There's a rule about one-syllable adjectives that end in a single vowel and a consonant, that duplicates the consonant in the comparative form:
big --> bigger
hot --> hotter
I've been asking around to native english speakers and nobody seems to recall this specific rule, and the odd thing is it doesn't apply in the adjective "new":
new --> newer, not newwer
So, some students were wondering why "new" isn't considered an irregular adjective like bad (worse instead of "badder"), good (better instead of goodder), etc..
Usually I look up in a "A practical English Grammar" by Audrey Jean Thomson, A.V. Martinet, Oxford University Press - Fourth Edition to answer all my doubts, but this one keeps on puzzling me.