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Drivetrain Crawl Ratio & Gear Tooth Ratio

Multiply transmission, transfer-case and axle ratios, and calculate a separate axle ratio from ring and pinion tooth counts.

  • Formula & worked example
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Calculator inputs

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How to use this calculator

  1. Enter the known values in the units shown. Results update as you type.
  2. Where results are editable, change one to solve backwards. Lock a value to hold it fixed.
  3. Use the worked example to check the method. Reset restores the starting fields.

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Inputs and results stay in this browser tab. Bookify does not upload or store the values you enter.

Formula and method

Transmission 4:1, transfer case 2:1 and axle 4:1 produce a 32:1 crawl ratio.

Crawl ratio = transmission × transfer × axle; tooth ratio = ring teeth / pinion teeth

Worked example

Enter these known values and leave the other values blank.

Transmission ratio (TG)
4 : 1
Transfer gear ratio (TCG)
2 : 1
Axle gear ratio (AGR)
4 : 1
Number of ring gear's teeth
41
Number of pinion's teeth
10
Crawl ratio
32 : 1
Axle gear ratio
4.1

Assumptions and limitations

  • Ratios are positive input-to-output speed reductions. Tooth counts must be positive integers.
  • The tooth-count section is independent: its result is not automatically copied into the axle-ratio input above. Enter it there to include it in the drivetrain product.
  • This ideal ratio excludes tire radius, converter slip and mechanical loss. It does not determine wheel force or vehicle capability.

Common questions

What should I check before using this result?

Ratios are positive input-to-output speed reductions. Tooth counts must be positive integers.

References

The calculation equations, inverse formulas, units, and input rules were imported from this source. Bookify provides the interface and equation solver.

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