A little worried about commuting to work tomorrow

[RichardB]

For those who appreciate quantative analysis, the relevant diameters are 18mm and 27.5mm.
Interestingly (or not, but this IS Cycle Chat) bitd a farthing/halfpenny is/was 20mm and 25mm.
Still 'all in the mind'.

One of the unexpected advantages of decimalisation. Post-71, a frightened person's orifice widens by 53.8%, whereas before it was only 25%.

A trick the 'metric martyrs' missed, I feel.