The standard loadwheel on a PCR/LTR uniformity machine is 33.6 inches in diameter and has a circumference of about 105 inches. A 225/70 R16 tire has a diameter of 28.4 inches and a circumference of about 89 inches. So a one-revolution test of the tire will use 89/105 of the loadwheel circumference. In our patent pending process of characterization and compensation, if a single tire is tested multiple times such that its waveforms are distributed evenly around the circumference of the loadwheel and averaged, the tire values will be lost and the loadwheel influence will emerge as a waveform which shows the effect of the loadwheel. In figure 2 we can see a force diagram that shows how the out-of-roundness of the loadwheel shown in figure 1 creates unwanted effects in the measurement of a tire.
Figure 2 is in fact, a plot of the waveform showing the EFFECT of the loadwheel out-of-roundness. Looking at that plot you can see that if the part of the loadwheel at about 20 degrees to 130 degrees was used to test the tire, it could remove as much as 0.15 LBS of force. And if the part of the loadwheel at about 210 to 310 degrees were used to test the tire, it could add about 0.2 LBS.. Then it would follow that a compensation waveform could be developed from the characterization waveform such that the total of both waveforms would result in a sum of ZERO.
And finally, note how the standard measurement for loadwheel out-of-roundness done by all tire uniformity machine maintenance people is shown in figure 1. Can you see how it bears a striking resemblance in SHAPE to the force characterization shown in figure 2? That would be expected as loadwheel out-of-roundness is a large contributor to a machine’s measurement variance.
Until now, little could be done for a loadwheel that had reached an unacceptable level of out-of-roundness except to have it removed and refurbished.
Now with Machine Effect Characterization and Compensation (MECC), the characterization routine can be run and in just a few minutes a characterization waveform similar to the one shown in figure 2 can be developed and from that a compensation waveform. With MECC, a uniformity machine with a loadwheel in less than ideal condition can continue operating and reliably testing tires.
We’ve just explained how MECC compensates for deficiencies with the loadwheel, but the great news is that we have a MECC process for rims and spindle adapters also!