The bike comes with 170/80-15 rear.
This provides a diameter of approx. 670mm. - very similar to 120/90-18 rear!
I am of course not suggesting you convert to this size; just saying.
Apart from tire width, there are other considerations: ride height (the height of your seat above the pavement).
For example, if you go 180/70-15 your tire will be wider, but your seat will also become 10mm closer to the pavement.
This will negatively affect your cornering clearance and also slow your steering (by increasing trail).
In a perfect world you'd trade in your 15" rear rim and lace up a 16" with 160/80-16 rubber.
This would 'de-cruiser' the bike and make it more of a genuine road bike (that handles).
Actually ANY change in tire/wheel from stock will drop your seat height - this is because the stock combo is in fact as tall as is possible to specify.
(On a 15"! I know; I too was shocked.)
But the 160/80-16 is almost there - only 8mm less.
Personally I hate the look of the puny 15" and giant tire (from the side).
Needs more wheel and less tire if you ask me (from the side).
Bike's never gonna handle well if you're riding twisties with that big bulbous black (stock) lump on the rear.
Tire is so big it actually provides supension, kinda like a Formula 1 car, heheh...
Not to mention 160/80-16 tire weighs only ~12 pounds - far less than stock tire (~20 pounds).
Regards
