Ojisan rider post=847183My wheel size is 18 x 2.15. Stock tire should be 120/90/18,
should I go with 120/80 or 130/90?
I would definitely go with the 120/80-18. The width will be similar to the stock 120/90-18, but the overall diameter will be a bit smaller. With the 130/90, it will be both wider
and taller than the stock tire.
According to the tire manufacturers, a 120 is a bit wide for a 2.15" wheel, even though most of us run a 120 on our KZs. The Avon RoadRider mk2 and Bridgestone BT45 and BT46 all call out a 2.5" minimum wheel width, and are all measured on a 2.75" rim.
I tried to run a 130 on my bike and it chewed up the inside of my chain guard and also the tire side wall cracked quickly which may be, I'm guessing, due to the stress of squeezing onto a thin rim.
Another size option might be a 4.00-18. Depending on the manufacturer, these are often pretty close to a 120/90. The RR2 and BT46 list 116 width, while the BT45 lists 119mm width. But the 4.00 might actually be closer in size to the 120 than you think. As I mentioned, the 120s seem to typically be measured on a 2.75" rim, while the 4.00-18 are measured on a 2.5" (Avon and BT46) or 2.15" (BT45). A 120 squeezed onto a 2.15" instead of 2.75" might actually end up narrower than the BT45 4.00-18, advertised as 119 on a 2.15".
Yet another thing to watch out for is the size "number" vs the actual size. A 120 is not always a 120. For example, the RR2 120/80-18 is specified as 120, but the 120/90-18 is specified as 129mm. While the BT46 120/90-18 is 119, and the 130/90-18 is 136. The RR2 120/90-18 is 10mm wider than the same size BT46. This can make a big different if you're close to the clearance limits for you chain guard or front fender or whatever.
www.avontyres.com/en-us/tyres/roadrider-mkii#page-2
www.bridgestone.com/products/motorcycle_...oducts/detail/pr176/
www.bridgestone.com/products/motorcycle_...oducts/detail/pr015/