Quote:
Originally Posted by sperry
That's only true on a dyno w/o a proper fan. Have you seen GST's dyno? They've got a 3' squirrel cage 240V fan that puts out a 100mph breeze. It's basically a wind tunnel in there.
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Well, true- but that airflow isn't actually a force applied against the acceleration against the car.
The way dynos account for the missing air resistance is through simple physics. If you know the drag coefficient of the car reasonably closely (and dyno software comes with presets for nearly every commonly tuned car) it's just a matter of subtracting the function of air resistance vs. speed for that car from the power read by the rollers. Road tuning, on the other hand, has no way to account for varying winds, varying slopes in the road, and therefore have a higher margin of error than shop dynos.