Wheels and Tires Vibration
Even though no problems may be found as the tire rotates on the balancer, when the tire experiences a load, the transition of the harder and softer sections of the tire may create a series of harmonic vibrations as the various sections of the tire contact and leave the road surface. Depending on conditions, this harmonic may occur once per tire revolution, or in a series of multiple vibrations per revolution. It's possible that this phenomenon may vary according to changes in tire pressure, vehicle speed, individual tire load and road surface conditions, all of which may serve to reduce and/or amplify the vibration problem. In other words, the vibration the driver feels may not occur at any one rate of speed, or on any particular road surface, because the problem may appear only under a specific combination of these variables.
If a tire and wheel will not balance properly, or if a vibration exists after a successful balance job, don't automatically blame the tire. If you haven't checked the hub and wheel, you may be jumping to conclusions. If, however, all balance and chassis parts variables have been exhausted, then it may be time to suspect a radial force variation problem.
To check for and attempt to actually verify a dynamic radial run out condition, a spin-balancer with a built-in load roller is recommended. This type of balance machine places a load (which attempts to simulate road load) onto the tire as it spins, while monitoring and recording variances of run out. If load variation is found, it may be corrected to an acceptable level via balancing weights. In extreme cases, it may verify that the tire should be replaced.