20" tyre minefield - can I replace ISO 28-440 with 500A?

pulck
pulck Posts: 24
edited November 2017 in Family & kids cycling forum
My daughter has just inherited a vintage Peugeot Parisienne. It's a beautiful bike but it could do with smartening up so I'm trying to replace the tyres. However, it has 20" wheels and I've discovered this is a bit of a minefield for a know-nothing like me.

On the current tyres it is marked 'ISO 28-440 / metric 500x28A', which I can't find anywhere.... Well, that's not strictly true.... I can find 1 brand for sale in that size (Hutchinson) but they are boring plain black and not the beautiful whitewalls currently on the bike.

However, the rim has '500A' stamped on it which, according to this table, is ISO 32-440: https://www.cyclinguk.org/cyclists-library/components/wheels-tyres/tyre-sizes

Does this mean I could fit 500A tyres (in which size there seems to be an abundance of whitewalls, e.g. Raleigh Perfect Whitewall)?

I am confused because apart from the width being different, according to the above table, 28-440 and 32-440 tyres are NOT the same diameter (19.5" vs 19.8")!

Then the other issue is that 500A tyres are usually listed as 37-440 / 500x35A, which means they'd be 9mm wider than the current tyres.

What is the tolerance for differing tyre sizes. Should I just give up and go with the plain black 28-440s???

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