Author Topic: Front tyre incorrect slip angle  (Read 1273 times)

Stout Johnson

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Re: Front tyre incorrect slip angle
« Reply #30 on: June 02, 2017, 06:54:48 PM »
I think we are talking many different things now here.
  • There's definitely the thing where the virtual rider tries to pick up the bike by counter-steering when the tires are already on the grip threshold, which causes the front to fold. I think this behaviour can only be removed by either limiting the lean to uncritical values or if Piboso changes the way the virtual rider counter steers in high lean angles (in a way Vin97 described, shifting rider weight for a brief moment to compensate for the steering input - which is what riders in reality do)
  • There is the thing which CapeDoctor describes. I guess we have to wait for his video to be sure what he is referring to. From what I understand it could be the behaviour when accelerating during lean which sometimes causes a small power slide, causing the rear to come around a bit and the front also 'biting' towards the inside of the corner. Maybe it is that what he means?
  • The things mentioned above are most likely unrelated to the inital topic of this thread described as 'Front tyre incorrect slip angle'. But I am not sure whether this is a good title for the behaviour, as I doubt that there is actual front wheel slip happening. What we see is the front wheel somehow being dragged unrealistically which in reality would have translate to front wheel slip. But in GPB I assume it is rather a visual/geometry/resultant force bug which causes it to look like front wheel slip. If there was actual front wheel slip computed by GPB the front tires would overheat and have unusual wear, which I never saw happening. I therefor referred to this problem as 'front wheel misalignment bug' when I pointed it out before.
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Fightone

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Re: Front tyre incorrect slip angle
« Reply #31 on: June 02, 2017, 08:00:28 PM »
But I am not sure whether this is a good title for the behaviour, as I doubt that there is actual front wheel slip happening. What we see is the front wheel somehow being dragged unrealistically which in reality would have translate to front wheel slip. But in GPB I assume it is rather a visual/geometry/resultant force bug which causes it to look like front wheel slip.
You are right, that's something we already figured out here. I'm also not sure if real slipping is happening or not in the game engine, but its definitely not related to slip angles being defined by the tyre spec.
Anyway, I called the topic like that because visual position of the bike in relation to the surface IRL is determined exactly by front to rear slip angles relation, that's why "unrealistic front wheel slip" was the first logical assumtion.
« Last Edit: June 03, 2017, 10:11:58 AM by Fightone »

HornetMaX

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Re: Front tyre incorrect slip angle
« Reply #32 on: June 03, 2017, 12:24:06 PM »
I'm also not sure if real slipping is happening or not in the game engine
You're gonna make somebody angry with that :)
Of course real slipping happens in the game engine: when they tyre diagram (force vs long slip or lat slip) crosses the origin, that means that if the tyre is not slipping it is not generating any force.
As in GPB you're able to take turns and to accelerate from stop, slipping is happening :)

but its definitely not related to slip angles being defined by the tyre spec.
Not sure what you mean with "slip angles being defined by the tyre spec": the tyre model does not define a "slip angle".
Also, what my tool show are the diagrams in pure longitudinal (i.e. no side slip) and pure lateral (i.e. no longitudinal slip). In real conditions you normally have both at the same time (and the maximum force is somehow shared between the two components).

Fightone

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Re: Front tyre incorrect slip angle
« Reply #33 on: June 03, 2017, 01:16:27 PM »
You're gonna make somebody angry with that :)
Of course real slipping happens in the game engine: when they tyre diagram (force vs long slip or lat slip) crosses the origin, that means that if the tyre is not slipping it is not generating any force.
As in GPB you're able to take turns and to accelerate from stop, slipping is happening :)
Thanks cap, I agree  :)
Also, what my tool show are the diagrams in pure longitudinal (i.e. no side slip) and pure lateral (i.e. no longitudinal slip). In real conditions you normally have both at the same time (and the maximum force is somehow shared between the two components).
I double that.
with "slip angles being defined by the tyre spec": the tyre model does not define a "slip angle".
well, it does in a way. Of course in collaboration with other factors i.e. what the bike is doing on the road etc but lets not argue over nothing.
Most importantly, tyre model is something that should define a max slip angle that could be reached with that tyre and that's not happening with GP Bikes.
What I meant when I say that, is that I'm not sure if this "unrealistic dragging of the front tyre" is caused by slip angle being calculated in the phys. engine (because as noted by Stout Johnson it indeed doesn't look like regular slipping or the tyre) or it is just some "game magic" overlayed on physics and causing this dragging. Anyway it's very wrong and remains a problem.

So as the bottom line: I don't doubt that slipping is modelled in the phys. engine, that's something that I checked first hand while playing with tyre characteristics. I doubt that this weird slipping is the same kind of slipping as "normal one" happening because of the tyre flex, while generating force.
« Last Edit: June 03, 2017, 01:35:38 PM by Fightone »

HornetMaX

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Re: Front tyre incorrect slip angle
« Reply #34 on: June 03, 2017, 04:20:41 PM »
So as the bottom line: I don't doubt that slipping is modelled in the phys. engine, that's something that I checked first hand while playing with tyre characteristics. I doubt that this weird slipping is the same kind of slipping as "normal one" happening because of the tyre flex, while generating force.
OK then, we're set.

But ... slipping happens because of tyre flex  ?! :o

Hawk

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Re: Front tyre incorrect slip angle
« Reply #35 on: June 03, 2017, 04:44:34 PM »
As I understand the theory, a tyre is slipping all the time it's in motion, whether under acceleration or not?

Hawk.

Fightone

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Re: Front tyre incorrect slip angle
« Reply #36 on: June 03, 2017, 05:00:01 PM »
But ... slipping happens because of tyre flex  ?! :o
Slipping as "slipping friction" - no, it's a physical process when friction surfaces are moving in relation to each other while in contact.
Slipping of the tyre - as a physical phenomena when rotation direction of the tire (not a deam vector :D, but where the wheel is "pointed") is not matching direction of its headway motion - yes, I can say that it's caused by tire flex, cause otherwise peak slip angle would tend to 0 while stiffness of the wheel tends to infinity (if we take regular rubber static/slipping frinction values).
So if it weren't for tyre flex - there would be effectively no slip angle while going around the track fast "i.e. having maximum out of the tyre".
As I understand the theory, a tyre is slipping all the time it's in motion, whether under acceleration or not?

Hawk.
Correct. To be exact: it's always slipping while producing force, not just in motion.
« Last Edit: June 03, 2017, 05:02:15 PM by Fightone »

Become dust

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Re: Front tyre incorrect slip angle
« Reply #37 on: June 03, 2017, 05:16:09 PM »
I wonder if this discussion would interest Piboso? or perhaps many similar discussion threads has been created before.

even both i bet

Fightone

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Re: Front tyre incorrect slip angle
« Reply #38 on: June 03, 2017, 05:21:15 PM »
I wonder if this discussion would interest Piboso?
I hope so. Not the whole discussion but at least the bug we are talking about. Vehicle behaviour is imho the most important thing for a simulator so I guess a lot of people would appreciate that fix (eventhough they might not realize what's exactly the problem while playing GP Bikes, but they should definitely feel the improvement).

HornetMaX

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Re: Front tyre incorrect slip angle
« Reply #39 on: June 03, 2017, 05:46:54 PM »
Slipping as "slipping friction" - no, it's a physical process when friction surfaces are moving in relation to each other while in contact.
Slipping of the tyre - as a physical phenomena when rotation direction of the tire (not a deam vector :D, but where the wheel is "pointed") is not matching direction of its headway motion - yes, I can say that it's caused by tire flex, cause otherwise peak slip angle would tend to 0 while stiffness of the wheel tends to infinity (if we take regular rubber static/slipping frinction values).
So if it weren't for tyre flex - there would be effectively no slip angle while going around the track fast "i.e. having maximum out of the tyre".
I disagree. Slipping, longitudinally or laterally, does not happen because of tyre flex. You can slip with a perfectly rigid "tyre".

As I understand the theory, a tyre is slipping all the time it's in motion, whether under acceleration or not?
Correct. To be exact: it's always slipping while producing force, not just in motion.
So in fact it's not correct: it's slipping if it is generating force. Ideally it could be in motion (constant speed and direction) without any slip.

The problem is that most people thinks of "slipping" as in extreme cases (e.g. locking while braking or doing a burn standing still).
In fact, when accelerating mildly to move from 90Khm to 100Khm, your rear tyre is generating a force and hence slipping a bit.
Fore example, it could be that the tyre forward velocity (the velocity of the tyre axle) is 95 Kmh while the velocity of the contact patch relative to the ground is 97 Kmh: it is slipping, even if a naked eye won't detect it (nor the rider on the bike).

Fightone

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Re: Front tyre incorrect slip angle
« Reply #40 on: June 03, 2017, 06:06:19 PM »
Slipping as "slipping friction" - no, it's a physical process when friction surfaces are moving in relation to each other while in contact.
Slipping of the tyre - as a physical phenomena when rotation direction of the tire (not a deam vector :D, but where the wheel is "pointed") is not matching direction of its headway motion - yes, I can say that it's caused by tire flex, cause otherwise peak slip angle would tend to 0 while stiffness of the wheel tends to infinity (if we take regular rubber static/slipping frinction values).
So if it weren't for tyre flex - there would be effectively no slip angle while going around the track fast "i.e. having maximum out of the tyre".
I disagree. Slipping, longitudinally or laterally, does not happen because of tyre flex. You can slip with a perfectly rigid "tyre".
You should notice that I'm talking about "peak slip angle" and "maximum performance out of the tyre". I'm not talking about any possible slip, that's obvious.. Type of physics that I'm trying to discuss here is "racing-wise" not just "any slip of anything anywhere".
Correct. To be exact: it's always slipping while producing force, not just in motion.
So in fact it's not correct: it's slipping if it is generating force. Ideally it could be in motion (constant speed and direction) without any slip.
You said incorrect and just repeated what I wrote. :)

P.S. Anyhow, I long lost the taste for fights over physics, that's what I've been doing for years in the past so if you want recognition - I subscribe to your latest explanations about tyre dynamics. :) They are accurate.

What I'm really interested here - is only fixing the issue in the game that's obvious to all of us.
« Last Edit: June 03, 2017, 06:14:35 PM by Fightone »

HornetMaX

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Re: Front tyre incorrect slip angle
« Reply #41 on: June 03, 2017, 06:13:07 PM »
You should notice that I'm talking about "peak slip angle" and "maximum performance out of the tyre". I'm not talking about any possible slip, that's obvious.. Type of physics that I'm trying to discuss here is "racing-wise" not just "any slip of anything anywhere".
So you mean that with a rigid tyre the peak slip angle is zero ? :o

Or maybe by "peak slip angle" you mean "the smallest slip angle at which the tyre generates the maximum force over all possible slip angles" ?
Which would be a pretty unusual definition of "peak" ...

Correct. To be exact: it's always slipping while producing force, not just in motion.
So in fact it's not correct: it's slipping if it is generating force. Ideally it could be in motion (constant speed and direction) without any slip.
You said incorrect and just repeated what I wrote. :)
Because you told Hawk he was correct before adding something that, in facts, says he was wrong (thing on which I agree).

Fightone

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Re: Front tyre incorrect slip angle
« Reply #42 on: June 03, 2017, 06:21:34 PM »
You should notice that I'm talking about "peak slip angle" and "maximum performance out of the tyre". I'm not talking about any possible slip, that's obvious.. Type of physics that I'm trying to discuss here is "racing-wise" not just "any slip of anything anywhere".
So you mean that with a rigid tyre the peak slip angle is zero ? :o
No I mean that:
peak slip angle would tend to 0 while stiffness of the wheel tends to infinity (if we take regular rubber static/slipping frinction values).
no more no less. It's tending to 0 only with regular rubber friction coeffs but not necessarily for others materials.
Or maybe by "peak slip angle" you mean "the smallest slip angle at which the tyre generates the maximum force over all possible slip angles" ?
Which would be a pretty unusual definition of "peak" ...
No I meant "slip angle when tyre generates max lat force".
Because you told Hawk he was correct before adding something that, in facts, says he was wrong (thing on which I agree).
Maan.. ye, lets just finish it. :)


« Last Edit: June 03, 2017, 06:23:17 PM by Fightone »

CapeDoctor

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Re: Front tyre incorrect slip angle
« Reply #43 on: June 21, 2017, 08:03:59 AM »
hi guys
for what it's worth, i got a short replay where this front end issue i suffer with the RGV250 happens.
in the replay, you can see i am on my line, past the apex and starting to lift the bike and accelerate. as i accelerate, it looks like the front wheel turns in to the right.
i can assure you, i am NOT turning it in, it is the acceleration that is making it happen. i am essentially not steering here, simply letting the bike lift naturally with minimal input. adding throttle just forces it over to the side, and this makes no sense.
well, there's a short replay you can watch and judge for yourselves. maybe i am doing something inherently wrong here, but please remember, it doesn't happen that often - which makes it all the more frustrating when it does, lol.
replay: https://www.mediafire.com/?3wnbrz7ppkrjdt7

p.s: best way to watch the replay clip is to use the 'Free' cam., and rotate around so that you are looking at the front of the bike, then watch the clip. this is probably the easiest way to see what's happening. ;)
« Last Edit: June 21, 2017, 08:21:49 AM by CapeDoctor »

HornetMaX

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Re: Front tyre incorrect slip angle
« Reply #44 on: June 21, 2017, 05:36:46 PM »
@CapeDoc: downloaded the file, extracted fine, but when I put it in the right GPB folder, GPB doesn't see it (it sees my other replay files). Weird  :o