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Old 04-10-14, 09:52 AM   #1
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chain tensioner at end of derailer?

Hi ... I saw the following in the MIT V8 thread



To me it looks like a chain tensioner attached to the end of the tension pulley. Since it's a Brompton clone, I assume it's needed when the bike folds given that the distance between the derailer and crank decreases.

However I imagine that it could have other uses as well. The derailer in the picture might be a short cage rear derailer to minimize the chance of striking something on the ground. The additional chain tensioner could pick up additional slack from the length of chain needed for the triple.

Does anyone know what that thing is and where one might get one?
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Old 04-10-14, 11:17 AM   #2
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Fabricate , DIY.

apparently nobody even imports the whole 'mit' bike to the US let alone the parts ..

suntour decades ago made a 3 pulley cage

over on the I BoB list someone demo'd how they modified an existing RD .. they made the parts themselves.


a drill and a jewelers hand saw hand files and time can make things..


though the CAD CAM and 3D printer is now the other end of the Tech spectrum now.
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Old 04-10-14, 12:36 PM   #3
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suntour decades ago made a 3 pulley cage
awesome:



extraordinarily idiotic:

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Old 04-10-14, 12:53 PM   #4
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Like I said, Its so low to the ground it could be a kickstand ..

It's why an IGH makes so much more sense than a long cage RD on a small wheel folding bike ..
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Old 04-10-14, 03:53 PM   #5
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Like I said, Its so low to the ground it could be a kickstand ..

It's why an IGH makes so much more sense than a long cage RD on a small wheel folding bike ..
Agreed. I have just realised this is one advantage of dual drive instead of a triple. I have no problems with my short cage on my dual drive 349 bikes.

Can't the one from a birdie be used. That's unobtainable also?
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Old 04-10-14, 04:06 PM   #6
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Brompton's 3 speed if the chain length is right, (Fairly short) tucks right up high .. ..

then for me, the low gear is the 2nd range in the Mountain drive crank 54/21.6t [ a 50/20 is even numbers]


though running a 110 BCD speed-drive the 34t acts like a 54t when kicked in overdrive

(but chain never moves, 1 cog 1 chainring.) .
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Old 04-10-14, 04:26 PM   #7
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What's wrong with dual short cage derailleurs? It's such a simple arrangement and I bet it would work great.

Last edited by BassNotBass; 04-10-14 at 04:31 PM.
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Old 04-10-14, 05:24 PM   #8
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Like I said, Its so low to the ground it could be a kickstand ..
I think that the original picture in the thread had a Shimano SS or GS road derailer. I can't tell for sure.

There are reasons to pick something other than an IGH.
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Old 04-10-14, 05:26 PM   #9
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What's wrong with dual short cage derailleurs? It's such a simple arrangement and I bet it would work great.
That's interesting.
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Old 04-10-14, 06:12 PM   #10
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What's wrong with dual short cage derailleurs? It's such a simple arrangement and I bet it would work great.
i think its really down to the needs of the individual cyclist.

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Old 04-10-14, 06:51 PM   #11
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i think its really down to the needs of the individual cyclist.

Now that's what a pro can do with PS! LOL... simply awesome!!
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Old 04-11-14, 03:47 AM   #12
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. simply awesome!!
Huh. Somehow awesome isn't the word I would have picked...

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Old 04-11-14, 08:42 AM   #13
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Three derailers?!?

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Old 04-11-14, 10:32 AM   #14
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Ah, the humor potential of photo shop ..
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