Author Topic: Front tyre incorrect slip angle  (Read 1588 times)

Fightone

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Front tyre incorrect slip angle
« on: May 27, 2017, 11:51:56 AM »
Hello Piboso,

I hope you read this topic. This is the thing I felt wrong for a long time playing GP Bikes so I finally decided to post it here.

The issue is: I found that the front tyre has unrealistic slip angle profile what causes the bike understreer on the corner entry more than the real one. The issue is not with the tyre grip itself, which is ok but just with the slip angle profile (i.e. slip angle at which this max grip is generated).
To be exact: maximum grip of the front tyre is reached at a bit too high slip angles comparing to the rear tyre (while in real life difference in slip angles beetween front and rear is at least not that big).
It can even be noticed when you just look at some replay and notice that the front wheel is visually drifting along the track a bit unrealisticly like it's "shifting sideways" a bit on the corner exit when you pick up a bike - that's also this problem.
The issue should be related to some general game settings cause it's noticed on all bikes more or less and I haven't found anything related to tyre slip angles in the bike folders.

Unfortunatly I can't say exactly "how much" the angle profile is wrong because it's up to the feel but now it's too far off for sure. But ofc I'd be able to tell the right one if there'r a chance to play with it a bit and I'm ready to give that feedback.

I believe fixing it would improve real feel of bikes in the game and front of the bike will feel more "planted" to the group.
P.S. Folks, please don't jump into discussion if you don't know the exact physics I'm talking about.
P.S.S. If you have an idea where this setting can be hidded in the game files - you'r welcome.  :)
« Last Edit: May 27, 2017, 12:14:10 PM by Fightone »

h106frp

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Re: Front tyre incorrect slip angle
« Reply #1 on: May 27, 2017, 01:50:35 PM »
The .tyre file has the values you are looking for

Fightone

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Re: Front tyre incorrect slip angle
« Reply #2 on: May 27, 2017, 02:21:18 PM »
Can you point out where exactly? I don't see anything related to slip angles there.

h106frp

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Re: Front tyre incorrect slip angle
« Reply #3 on: May 27, 2017, 03:06:05 PM »
The values relate to the pacejka tyre model values so you will need to do some detective work. MAX posted a tool to help a bit
http://forum.piboso.com/index.php?topic=1920.0

It works like this
http://www.racer.nl/reference/pacejka.htm
« Last Edit: May 27, 2017, 03:27:42 PM by h106frp »

Fightone

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Re: Front tyre incorrect slip angle
« Reply #4 on: May 27, 2017, 07:58:25 PM »
Thanks! That's good stuff. Will try it out.

HornetMaX

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Re: Front tyre incorrect slip angle
« Reply #5 on: May 27, 2017, 08:56:35 PM »
P.S. Folks, please don't jump into discussion if you don't know the exact physics I'm talking about.
The values relate to the pacejka tyre model values so you will need to do some detective work. MAX posted a tool to help a bit
http://forum.piboso.com/index.php?topic=1920.0

It works like this
http://www.racer.nl/reference/pacejka.htm
Can you point out where exactly? I don't see anything related to slip angles there.
That's what I call getting off to a bad start ...

Anyway, the "front drifting" problem has been discussed a lot in the past, it's unlikely one can fix it by tampering with the tyre model (.tyre). It seems to be "baked" in the current physics.





Fightone

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Re: Front tyre incorrect slip angle
« Reply #6 on: May 29, 2017, 10:17:20 AM »
Well, I'll try and let you know if that works. Yet, I don't see a reason why adjusting slip angles won't help, it think it should.  :)
"That's what I call getting off to a bad start ..."
Why? I'm not an expert in this particular game and any simulation model, just I'm not interested in getting into phys. discussion with people who don't know how slip angles work and how they relate to real bike behaviour (it's a bit complicated in fact), that's why I wrote this.

BOBR6 84

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Re: Front tyre incorrect slip angle
« Reply #7 on: May 29, 2017, 12:46:44 PM »
MaX is the gpbikes resident, helpful genius!

The issue you posted about does need sorting out though.. I remember piboso saying it is a physics limitation.. Not sure what that means but doesnt sound good  :(

HornetMaX

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Re: Front tyre incorrect slip angle
« Reply #8 on: May 29, 2017, 01:39:12 PM »
Well, I'll try and let you know if that works. Yet, I don't see a reason why adjusting slip angles won't help, it think it should.  :)
"That's what I call getting off to a bad start ..."
Why? I'm not an expert in this particular game and any simulation model, just I'm not interested in getting into phys. discussion with people who don't know how slip angles work and how they relate to real bike behaviour (it's a bit complicated in fact), that's why I wrote this.
It just seemed funny that you ask  people without the necessary knowledge to stay out of the discussion but then, once pointed to the physics file you're a bit lost (and you state you're not interested to get into the physics).

There's no sucha thing as "adjusting slip angles". It's not as easy as "find the parameter responsible of the relationship between grip and slip angle, modify it and we're done".

If it was that easy, it would have been done already by one of the many modders that have played with this stuff.
It may even be the root cause of the unexpected behavior is not even in the tyre modelling ...

MaX is the gpbikes resident, helpful genius!
I'm less and less resident and never been a genius. But thanks :)

Fightone

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Re: Front tyre incorrect slip angle
« Reply #9 on: May 29, 2017, 05:51:51 PM »
Well, I'll try and let you know if that works. Yet, I don't see a reason why adjusting slip angles won't help, it think it should.  :)
"That's what I call getting off to a bad start ..."
Why? I'm not an expert in this particular game and any simulation model, just I'm not interested in getting into phys. discussion with people who don't know how slip angles work and how they relate to real bike behaviour (it's a bit complicated in fact), that's why I wrote this.
It just seemed funny that you ask  people without the necessary knowledge to stay out of the discussion but then, once pointed to the physics file you're a bit lost (and you state you're not interested to get into the physics).
No offence Max but you'r reading me somehow wrong. There's a difference between physics and physics simulation in computer games. So I'm pretty decent at first and not so good at second. So nothing controversial.
There's no sucha thing as "adjusting slip angles". It's not as easy as "find the parameter responsible of the relationship between grip and slip angle, modify it and we're done".
Will reply you when I finally get to play with these values.


CapeDoctor

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Re: Front tyre incorrect slip angle
« Reply #10 on: May 30, 2017, 06:48:17 AM »

Will reply you when I finally get to play with these values.


lol, mate, admire the enthusiasm, at least.
maybe best no-one here shatters your dream of finding this value, so we should wait in anticipation of your discoveries.  ;D

HornetMaX

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Re: Front tyre incorrect slip angle
« Reply #11 on: May 30, 2017, 07:10:59 AM »
No dream-shattering. If he's a basic understanding of physics he should have no trouble in getting how the tyre model works.

Side note: I think the link posted by h106frp (racer.nl) has a simplified model, the one used in GPB (and WRS, KRP) is described in Pacejka's book (Tyre and vehicle dynamics).
Still good to read throught the racer.nl stuff though, to get the overall idea.

Fightone

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Re: Front tyre incorrect slip angle
« Reply #12 on: June 01, 2017, 02:30:54 PM »
Hello folks.
I'm back with some results. There's no surprises :D it didn't work out but I have at least a few notes:
- there's no problem to adjust slip angle profile of the tyre, it can easily be done by altering p_Dy1 and p_Cy1 values with help of Max's tool, everything else is pretty much just a fine tuning.
- game doesn't really react to changes like it should. When you lowering peak slip angle the grip level also goes down for some unknown reason so if you set peak slip angle close to 0 - you will get grip level close to 0 as well what doesn't make any sense physically-wise. It can be compensated ofc with setting insanely high level of grip in the same tyre file (i used 15) but that just shows that there's some problem with physics engine.
- front wheel drift remains even with slip angles set ~ 0 (and grip level set to 15..) what proves that the phys engine doesn't work like it should as slip angle in the tyre profile obviously doesn't correspond with one in the game. I also tried to compensate front wheel drift by increasing rear wheel slip but it also doesn't work like it should i.e. something in bike behaviour changes (wobbling tendency, grip level etc) but not the real slip angle which remains the same.

So as a conclusion: some raw physics issue, can't be fixed by slip angles adjustments.

That's it. Any comments are welcome now. :)
« Last Edit: June 01, 2017, 02:39:50 PM by Fightone »

HornetMaX

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Re: Front tyre incorrect slip angle
« Reply #13 on: June 01, 2017, 02:52:23 PM »
- game doesn't really react to changes like it should. When you lowering peak slip angle the grip level also goes down for some unknown reason so if you set peak slip angle close to 0 - you will get grip level close to 0 as well what doesn't make any sense physically-wise.
I'm not sure what you mean with "if you set peak slip angle close to 0". Can you post the diagrams that come out of my tool and show what you think it's unexpected ?

PiBoSo

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Re: Front tyre incorrect slip angle
« Reply #14 on: June 01, 2017, 03:03:34 PM »
Hello folks.
I'm back with some results. There's no surprises :D it didn't work out but I have at least a few notes:
- there's no problem to adjust slip angle profile of the tyre, it can easily be done by altering p_Dy1 and p_Cy1 values with help of Max's tool, everything else is pretty much just a fine tuning.
- game doesn't really react to changes like it should. When you lowering peak slip angle the grip level also goes down for some unknown reason so if you set peak slip angle close to 0 - you will get grip level close to 0 as well what doesn't make any sense physically-wise. It can be compensated ofc with setting insanely high level of grip in the same tyre file (i used 15) but that just shows that there's some problem with physics engine.
- front wheel drift remains even with slip angles set ~ 0 (and grip level set to 15..) what proves that the phys engine doesn't work like it should as slip angle in the tyre profile obviously doesn't correspond with one in the game. I also tried to compensate front wheel drift by increasing rear wheel slip but it also doesn't work like it should i.e. something in bike behaviour changes (wobbling tendency, grip level etc) but not the real slip angle which remains the same.

So as a conclusion: some raw physics issue, can't be fixed by slip angles adjustments.

That's it. Any comments are welcome now. :)

Changing p_Dy1 directly changes the grip.
To change the lateral stiffness without lowering the grip you have to play with p_Cy1 and p_Ky1 only.