Tires/Propshaft - Speed Reference Chart (Vibration)
87chevy26Number: 88-45
Section: 0A
Date: Sept., 1987
Subject: TIRE AND PROPSHAFT SPEED REFERENCE CHART
Model and Year: ALL LIGHT DUTY TRUCKS
TO: ALL CHEVROLET DEALERS
Reed Tachometer usage requires calculating the speed of rotating components on a vehicle and relating it to the frequency of a vibration (reference Chevrolet Dealer service Bulletin 87-139 for Reed Tachometer usage instructions). The chart below was developed to simplify calculating driveline, wheel and tire RPM.
The procedure for using this chart is as follows:
- Determine the vehicle tire size and rear axle ratio.
- Drive vehicle and note the speed range that the vibration occurs at and the vibration frequency (using a Reed Tachometer).
- Locate the tire size in the first column that corresponds to the vehicle tire size. Select the speed range that the vibration occurs in and note the tire RPM. For example, a P215/60R14 tire turns 792 RPM at 55 mph.
- Calculate the propshaft RPM by multiplying the tire
RPM by the rear axle ratio. For example, 792 (tire RPM) x 3.08 (axle ratio) 2439 propshaft revolutions per minute.
- Relate the vibration frequency to the speed of the propshaft or wheels and tires. For example, a first order tire vibration in the above example would excite the 800 CPM reed on the Reed Tachometer.