The tires have a very large effect on motorcycle dynamics. In fact, they are essential both for riding comfort, being the first protection for the rider from road vibration, both for safety and performance because they play a leading role on stability and handling.
There are 3 categories of motorcycle tires: racing, road and off-road. For each of these categories, the market offers many models all having different characteristics from each other.
Multy-body codes, such as Fastbike, are used to perform virtual simulations of the dynamic behaviour of motorcycles. It's clear that if the tire changes, the behaviour of the motorcycle will change too. So, through simulations, it's possible to identify the most suitable tires for a particular motorcycle. To simulate the behaviour of a tire, the characteristic curves that can be obtained only through experimental measurements, are needed. Due to the lack of experimental data available in literature, the Motorcycle Dynamic Research Group has developed a specific machine which is named Mototyremeter.
With it, it's possible to identify the mechanical properties of motorcycle tires. Until now, with this equipment, the following quantities can be measured:
- the lateral force as a function of roll angle,
- the lateral force as a function of the sideslip angle,
- the self aligning torque,
- the twisting torque and the rolling resistance force.
Mototyremeter, respect other machines, makes it possible the measurement of tire properties with very high camber angle, up to 50°. This feature is very important because camber angle has a large influence of the forces and torques exerted on the road of the tire.
The rotating disk configuration is favourable for construction simplicity and less expensive than other configurations. But it takes into account that, in the rotating disk machine, the path of the wheel is circular, hence a force caused by the curvature adds to the lateral force caused by the sideslip and camber angles. The curvature force is always directed towards the disk outside and it must be corrected to obtain correct measures.
The graphs obtained from the experimental data allow to calculate the Pacejka coefficients, with fitting methods.