( Hello, my first question ... )

Assume two cars, each with exactly the same body, but one a scaled down version of the other (hence, aerodynamics approach equality):

"junior car" - has an engine that delivers 200 ft-lbs of torque and weighs 3000 pounds

"base car" - has an engine that delivers 400 ft-lbs of torque and weighs 6000 pounds

My question is this: isn't the effect of "mass" non-linear? Doesn't the junior engine have less than half the work to do to accelerate than the base car because momentum, friction, drive train length, drive train mass, turbo charger mass, gearing all drain power in a non-linear way; the larger a vehicle you make? I've done the G-search thing and haven't found any answer to this type of "real world" condition.

(Or, asking the same thing in a different way: would the two vehicles above accelerate with identical track times?)

Thanks for responding.


  • $\begingroup$ I agree with Harlemme's answer, but you say isn't the effect of "mass" non-linear. Just on that point, if you take $a = F/m $ and then double both the force and the mass, I would think about whether that would be linear. It's not directly applicable to ordinary cars, because the force part is hard to work out directly, but it would be applicable if you had two toy cars, one twice the mass of the other, that you push started. How much more force you would need to give the heavier car, to get the same acceleration for both? $\endgroup$ – user108787 Dec 11 '16 at 2:42

In the real world, at constant speeds, coefficient of drag matters more than the weight of the vehicle, at least within the normal range of vehicle weights, else a vehicle weighing 2500 lbs. would get twice the gas mileage of one weighing 5000 lbs., and this isn't true. Loss from drivetrain friction and other areas will be a constant percentage. In other words, no. The smaller vehicle would perform better under the conditions you stated if horsepower is equal.

  • 1
    $\begingroup$ +1 , Just as a side note, in the (semi-real) world of Formula 1 racing, the weight of the driver can play a large part. Sebastian Vettel weighs something as low as around 60 kg, which the car designers must really appreciate. I have two rather large elderly relations, when they get into the car, I can sure tell..... $\endgroup$ – user108787 Dec 11 '16 at 2:24
  • $\begingroup$ Lol...I had a car like that once...it was geared for economy, and when I had more than two passengers it felt like I was driving with the parking brake on... $\endgroup$ – Harlemme Dec 13 '16 at 20:57
  • $\begingroup$ This is my last few hours on the site, ( it's too addictive, my account will be deleted shortly) so I can ramble. Worst car moment: I worked on the engine, did not close the hood/ bonnet properly, doing 60 mph and hood suddenly flew up, I was as blind as a bat, even when I stopped the car the hood still stayed up...scaryiest car ride ever. Good luck on the site. $\endgroup$ – user108787 Dec 13 '16 at 21:13

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