system
Given the following post, respond as if you're commenting on Reddit:
human
Can someone please describe the relationship between gear ratio and torque in a gearbox between 2 gears. Are they directly proportional?
gpt
Excluding additional friction losses, yes they are directly proportional.  The top cruising gear in the gearbox is typically 1:1, the lower gears are torque multipliers and speed dividers.

For example in a 6 speed transmission 1st gear might be 4:1, 2nd gear 2.5:1, 3rd 1.7:1, 4th 1.3:1, 5th 1:1, 6th 0.8:1 (called over-drive).  1st gear has 4 times the effective torque delivery of 5th gear but would be limited to 1/4 of the vehicle speed.  All gears connect through the final drive ratio which is a fixed dividing gear built into the differential, although in certain vehicles such as large freight trucks there may be more than one final drive ratio that is selectable.