Issue link: http://read.dmtmag.com/i/34501
DETERMINING MICHELIN TIRE SIZE 1. Tire Size: MICHELIN radial truck tire sizes are ® designated by the nominal section width in inches or millimeters and the rim diameter (e.g. 11R22.5 or 275/80R22.5). The “R” indicates a radial tire. Truck tire sizes contain dimension and load index information and are marked in accordance with industry standards: FMVSS (Federal Motor Vehicle Safety Standard), TRA (The Tire and Rim Association, Inc.), ETRTO (European Tyre and Rim Technical Organisation), and ISO (International Standardization Organization). This index indicates the load capacity of the tire in single and in dual usage (e.g. 144/141K). See Appendix under General Information (Page 116) for complete ISO load index. Below are examples for tubeless tires. (See Section Seven for tube-type tire information.) Example: 11R22.5 11 = nominal cross section in inches R = radial 22.5 = rim or wheel diameter in inches Example: 275/80R22.5 LRG 144/141K 275 = nominal cross section in mm (metric) 80 = aspect ratio R = radial 22.5 = rim or wheel diameter in inches LRG = load range G 2. 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. Minimum dual spacing should be adjusted accordingly. 3. Nominal Wheel Diameter: Diameter of rim seat supporting the tire bead given in nearest half-inch numbers, e.g. 22.5". 4. Overall Diameter: The diameter of the unloaded new tire (measured from opposite outer tread surfaces). 5. Section Height: The distance from rim seat to outer tread surface of unloaded tire. 6. Aspect Ratio: A nominal number, which represents the section height, divided by the section width and expressed as a percentage. Example: Tire Size Aspect Ratio 11R22.5 90 275/80R22.5 80 445/50R22.5 50 7. Free Radius: One-half the overall diameter of the unloaded new tire. 8. 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 found in the application specific data books. See Appendix for listing of publications under Publications, Videos, and Websites (Page 139). 9. Tire Deflection: Free radius minus the loaded radius. 10. Minimum Dual Spacing: The minimum allowable lateral distance from tire tread centerline to tire tread centerline in a dual wheel arrangement. 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. Rolling circumference can be calculated from the revolutions per mile as follows: 63,360 COMPARATIVE SIZES LOW-PROFILE – STANDARD PROFILE MICHELIN 235/80R22.5 255/80R22.5 275/80R22.5 275/80R24.5 TRA 245/75R22.5 265/75R22.5 295/75R22.5 285/75R24.5 ® REPLACES 9R22.5 10R22.5 11R22.5 11R24.5 COMPARATIVE MICHELIN X ONE TIRE SIZES DUAL SIZE ® 11R22.5, 275/80R24.5 275/80R22.5 6 Section One: Tire Selection MICHELIN X ONE TIRE SIZE 455/55R22.5 445/50R22.5 ® ® Tire Revs./Mile = Rolling circumference in inches The tire revolutions per mile can be determined by measuring (using SAE J1025) or estimated by using a mathematical equation. See Appendix under Tire Revolutions Per Mile Calculation (Page 131). The accuracy of the tire revolutions per mile number is ±1%. 12. Rims: The approved/preferred rims are designated for each size tire. MICHELIN ® tires should only be mounted on the rims shown. The rim shown first is the preferred rim. Be sure to check rim manufacturer’s specifications.