I don't usually post, but i found a interesting video that deals with racing physics in games.

http://channel9.msdn.com/showpost.aspx?postid=314874

mentioning forza and that curve on the monitor both arent too promising but it still sounds interesting so ill give it a proper chance
nice find

Did anyone else follow why the 1 pool ball hitting the 2 others at exactly the same time has an undetermined result?

i wonder what this dude would think of LFS. I've never played forza or forza 2 so i can't comment.

I stopped watching a third of the way through when A) the guy said they're using the Pacejka formula and B) he apparently thinks longitudinal slip is when the wheel hub is rotating faster than the tire.

lol i was about to mention how 25 minutes in he starts talking about things that have caused so many flamewars and frustrated programmers.

lol @ the nascar jab 50 minutes in.

"at that point the tyre is now skidding and more slip gives you less grip"
bleah i know this would happen when i saw that screenshot

ok now he just claimed the wheel turns faster than the tyre ... im sure he knows a bit about coding but his physics knowledge is pretty appalling

Quote from Forbin :

I stopped watching a third of the way through when A) the guy said they're using the Pacejka formula and B) he apparently thinks longitudinal slip is when the wheel hub is rotating faster than the tire.

Isn't that true? ---> 0:47 http://www.youtube.com/watch?v=9O0b90G8Yhg

I dont want to start a flame war or something like that, I really just want to understand car physics as I notice it's getting more and more important as a hobby for me.

BTW Plasma Pong is a real eye-candy

Quote from Shotglass :

ok now he just claimed the wheel turns faster than the tyre ... im sure he knows a bit about coding but his physics knowledge is pretty appalling

I think it has more to do with bad wording (same for Forbin) than with knowledge, either for telling it comprehensively for a large crowd or for not being a car addict, thus using the wrong words...

@RedQuad: No, the hub spinning faster would mean that there is a slip between the wheel and the tire... As I said, probably wrong wording...

I thought he meant that the part of the tire that touches the road is initially spining slower then the hub without slip between hub/tire because of the flexible tire wall.

Thx for explanation Shotglass \/

Quote from RedQuad :

Isn't that true? http://www.youtube.com/watch?v=9O0b90G8Yhg

no theres 3 seperate effects

1) classic longitudinal slip - the tyre is rotating faster or slower than the rotation speed youd get from the tyres circumference and the distance traveled
in other words longitudinal slip is the difference between the behaviour youd expect from a rolling tyre (that it just rolls across the surface) and the actual behaviour which is that it turns slower or faster than it should

2) tyres winding up like in that video- tyres being made from rubber obviously are able to flex
the point where the forces are applied (the contact patch on the ground) is below the solid wheel so if youre braking the force pointing backwards on the contact patch will pull the contact patch backwards in relation to the wheel (which is the winding up you see in that video just that in the vid its under acceleration but for all that it matters in this discussion those 2 are identical)
an anology would be what happens with you in the car while youre braking - in this case the car represents the contact patch which applies forces through a non solid joint (the safety belt) to your body which represents the inert wheel
the important bit is the triangle you see in his drawing which represents the difference in the centre of the contact patch (where the forces are applied) and the line through the centre of the wheel intersecting with the road at a right angle

3) what hes talking about ... the wheel rotating faster than the tyre which should not happen in any circumstances and is definately not worth simulating

but... its seen quite a bit in drag racing as he mentioned. unless i am missunderstanding

Quote from bbman :

I think it has more to do with bad wording (same for Forbin) than with knowledge, either for telling it comprehensively for a large crowd or for not being a car addict, thus using the wrong words...

i doubt it he pretty clearly stated that the wheel rotates faster than the tyre and even had flex lines to explain this ridiculous idea

about that dragster video at 0.47 if you look closely at the wheels nuts and bolts and the good year lable on the tyre you can clearly see that they are allways rotating at the same speed with the slight exception of very short transient states while the tyre goes into extreme flex (the guy in the vid is talking about steady state though)

He was grasping for words the whole time (except for physical expressions), so I think he just had no clue how to express it right, especially if interviewed by a developer network (who you can assume have no clue about cars or racing in general)... It would be pretty bad if a physicist had an appaling knowlegde of physics...

Am sure he was just dumbing down the language so more people could follow. i know i tend to do that when explaining something that i don't want to go into great detail.
Did anyone watch up to the part with the chassis flex demo. found that to be one of the more interesting part.

yeah, i just downloaded the demo of the truck one. someone posted a thread on it ages ago.

That video features Brian Beckman who is perhaps best known in sim racing circles for his 'Physics of Racing' series of papers. He's a professional physicist and amateur autocrosser. He holds a PhD in Astrophysics from Princeton University, has served as a Senior Engineer and Section Manager at the Jet Propulsion Labratory and is currently a Senior Software Architect at Microsoft. His credentials and experience are practically impeccable.

Quote from BuddhaBing :

His credentials and experience are practically impeccable.

and yet he obviously doesnt know what hes talking about as far a tyres are concerned

All of us think LFS is the best racing sim game.

?

Quote from Shotglass :

and yet he obviously doesnt know what hes talking about as far a tyres are concerned

Are you seriously saying you are more of an expert than him?

Quote from Shotglass :

ok now he just claimed the wheel turns faster than the tyre ... im sure he knows a bit about coding but his physics knowledge is pretty appalling

Not the whole tyre but what he said is actually true for the front part of the contact patch when accelerating, which has smaller angular velocity than the wheel hub in that case. The video was probably meant as a popular lecture and obviously things are simplified, because being precise would take too much time.

Wow I like the wallpaper. What is it? An octopus? :cookiemon

w126 - there's simplifying things for the audience, and then there's just being too simple and incorrect

Quote from BrandonAGr :

Are you seriously saying you are more of an expert than him?

no im saying hes just plain wrong in everything he said about longitudinal tyre forces and also everything he said about the shape of the lateral curves past peak

especially his explanation on the (incorrect) shape of the lateral curves shows an untter misunderstanding about whats happening

Quote from w126 :

Not the whole tyre but what he said is actually true for the front part of the contact patch when accelerating, which has smaller angular velocity than the wheel hub in that case. The video was probably meant as a popular lecture and obviously things are simplified, because being precise would take too much time.

you mean as in the angular velocity is not uniform along the whole circumference of the tyre ? while this is most certainly true to some degree for these dragster tyre the effect should be negligible on road car tyres

but the important bit is that he defined longitudinal slip with that explanation which is plain and simply wrong for the longitudunal slip that goes into the pacejka model