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### #ActualEdy

Posted 01 October 2012 - 05:05 AM

In summary, you need these kind of formulas only when developing high-end ultra-realistic vehicle simulation with real tire sets (think on netKar Pro, rFactor, etc). But you are not required at all to use these approaches for developing realistic vehicle physics. These methods are inherited from the automotive industry and it's quite difficult to implement them properly in video games.
Really ? oO i just learned it. I had the feeling a lot of games (like GTA, or even more arcade games) use the curve approach, even if they tweak it rather than directly implementing the formula. Your framework doesnt seems too much realistic to me, and it's using it right ? I was just plotting simple curves scaled by weight load, and (re)discovered today, that forces do not linearly increase with Fz, thus making proper use of the formula important to me, or at least it is what i was thinking until i read this.

Yes, you can use a curve approach, but not necessarily a pacejka one. As Kunos pointed out in another of his replies, once you see the pattern of the real friction curves you can use any method for reproducing them. That framework uses those patterns as you can see at the demo (press B, then shift-B to see the curves). However, that framework is based on a workaround to the standard wheel component of the physics engine (no real-world physics on the tire). So things like lateral-longitudinal force combination are roughly calculated, and the method is targeted for gameplay instead of realism.

> Use wheel distance to CG to calculate weight transfer lateraly and longitudinal. Combine those two.
This is most probably wrong... you don't calculate weight transfer, it should be automatically happening in your rigid body physics

That's right, you don't need to calculate this. In my case (Unity 3D) I have rigid body physics that just work. So my vehicle is constructed simply as a rigid body with 4 contact points and a simple suspension on each one (spring + damper). If I put this "vehicle" over a terrain it will behave as if it is sliding on ice (no friction) but suspension, weight transfer and weight load at each contact point will just work.

What my tire simulation does is simply applying the appropriate force at each contact point according to the vertical load on that point. If the forces are calculated and applied properly, then the rigid body will behave as a vehicle by itself, which actually does in my work-in-progress framework.

### #2Edy

Posted 01 October 2012 - 05:04 AM

In summary, you need these kind of formulas only when developing high-end ultra-realistic vehicle simulation with real tire sets (think on netKar Pro, rFactor, etc). But you are not required at all to use these approaches for developing realistic vehicle physics. These methods are inherited from the automotive industry and it's quite difficult to implement them properly in video games.
Really ? oO i just learned it. I had the feeling a lot of games (like GTA, or even more arcade games) use the curve approach, even if they tweak it rather than directly implementing the formula. Your framework doesnt seems too much realistic to me, and it's using it right ? I was just plotting simple curves scaled by weight load, and (re)discovered today, that forces do not linearly increase with Fz, thus making proper use of the formula important to me, or at least it is what i was thinking until i read this.

Yes, you can use a curve approach, but not necessarily a pacejka one. As Kunos pointed out in another of his replies, once you see the pattern of the real friction curves you can use any method for reproducing them. That framework uses those patterns as you can see at the demo (press B, then shift-B to see the curves). However, that framework is based on a workaround to the standard wheel component of the physics engine (no real-world physics on the tire). So things like lateral-longitudinal force combination are roughly calculated, and the method is targeted for gameplay instead of realism.

> Use wheel distance to CG to calculate weight transfer lateraly and longitudinal. Combine those two.
This is most probably wrong... you don't calculate weight transfer, it should be automatically happening in your rigid body physics

That's right, you don't need to calculate this. In my case (Unity 3D) I have rigid body physics that just work. So my vehicle is constructed simply as a rigid body with 4 contact points and a simple suspension on each one (spring + damper). If I put this "vehicle" over a terrain it will behave as if it is sliding on ice (no friction) but suspension, weight transfer and weight load at each contact point will just work.

What my tire simulation does is simply apply the appropriate force at each contact point according to that point's load. If the forces are calculated and applied properly, then the rigid body will behave as a vehicle by itself, which actually does in my work-in-progress framework.

### #1Edy

Posted 01 October 2012 - 04:57 AM

In summary, you need these kind of formulas only when developing high-end ultra-realistic vehicle simulation with real tire sets (think on netKar Pro, rFactor, etc). But you are not required at all to use these approaches for developing realistic vehicle physics. These methods are inherited from the automotive industry and it's quite difficult to implement them properly in video games.
Really ? oO i just learned it. I had the feeling a lot of games (like GTA, or even more arcade games) use the curve approach, even if they tweak it rather than directly implementing the formula. Your framework doesnt seems too much realistic to me, and it's using it right ? I was just plotting simple curves scaled by weight load, and (re)discovered today, that forces do not linearly increase with Fz, thus making proper use of the formula important to me, or at least it is what i was thinking until i read this.

Yes, you can use a curve approach, but not necessarily a pacejka one. As Kunos pointed out in another of his replies, once you see the pattern of the real friction curves you can use any method for reproducing them. That framework uses those patterns as you can see at the demo (press B, then shift-B to see the curves). However, that framework is based on a workaround to the standard wheel component of the physics engine (no real-world physics on the tire). So things like lateral-longitudinal force combination are roughly calculated, and the method is targeted for gameplay instead of realism.

Use wheel distance to CG to calculate weight transfer lateraly and longitudinal. Combine those two.
This is most probably wrong... you don't calculate weight transfer, it should be automatically happening in your rigid body physics
Sorry, i meaned load transfer and not weight transfer, i offen misuse those two words. My dynamic load transfer happens with acceleration in the car body. So to know the real weight on a body point, i have to find out its distance to CG, and then use long/lat acceleration. As i do not use a physics engine (except for the collision detection part), i code weight transfer as much as simple forces integration. So AFAIK it cannot happen automatically unless i use a real 3D engine and feed him with some values. I get front/lat acceleration depending on current acceleration values, which themselves depends on previous ticks generated forces.
The real weight transfer, which happens when the car CG is displaced occurs indeed automatically as a suspension or an other is going up or down. I'll edit my post to use correct terms.

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