Author Topic: Front tyre incorrect slip angle  (Read 1272 times)

Fightone

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Re: Front tyre incorrect slip angle
« Reply #15 on: June 01, 2017, 03:29:31 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 ?
Meaning that max lateral force is reached at ~<3 degrees of slip angle or so, not 15-20. I'll send you diagrams a bit later.
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.
Thanks! Maybe I missed something but it seemed to me that maximum lat. force remained the same in the Max's tool while I was altering that parameter. I'll recheck and let you know.

Fightone

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Re: Front tyre incorrect slip angle
« Reply #16 on: June 01, 2017, 08:41:05 PM »
2Max: attaching the diagram.
2Piboso - thanks for the advice! My bad here, indeed I didn't notice that p_Dy1 was influencing general grip.
So with p_k1 value I can play with max slip angles and it works!

The only problem remaining is that it's still not enough to overcome "fron tire slipping issue" i.e. even setting slip angle close to 0 doesn't demolish slipping of the front tyre. And compensating it with rear wheel slipping requires setting unrealistic values so the bikes starts behaving weird, so it's not a solution. So still, the issue is incorporated somewhere in the physics engine, not in tyres..

« Last Edit: June 01, 2017, 08:45:01 PM by Fightone »

HornetMaX

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Re: Front tyre incorrect slip angle
« Reply #17 on: June 01, 2017, 08:43:17 PM »
2Max: attaching the diagram.
It's not attached but no longer really needed anyway: I got what you tried to do and yeah, using p_Dy1 was not the right way, as explained by PiBoSo.

EDIT: it just appeared.

The only problem remaining is that it's still not enough to overcome "fron tire slipping issue" i.e. even setting slip angle close to 0 doesn't demolish slipping of the front tyre. And compensating it with rear wheel sleeping requires setting unrealistic values so the bikes starts behaving weird, so it's not a solution. So still, the issue is incorporated somewhere in the physics engine, not in tyres..
:)
« Last Edit: June 01, 2017, 08:45:39 PM by HornetMaX »

Fightone

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Re: Front tyre incorrect slip angle
« Reply #18 on: June 01, 2017, 08:49:18 PM »
Yea, I added it a "second" after the post) showing the last setup I tried, but yeah.. it's not really needed anymore after I made sure myself that the issue is not in tyres specification. :)
« Last Edit: June 01, 2017, 08:54:18 PM by Fightone »

CapeDoctor

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Re: Front tyre incorrect slip angle
« Reply #19 on: June 02, 2017, 08:01:22 AM »
hey guys
been following this thread, and i wanted to ask something which may or may not be related.
not being sure about slip angles and such, i'll try and convey it in layman rookie terms, and hopefully the more physics savvy guys will know what i'm on about.
so, again, in this case, the bike that this happens most to me with is the RGV250, but that could just be because it's the bike i ride most, currently.
so what sometimes happens is, i'm feeling the front tire 'biting' nicely under braking into a corner, pretty low lean, and now i'm exiting the corner, slowly lifting the bike and accelerating out - i can feel the tire gripping nicely on the bottom side of the tire.
then, instead of gripping more onto the main tread of the tire as i try to lift and accelerate at the same time, it seems to start gripping more and more up the side of the tire, so that if i keep accelerating, it just 'bites' back down on the SIDE of the tire and causes the front to tuck in.(BITE in, more like)  ;D
this does NOT happen very often, but it has happened enough times for me to ask about it.
is this something that could happen in reality? i've not had the 'nads to try this sort of high speed low lean cornering in reality much, lol... it just doesn't seem right, though....
anyway, hope i've explained it okay, and after all that, i hope it's somehow related to this thread.
if not, well, apologies in advance. i'll move this to a new thread if needed. ;)

Fightone

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Re: Front tyre incorrect slip angle
« Reply #20 on: June 02, 2017, 08:47:02 AM »
i can feel the tire gripping nicely on the bottom side of the tire.
then, instead of gripping more onto the main tread of the tire as i try to lift and accelerate at the same time, it seems to start gripping more and more up the side of the tire, so that if i keep accelerating, it just 'bites' back down on the SIDE of the tire and causes the front to tuck in.(BITE in, more like)  ;D
To be honest I don't quite understand the concept of "bottom" and "side" of the tire in your explanation. I mean: part of the tire gripping the ground depends on the lean angle so how side of the tyre can start gripping more if you'r lifting the bike out of the corner? I'm confused.  :)
« Last Edit: June 02, 2017, 08:52:57 AM by Fightone »

CapeDoctor

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Re: Front tyre incorrect slip angle
« Reply #21 on: June 02, 2017, 09:39:50 AM »
yes, it's kind of hard to explain, and it has me confused as well, which is why i'm asking about it.

maybe this diagram can help a bit more:


so when i talk about the 'bottom' i'm talking about the actual tread part of the tire, in this pic the section covered with 'A'
when i say the side, i really mean it starts to grip more towards the 'B' section in the diagram, and if i accelerate, this gets worse and the tire basically just pulls me to the ground with sheer grip.
as if the section of the tire that's gripping is literally crawling up the side of the tire as i accelerate..... so, from A to B and BEYOND....
it doesn't happen often - REPEAT - it does not happen often.
when it does, though, i'm talking HEAVY gripping situations with the mad 2 stroke power-band.
and i have to back off the throttle in what should otherwise be the perfect time to be ON the throttle.


HornetMaX

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Re: Front tyre incorrect slip angle
« Reply #22 on: June 02, 2017, 09:55:52 AM »
so when i talk about the 'bottom' i'm talking about the actual tread part of the tire, in this pic the section covered with 'A'
GPB has no notion of part A (bottom) and part B (side): the tire profile is round (circle arc).

CapeDoctor

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Re: Front tyre incorrect slip angle
« Reply #23 on: June 02, 2017, 10:14:30 AM »
Max, so by that reckoning, then what is happening to me in this situation is correct?
am i just asking too much grip at too low/high an angle...?

         :)

Fightone

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Re: Front tyre incorrect slip angle
« Reply #24 on: June 02, 2017, 10:31:31 AM »
Max, so by that reckoning, then what is happening to me in this situation is correct?
am i just asking too much grip at too low/high an angle...?

         :)
Eventhough, I still don't fully understand what's happening I can tell you that what you describe sounds strange. In fact, front wheel never ever can wash away after you already started accelerating (that's possible only in the very first moment of opening the trottle on max lean angle, because of the front tyre instant unload).When you are already acelerating our of the corner - only rear tire can slip away.

Now a question for me: how can a front tyre crawl on the side if you'r picking up the bike? How can this happen geometrically-wise? I don't understand how can a front tyre start gripping in the B section if the section itself is fully determined by the lean agle, that's what's bugging me in your explanation. :)
« Last Edit: June 02, 2017, 10:53:04 AM by Fightone »

CapeDoctor

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Re: Front tyre incorrect slip angle
« Reply #25 on: June 02, 2017, 11:37:04 AM »
Fightone, mate, the thing that's bugging you about my explanation is the very same thing that's bugging me, as i don't believe this should ever happen in reality, just as you say. however, it does happen to me on occasion and i find it very strange.
that's the whole reason for my post.
so, the same thing is bugging us both there, lol

i can make a replay of it, but a replay is not going to give you the feel  of what is happening, so that's useless.
and it definitely feels like the grip is actually forcing me over, it doesn't feel like a front washout.
i suffer plenty of those, and they are normal (well, if you ride that way, of course)
this is a complete different feeling - and what makes it difficult is that it has caused me to crash each time it happens.
you can think for yourself - you're leaned far over coming out of a corner, and you basically HAVE to accelerate, otherwise the bike will fall over.
and when this happens, if i accelerate, the bike will also fall over because the grip is pulling me down on the side.
so, i'm screwed either way - back off or fall over, accelerate or fall over.
each options results in falling over.
again, though - i want to remind everyone reading this - it does NOT happen very often at all.
i'd say, 3 or 4 times of 100.
and so far, only with my preferred ride - RGV250.
possibly with another bike, but i'm not really sure about that.... 

Fightone

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Re: Front tyre incorrect slip angle
« Reply #26 on: June 02, 2017, 11:51:20 AM »
i can make a replay of it, but a replay is not going to give you the feel  of what is happening, so that's useless.
and it definitely feels like the grip is actually forcing me over, it doesn't feel like a front washout.
Please make one if you can, I'm very good at looking at replays..) Just beetter make 2: tank view and outside (auto).
+
and it definitely feels like the grip is actually forcing me over, it doesn't feel like a front washout.
Does this sudden grip force your front out or inside the turn?

HornetMaX

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Re: Front tyre incorrect slip angle
« Reply #27 on: June 02, 2017, 11:54:44 AM »
Max, so by that reckoning, then what is happening to me in this situation is correct?
am i just asking too much grip at too low/high an angle...?
Hard to say. Losing the front exiting is a bit unusual.
We know the virtual rider sometimes over-reacts when the front slides and steers more into the turn trying to lift the bike (and hence making things worse ,losing the front completely).
If you have a video or replay maybe ...

CapeDoctor

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Re: Front tyre incorrect slip angle
« Reply #28 on: June 02, 2017, 12:06:22 PM »
okay, i'll do a replay next time it happens, but as i mentioned already, a replay won't give you the feel of what the bike is doing as the rider.
most likely, it'll look like a regular washout in a replay, but who knows - there may be some clue to an experienced eye.
you should at least see that i am accelerating when this happens...
as you say, it's not like i'm actually 'losing' the front, but more like the part of the tire that is gripping is literally forcing me over.
as i accelerate, so the grip increases AND starts to pull me over quicker.
okay, for sure a replay of the next time ;)

vini97

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Re: Front tyre incorrect slip angle
« Reply #29 on: June 02, 2017, 01:01:03 PM »
i think i know exactly what you mean and it's hard to demonstrate with a replay.
if you ride very long sweeping lines with no brake or throttle at max lean (lorenzo/250 style), eventually there comes a point of no return (on some bikes and tracks) where you know that you are doomed and that there is no way to get the bike up again. all that happens before you even get a hint of actual feedback (chatter) from the front.

the only thing that saves me sometimes (apart from simply chosing a different, less smooth line or, worst case, not going max lean angle) is to go into the corner with very low rider lean. when i reach that point i lean the rider all the way and this often makes the bike stand up just enough to avoid the front washout.

this is of course very bad for two-strokes because the lack of engine brake requires these kind of lines.
« Last Edit: June 02, 2017, 01:18:29 PM by vini97 »
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