Road Force Measurement is new to the automotive service industry. This new measurement identifies tire and wheel uniformity, which has been measured for years in assembly plants and manufacturing facilities. Road Force can be used to solve uniformity related tire and wheel vibrations. Tire/wheel assembly uniformity can only be measured under load. The load roller on the GSP9700 performs a computer simulated "road test". It measures the tire/wheel assembly to determine how "round" the assembly is when rolling under a load. If a tire were not exposed to the road surface, then balance would be more than sufficient. However, not all tires roll round under a load. For example, an egg-shaped tire/wheel assembly can be balanced about its axis, but an egg-shaped tire-wheel loaded against a surface would not give a smooth ride.
Explained another way. If you were to drill a hole through a concrete block in such a manner that you could attach it to a spin-balancer, you could, by adding or subtracting weight make that concrete block spin smoothly with absolutely no vibration. Now take that same concrete block, or more specifically 4 of them, and attach them to your vehicle. Smooth ride? No!
To understand the effects of radial force variation on vibration, a model of a tire can be used. The sidewall and footprint can be understood as a collection of springs between the rim and the tire contact patch. If the "springs" are not of uniform stiffness, a varied force is exerted on the axle and causes it to move up and down as the tire rotates and flexes. This movement creates a vibration in the vehicle unrelated to balance.
Getting back to the Hunter GSP9700. It solves vibration problems balancing can't fix!
The machine works through a large roller which is pushed against the tread of the tire with 700 pounds of force as the tire rotates. During this force application cycle there are micro-sensors inside the machine that monitor variances in road force. A computer in the machine converts these readings into numbers for the technician. These numbers tell if the tire is good or bad and also if the road force variation can be brought into spec by rotating the tire on the wheel. Sounds complicated, but only to a point. In the hands of a trained technician the job can be performed without a hitch. By having this done, you instantly know
– are the tires good
– are the tires bad
– do I need to replace the tires
– do I need to matchmount the tires
– do I need to look elsewhere in the car.
You can view a video of how the Hunter GPS9700 works on the following link.
http://www.gsp9700.com/pub/images/video/gsp9700_T1_video.cfm
