Discussion
I'm not too bright and my physics is fairly rusty. Instead of working this afternoon I have been scouring the internet for an answer to this car question, because scribbling on bits of paper is not giving me the answer thats been decided in the biker forum. I think I'm probably wrong but I want to know why in simple to understand terms. I even tried it on my bike this evening and I seem to be getting exactly the opposite of what everyone tells me I'm getting, so I'm confused.
When you pull the handbrake on in a car travelling in a straight line, does the back of the car go up or down, and why.
Should I make this a poll, or am I in a minority of one and should just go and stand beside the wall with my dunces hat on. Calling on the great PH unwashed
.
When you pull the handbrake on in a car travelling in a straight line, does the back of the car go up or down, and why.
Should I make this a poll, or am I in a minority of one and should just go and stand beside the wall with my dunces hat on. Calling on the great PH unwashed
.It goes down because of the forces at work, brakes grab at the back so momentum pivots around that in a clockwise direction and presses down on the suspension and down goes the back of the car.
If you slam on the brakes normally they grab at the front so the reverse happens and the car 'pivots' around that instead, again clockwise, this time lifting the rear of the car.
I think.
If you slam on the brakes normally they grab at the front so the reverse happens and the car 'pivots' around that instead, again clockwise, this time lifting the rear of the car.
I think.
tossbag said:
ludicrous speed said:
would have thought it raises slightly due to the weight shifting forwards?
This. The centre of the car is a pivot point so no matter if front or rear brakes are applied the rear goes up slightly.go out and try it
Obviously everyone else has as weak a grasp of physics as you. 
The back of the car goes up under braking, whichever wheels you brake on (assuming the car is travelling forwards). The mass of the car will tend to continue travelling forwards and so any delecerative force will cause it to try to pivot around its centre of gravity so that the CoG is directly in front of the point at which the force is being applied. In this case, the force is being applied at the interface between the rear wheels and the road, so the CoG tries to pivot forwards and DOWN towards a line directly in front of the contact patch. This shifts the weight forwards, reducing the overall force ont he rear springs causing them to decompress.
It wont go up very much, because the friction lowers as the weight shifts off the back wheels. But it will go up.
To all the people who are saying "down": why?
ETA: Actually I will revise that slightly, and say it depends on where the mass of the vehicle is located. It's possible that both the front and rear will squat, but the front will always squat more than the rear, so the car will tilt forwards.
The back of the car goes up under braking, whichever wheels you brake on (assuming the car is travelling forwards). The mass of the car will tend to continue travelling forwards and so any delecerative force will cause it to try to pivot around its centre of gravity so that the CoG is directly in front of the point at which the force is being applied. In this case, the force is being applied at the interface between the rear wheels and the road, so the CoG tries to pivot forwards and DOWN towards a line directly in front of the contact patch. This shifts the weight forwards, reducing the overall force ont he rear springs causing them to decompress.
It wont go up very much, because the friction lowers as the weight shifts off the back wheels. But it will go up.
To all the people who are saying "down": why?
ETA: Actually I will revise that slightly, and say it depends on where the mass of the vehicle is located. It's possible that both the front and rear will squat, but the front will always squat more than the rear, so the car will tilt forwards.
Edited by kambites on Tuesday 17th August 19:45
Under normal braking yes, as the brakes are applied to the front wheels more than the back wheels.
The handbrake however, which is what this question is about specifically only fixes the rear wheels, so the rear of the car squats.
Now I might be s
t at physics but comprehension doesn't appear to be one of your strong points to be fair.
The handbrake however, which is what this question is about specifically only fixes the rear wheels, so the rear of the car squats.
Now I might be s
t at physics but comprehension doesn't appear to be one of your strong points to be fair.kambites said:
Obviously everyone else has as weak a grasp of physics as you.
The back of the car goes up under braking, whichever wheels you brake on (assuming the car is travelling forwards). The mass of the car will tend to continue travelling forwards and so any delecerative force will cause it to try to pivot around its centre of gravity so that the CoG is directly in front of the point at which the force is being applied. In this case, the force is being applied at the interface between the rear wheels and the road, so the CoG tries to pivot forwards and DOWN towards a line directly in front of the contact patch. This shifts the weight forwards, reducing the overall force ont he rear springs causing them to decompress.
It wont go up very much, because the friction lowers as the weight shifts off the back wheels. But it will go up.
To all the people who are saying "down": why?
ETA: Actually I will revise that slightly, and say it depends on where the mass of the vehicle is located. It's possible that both the front and rear will squat, but the front will always squat more than the rear, so the car will tilt forwards.
I love it when a smart arse get it wrong and has to edit his smoke and mirrors baffle and bullsh-tThe back of the car goes up under braking, whichever wheels you brake on (assuming the car is travelling forwards). The mass of the car will tend to continue travelling forwards and so any delecerative force will cause it to try to pivot around its centre of gravity so that the CoG is directly in front of the point at which the force is being applied. In this case, the force is being applied at the interface between the rear wheels and the road, so the CoG tries to pivot forwards and DOWN towards a line directly in front of the contact patch. This shifts the weight forwards, reducing the overall force ont he rear springs causing them to decompress.
It wont go up very much, because the friction lowers as the weight shifts off the back wheels. But it will go up.
To all the people who are saying "down": why?
ETA: Actually I will revise that slightly, and say it depends on where the mass of the vehicle is located. It's possible that both the front and rear will squat, but the front will always squat more than the rear, so the car will tilt forwards.
Edited by kambites on Tuesday 17th August 19:45
edit
did you even read the opening question properly? i'll give you a wee clue
Handbrake Doh!!!!
Edited by y2blade on Tuesday 17th August 19:48
kambites said:
Obviously everyone else has as weak a grasp of physics as you.
The back of the car goes up under braking, whichever wheels you brake on (assuming the car is travelling forwards). The mass of the car will tend to continue travelling forwards and so any delecerative force will cause it to try to pivot around its centre of gravity so that the CoG is directly in front of the point at which the force is being applied. In this case, the force is being applied at the interface between the rear wheels and the road, so the CoG tries to pivot forwards and DOWN towards a line directly in front of the contact patch. This shifts the weight forwards, reducing the overall force ont he rear springs causing them to decompress.
It wont go up very much, because the friction lowers as the weight shifts off the back wheels. But it will go up.
If that comment was aimed at me you might want to read this.The back of the car goes up under braking, whichever wheels you brake on (assuming the car is travelling forwards). The mass of the car will tend to continue travelling forwards and so any delecerative force will cause it to try to pivot around its centre of gravity so that the CoG is directly in front of the point at which the force is being applied. In this case, the force is being applied at the interface between the rear wheels and the road, so the CoG tries to pivot forwards and DOWN towards a line directly in front of the contact patch. This shifts the weight forwards, reducing the overall force ont he rear springs causing them to decompress.
It wont go up very much, because the friction lowers as the weight shifts off the back wheels. But it will go up.
Edited by kambites on Tuesday 17th August 19:42
http://www.pistonheads.com/gassing/topic.asp?h=0&a... to use the back brake?
I'm already convinced it goes up, but unfortunately that gives you a few uncomfortable questions to answer. Like, why do road motorcycles have rear brakes, and why do all the bikers disagree with you and me when they have a very large combined experience?
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