Crawl Ratio Calculator

Calculate the crawl ratio of a vehicle from the transmission ratio, transfer case ratio, and axle gear ratio.

Gear ratio42.4:14 × 10.6 across two stages

TypeReductionslower and stronger at the output

Output speed18.868 rpm0.3145 revolutions a second

Output torque15,957.664 N·m11,769.769 lbf·ft

Torque multiplication39.8942×the ratio less 5.91% lost to friction

Input power33.5103 kW

Output power31.5299 kWpower is what a gearbox cannot increase — only redistribute between torque and speed

Power lost as heat1.9805 kW

Hunting ratio?yes — tooth counts are coprimeevery tooth on one gear eventually meets every tooth on the other, so wear spreads evenly

Revolutions of the driving gear per output turn42.4

The formula

ratio = driven teeth ÷ driving teeth; torque and speed trade inversely

Torque and speed, never both

A gear ratio is the driven tooth count divided by the driving one. Above one it is a reduction: the output turns more slowly and with proportionally more torque. Below one it is an overdrive, trading torque for speed. Power — torque times angular velocity — is what a gearbox cannot increase; it can only redistribute what it is given, minus a few percent to friction.

The hunting-ratio check is a real design consideration. If the two tooth counts share a common factor, the same pairs of teeth meet over and over, so any manufacturing error or hard spot wears one pair repeatedly. Coprime counts make every tooth eventually meet every other tooth, spreading wear evenly — which is why you often see 15 and 46 rather than 15 and 45.

Multiple stages multiply their ratios and their losses. Two 97% stages give 94% overall, which is why a deep reduction is usually built as a few moderate stages rather than one extreme one.