Radial Runout
Radial RunoutRadial runout is the egg-shaped deviation from a perfect circle and is measured perpendicular on a circumference. On a wheel and tire assembly this usually means measuring the center tire tread rib, although other tread ribs can be measured as well. The center rib is usually a solid rib, easy to measure and normally indicative of the condition of the tire as a whole. It is important to keep in mind that any rib with excessive runout can cause a concern. Total runout is the reading from the gauge. The high spot is the location of maximum runout.
NOTE: Warm up the tires prior to taking any measurements, this will eliminate slight flat spotting. This is done during a road test.
1. CAUTION: Use only special tool 204-354, any time tire pressures are measured, to be sure that accurate values are obtained.
CAUTION: Place the air chuck straight on the valve stem to inflate the tire. Do not cock the air chuck during the inflation cycle. Doing so can damage the valve stem and cause air leaks.
CAUTION: Ford Motor Company suggests using a round head air chuck on tire pressure sensors; it is not recommended to use air chucks with long shanks. Doing so can cause tire pressure sensor valve stem damage and loss of tire pressure.
Make sure that the tire pressures are set to the correct pressure as indicated on the vehicle label.
2. With the vehicle in NEUTRAL, position it on a hoist. Refer to Vehicle/Testing and Inspection.
3. Make sure that all 4 positions can be measured. If measurements are to be taken with the wheel and tire assembly off the vehicle, mount each assembly on a suitable dynamic balancing machine.
4. For future reference of the original wheel and tire assemblies position on the wheel hub, index-mark the wheel and a wheel stud.
5. Position the runout gauge to take a radial measurement.
^ Rotate the wheel and tire assembly (or wheel) to locate the low spot.
^ Adjust the runout gauge to read 0.
^ Rotate the wheel and tire assembly (or wheel) one complete revolution to make sure that the low spot has been found and that the runout gauge dial returns to a 0 reading.
6. NOTE: If there is a vast difference in measurements taken from a wheel and tire assembly checked (on the vehicle) compared to readings taken (off the vehicle), check for excessive bolt circle runout, excessive hub runout or a fitting concern between the hub and wheel.
While slowly and constantly rotating the wheel and tire assembly (or wheel), measure the radial runout.
^ Note the variance (runout) from 0 on the dial of the gauge.
^ If the runout reading of a wheel and tire assembly is not within 1.27 mm (0.050 inch), locate and mark the high spot and proceed to Match Mounting Step 1 to correct the concern.
^ If the runout reading of a wheel is not within 1.27 mm (0.050 inch), install a new wheel.