The forces required to control a car while cornering come from 4 small contact patches between the tire and road. Maximizing the average speed through the turn is almost entirely dependent upon the lateral force developed at these four points by the tires. Historically, these forces have not been measured directly, but secondary results such as lateral acceleration have been measured as an indicator of the total lateral force on the vehicle. In addition, tire characteristics have been measured from steady state measurements collected on a Force and Moment machine.
Halliday Technologies Inc. has developed the Grip Evaluation and Management device, GEM, with which the lateral force developed by each tire mounted on a vehicle can be measured directly and recorded dynamically. The GEM device is patented in the USA and patents are pending in more than 20 other countries.
This paper describes the operation of the GEM device, and presents some of the data collected to date.