Measurements help, and can be quick and dirty for tire sizing.

https://www.sheldonbrown.com/tire-sizing.html

I usually just look at the sidewall to look for one of the numbers above (507, 520, 540 (and for vintage, 547)), and hopefully a width designation.

Anyway, if you measure the rim diameter in cm/mm, subtract about 1cm, 10mm as per Sheldon Brown for the rim depth to get the approximate Bead Seat.

Depending on the seat height, putting a foot down can be problematic.

But, also be aware about the differences between riding in a straight line vs turning. Hopping over ruts or center grassy areas? Descents?