A power bunny is a method of mitigating your speed loss during bunnyhops by strafing on the ground. This is done because you spend at least one frame on the ground when bunnyhopping in quake, as opposed to many other games with bunnyhopping such as Half-Life where you can instantly jump.
The quick non-mathematical version is that you can no longer strafe in certain forward directions once you are traveling at a high speed. As you go faster, the possible angles get pushed further away into the sides, away from the center. This is also why you can't simply hold W in the air to gain lots of speed.
With always run off, while holding a strafe+forward key, your acceleration angle will be at +/- 60.26 degrees, pretty far away from the center. With always run on, while holding a strafe+forward key, your acceleration angle will be at +/- 41.19 degrees, closer to the center. Turns out that the cut off where you can no longer gain speed is typically somewhere in between these two angles. Logically this also means that only holding +forward doesn't give you a power bunny, holding a strafe key is also mandatory.
| Method | Speed |
|---|---|
| Speed before landing | 559.277 ups |
| TAS strafing | 552.679 ups |
| +forward, +moveleft, always run off | 549.991 ups |
| +forward, +moveleft, always run on | 528.206 ups |
| No powerbunny | 528.206 ups |