Special motorcycle tire: how and why to reduce the size of the rear tire?

Some motorcycles - roadsters and sports bikes - are equipped with a 190mm rear tire, but many users would like to reduce the width, in particular, to gain maneuverability. For them, Moto-Station sums up.

Sports roadster owners, and even sports ones, often ask this question: “My bike has a 190mm tire at the rear, can I fit 180mm to get the maneuverability? To answer this question raised during the tire and chassis training at CCI Le Mans and at Bridgestone technicians, several parameters need to be taken into account.

First of all, as a precautionary measure, the manufacturer never advises to deviate from the permitted tire sizes on their motorcycle. On the other hand, for some cars it is allowed to use rear tires of several sizes: 190 mm and 180 mm with the recommended height. Better to follow the manufacturer's recommendations.

In spite of everything, the tire professionals, and in particular the manufacturers grouped around the TNPF (tire standardization work for France), advise against completely changing the tire size, provided that the index and speed code, as well as the load index, are respected.

Changing Tire Size: Precautions

In practice, you should already check if your rim size can accommodate this change. For example, 190/55 X 17 tires are often fitted on 6 "rims versus 5,5" rims for 180/55 X 17 tires. Then, if someone decides to fit a 180 mm tire instead of 190 mm, the installation will have the tendency to split the tire bead by 180 mm. With this split, the tire manufacturer's shape will be changed: the tread is at risk of flattening, while the curvature of the tire between the tread and shoulder will also change.

In fact, in practice it is possible to achieve better handling no matter what, but the motorcycle's cornering behavior can be unnatural, with a loss of progressiveness. In addition, changing the angle will not match what was designed by the designer and manufacturer. However, this remains quite variable depending on the choice of tire. Indeed, some 180/55 X 17 tires are actually very wide, approaching 190mm. And these tires can be fun.

So, if you have decided to upgrade from 190 to 180 mm, check with your favorite tire dealer to find out which tires to choose according to your needs, as well as gather information from your motorized relatives and the Moto-Station forum, because that there is a lot of advice!