• It's an oldy and it has fenders, so I bet it's not 39-49mm. Not available in the 1970's and fenders don't fit.
    If you're lucky (questionable) it's 47-57mm. Still available and very small fenders fit somehow.
    Maybe it's even longer (centrepullbrakes). Brakes hard to get, function a bit old fashioned, but sufficient space for tyres and fenders.

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