Do 120-width tires really work better on the rear?

The Ninja 250's rear rim was designed for a 120 width tire; the EX250-E model came stock with a (now discontinued) Dunlop K530 120/80-16 rear tire. The EX250-F (1988+) model, however, has the same size rim, but comes stock with a Dunlop K630 130/80-16 tire. Kawasaki actually put a wider tire on their own rim than is ideal for the wheel width; the 130 is slightly pinched in the rim, while the 120 is right at home.

The 120/80-16 tire is better than a 130/90-16 (usual rear replacement) in many ways. First off, the 120/80-16 tire typically weighs four pounds less than a 130/90-16 of the same model. This means less dead weight on the chassis, less rotating mass for the engine to turn, and less unsprung weight for the suspension to carry. The lower profile is also more rigid. The tire width is the ideal size for the 2.5 inch-wide rear rim, so the contact patch may be better, depending on the model, while a quicker steering response is effected.

The 120/80 tire also just looks like a better fit on the rim than a huge 130/90. Some people think a bigger rear tire makes the bike look bigger, but a bigger tire should technically make the bike itself appear smaller by comparison.

Downsides to using the 120/80 include a loss in final gearing (3% less than a 130/80-16, 6% less than a 130/90-16) and a loss in ride height (about 1/2"-1"). A 120-width tire is a good choice for around-town riding, where the quicker performance can make a difference. For sport-touring, a 130-width tire will improve high-speed, straight-line stability.