Bead Contact Pressure Measurements at the Tire-Rim Interface

A method has been developed for measuring the normal contact pressure distribution at the interface between a tire and a rim using a miniature magnetostrictive transducer as the load sensor. The transducer itself is a 0.050 in. diameter nickel ferrite toroidal core wrapped with primary (excitation) and secondary (sense) windings. As the core is stressed, the magnetostrictive phenomenon causes an increase in the magnetic flux and a corresponding change in the induced output voltage across the sense windings. This voltage change is signal conditioned to yield a dc voltage output as a function of core stress which is proportional to the bead contact pressure.

Bead contact pressures were mapped at the interface between various radial tires and rims under static and dynamic loading conditions. Static pressure distributions obtained for the inflated but otherwise unloaded condition provide a measure of the conformability of the tire to the rim. Dynamic pressure distributions show stress patterns developed under straight-ahead rolling and cornering conditions.

With the aid of such bead contact pressure measurements, stress analysis studies of tires and wheels can now be conducted on a more rational basis than done in the past because the exact nature of the load distribution at the tire-rim interface is known for various tire loading conditions.