Time for a new front mech

[taximan]

I think its about time to replace my front mech, but I am a little puzzled over the clamp size. I measured the seat tube at 33 mm but the only size I can find near to what I require is (copied from ad)
34.9mm Clamp With Shims For 31.8mm Size (Can Be Removed)
Will this do the job or should I keep looking?

The bike is a Trek 8.1 DS dating from 2014 and has covered in excess of 20,000 miles

This is how I measured the diameter of the tube​

 

[Ajax Bay]

Very likely it's 34.9mm - look at where the lowest '0' is (I am verging on anti-trolling naivety here!)
Try measuring a known item and see what it measures: a home made calibration, if you like.
The distance the bike has covered will only have a limited effect on the diameter of the seat tube.

 

[winjim]

Very likely it's 34.9mm - look at where the lowest '0' is (I am verging on anti-trolling naivety here!)
Try measuring a known item and see what it measures: a home made calibration, if you like.
The distance the bike has covered will only have a limited effect on the diameter of the seat tube.

I agree. Remember you read a Vernier scale by lining up the sliding scale with the fixed. Where they exactly align is the correct measurement.

Edit: kind of. That's not quite right is it? It's still early. Anyway, that scale is reading 35mm more or less. Zero line for whole numbers, alignment of sliding with fixed scale for fractions.

 

[taximan]

I agree. Remember you read a Vernier scale by lining up the sliding scale with the fixed. Where they exactly align is the correct measurement.

Edit: kind of. That's not quite right is it? It's still early. Anyway, that scale is reading 35mm more or less. Zero line for whole numbers, alignment of sliding with fixed scale for fractions.

Showing my ignorance, I didn't know that.

 

[winjim]

Showing my ignorance, I didn't know that.

Sorry, that's a bit of a rubbish explanation. Here's an example. The zero line is at 26mm plus a halfish, the sliding scale aligns with the fixed one at the second division past the six. Each division is 0.02mm. Add them all up and you get 26.64mm. Obviously you don't need that level of precision for a seat tube so just looking at where the zero line is should be good enough.

 

[taximan]

Sorry, that's a bit of a rubbish explanation. Here's an example. The zero line is at 26mm plus a halfish, the sliding scale aligns with the fixed one at the second division past the six. Each division is 0.02mm. Add them all up and you get 26.64mm. Obviously you don't need that level of precision for a seat tube so just looking at where the zero line is should be good enough.

View attachment 604054

Thanks for that winjim 👍👍

 

[Ajax Bay]

The OP's vernier calipers read 35.18mm or 1.389"