Tire Combinations (Tractors with Front-Wheel Drive)

The size ratio of the front wheels to the rear ones is precisely determined in order to produce a positive front wheel lead of between 1.5 and 4%. Otherwise the tires will become deformed or suffer undue wear. To ascertain the correct ratio when changing tires, proceed as follows:

Ascertain tractor data:

1. Transmission ratio of the differential gear pair. This information is displayed on the transmission serial number plate. The following pairs are possible:

   	Gear pair	Transmission ratio
   	47/10	4,700
   	53/10	5,300
   	51/9	5,667
   	47/8	5,875

2. Transmission ratio of front axle. This figure is displayed on the front axle serial number plate. The following ratios are possible:

   • 13,125
   • 15,692
   
   

3. Transmission ratio of gear pair for front-wheel drive axle output. This information is displayed on the transmission serial number plate. The following ratios are possible:

   • 1,446 IVT
   • 1,465 IVT
   • 1,497 IVT
   • 1,532 IVT
   • 1,564 IVT
   • 1,597 IVT
   • 1,625 IVT
   • 1,658
   • 1,692
   • 1,725
   • 1,760
   • 1,795
   • 1,833
   • 1,870
   • 1,907
   • 1,943
   • 1,990
   • 2,028
   
   

For tractors with IVT, only the ratios marked with the letters IVT are applicable.

Ascertain tire data:

1. Select tires with suitable load-bearing capability.

2. Select tires appropriate to the tractor's top speed.

3. From the manual, ascertain the rolling circumference of the tire desired for the rear wheel.

4. From the manual, ascertain the rolling circumference of the tire desired for the front wheel.

Ascertain the following data:

IMPORTANT: If a new pair of tires is selected, the Basic Control Unit (BCU) must be recalibrated; if the tractor has IVT, the User Interface Controller (UIC) and ground speed sensor (radar) must be recalibrated as well. See your John Deere dealer.

If the new rear tires have a higher SRI (speed/radius index) than the previous ones, the tractor's electronics must be recalibrated by your John Deere dealer.

Calculate the overall transmission ratio using the following formula:

		A1 * I1 * I3 * 100
	I =
		A2 * I2 * 102.75
	A1 =	Rolling circumference of front tires
	A2 =	Rolling circumference of rear tires
	I1 =	Rear axle ratio (7.0714)
	I2 =	Transmission ratio of front axle
	I3 =	Transmission ratio of the differential gear pair

Calculated transmission ratio	Transmission ratio of the required gear pair
(corresponds to a pos. front wheel lead of 1.5 - 4.0%)	(corresponds to desired average value of pos. front wheel lead)
1,428 — 1,451	1,446
1,452 — 1,479	1,465
1,480 — 1,514	1,497
1,515 — 1,548	1,532
1,549 — 1,580	1,564
1,581 — 1,614	1,597
1,615 — 1,645	1,625
1,646 — 1,672	1,658
1,673 — 1,711	1,692
1,712 — 1,739	1,725
1,740 — 1,779	1,760
1,780 — 1,812	1,795
1,813 — 1,853	1,833
1,854 — 1,886	1,870
1,887 — 1,926	1,907
1,927 — 1,964	1,943
1,965 — 2,011	1,990
2,012 — 2,062	2,028

Ascertain the gear pair that is appropriate for the overall transmission ratio.

Sample calculation

The intention is to fit a 6430 tractor with 600/65R38 and 540/65R24 tires, made by a certain manufacturer.

1. The transmission ratio of the differential gear pair is 5.667.

2. The transmission ratio of the front axle is 15.692.

3. The transmission ratio of the gear pair for the front wheel drive axle output is 1.870.

4. The rolling circumference of the tire on the rear wheel is 5263 mm (207.2 in.).

5. The rolling circumference of the tire on the front wheel is 3923 mm (154.4 in.).

6. Calculate the overall transmission ratio.

3923 * 7,0714 * 5,667 * 100
	= 1,852
5263 * 15,692 * 102,75

The gear pair that is required must have a ratio of 1.833.