Axle Ratio and tow rating

Sport45 wrote:
The engineer in me just got hung up on the "power" term.

Power, force, torque, and work are terms with specific (and different) meanings in my line of work.

In your example with the torque multiplier above it takes twice the force with the 5-1 vs the 10-1 multiplier. The power used relates to how fast you turn the wrench. If you turn it at twice the speed using the 10-1 multiplier the power is the same. If you turn the wrench the same speed in both cases the 10-1 multiplier is using half the power. (Because you're turning the bolt half as fast.)

Love when fellow engineers are around so we can speak the same language!


For some reason the concept of torque vs hp confuses the most people; I feel is because people try to separate the two, rather than seeing them as coupled pairs like space-time. The coupler in this case is rpm, or angular velocity.

Here's one example I like show people. My 2014 Ram 1500, Hemi, 8 spd, is offered in 2 gear ratios: 3.21 and 3.92.

Either out of pure coincidence, or RAM's intentional design, it just so happens the gear ratio spacing of the ZF 8 speed is nearly identical to the split between 3.21 and 3.92.

Meaning, given a road speed of say, 60 mph, you get the exact same rpm (within 200 rpm) with the 3.21 truck in 7th, and 3.92 in 8th; or 3.21 in 6th, and 3.92 in 7th, and so on.

In this case, how does choosing the 3.92 gears have any advantage over a 3.21? The answer is it doesn't; except for the most extreme case of starting out at full GCWR, up a 25% grade... But considering the ZF's ultra deep 4.7:1 1st gear, you're almost never short on startability.

Otherwise, on every hill, ever speed, that you can ever imagine, the two trucks performs identical. The 3.21 truck is simply in 1 gear lower than the 3.92 truck. Neither trucks "puts down more power" than the other, because simple machinery like gear sets cannot create power.