John wrote:

Interesting, it got me thinking if the tires I have on now are really
the width that they claim to be. I measured them and found out they are
not. The 38mm is really only 34mm and the 42mm is really only 38mm
wide. Both are different make tires. Is this common for tires to be a
shorter width then they're marked for?

It's very common. So common, in fact, that the only way to know for
sure what size your tire will be is to mount one, inflate it, and
measure it.

It's a decent rule of thumb, in my observation, to assume that a given
tire is one size category smaller than claimed, e.g. "35mm" is actually
about 32mm, "38mm" is more like 35mm, etc. Probably three out of every
four tires I've tried come out that way.

Chalo Colina