the shift as the hill leveled out. I tried to skip 2 up in the rear and one down in the front, while idling the legs. I'll check out the front chain watcher.

Rides4Beer

Yup, you can, as mentioned it takes some practice. I've gotten pretty good at dropping two gears on the rear while simultaneously dropping to the little ring up front, makes for a smooth transition when you're climbing and end up cross chained on the big ring. Just takes a soft pedal, you want to keep tension on the chain, but not a heavy load.

I usually only have to do it when I'm in a tight/fast group, where I probably could have kept climbing in the big ring, but the group slows down too much and I have to drop it down. But def practice it before you do it in a group, dropping a chain on a hill in a group is no fun at all. If I'm riding solo, I either keep climbing in the big ring, or plan ahead and already have it dropped before I hit the hill and don't have to shift both at the same time.

rm -rf

I think I usually shift the front first, then immediately shift 2 or3 gears in the back. Doing both at once seems fine, but I like to avoid the small chance of a dropped chain.

With a climb just ahead, my goal is to shift the front to the smaller chainring. With my cassette, shifting 3 harder gears gives me just about the same cadence as I had. (It depends on the cassette cog size differences--wider range cassettes need fewer shifts.) But often, I want to start getting to easier gears, so I might only shift a couple of clicks. As the grade steepens, I keep shifting.

rm -rf

"Chain catcher" is the generic name for these. With the chain on the small ring and largest cog, it needs to be adjusted to barely clear the side of the chain. Have someone hold the rear wheel off the ground, turn the crank slowly by hand, and use a piece of paper as a feeler between the chain and the catcher. It shouldn't be rubbing, but try to make the gap very small.

I've seen chains fall off, even with a chain catcher -- that was likely not adjusted quite right. Then the chain is stuck behind the catcher -- it's difficult to get it back on the chainring.

csaxby

I shift front and back simultaneously almost every time I shift the front. I'm sure I've dropped the chain before, but not any more often than when shifting the front on its own. I actually dropped my chain this past weekend while shifting the front only (big ring to small at a pretty high cadence to get ready for a hill). This is anecdotal, of course.

When going from the small ring to the big ring, I shift the back to a larger sprocket to make the jump to the big ring less noticeable. I usually return the back to the sprocket I was riding originally within 10 or 15 seconds. I do the same (in "reverse") when going from the big ring down to the small.

wipekitty

I generally avoid shifting both at once - I usually drop the chainring then shift 2-3 (harder) in back, or sometimes shift rear then front if it's an easy grade with a larger climb ahead.

I've yet to drop a chain by shifting both simultaneously, but sometimes there will be a gross clunky sound from confusion between the chain and the rear cog. This could be a function of my setup (I am running 5800, so not the newest 105).

cycledogg

Is there an advantage for doing this?

Sy Reene

Never thought about, but do it all the time.. because Campy

f4rrest

Chris Froome lost a chain doing a double shift a couple years ago in Le Tour, didn't he?

caloso

Yes, I use this often in rolling hills. You'll be bombing along in the big ring but hit a short, sharp hill. Double shift to put it in more or less the same ratio, but in the lower range. This works beautifully with Campy: just hit both thumb buttons.

Princess_Allez

Thanks for all the advice, guys. I ordered a ktech chain catcher. Hopefully that solves my chain woes. I'll practice the technique more as I go along. Thank God I'm on an aluminum bike and not a carbon; though I'm still not happy about the gash(es)

cycledogg

I advise against this tactic. It will cause problems and increase your chance to ruin your frame. There is no significant advantage to performing this technique.

Racing Dan

Is it really a shimano crank? My humble 4700 crank has never dropped a chain and I double shift all the time. My old FSA was more finicky. I do let off a bit while shifting. Maybe that helps, but I just cant stand the clonk, clonk, clonk! you get If you shift at full torque.

phtomita

Normally when moving front to smaller chainring, I go together to a smaller sprocket on my rear without issue.

kingston 

I never noticed that I had to do this until I got a compact crank a few years ago. It came with my first set of brifters, which are campagnolo, and I still think it's annoying.

Zaskar

I've done this - drop the front, drop two or three in the back - countless times... all on Shimano drive trains. I've never dropped a chain. I do let up for that split second - is that the "technique" you guys are referring to? Seems pretty intuitive. Don't over think it.

downhillmaster

This

rubiksoval

I never drop from the big chainring to the small at the same time as a rear shift, but I'll shift from little chainring to big while dropping a couple gears in the back when I need to stay on the gas.

Princess_Allez

This is what I did when the chain came off. However, I was banking left at the same time, while crossing over a gutter. I'm guessing it was the combination of it all that caused chattering with the chain, which further caused it to fall off the chain ring.

phtomita

When I do this I don't put much power on the pedals - I do pedal hard before doing it to gain some speed, then kind of spin out reducing the cadence and shift both so they will switch properly before going back to cadence/power I was putting on the pedals.
If is a long non steep hill followed by a steep climb, I noticed I gear up the rear while on big chainring, get momentum and then switch front and rear with the technique above. If not, it gets too light and you end up loosing your momentum or you have to increase a bunch your cadence (that doesn't work for me).

Caliper

Most of my FD shifts are in tandem with a RD shift to keep the ratio jump in check. Doing this makes the big ring far more accessible as you get in there without either a big drop in cadence or a big delay. I have never dropped the chain from this. If you drop the chain, I'd think that the FD limit screws are out of whack.

Princess_Allez

This.

Princess_Allez

I'm new to cycling so this is a possibility. I bought my bike brand new. I did only a few miles before the chain fell off the rear. I took the bike in to have it adjusted and everything seems fine. However, when I shift the front chainring it takes a little longer than expected (at times). The rear seems to be inbetween gears when I'm in the largest cog, and sometimes will shift down when I pedal out of the saddle. It's kinda annoying that my bike has suffered superficial marks because it hasn't been tuned right.