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### #ActualPochyPoch

Posted 12 September 2012 - 07:10 PM

Hi,

That's bad for me because i get much better results applying the lateral force directly to car chassis regardless of steering angle (but i take it in count for slip angle calculation). Maybe i just need to tune pacejka curve to respond to the fact it changes the car behaviour somehow. A little change alway seems dramatic in result at first, but maybe it is the right way to go and i need to adapt my curves which are really trivials for now.

Although i'm no expert, i always understood that a stationary car spinning on the spot with the steering centred produces no longtitude forces from the tires to move the car forwards or backwards. But only lateral forces to slow down the rate of spin.

As i understand it, when wheels are centered, the lateral response will be perpendicular to wheels, and will then slow down car rotation, but it will not introduce longitudinal force. The longitudinal force component present on the wheel during spinning will just introduce a diffrent slip angle result.

I re-checked marcos page for the steering section. He claims, after determining lateral force using pacejka curve, that they have to be applied to the car body. He will apply both lateral forces directly to car body, and then use them separatly to calculate torque and finally introduce some yaw. Fine for me, but what does he have to say about the lateral component of the front wheels ? This :

The lateral forces of the four tyres have two results: a net cornering force and a torque around the yaw axis. The cornering force is the force on the CG at a right angle to the car orientation and serves as the centripetal force which is required to describe a circular path. The contribution of the rear wheels to the cornering force is the same as the lateral force. For the front wheels, multiply the lateral force with cos(delta) to allow for the steering angle.

Fcornering = Flat, rear + cos(delta) * Flat, front

I'm quite rusted with my trigonometry, so i'm not 100% sure, but i think that will act as if the lateral response IS indeed perpenducular the the wheel, according to steer angle, BUT that he is suggesting to take only the force component that is projected on the car side axis. So if the front wheels are centered, 100% of the force will be applied. But if the wheel is steering at 60°, only 50% of the force is applied to the car.

But he is only calculating centripetal force and torque, so i guess only the truly lateral component does it. He may have "forget" the sin(dela)*Flat, front which is supposed to slow down the car as it is cornering, but maybe it is not that important for the car behaviour ? If i release the gaz pedal, it may slow down the car by a similar amount. If i'm right, that would mean, that i just should try to have better steerAngle/steerSpeed/lateralCurves constants instead of looking at the maths.

---

One other question as i'm experimenting if i may :

Do you know if traction circle should be applied before or after taking count of weight load ? Because when i slow down the car in/before curves, so much weight get transfered to the front that the lateral force increase happens way too fast and the car can make an half-turn really easily. I feel like traction circle should be capped at some maximum load or maybe my weight transfer needs a real spring instead of a simplistic time integration of the weight transfer.

By the way, it feels a bit strange to me that only weight transfer due to +/- acceleration affects cornering capacity in curves. Am i missing something here or again, should i just tune weight transfer speed to get something smoother to drive ?

EDIT : after re-reading closely PHORS articles, it seems only acceleration/weight transfer affects available traction and it is supposed to scale linearly with weight load, indefinitely. http://phors.locost7.info/phors07.htm

---

Thanks for your help and sharing your experience ! You say you are not expert, but given the quality of your racing game, i'll take your advices very seriously ! It's exactly the kind of feeling i want, only more arcade-ish.

### #7PochyPoch

Posted 12 September 2012 - 06:18 PM

Hi,

That's bad for me because i get much better results applying the lateral force directly to car chassis regardless of steering angle (but i take it in count for slip angle calculation). Maybe i just need to tune pacejka curve to respond to the fact it changes the car behaviour somehow. A little change alway seems dramatic in result at first, but maybe it is the right way to go and i need to adapt my curves which are really trivials for now.

Although i'm no expert, i always understood that a stationary car spinning on the spot with the steering centred produces no longtitude forces from the tires to move the car forwards or backwards. But only lateral forces to slow down the rate of spin.

As i understand it, when wheels are centered, the lateral response will be perpendicular to wheels, and will then slow down car rotation, but it will not introduce longitudinal force. The longitudinal force component present on the wheel during spinning will just introduce a diffrent slip angle result.

I re-checked marcos page for the steering section. He claims, after determining lateral force using pacejka curve, that they have to be applied to the car body. He will apply both lateral forces directly to car body, and then use them separatly to calculate torque and finally introduce some yaw. Fine for me, but what does he have to say about the lateral component of the front wheels ? This :

The lateral forces of the four tyres have two results: a net cornering force and a torque around the yaw axis. The cornering force is the force on the CG at a right angle to the car orientation and serves as the centripetal force which is required to describe a circular path. The contribution of the rear wheels to the cornering force is the same as the lateral force. For the front wheels, multiply the lateral force with cos(delta) to allow for the steering angle.

Fcornering = Flat, rear + cos(delta) * Flat, front

I'm quite rusted with my trigonometry, so i'm not 100% sure, but i think that will act as if the lateral response IS indeed perpenducular the the wheel, according to steer angle, BUT that he is suggesting to take only the force component that is projected on the car side axis. So if the front wheels are centered, 100% of the force will be applied. But if the wheel is steering at 60°, only 50% of the force is applied to the car.

But he is only calculating centripetal force and torque, so i guess only the truly lateral component does it. He may have "forget" the sin(dela)*Flat, front which is supposed to slow down the car as it is cornering, but maybe it is not that important for the car behaviour ? If i release the gaz pedal, it may slow down the car by a similar amount. If i'm right, that would mean, that i just should try to have better steerAngle/steerSpeed/lateralCurves constants instead of looking at the maths.

---

One other question as i'm experimenting if i may :

Do you know if traction circle should be applied before or after taking count of weight load ? Because when i slow down the car in/before curves, so much weight get transfered to the front that the lateral force increase happens way too fast and the car can make an half-turn really easily. I feel like traction circle should be capped at some maximum load or maybe my weight transfer needs a real spring instead of a simplistic time integration of the weight transfer.

By the way, it feels a bit strange to me that only weight transfer due to +/- acceleration affects cornering capacity in curves. Am i missing something here or again, should i just tune weight transfer speed to get something smoother to drive ?

---

Thanks for your help and sharing your experience ! You say you are not expert, but given the quality of your racing game, i'll take your advices very seriously ! It's exactly the kind of feeling i want, only more arcade-ish.

### #6PochyPoch

Posted 12 September 2012 - 06:18 PM

Hi,

That's bad for me because i get much better results applying the lateral force directly to car chassis regardless of steering angle (but i take it in count for slip angle calculation). Maybe i just need to tune pacejka curve to respond to the fact it changes the car behaviour somehow. A little change alway seems dramatic in result at first, but maybe it is the right way to go and i need to adapt my curves which are really trivials for now.

Although i'm no expert, i always understood that a stationary car spinning on the spot with the steering centred produces no longtitude forces from the tires to move the car forwards or backwards. But only lateral forces to slow down the rate of spin.

As i understand it, when wheels are centered, the lateral response will be perpendicular to wheels, and will then slow down car rotation, but it will not introduce longitudinal force. The longitudinal force component present on the wheel during spinning will just introduce a diffrent slip angle result.

I re-checked marcos page for the steering section. He claims, after determining lateral force using pacejka curve, that they have to be applied to the car body. He will apply both lateral forces directly to car body, and then use them separatly to calculate torque and finally introduce some yaw. Fine for me, but what does he have to say about the lateral component of the front wheels ? This :

The lateral forces of the four tyres have two results: a net cornering force and a torque around the yaw axis. The cornering force is the force on the CG at a right angle to the car orientation and serves as the centripetal force which is required to describe a circular path. The contribution of the rear wheels to the cornering force is the same as the lateral force. For the front wheels, multiply the lateral force with cos(delta) to allow for the steering angle.

Fcornering = Flat, rear + cos(delta) * Flat, front

I'm quite rusted with my trigonometry, so i'm not 100% sure, but i think that will act as if the lateral response IS indeed perpenducular the the wheel, according to steer angle, BUT that he is suggesting to take only the force component that is projected on the car side axis. So if the front wheels are centered, 100% of the force will be applied. But if the wheel is steering at 60°, only 50% of the force is applied to the car.

But he is only calculating centripetal force and torque, so i guess only the truly lateral component does it. He may have "forget" the sin(dela)*Flat, front which is supposed to slow down the car as it is cornering, but maybe it is not that important for the car behaviour ? If i release the gaz pedal, it may slow down the car by a similar amount. If i'm right, that would mean, that i just should try to have better steerAngle/steerSpeed/lateralCurves constants instead of looking at the maths.

---

One other question as i'm experimenting if i may :

Do you know if traction circle should be applied before or after taking count of weight load ? Because when i slow down the car in/before curves, so much weight get transfered to the front that the lateral force increase happens way too fast and the car can make an half-turn really easily. I feel like traction circle should be capped at some maximum load or maybe my weight transfer needs a real spring instead of a simplistic time integration of the weight transfer.

By the way, if feels a bit strange to me that only weight transfer due to +/- acceleration affects cornering capacity in curves. Am i missing something here or again, should i just tune weight transfer speed to get something smoother to drive ?

---

Thanks for your help and sharing your experience ! You say you are not expert, but given the quality of your racing game, i'll take your advices very seriously ! It's exactly the kind of feeling i want, only more arcade-ish.

### #5PochyPoch

Posted 12 September 2012 - 06:14 PM

Hi,

That's bad for me because i get much better results applying the lateral force directly to car chassis regardless of steering angle (but i take it in count for slip angle calculation). Maybe i just need to tune pacejka curve to respond to the fact it changes the car behaviour somehow. A little change alway seems dramatic in result at first, but maybe it is the right way to go and i need to adapt my curves which are really trivials for now.

Although i'm no expert, i always understood that a stationary car spinning on the spot with the steering centred produces no longtitude forces from the tires to move the car forwards or backwards. But only lateral forces to slow down the rate of spin.

As i understand it, when wheels are centered, the lateral response will be perpendicular to wheels, and will then slow down car rotation, but it will not introduce longitudinal force. The longitudinal force component present on the wheel during spinning will just introduce a diffrent slip angle result.

I re-checked marcos page for the steering section. He claims, after determining lateral force using pacejka curve, that they have to be applied to the car body. He will apply both lateral forces directly to car body, and then use them separatly to calculate torque and finally introduce some yaw. Fine for me, but what does he have to say about the lateral component of the front wheels ? This :

The lateral forces of the four tyres have two results: a net cornering force and a torque around the yaw axis. The cornering force is the force on the CG at a right angle to the car orientation and serves as the centripetal force which is required to describe a circular path. The contribution of the rear wheels to the cornering force is the same as the lateral force. For the front wheels, multiply the lateral force with cos(delta) to allow for the steering angle.

Fcornering = Flat, rear + cos(delta) * Flat, front

I'm quite rusted with my trigonometry, so i'm not 100% sure, but i think that will act as if the lateral response IS indeed perpenducular the the wheel, according to steer angle, BUT that he is suggesting to take only the force component that is projected on the car side axis. So if the front wheels are centered, 100% of the force will be applied. But if the wheel is steering at 60°, only 50% of the force is applied to the car.

But he is only calculating centripetal force and torque, so i guess only the truly lateral component does it. He may have "forget" the sin(dela)*Flat, front which is supposed to slow down the car as it is cornering, but maybe it is not that important for the car behaviour ? If i release the gaz pedal, it may slow down the car by a similar amount. If i'm right, that would mean, that i just should try to have better steerAngle/steerSpeed/lateralCurves constants instead of looking at the maths.

---

One other question as i'm experimenting if i may :

Do you know if traction circle should be applied before or after taking count of weight load ? Because when i slow down the car in/before curves, so much weight get transfered to the front that the lateral force increase happens way too fast and the car can make an half-turn really easily. I feel like traction circle is capped to a maximum load or maybe my weight transfer needs a real spring instead of a simplistic time integration.

---

Thanks for your help and sharing your experience ! You say you are not expert, but given the quality of your racing game, i'll take your advices very seriously ! It's exactly the kind of feeling i want, only more arcade-ish.

### #4PochyPoch

Posted 12 September 2012 - 06:11 PM

Hi,

That's bad for me because i get much better results applying the lateral force directly to car chassis regardless of steering angle (but i take it in count for slip angle calculation). Maybe i just need to tune pacejka curve to respond to the fact it changes the car behaviour somehow. A little change alway seems dramatic in result at first, but maybe it is the right way to go and i need to adapt my curves which are really trivials for now.

Although i'm no expert, i always understood that a stationary car spinning on the spot with the steering centred produces no longtitude forces from the tires to move the car forwards or backwards. But only lateral forces to slow down the rate of spin.

As i understand it, when wheels are centered, the lateral response will be perpendicular to wheels, and will then slow down car rotation, but it will not introduce longitudinal force. The longitudinal force component present on the wheel during spinning will just introduce a diffrent slip angle result.

I re-checked marcos page for the steering section. He claims, after determining lateral force using pacejka curve, that they have to be applied to the car body. He will apply both lateral forces directly to car body, and then use them separatly to calculate torque and finally introduce some yaw. Fine for me, but what does he have to say about the lateral component of the front wheels ? This :

The lateral forces of the four tyres have two results: a net cornering force and a torque around the yaw axis. The cornering force is the force on the CG at a right angle to the car orientation and serves as the centripetal force which is required to describe a circular path. The contribution of the rear wheels to the cornering force is the same as the lateral force. For the front wheels, multiply the lateral force with cos(delta) to allow for the steering angle.

Fcornering = Flat, rear + cos(delta) * Flat, front

I'm quite rusted with my trigonometry, so i'm not 100% sure, but i think that will act as if the lateral response IS indeed perpenducular the the wheel, according to steer angle, BUT that he is suggesting to take only the force component that is projected on the car side axis. So if the front wheels are centered, 100% of the force will be applied. But if the wheel is steering at 60°, only 50% of the force is applied to the car.

But he is only calculating centripetal force and torque, so i guess only the truly lateral component does it. He may have "forget" the sin(dela)*Flat, front which is supposed to slow down the car as it is cornering, but maybe it is not that important for the car behaviour ?

---

Do you know if traction circle should be applied before or after taking count of weight load ? Because when i slow down the car in/before curves, so much weight get transfered to the front that the lateral force increase happens way too fast and the car can make an half-turn really easily. I feel like traction circle is capped to a maximum load or maybe my weight transfer needs a real spring instead of a simplistic time integration.

---

Thanks for your help and sharing your experience ! You say you are not expert, but given the quality of your racing game, i'll take your advices very seriously ! It's exactly the kind of feeling i want, only more arcade-ish.

### #3PochyPoch

Posted 12 September 2012 - 06:09 PM

Hi,

That's bad for me because i get much better results applying the lateral force directly to car chassis regardless of steering angle (but i take it in count for slip angle calculation). Maybe i just need to tune pacejka curve to respond to the fact it changes the car behaviour somehow. A little change alway seems dramatic in result at first, but maybe it is the right way to go and i need to adapt my curves which are really trivials for now.

Although i'm no expert, i always understood that a stationary car spinning on the spot with the steering centred produces no longtitude forces from the tires to move the car forwards or backwards. But only lateral forces to slow down the rate of spin.

As i understand it, when wheels are centered, the lateral response will be perpendicular to wheels, and will then slow down car rotation, but it will not introduce longitudinal force. The longitudinal force component present on the wheel during spinning will just introduce a diffrent slip angle result.

I re-checked marcos page for the steering section. He claims, after determining lateral force using pacejka curve, that they have to be applied to the car body. He will apply both lateral forces directly to car body, and then use them separatly to calculate torque and finally introduce some yaw. Fine for me, but what does he have to say about the lateral component of the front wheels ? This :

The lateral forces of the four tyres have two results: a net cornering force and a torque around the yaw axis. The cornering force is the force on the CG at a right angle to the car orientation and serves as the centripetal force which is required to describe a circular path. The contribution of the rear wheels to the cornering force is the same as the lateral force. For the front wheels, multiply the lateral force with cos(delta) to allow for the steering angle.

Fcornering = Flat, rear + cos(delta) * Flat, front

I'm quite rusted with my trigonometry, so i'm not 100% sure, but i think that will act as if the lateral response IS indeed perpenducular the the wheel, according to steer angle, BUT that he is suggesting to take only the force component that is projected on the car side axis. So if the front wheels are centered, 100% of the force will be applied. But if the wheel is steering at 45°, only 50% of the force is applied to the car.

But he is only calculating centripetal force and torque, so i guess only the truly lateral component does it. He may have "forget" the sin(dela)*Flat, front which is supposed to slow down the car as it is cornering, but maybe it is not that important for the car behaviour ?

---

Do you know if traction circle should be applied before or after taking count of weight load ? Because when i slow down the car in/before curves, so much weight get transfered to the front that the lateral force increase happens way too fast and the car can make an half-turn really easily. I feel like traction circle is capped to a maximum load or maybe my weight transfer needs a real spring instead of a simplistic time integration.

---

Thanks for your help and sharing your experience ! You say you are not expert, but given the quality of your racing game, i'll take your advices very seriously ! It's exactly the kind of feeling i want, only more arcade-ish.

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