
 8R Series Tractor 

 The tire industry has been converting 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 index number or group size designation (regardless of tire width or rim diameter) if their rolling circumferences are similar.
Understanding tire group size is important for proper tractor setup when equipped with an MFWD or IndependentLink Suspension (ILS™).
  
 Front axle marked with “5” 

 Tractors equipped with a 1300 Series MFWD axle always have front tires that are five group sizes smaller than the rear tire group size. Tractors with IndependentLink Suspension or the 1500 Series MFWD axle can be ordered with front/rear tire combinations that are four or five group sizes different. However, when tires are selected during the ordering process of the tractor, a “4” or “5” marking will be placed on the front axle. All replacement tires installed on the tractor must match the group size difference (four or five steps).
NOTE: The group size marking (4 or 5) is located on the front axle just to the left of the steering cylinder on the left side of the tractor.
Mismatched tire sizes effect electronic transmission control, which may vary tractor ground speed. Mismatched tires may also increase wear on the tires and drivetrain components.
The metric tire rating system allows manufacturers to design tires that better meet specification requirements for diametertowidth 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. 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 =
18.89in section width tire 
Formula for English to
metric to conversion:
multiply English number (in inches)
by 25.4 to get millimeters 
Example:
18.4in 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 
540/75R34 

320/85R38 
380/80R38 
620/75R30 

380/80R34
(14.9R34)

420/85R34 


420/9030
(16.9R30)

480/70R34 


480/70R30
(18.4R30)

540/65/R34 


600/70R28 
600/70R30 

Rear 
Group 46 
Group 47 
Group 48 

420/80R46 
380/90R50
(14.9R50)

380/90R54 

480/80R42
(18.4R42)

480/80R45
(18.4R46)

480/80R50


520/85/R38
(20.8R38)

520/85R42
(20.8R42)

520/85R46 


620/70R42 
620/70R46 


710/70R38 
710/70R42 



800/70R38 

Group 46 
Group 47 
Group 48 

420/80R46 
380/90R50
(14.9R50)

380/90R54 
  
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, a 157 LI means the tire has a maximum loadcarrying 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 9,100 lb x 2 tires). The loadcarrying capacity per tire is reduced by 12 percent when the tires are used in dual application so there would be 14520 kg (32,030 lb) carrying capacity for the axle (4125 x 0.88 x 4 tires or 9,100 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)
Tread designation  The tread designation is used to describe the tread and indicate tire usage. Designs offered are all lug or bartype tires and are separated into one of three specifications: R1, R1W, or R2.
R1 is a standard tread and is used primarily for general dryland 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 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 widespaced 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 rowcrop 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.
  



Last Updated : 25Jul2013 
 
 