[Falafel Combo]

Is there a scientific reason why BMW's (and I guess other cars) always kick the tail out to the right, when traction breaks? I've almost never seen a cars rear end swing to the left.


Also, isn't this something the locking differential should have mitigated?

[Needsdecaf]

Originally Posted by Falafel Combo

Is there a scientific reason why BMW's (and I guess other cars) always kick the tail out to the right, when traction breaks? I've almost never seen a cars rear end swing to the left.


Also, isn't this something the locking differential should have mitigated?

Yes, it is a law of physics. Rotational torque always produces a force vector 90 degrees to the direction of rotation. It is always the same direction in relation to the rotation. It is most easily understood by the "right hand rule". Roll your fingers over like you were gripping a bike handle. Stick your thumb out. Your fingers are pointing in the direction of rotation, and your thumb is pointing in the direction of the force vector. In the event of a car moving forward, the force points left, which pushes the back of the car to the right.

Normally when the car is moving forward, the rear tires prevent the car from moving sideways, as the torque vector is not particularly sting. But when the wheels spin and traction is lost.....

[Needsdecaf]

A little example

[Needsdecaf]

Originally Posted by Needsdecaf

A little example

Sorry, pasted wrong pic.

[Falafel Combo]

Originally Posted by Needsdecaf

Yes, it is a law of physics. Rotational torque always produces a force vector 90 degrees to the direction of rotation. It is always the same direction in relation to the rotation. It is most easily understood by the "right hand rule". Roll your fingers over like you were gripping a bike handle. Stick your thumb out. Your fingers are pointing in the direction of rotation, and your thumb is pointing in the direction of the force vector. In the event of a car moving forward, the force points left, which pushes the back of the car to the right.

Normally when the car is moving forward, the rear tires prevent the car from moving sideways, as the torque vector is not particularly sting. But when the wheels spin and traction is lost.....

Smart explanation. Thanks man!

[CanAutM3]

Originally Posted by Needsdecaf

Yes, it is a law of physics. Rotational torque always produces a force vector 90 degrees to the direction of rotation. It is always the same direction in relation to the rotation. It is most easily understood by the "right hand rule". Roll your fingers over like you were gripping a bike handle. Stick your thumb out. Your fingers are pointing in the direction of rotation, and your thumb is pointing in the direction of the force vector. In the event of a car moving forward, the force points left, which pushes the back of the car to the right.

Normally when the car is moving forward, the rear tires prevent the car from moving sideways, as the torque vector is not particularly sting. But when the wheels spin and traction is lost.....

Are you talking about gyroscopic effect? I can assure you there is none of that here.

Cars can slide to either side. Any angle in the steering wheel will have the greatest impact on which side the car will slide. The incline on the road also has an impact. Since most roads crest in the middle, traveling on the right side of the road will cause the car to slide to the right.

[CanAutM3]

Originally Posted by Needsdecaf

A little example

Originally Posted by Needsdecaf

Sorry, pasted wrong pic.

That has absolutely nothing to do with it. The picture you posted is simply the convention of how a torque vector is represented in the cartesian referential to indicate in which direction it is applied. There is no actual longitudinal force in the direction of the thumb.

[CanAutM3]

Originally Posted by Falafel Combo

Smart explanation. Thanks man!

See my posts above...

[harkes]

Originally Posted by Falafel Combo

Is there a scientific reason why BMW's (and I guess other cars) always kick the tail out to the right, when traction breaks? I've almost never seen a cars rear end swing to the left.


Also, isn't this something the locking differential should have mitigated?

My AE86 always step out to the left. Same type diff as the M4...

[Boss330]

Originally Posted by Falafel Combo

Is there a scientific reason why BMW's (and I guess other cars) always kick the tail out to the right, when traction breaks? I've almost never seen a cars rear end swing to the left.


Also, isn't this something the locking differential should have mitigated?

To allow water to escape on a road surface, all roads are crowned in the center. Ie the road is highest in center and falls down on each side with a couple of degrees inclination.

As we (or most countries) drive on the right hand side of the road, the car is on the right side of the road and the road surface falls to the right on that side (the road is lower at the curb than it is at the center line). The car is actually sitting at the road with a slight lean towards the right side (and the opposite of course in countries where they drive on the left hand side). When both wheels spin you have the same effect as standing on ice on a slope. You are not sliding up the slope, but down towards the lowest point...

And both wheels spinning is necessary for this to happen. If one wheel just rolls, it doesn't loose traction and will steer the car. This effect is therefore more pronounced on a car with a locking diff.

Best explanation I can think of

EDIT:

On a one lane road, the crown is also in the center, which means that the crown on the road is actually under the centerline of the car. On such a road the car should either kick left or right, depending on how centered the car is relative to the crown of the road.

On a race track, the road does not have a crown in the center of the surface AFAIK. It's either flat(ish) or in a homogenous angle across the entire surface (at that specific point). This is also true in a corner on a public road. There is no crown in the center of a turn, but rather the entire surface is banked down towards the apex of the corner.

[cmg5461]

Originally Posted by CanAutM3

That has absolutely nothing to do with it. The picture you posted is simply the convention of how a torque vector is represented in the cartesian referential to indicate in which direction it is applied. There is no actual longitudinal force in the direction of the thumb.

Correct, the gyroscopic effect will cause the car to roll counter clockwise, longitudinally. Assuming the tires are spinning forward. All this does is put a tiny bit more force on the left tire, and remove a tiny bit of force on the right tire. The inertia from the tires spinning compared to the inertia of the car rotating around the z axis is very small. Too small to be noticeable.

[CanAutM3]

Originally Posted by cmg5461

Correct, the gyroscopic effect will cause the car to roll counter clockwise, longitudinally. Assuming the tires are spinning forward. All this does is put a tiny bit more force on the left tire, and remove a tiny bit of force on the right tire. The inertia from the tires spinning compared to the inertia of the car rotating around the z axis is very small. Too small to be noticeable.

I don't know if I am missing something, but IMO, if the car is travelling forward with the rear tires spinning, there aren't any gyroscopics effect at all at play. Once the car starts to yaw, then yes, the negligible effect you mentions comes into play. So gyroscopic effects are not involved in determining which side the car will slide.

[cmg5461]

Originally Posted by CanAutM3

I don't know if I am missing something, but IMO, if the car is travelling forward with the rear tires spinning, there aren't any gyroscopics effect at all at play. Once the car starts to yaw, then yes, the negligible effect you mentions comes into play. So gyroscopic effects are not involved in determining which side the car will slide.

Gyroscopic effects are still there in any direction you are moving. Google bike wheel gryoscope. This is the principle on which plane gyroscopes work. If they didn't work in longitudinal direction of travel, how would planes tell which direction they're moving?

It's a game of inertia. But the magnitude is too small to notice. I was agreeing with you :P

[CanAutM3]

Originally Posted by cmg5461

Gyroscopic effects are still there in any direction you are moving. Google bike wheel gryoscope. This is the principle on which plane gyroscopes work. If they didn't work in longitudinal direction of travel, how would planes tell which direction they're moving?

It's a game of inertia. But the magnitude is too small to notice. I was agreeing with you :P

We are getting a bit deep, but I still dissagree. Gyroscopic effects only come into play when the axis of roation is rotated. If the axis is moved longitudinally in any direction, there is no gyroscopic effect.

If anything, the gyroscopic effect of the spinning wheels will want to keep the car going straight .

The gyroscopes in the navigation system of aircrafts are used to calculate changes in direction, a change of direction changes the rotation axis of the gyroscope. When the plane flies in a straight line, the position is established through the ground speed calculated by the on-board accelerometers.

[cmg5461]

Originally Posted by CanAutM3

We are getting a bit deep, but I still dissagree. Gyroscopic effects only come into play when the axis of roation is rotated. If the axis is moved longitudinally in any direction, there is no gyroscopic effect.

If anything, the gyroscopic effect of the spinning wheels will want to keep the car going straight .

The gyroscopes in the navigation system of aircrafts are used to calculate changes in direction, a change of direction changes the rotation axis of the gyroscope. When the plane flies in a straight line, the position is established through the ground speed calculated by the on-board accelerometers.

Spot on, I was referring to the spinning wheels this whole time Did I say position? Thought I said direction

[V1.47fan]

Originally Posted by CanAutM3

We are getting a bit deep, but I still dissagree. Gyroscopic effects only come into play when the axis of roation is rotated. If the axis is moved longitudinally in any direction, there is no gyroscopic effect.

If anything, the gyroscopic effect of the spinning wheels will want to keep the car going straight .

The gyroscopes in the navigation system of aircrafts are used to calculate changes in direction, a change of direction changes the rotation axis of the gyroscope. When the plane flies in a straight line, the position is established through the ground speed calculated by the on-board accelerometers.

I thought pitot tubes (pitot-static system ) determines the airspeed and then ground speed is determined by substracting headwind or adding tailwind to true airspeed. I think GPS ground speed is for ETA purposes only.

That's why there has been a few airliner crashes over the years as a result of the pitot tubes or static ports being obstructed.

http://en.m.wikipedia.org/wiki/Air_France_Flight_447

http://en.m.wikipedia.org/wiki/Birgenair_Flight_301

http://en.m.wikipedia.org/wiki/Aeroper%C3%BA_Flight_603

[CanAutM3]

Originally Posted by V1.47fan

I thought pitot tubes (pitot-static system ) determines the airspeed and then ground speed is determined by substracting headwind or adding tailwind to true airspeed. I think GPS ground speed is for ETA purposes only.

That's why there has been a few airliner crashes over the years as a result of the pitot tubes or static ports being obstructed.

http://en.m.wikipedia.org/wiki/Air_France_Flight_447

http://en.m.wikipedia.org/wiki/Birgenair_Flight_301

http://en.m.wikipedia.org/wiki/Aeroper%C3%BA_Flight_603

OT, but I will entertain nonetheless

There are multiple redundant measuring systems in aircrafts. Air speed measured through a pitot tube is one of the more important measures as air speed is critcal to establish available lift.

However, air speed is not much use to precisely establish position since it is practically impossible to measure wind speed accurately. The method you describe is used on small airplanes that don't have elaborate navigation systems, but the pilot will also need to use visual references on the ground to establish his true position.

On more sophistcated aircraft, before the days of GPS, navigation systems using accelerometers and gyroscopes were used to precisely establish the position of the aircraft. These inertial systems can still be found in modern aircraft as redundent positioning systems to the GPS.

http://en.m.wikipedia.org/wiki/Inert...igation_system

[V1.47fan]

Originally Posted by CanAutM3

OT, but I will entertain nonetheless

There are multiple redundant measuring systems in aircrafts. Air speed measured through a pitot tube is one of the more important measures as air speed is critcal to establish available lift.

However, air speed is not much use to precisely establish position since it is practically impossible to measure wind speed accurately. The method you describe is used on small airplanes that don't have elaborate navigation systems, but the pilot will also need to use visual references on the ground to establish his true position.

On more sophistcated aircraft, before the days of GPS, navigation systems using accelerometers and gyroscopes were used to precisely establish the position of the aircraft. These inertial systems can still be found in modern aircraft as redundent positioning systems to the GPS.

http://en.m.wikipedia.org/wiki/Inert...igation_system

They dont use accelerometers to determine ground speed, the INS systems are old systems in reference to navigation, dead reckoning.
Once the pito-static system quit working, you dont have redudant accelerometers that gives you TAS that's why some airliners crashed.

[cmg5461]

Originally Posted by V1.47fan

They dont use accelerometers to determine ground speed, the INS systems are old systems in reference to navigation, dead reckoning.
Once the pito-static system quit working, you dont have redudant accelerometers that gives you TAS that's why some airliners crashed.

The only planes we should be talking about here is the M4 taking flight

[CanAutM3]

Originally Posted by V1.47fan

They dont use accelerometers to determine ground speed, the INS systems are old systems in reference to navigation, dead reckoning.
Once the pito-static system quit working, you dont have redudant accelerometers that gives you TAS that's why some airliners crashed.

But oh yes they do, INS systems used accelerometers to establish ground speed and then establish position relative to the ground. And yes, it is old tech.

When did I ever mention that accelerometers were used to establish airspeed . I agree, pitot are the only accurate and reliable measure of air speed.

[TrevorM3]

science and laughs all in one thread.

[Boss330]

Originally Posted by CanAutM3

But oh yes they do, INS systems used accelerometers to establish ground speed and then establish position relative to the ground. And yes, it is old tech.

When did I ever mention that accelerometers were used to establish airspeed . I agree, pitot are the only accurate and reliable measure of air speed.

Trying to keep this OT

Your profile pic needs updating