I've got an older cyclecross bike that I ride on loose gravel/sand roads. It has ALEX rims, marked ETRTO 622x16. It has 700x30 Kenda tires on it now. Will a 700x32 or 700x35 tire work on the rim? I'm looking for more floatation in the sand and access to a wider variety of tires. Clearance wise I have room. Many thanks.
I’ve used DT Swiss RR415 rims which have only 13 or 14mm internal width on my cyclocross. They did look comical with 35mm tires and had a tendency to buckle in tight turns at low pressure. Apparently the official recommendation for them was 20 to 30mm.
I think you’ll be fine with 16mm, but it is kind of marginal.
Sheldon Brown's website suggests that you may get away with going a bit wider, at the expense of putting extra pressure on the rim and sidewall of the tyre.
The obligatory table by Sheldon Brown: https://www.sheldonbrown.com/tire-sizing.html#width
It does not have an entry for 16C rims, but since 15C rims work with up to 32mm tires and 17C rims work with up to 37mm tires, I guess 35mm is probably the max.
However, I should warn you that neither 32mm nor 35mm tires float on sand. For that, you need a fatbike.