Issue link: https://read.dmtmag.com/i/34500
DEFINITIONS Standard and Low Profile radial truck tire sizes can be more easily understood by breaking down the formula into the three components: the section width in inches or millimeters, aspect ratio, and rim/wheel diameter. 1. Tire Size: Standard Size example: 11R22.5 – 11 inch nominal section width, with a height between 90 and 100% of the section width – R = radial – 22.5 wheel diameter Low Profile example: 445/50R22.5 – 445 millimeter nominal section width – 50 is the aspect ratio expressed as a height to width percentage – R = radial – 22.5 wheel diameter 2. Aspect Ratio: A nominal number, which represents the section height, divided by the section width expressed as a percentage. Example 445/50R22.5 Aspect Ratio = 50 3. Rims: The approved/preferred rims are designated for each size tire. MICHELIN ® X One tires should only ® be mounted on the rims shown in the application specific data book. 4. Overall Width: The maximum width (cross section) of the unloaded tires including protruding side ribs and decorations as measured on the preferred rim. Overall width will change 0.1 inch (2.5 mm) for each 1⁄4 inch change in rim width. 5. Overall Diameter: The diameter of the unloaded new tire (measured from opposite outer tread surfaces). 6. Free Radius: One-half the overall diameter of the unloaded new tire. 7. Nominal Wheel Diameter: Diameter of rim seat supporting the tire bead given in nearest whole numbers, e.g. 22.5". 8. Section Height: The distance from rim seat to outer tread surface of unloaded tire. 9. Loaded Radius: The distance from the wheel axle centerline to the supporting surface under a tire properly inflated for its load according to the load and inflation tables. 10. Deflection Appendix 71 7. Nominal Wheel Diameter 9. Loaded Radius 10. Tire Deflection: Free radius minus the loaded radius. 11. Tire Revolutions Per Mile: Revolutions per mile for a tire size and tread is defined as the number of revolutions that the new tire will make in one mile. Data is normally presented for the loaded tire at its rated load and inflation in the drive position. Tire revolutions per mile (Tire Revs./Mile) can be determined by measuring using SAE J1025 or estimated by calculating using a mathematical equation. Michelin Equation: Tire Revs./Mile = 20,168 ⁄(O.D. - .8d) O.D. = Overall Diameter d = Correction for deflection d = (O.D. ⁄2) – SLR SLR = Static Loaded Radius (MICHELIN Truck Tire Service Manual - MWL40732) At Michelin, the tire revolutions per mile are officially determined using the Society of Automotive Engineers (SAE) Recommended Practice. The test tires are placed as singles on the drive axle of the test vehicle and set to the corresponding pressure. The vehicle is then driven over a straight 2-mile section at 45 mph while the number of revolutions are counted. (Since speed minimally affects the results for radial tires, other speeds are allowed.) Averaging 4 runs that are within 1% of each other then derives the tire’s revolutions per mile measurement. 4. Overall Width 8. Section Height 6. Free Radius 3. Rim Width 5. Overall Diameter C L