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Discussion Starter · #1 ·
I am ordering a groupset online and part of the oder form is selecting a front derailler. The option's are braze on, 31.8 or 34.9 clamp on. I have not been able to find the specs on my bike as far as what this measurement is in any on-line literature. My preference would be clamp on. Any idea where I can find this diameter?
 

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Rub it............
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What kind of bike is it? It varies from manufacturer to manufacturer. The easiest way would be to take a pair of digital calipers and measure the OD of the seat tube.

Well with braze on - there is usually a bracket that is bolted/riveted/moulded onto the seat tube.

 

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Discussion Starter · #3 ·
frdfandc said:
What kind of bike is it? It varies from manufacturer to manufacturer. The easiest way would be to take a pair of digital calipers and measure the OD of the seat tube.

Well with braze on - there is usually a bracket that is bolted/riveted/moulded onto the seat tube.

The bike is a 2008 Opus Fidelio. Currently running Shiamo Sora clamp on. I plan to do the build up myself and did not want to have to do any welding/brazing and I don't have any calipers.
 

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Pull the Sora off and look inside the clamp. It should have the sizing stamped inside the clamp.
 

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Or wrap a sewing tape measure around the tube to measure the circumference, and divide by pi to get the diameter
 

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Another cheap and easy way to measure is to use an adjustable wrench (crescent)...tighten the jaws until they're just touching the sides of the frame tube and then measure the distance between jaw faces with a metric ruler.
 

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SilverStar said:
Another cheap and easy way to measure is to use an adjustable wrench (crescent)...tighten the jaws until they're just touching the sides of the frame tube and then measure the distance between jaw faces with a metric ruler.
I forgot about that one, the post-calibrated caliper. It works.
 

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Discussion Starter · #8 ·
SilverStar said:
Another cheap and easy way to measure is to use an adjustable wrench (crescent)...tighten the jaws until they're just touching the sides of the frame tube and then measure the distance between jaw faces with a metric ruler.
Thanks, I'll try this.
 
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