Re: [CR]Frame Flex

(Example: Framebuilders:Rene Herse)

Date: Thu, 29 Sep 2005 15:06:21 -0400
From: "Steve Maas" <>
To: <>, dan kasha <>
Subject: Re: [CR]Frame Flex

Some time ago, unconvinced by the idea that frame flex causes ghost shifting, I made some measurements on a couple of my bikes, all six-speed rears with Campagnolo NR or SR derailleurs, and calculated the amount of flex of the chainstay necessary to cause a shift. A simple geometry problem. I don't have the precise results with me now, since I'm away from home, but it turns out to be a ridiculously large amount. The chainstay would have to look like an archer's bow, and would certainly break long before it bent that much.

It's also interesting to note that ghost shifting always goes in one direction, never seems to shift back after the force that supposedly bends the frame is removed, or that it doesn't happen reliably each time the same force is applied. This all points to simple cable slippage. I've never come up with a convincing explanation, however, of why it often seems to happen when the pedal is hammered. (I've never had a bike that does this reliably, so I haven't made a similar observation.) Dan's experience sheds a little light on this issue.

Steve Maas Dublin, Ireland

>I heard lots of talk about a test for frame flex being if it ghost shifts when you climb a hill out of the saddle. The twisting of the frame changing the tension of the rear derailleur cable, causing a shift. About 5 years ago I set up this cannondale with all vintage parts. NR derailleur and shift levers, Modolo Pro brakes, the wheels I mentioned. And first ride, I figured this was going to be great. And on every hill, I was getting a ghost shift. I couldn't figure it out, until finally I realized I had to tighten the shift lever a bit more. Once I got it right, the ghost shifts where gone. So, was it the mighty Cannondale twisting? No, it did not do it before with the indexed derailleur set-up. What I also realized is that it never did it if I was in the saddle, even if I had virtually no weight on the saddle. But once I was out of the saddle, I started to rock the bike laterally, and noticed that the lower portion of the chain now flops around some. I suspect!
    that this
> puts an ever so slight force on the derailleur cage and moves it - especially if the shift lever is set at the limit of friction.
>I tell this long dull story because I firmly (I should be careful using this word) think that there is a lot more faux stories out there than real.
> .........
>Dan Kasha
>Seattle, WA
>Yahoo! for Good
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