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Old 03-15-14, 02:16 PM   #1
Pedalitis
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TA crankset question

I have a vintage TA double crankset - 48/34 rings - and I'm building up a bike with a Suntour Cyclone 7000 6-speed set up on the back.
When cross-chaining from the small chain ring to the smallest sprocket on the freewheel, the chain rubs on the inside of the outer chainring.
I've tried wider BBs - up to 123mm - and spacers but still have the problem. Rear dropouts are 124mm spacing and the rear wheel dish is spot on. Is this just something I'm going to have to live with, and avoid cross-chaining, or is there a simple solution to the problem that I'm missing?

I use the same crankset on other vintage bikes with 5-speed freewheels and have no problems but the 6-speed is considerably wider. Maybe its the narrow Q of the crankset that makes it unsuited to this set-up?
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Old 03-15-14, 03:31 PM   #2
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Avoid cross chaining. It is not mechanically efficient. There is likely a combination using the large chainring that will yield the same result. Guessing you have a 14 as your smallest cog, 48/20 yields the same ratio at your 34/14. You likely have something close on your freewheel
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Old 03-15-14, 03:41 PM   #3
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If the large chainring is not actually grabbing and lifting the chain to initiate an undesired shift, then the chain interference is not severe. You might simply have the chainrings too close to the chain centreline - i.e. the chainline measurement is too low. You should check it and see. If you need to adjust it you can either add a spacer under the fixed cup of the BB or get a longer BB. I found I could set up a 44/30 TA Cyclotourist with a 10-speed rear end and a 10 speed chain based on correct setting of the chainline and a rear triangle that is not offset. You can use the string test (see Sheldon Brown) to check if the rear triangle has an offset, and can measure chainline with a millimetre ruler.

Chain width can also be important, if the chainline adjustment doesn't work.
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Old 03-15-14, 03:46 PM   #4
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I pretty much stick to 8 possible speeds with a 2 x 5 set-up(classic 10 speed) and 10 possible gears with a 2 x 6 combo.

What I have discovered is older 10 speeds like Peugeot UO-8's have really long chainstays so you can run all 10 gears without warping the chain to much. One of the many benefits of long chainstays. Unfortunately not too many bikes other than some touring bikes have that chainstay length.

What kind of bike are you working on?
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Old 03-15-14, 05:57 PM   #5
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Originally Posted by big chainring View Post
What I have discovered is older 10 speeds like Peugeot UO-8's have really long chainstays so you can run all 10 gears without warping the chain to much. One of the many benefits of long chainstays.
+1. Short chainstays combined with a wide difference in chainring sizes on the crank exacerbate this problem. If you can't avoid cross-chaining, you may need to move the chainline further out, but this may create a new set of problems.
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Old 03-15-14, 06:50 PM   #6
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+1. Short chainstays combined with a wide difference in chainring sizes on the crank exacerbate this problem. If you can't avoid cross-chaining, you may need to move the chainline further out, but this may create a new set of problems.
I had this with a TA crankset on a Schwinn Sports Tourer when I put in a sealed BB and was running a six speed freewheel. Messed with a spacer on the drive side but it bothered me to look down there and see that the crank arms were then offset to the right. Couldn't really feel it when riding but it seemed odd. So, in the end, I went with a longer BB and moved both sides farther out Still rubs a little when in the smallest cog on the rear. So, when not climbing, I ride the big front ring and a couple steps higher on the rear. Most of the time, I'm riding in the third or forth rear cog and the big front ring and the chain-line is about perfect. Figured since this is my preferred primary flatland gear, this made sense.
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