In my experience most folding pedals have a limited life since the two bearings (or in the case of the Brompton folding pedal only one) are too close together, resulting in increased wear.
An alternative which has the two bearings well spaced is the removeable pedal made by MKS. These can be removed and re-fitted in seconds and have another advantage as an anti theft device. A bike with no pedals is not going to be ridden away very quickly.
Here in UK there is a good choice of 20" tyres, both smooth and knobbly.