I have a 1980 Yamaha 175 tri-moto. I want to put a more aggressive rear tire on. Currently it has 21x11-8.5 ballon tires and I'd like something like ITP or Matrix.

Does anyone know what would work?
Is there and manufacture that still make an aftermarket 3 hole machined rims?

 

I put 21 inch strykers on mine and they work great! Don't go any taller or you will lose some of your climbing ability due to gear ratio change because of tire height.