Calculate Tire Combination - (on 6105R to 6125R Tractors)

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”

    Transmission

    SRI

    Gear pair

    		  

    PowrQuad™ transmission 16/16, 30 km/h

    700 - 725

    47/10

    4.7

    750 - 825

    53/10

    5.3

    PowrQuad™ transmission 16/16, 40 km/h

    700 - 800

    47/12

    3.917

    825

    49/11

    4.455

    PowrQuad™ transmission 24/24, 40 km/h

    700 - 725

    47/10

    4.7

    750 - 825

    53/10

    5.3

    PowrQuad™ transmission 24/24, 50 km/h

    700 - 775

    47/12

    3.917

    800 - 825

    49/11

    4.455

    AutoPowr™ transmission, 40 km/h and 50 km/h

    700 - 825

    49/11

    4.455

  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”

    Transmission

    SRI

    		  

    PowrQuad™ transmission 16/16, 30 km/h

    550 - 650

    700 - 825

    15.692

    750 - 775

    875

    19.091*

    PowrQuad™ transmission 16/16, 40 km/h

    550 - 625

    700 - 800

    13.125

    600 - 650

    825

    15.692

    PowrQuad™ transmission 24/24, 40 km/h

    550 - 650

    700 - 825

    15.692

    PowrQuad™ transmission 24/24, 50 km/h

    550 - 600

    700 - 775

    13.125

    600 - 650

    800 - 825

    15.692

    AutoPowr™ transmission, 40 km/h and 50 km/h

    550 - 650

    700 - 825

    15.692

    * Not with suspended front axle with brake

  3. The transmission ratio of gear pair for front-wheel drive axle output is “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”

    • 1.373

    • 1.491

    • 1.615

    • 1.750

    • 1.406

    • 1.522

    • 1.648

    • 1.784

    • 1.436

    • 1.553

    • 1.683

    • 1.826

    • 1.466

    • 1.583

    • 1.716

    • 1.861

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 “A2”.

  4. From the manual, ascertain the rolling circumference of the tire desired for the front wheel “A1”.

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  7.0714 

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

Transmission ratio of the
required gear pair

(corresponds to a positive front wheel lead of 1.5 - 4.0%)

(corresponds to desired average value of positive front wheel lead)
 

1.356 — 1.390

1.373

1.391 — 1.421

1.406

1.422 — 1.451

1.436

1.452 — 1.479

1.466

1.480 — 1.505

1.491

1.506 — 1.538

1.522

1.539 — 1.566

1.553

1.567 — 1.598

1.583

1.599 — 1.630

1.615

1.631 — 1.664

1.648

1.665 — 1.700

1.683

1.701 — 1.733

1.716

1.734 — 1.767

1.750

1.768 — 1.804

1.784

1.805 — 1.843

1.826

1.844 — 1.884

1.861

Sample calculation

The intention is to fit a tractor with 18.4R38 and 13.6R28 tires, made by a certain manufacturer.

  1. The transmission ratio of differential gear pair “I3” is  4.455 .

  2. The transmission ratio of front axle “I2” is  15.692 .

  3. The transmission ratio of rear axle ”I1” is  7.0714 .

  4. The transmission ratio of the currently installed gear pair “I” for the front-wheel drive axle output is 1.648.

  5. The rolling circumference of tire “A2” on the rear wheel is  5258  mm (207.0 in.)

  6. The rolling circumference of tire “A1” on the front wheel is  3893  mm (153.7 in.).

  7. Calculate the overall transmission ratio.

 

3893 x 7.0714 x 4.455 x 100

= 1.447

5258 x 15.692 x 102.75

The required gear pair must have the transmission ratio 1.436.

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
  • Replace oil sight-glass

OULXA64,0002D66-19-20130109