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Old 05-03-08, 10:48 AM   #1
Donegal
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BB Width and Cross-Chaining

I am finding a problem with the newer-styled outboard bearing bottom brackets. On my newest road bike, a Kuota Kredo, the extreme width of the bottom bracket coupled with the outboard bearings creates a cross chaining when in the lowest two to three gears. The chainline is fairly extreme to anything but the outside half of the cassette. This situation is aggravated on the big chainring. I am comparing it to another carbon frame, my Aegis Victory with a Campy Record, old style bottom bracket. The chain seems to have fewer obtuse angles. The chain lines up better on the Victory than the newer Kuota. Since cross-chaining creates an energy loss, is this affecting performance? Will all new frames with wide bottom brackets face this challenge? I really noticed the cross-chain with a new chain whose links are still fairly stiff and straight. They hit the front rings at an angle and cause a good bit of noise which would make you believe you were out of adjustment. The carbon frame resonates the sound and it multiplies the volume.

When I pulled the old chain off, I could feel how loose it was side to side, it had stretched in all directions.
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Old 05-03-08, 02:01 PM   #2
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Don't rely on your eyeball. Measure the actual chainline.
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Old 05-03-08, 02:53 PM   #3
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Hi DMF, I know it sounds crazy but I have checked the line of the chain over the front rings. Even in the small ring, the chain is pulled tight to the inside over the teeth. This causes a bit of bind and tons of noise which is relaly loud through the frame. I looked all over to see if the chain was dragging on the derailleur, if the rear dereailleur was out of sync, etc. My first 2-3 gears are tough on the chain even in the small sprocket. I used to ride my Litespeed cross-chained in the big gear and it was OK. This thing is squawking big. I can trim out the derailleur to not drag but the chain drags across the teeth.
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Old 05-03-08, 05:25 PM   #4
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Have you ever changed the jokey wheels in your RD? just a tought because if the J wheels are quite bad or old the train starts to get noisy.

Thanks.
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Old 05-04-08, 07:32 PM   #5
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Originally Posted by ultraman6970 View Post
Have you ever changed the jokey wheels in your RD? just a tought because if the J wheels are quite bad or old the train starts to get noisy.

Thanks.
Hi Ultraman;

The bike is basically new, and the noise I get is from the chain being pulled across the top of the front rings at an angle. It seems that this bike likes to be ridden in the top 7-8 gears and doesn't like wimps or the bottom gears.

I am a noise fanatic. I am constantly tuning my friends derailleurs because I can't stand the clicking. My Kuota is exceptionally noisy because everything echos through the hollow carbon frame. Even my freewheel is noisy. I will watch the cross chaining and watch for chain wear. I am just looking at what I consider could be a design flaw.
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