A fleet of heavy-duty cushion-tire forklifts operating in a concrete products yard was experiencing a bizarre, recurring failure. The right-side drive tire kept delaminating. The solid rubber cushion tire would cleanly shear away from the steel band pressed onto the hub, making the truck undriveable. The tire vendor insisted they were defective tires and replaced them three times. When the fourth tire sheared off in the exact same way, the shop looked deeper.
Cushion tires are not bolted to the wheel; they are vulcanized and mechanically pressed onto a steel rim under immense pressure. For the rubber to shear cleanly away from the steel band, the tire has to be experiencing extreme, asymmetric torque-twisting forces far beyond normal driving.
We put the forklift on a lift and examined the drive axle and motor. The drive motor sits directly above the axle, connected by a short, heavy-duty coupling. We grabbed the motor and tried to rock it. The front motor mount-the thick rubber biscuit that bolts the motor to the frame-was completely torn in half.
Every time the operator accelerated hard from a stop, the torque of the drive motor caused it to violently twist on its broken mount. Because the motor was no longer securely held, its output shaft shifted laterally by half an inch. This lateral shift transferred directly down into the drive axle, causing the right-side wheel hub to tilt inward by a fraction of a degree. Every rotation of that tilted hub acted like a cheese slicer against the solid rubber tire, shearing the vulcanized bond between the rubber and the steel rim. The right tire was taking 100% of the torque-induced misalignment stress. We replaced the $50 motor mount, and the tires never sheared again. When a tire fails repeatedly on one side, always check the rigid alignment of the axle and motor before blaming the rubber.
