Right, this isn’t as daft a question as it sounds. Hopefully.

I’ve got an old shopper bike that I’m fixing up for the Mrs. It needs new tyres. The old ones are that far gone that I can’t see what size they are, and there’s nothing printed on the rims.

They’re definitely bigger than 26″ mtb wheels, and definitely smaller than 700c gravel wheels.

A bit of googling suggests they could be 27″ touring wheels, but they could also possibly be 650b.

Before I start ordering tyres that don’t fit, is there a standard way to measure bike wheels? So do I measure the diameter rim edge to rim edge, or is it measured tyre edge to tyre edge? And does it vary with different wheel sizes?

Hope that makes sense. Help me singletrack!

More than you ever needed to know on Sheldon Brown. Sometimes slightly out of date but probably appropriate for what you need.
https://www.sheldonbrown.com/rim-sizing.html

Perfect! Thank you. I should have thought to look on Sheldon.

So, what size was it ? You can’t leave us in suspense ?

I’m going for 26 1 3/8

Ha sorry, been busy painting the house and not had chance to look till now.

Turns out @simondbarnes has nailed it, the old tyres do still have the lettering on the casing and say 26 x 1 3/8 and 37 – 590. Not sure how I missed that, but never mind.

So that leads me on to my next question – will these fit? They say 35-590, which I think should mean they’re a little bit narrower but the right diameter.

will these fit?

Yes

Ta muchly.