I recently bought a Peugeot folding bike, and one of the tires is completely rotten, with the other not far behind. I went to my lbs for help, actually a couple of them, only to find they are a completely arbitrary size. the tires are larger than a 20" and smaller than a 24". They seem to be around 22". There are no size distinctions on either the wheels or the tires other than "550 1/2". Is there anyone out there who knows where I can buy replacement tires? If not any suggested plans of attack would be helpful. I have built up many a french bike, and am fully aware of their eccentricities, but this one has got me stumped.

Here's a wheel sizing chart:

https://www.bikecult.com/works/wheelsizes.html

See the second category, small tire sizes. It looks like there are French Metric 550A, B and C sizes, corresponding to 490, 484 and 470 ISO metric sizes. Not common US sizes, unfortunately.

Try the Folding Bikes subforum, I'm guessing someone there would know more.

If you can't find matching tires, one option might be to build up some 451 wheels, this is not a hugely popular size, but some folders and recumbents still use it and a decent, though limited, selection of tires are available. There is an active 451 wheel/tire thread on the folding bike subforum right now.

Thanks for the advice. I was able to fing the tires on the Harris Cyclery page though.