Calculate Tire Combinations - (on Tractors 6170R to 6210R)

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:

Also see illustration in this section.

1. The transmission ratio of the differential gear pair is “I3”. These values are displayed on the product information plate on the left side of the radiator. The following pairs are possible:

   Transmission ratio of differential ..............		“I3”
   	Gear pair
   PowrQuad™ transmission, 50 km/h AutoPowr™ transmission	48/10	4.8
   PowrQuad™ transmission, 40 km/h DirectDrive transmission	52/10	5.2

2. The transmission ratio of the front axle is “I2”. This figure is displayed on the front axle serial number plate. The following ratios are possible:

   Transmission ratio of front axle ..............		“I2”
   • 6170R to 6210R ..............		13.160

3. The transmission ratio of gear pair for front wheel drive axle output “I”. These values are displayed on the product information plate on the left side of the radiator. The following pairs are possible:

   Transmission ratio of front wheel drive axle output “I”
   PowrQuad™ transmission, 50 km/h AutoPowr™ transmission	PowrQuad™ transmission, 40 km/h DirectDrive transmission
   • 1.697	• 1.833
   • 1.727	• 1.875
   • 1.758	• 1.917

Ascertain tire data:

1. Select tires with suitable load capacity.

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:

Calculate the overall transmission ratio using the following formula.

	I =	A1 x I1 x I3 x 100
		A2 x I2 x 102.75
A1 =	Rolling circumference of front tires
A2 =	Rolling circumference of rear tires
I1 =	Rear axle ratio is  6.40
I2 =	Transmission ratio of front axle
I3 =	Transmission ratio of the differential gear pair
102.75 =	A fixed value to determine the required front wheel lead

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

Calculated transmission ratio “I”		Transmission ratio of the required differential gear pair
(corresponds to a positive front wheel lead of 1.5 - 4.0%)		(corresponds to desired average value of positive front wheel lead)
PowrQuad™ transmission, 50 km/h AutoPowr™ transmission	1.676 — 1.713	1.697
	1.714 — 1.740	1.727
	1.741 — 1.779	1.758
PowrQuad™ transmission, 40 km/h DirectDrive transmission	1.811 — 1.854	1.833
	1.855 — 1.895	1.875
	1.896 — 1.940	1.917

Sample calculation

The intention is to fit a tractor with 710/70R38 and 600/65R28 tires, made by a certain manufacturer.

1. The transmission ratio of differential gear pair “I3” is  5.2 .

2. The transmission ratio of front axle “I2” is  13.16 .

3. The transmission ratio of rear axle ”I1” is  6.40 .

4. The transmission ratio of the currently installed gear pair “I” for front wheel drive axle output is 1.833.

5. The rolling circumference of the tire “A2” on the rear wheel is  5780  mm (227.6 in.).

6. The rolling circumference of tire “A1” on the front wheel is  4444  mm (175.0 in.).

7. Calculate the overall transmission ratio.

	4444 x 6.40 x 5.2 x 100	= 1.892
	5780 x 13.160 x 102.75

The required gear pair must have the transmission 1.875.

IMPORTANT: In this example, the gear pair that is currently installed for front-wheel drive axle output must be replaced with a different pair.

IMPORTANT: If the transmission ratio is changed, the following service must be performed by a John Deere™ dealer:

• Change the gear pair for the front-wheel drive output
• Change tire size in the software of the control units