I am rebuilding a 1980's Lo Pro time trial bike. It came with a new old stock Gipiemme Techno m416 front wheel. I assumed it is a 650c but when fitting a new tyre found the tyre was marginally too big. After a pleasent couple of hours we came to the conclusion it seems to be 26" as in a mountain bike (559 diameter). Before I buy a 26 x 1" mountain bike slick tyre does anyone know if this is likely to be the case?