Tire Facts, Some Basic Tire Information Group sizes The tire industry has converted to metric size designations when describing agricultural tires. In addition, tires are placed into groups by their rolling circumference index (RCI), commonly referred to as group size. Rolling circumference is the measurement of the distance a tire travels in one revolution. Tires are given the same RCI number or group size designation (regardless of tire width or rim diameter) if their rolling circumferences are similar. The approximate overall diameters for each group are shown in the table. Group Overall diameter 42 1498 mm (59 in.) 43 1600 mm (63 in.) 44 1676 mm (66 in.) 47 1955 mm (77 in.) 48 2057 mm (81 in.) 49 2172 mm (85.5 in.) Understanding tire group size is important for proper tractor setup, with regard to maintaining proper tire overspeed between axles. This means that tires must be properly matched to ensure proper step reduction of group size in order for front tires to rotate at the proper speed relative to rear tires. Mismatched tire sizes affect electronic transmission control, which may vary tractor ground speed. Mismatched tires may also increase wear on the tires and drivetrain components Reference the 8R Series Tractor tire offerings for 8R front and rear tire matching guidelines. Reference the 7R Series Tractor tire offerings for 7R front and rear tire matching guidelines. Tire terminology The metric tire rating system allows manufacturers to design tires that better meet specification requirements for diameter-to-width and rolling circumference dimensions, which are critical for MFWD tires. Specific tire information is often available from the tire manufacturer, dealer, or the John Deere online configurator/Build Your Own tool. Tire terminology for both standard and metric tires is described below. Standard size tire 18.4R46 18.4 = tire section width (inches) R = radial construction 46 = rim diameter (inches) (this is not the total tire height or group size) Metric size tire 520/85R42 158 A8 R1 520 = tire section width (mm) 85 = aspect ratio R = radial construction 42 = rim diameter (inches) (this is not the total tire height or group size) 158 = load index A8 = speed symbol R1 = tread designation NOTE: Detailed tire terminology definitions are described below. Common conversions between metric and standard tire sizes Tire size conversion chart Inch size Metric conversion (mm) 11.4 290 12.4 315 12.6 320 13.6 345 14.9 378 15.0 380 16.5 420 16.9 429 18.4 467 18.9 480 20.5 520 20.8 528 22.8 580 23.1 587 23.6 600 24.4 620 25.6 650 28.0 710 30.0 750 30.5 775 31.5 800 35.4 900 Formula for metric- to-English conversion: divide the metric number (in mm) by 25.4 to get inches Example: 480-mm section width/25.4 = 18.89-in. section width tire Formula for English-to- metric conversion: multiply English number (in inches) by 25.4 to get millimeters Example: 18.4-in. section width X 25.4 = 467-mm section width tire Common tire sizes by group size Front Group 42 Group 43 Group 44 290/90R38 320/80R42 380/80R42 320/85R38 380/80R38 420/85R38 380/80R34 (14.9R34) 420/85R34 540/75R34 420/9030 (16.9R30) 480/70R34 620/75R30 480/70R30 (18.4R30) 540/65/R34 600/65R34 600/70R28 600/70R30 650/60R34 Rear Group 47 Group 48 Group 49 380/90R50 (14.9R50) 320/105R54 380/90R54 480/95R50 710/75R42 480/80R45 (18.4R46) 480/80R50 900/60R42 520/85R42 (20.8R42) 520/85R46 620/70R42 620/70R46 710/70R38 710/70R42 800/70R38 NOTE: Not all tires listed in the chart are available on all John Deere Tractors. See your local John Deere dealer for assistance in choosing the proper tires for specific tractor models. Tire terminology definitions Aspect ratio - Number that provides the tire sidewall height relative to the tire width. Load index (LI) - A uniform method to report the load-carrying capacity of a tire. For example, 157 LI (see LI chart below) means the tire has a maximum load-carrying capacity of 4125 kg (9100 lb) at the speed specified by the speed symbol when the tire is inflated to its rated inflation pressure. When a tire is used in single application, there would be 8250-kg (18,200-lb) carrying capacity for the axle (4125 kg x 2 tires or 9100 lb x 2 tires). The load-carrying capacity per tire is reduced by 12 percent when the tires are used in dual application, so there would be 14,520-kg (32,030-lb) carrying capacity for the axle (4125 x 0.88 x 4 tires or 9100 x 0.88 x 4 tires). When comparing tires, the higher the load index number, the higher the load capacity. Example of load index based on tire size: A 520/85R42 with a 157 LI and an A8 speed symbol has a maximum load of 4125 kg (9100 lb) at the required cold inflation pressure of 159 kPa (23 psi) and maximum speed of 40 km/h (25 mph). A 480/80R46 with a 158 LI and an A8 speed symbol has a maximum load of 4250 kg (9350 lb) at the required cold inflation pressure of 241 kPa (35 psi) and maximum speed of 40 km/h (25 mph). Speed symbol - The top speed a tire is designed to travel. A8 is rated for 40 km/h (25 mph). B is rated for 50 km/h (31 mph). D is rated for 65 km/h (40 mph). The speed symbol designation alone does not determine suitability for use on 50 km/h tractors. Tire/wheel assemblies for 50-km/h tractors are specified by John Deere to tighter run out (the amount of sideways motion or wobble in a wheel or tire as it rotates) requirements than for non-50-km/h tractors. The low point of the tire radial run out and the high point of the wheel assembly are determined by measurement and marked by the supplier. The low point of the tire is aligned with the high point of the wheel during assembly by the supplier. The purpose of this requirement is to reduce assembly run out in order to provide improved ride quality. This assembly process is referred to as match mounting. Tread designation - The tread designation is used to describe the tread and indicate tire usage. Designs offered are all lug- or bar-type tires and are separated into one of three specifications: R1, R1W, or R2. R1 is a standard tread and is used primarily for general dry-land farming. These tires have the shortest lug height and the narrowest spacing between lugs. R1W is a wet traction tread for wet, sticky soil conditions. This tread fills the gap between R1 and R2 tires having a deeper lug with wider spacing than R1 tires but shorter and narrower than R2. R1W is defined as having a lug height about 20 percent deeper than an equivalent R1 tire, but this could vary from 15 percent to 35 percent depending on the tire and manufacturer. R2 is a tread type used typically with crops grown in wet soils or flooded fields. Tread depth of R2 tires is approximately twice as deep as R1 tires. R2 tires also have the widest spacing between lugs to allow mud to shed easier. The wide-spaced lugs can show extra wear and cause problems with vibration when roading. R2 tires may not pull as well as R1 or R1W tires in drier soil conditions found in most row-crop applications. Typically, tires with R2 tread should be matched on the front and rear of a tractor while R1 and R1W treads can be mixed or matched on the same tractor to meet requirements or preference. Turning radius Turning radius (1) Turning radius is measured from the center of the turn to the center of the outside tire (1). Refer to the operator’s manual for tread settings information
Posted on: Wed, 22 Oct 2014 12:48:30 +0000
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