Some time ago I was told that for every 100lbs you reduced in weight, you cut your 1/4 mile time by a tenth (.10)
How true is this?
Is a 3000lb car 1 second faster than a 4000lb car given the same HP etc?
Lets try it on a hp level.
How much faster could a 300hp car vs a 200hp car if everything else is (in theroy) the same?
And to further your question, “does a 300hp, 3,000lb car ET the same as a 400hp, 4000lb car?”, because extra weight would help tires catch traction, right?
To somewhat answer you, “yes”, all things same, a 3,000lb car is about 1sec faster than 4,000lb car.
There is a certain sliding scale of power to overcome drag at speed, so there has to be a certain amount that can decrease ET.
Gearheadotaku said:
Some time ago I was told that for every 100lbs you reduced in weight, you cut your 1/4 mile time by a tenth (.10)
How true is this?
At best it's only somewhat true inside a certain range. Otherwise, if I took a stock Miata and reduced the weight to zero, it would still take 13 seconds to do a quarter mile. :)
The first post on this page by Wheels77 mentions 80 ounces as an equivalent to 1 horsepower.
The rest of that page and the next one break it down further.
Lots of online calculators, here is one:
At start speeds with high power, the key performance indicator is the ratio of power to traction. This is in speed ranges where wheelspin is an issue and 4wd improves acceleration.
At intermediate speeds (nit traction dominated and not well into triple digits speeds) the key ratio is power to weight. The rule of thumb there is most accurate in this range for a typical sedan with a power to weight ratio in the neighborhood of 10% (in hp/lb).
Well into triple digit speeds traction isn’t an issue and weight doesn’t even much matter - it becomes a matter of power to aerodynamic drag.
The fastest cars have to worry about all three. An old Miata only initially needs to focus on power to weight to improve performance.
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