YACT: If a car has an acceleration of 1G+, it accelerates faster then free-fall, right?
- Thread starter ndee
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Hayabusa Rider
Admin Emeritus & Elite Member
- Jan 26, 2000
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Simple explanation (i.e. not technically correct): Go around a sharp corner (most test use a 200' diameter circle) and measure how hard you are "pushed" to the outside of the car. If you are pushed against the door just as hard as you are down from gravity then you are going at 1.0g, most cars are in the .8 - .9 range. This test basically shows you how much grip the car has (or better yet, how much grip the tires have).
1G is pretty fast accleration, a car that goes from 0 to 60 mph in 6 secs is only about .45G, if i calculated correctly.
not to mention that it is pretty much impossible for a car to reach 1g. It's been a while since I took physics or anything, but I am pretty sure that a car's max acceleration is limited by the friction between the car's wheel and the road.
Assuming a rubber tire has a coeffecient of friction around .9 or so and that half of the car's weight is over its rear tires (if it is rwd), than the max possible acceleration should be only .45g.
well, theoretically, I guess it is possible, but like I said above, it would require tires with a coef. of friction greater than 1 (ie, hard-core "racing" tires).
silverpig
Lifer
- Jul 29, 2001
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Some of you guys are mixing up lateral accel with linear. 0-60 mph times are linear accel in which case your car would need a 0-60 time of ~2.8 seconds (off the top of my head, could be wrong, but it's about there) to get to 1 G of accel in a straight line.
When you see the 1.01 G rating in a car magazine for a modded Viper, that's the lateral accel where they take the car on a skid pad and drive it in a circle faster and faster until it spins out. This doesn't test the engine power at all, but is all about tire grip (and downforce/lift but that's hardly applicable to the civics with wings).
I think F1 cars can hit 5 or 6 Gs laterally (turning accel) because of the enormous downforce produced by the cars, as well as their hot sticky racing slicks.
When you see the 1.01 G rating in a car magazine for a modded Viper, that's the lateral accel where they take the car on a skid pad and drive it in a circle faster and faster until it spins out. This doesn't test the engine power at all, but is all about tire grip (and downforce/lift but that's hardly applicable to the civics with wings).
I think F1 cars can hit 5 or 6 Gs laterally (turning accel) because of the enormous downforce produced by the cars, as well as their hot sticky racing slicks.
In straight-line acceleration a RWD/FWD car (assuming no weight transfer F/R, which is why RWD is better in practical applications where there is weight transfer), with an LSD your limit would be 1/2 of the cornering force (1/2 as many tires gripping). This is also assuming same size front & rear tires (which is not the case on most high-power cars, especially those designed for good acceleration).
I have a magazine here that has 0.98g for acceleration (0-60 4.9sec) and 1.11g for braking numbers (70-0 161ft) on a vehicle. Not lateral g's (those are 0.94g and 0.91g for left and right respectively). I don't know what they use to measure or how they came to those figures, but I'd be curious to find out.
Acceleration is measured by (wait for it)... an accelerometer! In the most simplistic form, these are devices that measure the deviation from vertical of a hanging weight. The weight has a constant force of 1 g making it hang vertically. Horizontal acceleration will result in an inertial force causing it to not be vertical. I think the ones in use now, instead of measuring the movement of a weight, actually measure the force tending to push it away from vertical.
For F1 cars, I thought it was around 4 or 5 but yeah, you are right. I wasn't mixing up lateral accel with linear I think. I don't remember the formula for linear acceleration, if someone could help me out real quick? I wanna calculate how fast the car has to be from 0-60, so that he has a little more then 1G acceleration.
1g is 32.2 ft/sec/sec. So to find out the 0 to 60mph time for a 1 g acceleration you will have to equate the integral of 32 ft/sec/sec to 88 feet per second. So I guess it would require a 0 to 60 time of a little less than 3 seconds. That's average, of course. Actual cars have accelerations that are far from linear. (I think that's right. It's late and I just got home from a party.)
Are you sure you aren't thinking of skidpad Gs? They drive the car around a skidpad until it slides. The max centrifugal force is the Gs that they use as "skidpad Gs".
100% not Skidpad Gs. I told my friends that there are some cars, that accelerate faster then the free fall, and they said "nah you stupid, the car would need an acceleration of 10G". And I was like "nooooooo friggin' way. If you have a vertical road and you let one car fall down in the free fall just next to the road, and one car could drive on the that road with more then 1G, it would be faster then free fall." They insisted that they were right and so did I 
true, but if the coefficient of friction between the tires and the road is equal to or greater than 1, then an AWD vehicle could accelerate at one g without spinning tires (spinning tires decreases acceleration)
for a two wheel drive vehicle, assuming the weight is 50% front wheels, 50% back wheels, the coefficient of friction would have to be at least 2.
A cf of 1 is easy, 2 . . . maybe racing slicks on special pavement, but I dunno.
to see if it has a coefficent of on, put it on a 45 degree slope. If it doesn't slide down, cf>= 1. easy as that.
AWD vehicles can potentially accelerate twice as fast as anything else on the road . . . I wonder why big street ricers don't get an AWD subaru and drop some huge engine into it. It woudln't slip its tires until it was accelerating twice as fast as the little Honda that is now behind it . . . .
but you would need to mod the engine enough so that it was signifigantly more powerful. . . . Most cars rarely burn out, until you get to the drag racers Mustang Cobra types, although I still thing a track car would be better off with AWD. Mor expensive . . . but much . . . . better.
edit: Mass of a car has absolutely nothing to do with max acceleration without spinning the tires. friction varies directly with mass, but acceleration varies inversly. The two masses cancel. Work it out, if you don't believe me.
coeffiecienct of friction of 2? is that even possible? doesnt that mean the friction force would be twice the weight of the car? provided that the car is on a leveled track. what kinda accleration do u need to oppose this kinda of friction force?
friction=2mg
forward force has to be greater than 2mg (to make the netforce more than 0) for the car to accelerate, so ma>2mg, cancell out the m's,which yields to accleration of at least 2g in order for the thing to acclerate because there is such a big friction force, is that even possible for linear acceleration?, thats like having a car going from 0-60 faster than 1.4 secs.
and we arent even counting the drag force, which will be significant when the car reaches high speeds.
friction=2mg
forward force has to be greater than 2mg (to make the netforce more than 0) for the car to accelerate, so ma>2mg, cancell out the m's,which yields to accleration of at least 2g in order for the thing to acclerate because there is such a big friction force, is that even possible for linear acceleration?, thats like having a car going from 0-60 faster than 1.4 secs.
and we arent even counting the drag force, which will be significant when the car reaches high speeds.
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