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Flex and exiting big ring(10 posts)

Flex and exiting big ringKristin
Nov 2, 2001 10:55 AM
Victors' post reminded me of a question. I've heard other people talk about this, so I imagine its a common predicament. If I forget to leave the 52 ring before climbing a hill, I often find myself stuck in that gear. I'm guessing this has to do with flex. Is there anything that can be done about it...besides remember to shift earlier?
re: Flex and exiting big ringvanzutas
Nov 2, 2001 10:59 AM
It has nothing to do with flex.
The front deraileur has to push in on the chain to get it to shift to the smaller ring. when there is a significant amount of tension in the chain the deraileur can not push the chain in far enough to get it to fall off the big ring onto the small one.

If this happens. get a little bit of speed up then sit down and put as little pressure as you can on the pedals but keep them spinning while trying to shift. this will put less tension on the chain. you may end up coming to a complete stop and falling on your side though. It somethimes takes me a few tries.

Adam
ya, what vanzutas said and...heavy weight
Nov 2, 2001 11:12 AM
at least in my experience, this is one of times you are most likely to drop your chain.
what happens?Dog
Nov 2, 2001 11:42 AM
You say you are "stuck in that gear." Does that mean you shift and nothing happens? Sounds like you either need to adjust the alignment of your derailleur cage, or the cable needs a little less tension, maybe.

When this happens, what gear in the back are you typically in? The front should shift down a little easer when the rear is on the bigger cogs, as the chain alignment is pulling it that way to start with.

I doubt very much it has anything to do with frame flex. Flex would more likely make it shift by itself, assuming it were extreme.

Doug
What they said...Kristin
Nov 2, 2001 1:32 PM
What Guido and Vanzutas said pretty much describes it. I can get the deraileur to touch the chain, but its not enough to knock it off the ring. By the time this happens, I'm usually turning at 12 RPM and in deep $%*!. I've only fallen once so far.

I initially tought that this was an issue with frame flex. I figured that the c/stay was flexing out while the inward facing teeth (which would release the chain) ran thru derailuer. In otherwords, counter acting the direction of the chainring teeth. But what they said makes more sense.
try thisDog
Nov 2, 2001 1:41 PM
The derailleur cage should be pretty much parallel to the rings on the inside plate, but the outside plate should angle in a little toward the bottom/rear. Try moving the whole derailleur a tiny bit, rotating it a little clockwise as viewed from the top. This will help the derailleur cage pull the chain over. I've had the same problem and this fixed it.

You'll likely have to release all the tension on the cable before moving the derailleur, but it's easy to put back.

Doug
naw...guido
Nov 2, 2001 2:05 PM
If the derailleurs are out of alignment, they'll be reluctant to downshift or upshift on any cog combo. If they work smoothly on inner-inner or outer-outer combos, where the chain line is straight relative to the cogs, they're adjusted fine.

Some, guys usually, pedal in their outer chainrings all the time. You see them going up hills in their big rings and second to last inner sprockets. The chain grinds down the teeth to sharp points on the large ring. The chain has to flex sideways, so it gets stretched prematurely. Keep the chainline straight, and the drive train will work smoother and last longer.
FD height also...Savoirfaire
Nov 3, 2001 3:54 AM
If the front derailleur is set too close to the chainwheel (radially), it has a harder time shifting the chain off under some loads. Seat tube angle, along with cage profile in relation to the chainwheel can play a factor also.
I know what she's talking about. When you're being manly, or inbill
Nov 2, 2001 1:57 PM
Kristin's case, uber-girly (or, grrrly), and you get up the hill in the big ring but you turn the corner and there's another 100 yds of up and your mind says "OH SH*T" and your legs go phhttt, then you're mashing along at about 30 rpms and the chain is stuck HARD to the ring and just moving the derailer doesn't make it slide off. The only way to do it is to lighten up on the crank, and then the chain will slide over to the little ring.
re: stuck in large ring on hillsguido
Nov 2, 2001 1:14 PM
The angle of the chain is too extreme for a smooth shift. As you go up the hill, you donwnshift onto the large innermost cogs of the freewheel, pulling the chain-line over to the left of the big ring, and the sprockets don't want to release the chain when you shift.

The solution: shift to the small chainring first, before you get to the inner sprockets on the freewheel. The idea is to keep the chain line as straight as possible all the time, to minimize wear on the chain and sprockets, as well as to keep the shifting easy. Conventional wisdom is, as a general rule, use only the inner gears on the small chainring, and the outer on the large chainring. If you're in your 53, don't use the two inner, lowest gears, and when in the 39, don't use the two highest, outer gears.