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Old 01-28-2013, 04:23 PM   #13
Lomez
Yea...Sunday too
 
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Joined: Mar 2011
Location: Pasadena, CA
Oddometer: 248
Quote:
Originally Posted by sendler View Post
A reply from another site
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"Here's the problem... you can't disregard air resistance at higher speeds. That's like saying granite would float in water if you disregard gravity.

In top gear, you use a significant amount of your power due to wind resistance and friction. Only the remainder is used to accelerate the vehicle. Since you have less available power to accelerate the vehicle, you will accelerate slower.

It is also more "violent" in low gears because you have more torque at the wheels which is more likely to get the tire to lose traction or for the reaction to lift the nose of your vehicle upwards."

But consider this: What about the turbo diesel trucks in the link which all have a basically FLAT power curve. Could you then choose from 3rd, 4th, or 5th which would give the same exact power and road speed? Just a different rpm and torque multiplication. And expect the exact same level of acceleration? Crazy topic huh. I think 3rd will accelerate much harder.
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I don't think it can be known from the curves. The variable needed is fuel required to maintain speed, given a particular resistance. And yes, at higher speeds, the ONLY variable to consider is wind resistance (unless you're climbing, then you must deal with gravity, which accelerates against you at 30 feet per second per second). Around town, the only real consideration is resistance from inertia. SO.....a lighter vehicle gets better mpg. On the highway, all you care about is speed (wind resistance) and rate of vertical change (which requires horesepower)....so the more aerodynamic vehicle gets better MPG....or, you can just go slower (which is why scooters are rated at 100 mpg...yea, 100mpg at a constant 40 mph)
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