These range from 120/70, 120/80,130/60, 130/70, 140/60, 140/70 in the 12 inch rim size.
I'm getting ready to put a new rear tire on #2 and here were 2 that I had on hand that show the practical size range on a BR.
One is a 120/70-12 Rear Shinko tire....the shorter one with a circumference of 56".
the other is a 140/70-12 Michelin Pilot City....the taller one with a circumference of 61".
The difference is that the smaller one should have more bottom torque and spin up faster, giving a better 0-60 time
and the taller one should have higher top speed and better fuel mileage, for the simple fact that on the same bike, with all
other factors being equal, the Pilot City will push you slightly over 1 foot further down the road for every 3 complete
revolutions of the rear tire.... than will the Shinko.
I like running short tires on #2 and taller tires on BioHazard to best utilize their specific tuning.
The smaller rear tire will lower your bike at the seat by as much as 2" and will drag the centerstand sooner in corners.