Every underbone in Vietnam wears the same wheel diameter but not the same rubber. Learning to read the markings turns a spec-sheet mystery into a five-minute skill. Sizes below are manufacturer-published (retrieved 23 September 2026).
Reading the marking
70/90-17 means: 70 mm section width, 90 percent aspect ratio (sidewall height = 90 percent of width) on a 17-inch rim. The standard underbone fitment is 70/90-17 front with 80/90-17 rear - shared by the Wave Alpha, Blade, Wave RSX, Future 125, Super Cub and Sirius RC. Wider sport fitments: Winner R (90/80-17 front, 120/70-17 rear), Exciter 155 VVA (90/80-17 front, 120/70-17 rear), CBR150R (100/80-17 front, 130/70-17 rear), CT125 (80/90-17 both ends).
Tubes: still standard on the workhorse class
Yamaha’s Sirius page specifies tyres with inner tubes; the Exciter runs tubeless. Honda’s pages publish sizes without tube claims. Practically, the traditional laced/spoked underbone wheel needs a tube - our inner-tubes-versus-tubeless guide covers the puncture-behaviour difference, which matters at Hanoi speeds.
What the sizes mean for you
Rear 80/90-17 gives the classic underbone contact patch - narrow, cheap, long-lasting, and quick to steer. The 120/70 and 130/70 sport rears add grip and stability at the cost of price and drag in traffic. Whatever you run, replacement intervals are riding-condition questions: our tyre-care guide covers wear signs, and punctures on rental bikes have their own procedure. Contact us to confirm current availability of any model class.