How this calculator works
Speed reductions in series multiply. A numerically larger crawl ratio turns the wheels more slowly for the same engine speed and increases ideal wheel torque by the same factor. Enter numerical ratios such as 4.1, not ratio strings. The tooth-count modes refer to the axle ring and pinion only. Tyre size, converter slip, traction and drivetrain losses are outside this kinematic ratio.
Formula
Crawl ratio = transmission ratio × transfer-case ratio × axle ratio; axle ratio = ring teeth / pinion teeth.
Worked example
A 4:1 first gear, 2.5:1 low range and 4:1 axle produce 40:1 overall. A 41-tooth ring driven by a 10-tooth pinion has an axle ratio of 4.1:1.
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Frequently asked questions
Does tyre diameter change crawl ratio?
No. It changes road speed and contact force at a given wheel torque, but not the rotational gear reduction.
Does this include torque converter multiplication?
No. Converter behaviour varies with operating conditions and cannot be represented by a fixed gear ratio.
Can the answer be a fractional tooth count?
An actual gear needs whole teeth. Inverse tooth modes reject ratios inconsistent with a whole count.