Explosif [U.K. eBay]

That's a 16 Pip. You can tell from the 9cm head tube. 17s and 18s both have 11cm head tubes.

Presumably he must plan to provide a description when he has more time?
 
Thank you Anthony.

With regards to sizing a frame from a picture, I do indeed try to acknowledge your guidance - e.g. where an imaginary line drawn across the top of the tyres intersects the frame.

I find it very hard however to determine the length of a head tube from a random picture. I even put both frames next to each other on my monitor this morning! Perhaps you are able to judge it accurately by comparing it with the width of the top and down tubes?

I’m getting there though.

Pip.
 
His pictures aren't as good as we might wish, but they do illustrate quite well the top and down tubes almost touching as they meet the head tube. We've got used to that more recently with fat aluminium tubes, but it's really quite rare with a steel frame.

It's caused in this case by the bi-ovalising of the Columbus Max OR tubes, which are 3.6cm and 4.0cm deep at the front (from 2.8 and 3.2 deep at the rear). That 7.6cm doesn't leave much space above and below on a 9cm head tube, so no wonder they almost touch. In fact I've just measured the gap on a size 18 with an 11cm head tube and it's 1.5cm, so they really had to squeeze the top and down tubes onto the 2cm shorter head tube on the size 16.

Anyway, that's how you can tell that it's a size 16, from the fact that the top and down tubes almost touch.
 
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