Good conduct of including numbers in css classes
Perfect naming in any language allowing freedom for your names are:


Descriptive. (Makes it clear what it means at a glance)
Short. (less chance for typos, types faster and therefore easier to work with.)


In your case, the names only mean to affect the text size. So appropriate names would be something like:

text-medium {
    font-size: 1.4rem;
}
text-big {
    font-size: 1.6rem;
}


Since this makes it clear what they do.