Another item that may cause actual rates of seed or fertilizer to differ from delivery rates shown in the operator's manual is the amount of drive-wheel slippage.

While a certain amount of wheel slippage is normal, excessive drive-wheel slippage may cause undesirable changes in actual rates.

The rates shown in the operator's manual are based on approximately 12 percent drive wheel slippage.

Excessive drive-wheel slippage may be caused by binding or poorly lubricated parts, misaligned bearings or caked material in pesticide or fertilizer hoppers.

Down pressure springs, coulters, tine tooth attachments, or any other attachment that removed weight from drive wheels, may contribute to drive-wheel slippage and lower than expected rates.

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The amount of excessive drive-wheel slippage can be calculated.

1. Mark a length of field that would normally represent 30 drive wheel revolutions. Use the following formula to calculate the length of field to drive.

FORMULA:

Revolutions x Drive Wheel Rolling Circumference = Length of Field to Drive

EXAMPLE:

• 30 revolutions x 2.5 m = 75 m
• 30 revolutions x 8.3 ft = 250 ft

2. Mark drive wheel with a rubber hold-down strap, reflective tape or duct tape. This will help to count wheel revolutions.

3. With all rows planting under normal field conditions, drive a 76 m (250 ft) course at normal planting speed while another person counts drive-wheel revolutions.

4. Subtract number of revolutions observed over the course length from 30. Then divide this difference by 30.

EXAMPLE:

If 28 wheel revolutions are observed, there is 6.6 percent drive-wheel slippage.

30 - 28 = 2

2 ÷ 30 = 0.066

If drive-wheel slippage is greater than or less than 12 percent (baseline slippage), adjust seed transmission to obtain desired population.

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