If you love cars and have never taken a Physics class, don’t worry. There are only three things you need to know about Physics and cars. The first is Force is the amount of mass multiplied by acceleration. Second, Torque is the amount of rotational force the engine can do. Finally, Horsepower is calculated by the amount of force the car can pull at a given velocity. What that means in a drag race is that Horsepower doesn’t give you the full picture of who’s going to win. Take for instance this luxury drag race between a BMW M3, Cadillac ATS-V, and a freshly minted Alfa Romeo Giulia Quadrifoglio.
Looking at the spec sheet between the three and the podium finish looks set even before the race starts. We should expect the Giulia Quadrifoglio to come first, the ATS-V second, and the M3 to finish last.
Alfa Romeo Giulia Quadrifoglio: 505 horsepower
BMW M3 w/ Competition Pack: 443 horsepower
Cadillac ATS-V: 464 horsepower
However, a critical element in the horsepower calculation lies within the Force calculation. Something that has more mass will require a bit more force to move. Just like how your fat uncle will huff and puff after going up a flight of stairs, while children seem to have boundless energy. If we look at the sheer weight alone, the podium finish looks a bit differently
Alfa Romeo Giulia Quadrifoglio: 3571 lbs
BMW M3 w/ Competition Pack: 3439 lbs
Cadillac ATS-V: 3747 lbs
Looking at the weight comparison, the Cadillac ATS-V has a lot more weight to pull which will compromise its more than 20 horsepower advantage over the BMW M3. A more generally accepted metric to compare performance thus lies in the weight:power ratio.
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Weight:Power Ratio Comparison
(Smaller is better)
Alfa Romeo Giulia Quadrifoglio: 7.07 lbs/hp
BMW M3 w/ Competition Pack: 7.76 lbs/hp
Cadillac ATS-V: 8.07 lbs/hp
Looking at the above weight:power ratio comparison and we see that this closely estimates how the drag race will unfold. The Alfa Romeo Giulia Quadrifoglio (phew, that’s a mouthful) destroys the Cadillac ATS-V in this simple drag race, while just edging out the BMW M3. Looking at horsepower alone, we would expect the Cadillac ATS-V to take second place, but that’s not the case. We also can’t ignore the critical human element, since the drivers of the Italian Giulia and the American ATS-V seemed to have a better reaction time than the German M3 driver. Another drag race may ultimately provide a different story. However, over repeated races, we should expect the outcome to mimic the Weight:Power ratio ranking.
(Source: Motorsport Magazine)