Understanding basic tire information
7R Series Tractor

7R Series Tractor

8R Series Tractor

8R Series Tractor

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 when equipped with a mechanical front-wheel drive (MFWD).
 
Reference the 8R Series Tractor tire offerings story for 8R front and rear tire matching guidelines.
 
Reference the 7R Series Tractor tire offerings story for 7R front and rear tire matching guidelines.
 
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.
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 (percentage of sidewall height to section width)
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

 

 

600/70R28

600/70R30

 

Rear

  Group 47

Group 48

Group 49

 

380/90R50
(14.9R50)

380/90R54

480/95R50
710/75R42

 

480/80R45
(18.4R46)

480/80R50

   

 

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 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).
Load index chart
 

International load index numbers (per tire)

Load index

lb

kg

Load index

lb

kg

135

4800

2180

163

10700

4875

136

4940

2240

164

11000

5000

137

5080

2300

165

11400

5150

138

5200

2360

166

11700

5300

139

5360

2430

167

12000

5450

140

5520

2500

168

12300

5600

141

5680

2575

169

12800

5800

142

5840

2650

170

13200

6000

143

6000

2725

171

13600

6150

144

6150

2800

172

13900

6300

145

6400

2900

173

14300

6500

146

6600

3000

174

14800

6700

147

6800

3075

175

15200

6900

148

6950

3150

176

15700

7100

149

7150

3250

177

16100

7300

150

7400

3350

178

16500

7500

151

7600

3450

179

17100

7750

152

7850

3550

180

17600

8000

153

8050

3650

181

18200

8250

154

8250

3750

182

18700

8500

155

8550

3875

183

19300

8750

156

8800

4000

184

19800

9000

157

9100

4125

185

20400

9250

158

9350

4250

186

20900

9500

159

9650

4375

187

21500

9750

160

9900

4500

188

22000

10000

161

10200

4625

189

22700

10300

162

10500

4750

190

23400

10600

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 cane and rice or other crops grown in wet muck 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 (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. 
 
Last Updated : 25-Jul-2013