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Clydesdales/Athenas (200+ lb / 91+ kg) Looking to lose that spare tire? Ideal weight 200+? Frustrated being a large cyclist in a sport geared for the ultra-light? Learn about the bikes and parts that can take the abuse of a heavier cyclist, how to keep your body going while losing the weight, and get support from others who've been successful.

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Old 04-09-07, 01:07 PM   #1
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Phantom Shifting

As I've heard it called. Bike shifts by itself. I did a little reading and came up with cable stretch. I thought this a little silly since I haven't logged 10 mi. yet. However I have been a little concerned with how the bike was assembled, no that's not the right word, 'tuned' perhaps before it left the shop. I went back once because the front brake was fairly tight...not free spinning at all after the first ride. Despite me trying to adjust it, it would loosen but only on one side. I brought it down to the shop and the guy bent the tension spring a little and it's been fine since. A little thing like that. So I read a bit and tried adjusting the rear shifting cable at the shifter end. Can't really say there was a big change either way. Stopped by the shop today and he told me to bring it in and he'd check it for me. No quarrel with them about that, it's been an immediate fix when I go in.

I did flip it over on it's handlebars and seat and shifted through some gears and at some point it would make the noise as if the outside of the chain was rubbing against the next gear, although it doesn't do that when riding. I tried to narrow it down as to whether it happened when I was pressing too hard on the pedals etc. but it's fairly random.

Any insight on that one?

That said, I better than doubled my miles today. Which wasn't that hard to do when the baseline was 1mi. Nonetheless, only my fourth ride and my breathing was better and the heart area was comfortably warm instead of atom splitting pounding. Initial gains are nice
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Old 04-09-07, 01:56 PM   #2
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Sheldon Brown has an article on "autoshifting"

Question does it actually shift to another gear or is it just a "jump" in the same gear ? The reason I ask is I about a year ago I had a chain with a pin that was sticking out just a little bit and it would snag the derailler and cause a little jump.

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Old 04-09-07, 02:04 PM   #3
Bill Kapaun
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When my bike is upside down, the gear mesh etc. is a lot worse than when used normally.

I wouldn't tweek on it too much (yet). Let the LBS do their job. If you keep changing it on them, they won't have a baseline adjustment to work from.
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Old 04-09-07, 04:10 PM   #4
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I would suggest you mess with it a bit yourself if you are at all mechanically inclined as learning how to do this is invaluable if you end up becoming a regular cyclist. Making tiny adjustments during your riding will yield a crisp shifting bike and rear derailleur adjustment usually requires no tools. (unless you are setting the limit screws.) There are heaps of articles on how to do this, try the Park Tool repair help on the Park Tool website.
Generally the first thing you should consider it what gear you are in when this is happening. If for example you have the chain on the large ring in the front and the largest cog in the back then all bets are off. This is one of the gear combinations you simply shouldn't use as the chain is running at too much of an angle.
If you find it happens in appropriate combinations then you need to decide which way it shifts best, up or down. If your bike shifts down quickly when you go from a bigger cog to a smaller cog (eg: 4th to 5th) but shifts sluggishly when you go in the opposite direction your cable is too loose. If it shifts up quickly (eg: 5th to 4th) but is sluggish in the opposite direction your cable is too tight. The cable adjuster on the rear derailleur loosens the cable when you turn it clockwise and tightens the cable when you turn it counter clockwise. Obviously, if it is turned all the way out or in you will need to release the pinch bolt and make a rough adjustment before you start fiddling about. Keep in mind that the cable adjuster should be easily turned by hand if it binds don't try to force it as they are easily broken.
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Old 04-10-07, 09:23 PM   #5
Dewey Oxberger
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If it is jumping between two gears (back and forth) you just need to tweek the adjustment.

A page is worth a thousand words (maybe cause that's what it has):

If it's jumping more than two gears inspect your frame for cracks - carefully look for bad welds or cracks that might be allowing tons of frame flex.
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Old 04-10-07, 11:45 PM   #6
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I've turned my bike upside down before. Made a whole lot of noise. Mainly from the chain dragging on the derailleur cage in the front. I wouldn't suggest it.

Very easy adjustment though. Shift the bike to the smallest cog in the rear. When you've shifted all the way, the chain should be on the smallest cog. If not, turn the barrel adjuster till the chain drops into the proper position( smallest cog).

Then turn it back so that the chain just begins to rub against the second smallest cog. At that point, you should then turn the adjuster the opposite way so that the chain just barely backs away form the second cog and doesn't continue to drag against it. At that point, you should be in proper adjustment. If needed, you may make very small fine adjustments by turning the barrel adjuster 1/16 of a turn. Not much need to make fine adjustments.

I make my fine adjustments by shifting the chain up to the fourth cog. Listen for the rattling sound. If none, then you're good to go. If there is a small rattling sound, make small adjustmetns one way or the other till the sound vanishes. Now you're good to go!
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Old 04-11-07, 02:16 PM   #7
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If you have a trunk mounted bike rack, or a hitch mounted bike rack, you can use either as a repair stand. Beats beating up the bike by turning it upside down.
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Old 04-11-07, 06:21 PM   #8
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Originally Posted by Mr. Beanz
I've turned my bike upside down before. Made a whole lot of noise. Mainly from the chain dragging on the derailleur cage in the front. I wouldn't suggest it.
I would call this a case of very low chain tension, I flip the bike upside down all the time for maintenance, never had this problem. Did scratch the crap out of the bell one time though, forgot to loosen it, and twist it around like I usually do. I think I will need a stand now, too much crap on the bars to be flipping it over all the time.
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Old 04-15-07, 04:59 PM   #9
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A wise man once told me that 90% of all shifting problems can be fixed with a 1/2 turn counter clockwise on the rear dérailleur barrel adjuster.
Carpe who?
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