I took the bike and the new tires I ordered to a motorcycle tire shop. Back tire went on in 5 minutes, but he struggled with the front for over an hour before giving up. The problem was the 90/90 is just too small for the rim.... My old front tire was too worn out to reinstall so he installed a cheap 100/90 Kenda, first without a tube (went flat) then with a tube. By the time I rode the 25 miles home, it was flat again....
So now I have a bike with mismatched tires, one of them is flat and a 90/90 18 tire I can't return. I'm a bit annoyed about the outcome.
:/
~M