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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 type plate. The following pair is possible:
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Gear pair |
Transmission ratio |
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47/10 |
4,700 |
2.
Transmission ratio of front axle. This figure is displayed on the front axle serial number plate. The following ratio is possible:
3.
Transmission ratio of gear pair for front-wheel drive axle output. This figure can be found on the transmission serial number plate. The following ratios are possible:
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1,446
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1,465
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1,497
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1,532
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1,564
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1,597
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1,625
Ascertain tire data:
This information must be ascertained from the tire manufacturer's manual.
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.
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4.
From the manual, ascertain the rolling circumference of the tire desired for the front wheel.
Ascertain the following data:
IMPORTANT:
If a different tire combination is selected, or new rear tires are selected with an SRI (speed/radius index) higher 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:
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A1 * I1 * I3 * 100 |
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I = |
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A2 * I2 * 102.75 |
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A1 = |
Rolling circumference of front tires |
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A2 = |
Rolling circumference of rear tires |
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I1 = |
Rear axle ratio (7.0714) |
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I2 = |
Transmission ratio of front axle |
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I3 = |
Transmission ratio of the differential gear pair |
Ascertain the gear pair that is appropriate for the overall transmission ratio.
| 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 |
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 4.700.
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