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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. These values are displayed on the product information plate on the l.h. side of the radiator. The following pairs are possible:
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Gear pair |
Transmission ratio |
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48/10 |
4,8 |
2.
Transmission ratio of front axle. This figure is displayed on the front axle serial number plate. The following ratios are possible:
3.
Transmission ratio of gear pair for front-wheel drive axle output. These values are displayed on the product information plate on the l.h. side of the radiator. The following pairs are possible:
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:
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IMPORTANT:
Tires used on the front wheels must have a Speed Radius Index (SRI) of 700 mm (27.6 in.).
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 (6.40) |
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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) |
| 1,676 - 1,713 |
1,697 |
| 1,714 - 1,740 |
1,727 |
| 1,741 - 1,779 |
1,758 |
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 the differential gear pair is 4.8.
2.
The transmission ratio of the front axle is 13.160.
3.
The transmission ratio of the gear pair for the front wheel drive axle is 1.727.
4.
The rolling circumference of the tire on the rear wheel is 5812 mm (228.8 in.).
5.
The rolling circumference of the tire on the front wheel is 4398 mm (173.1 in.).
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