Gyro effect and counter-steering

[HornetMaX]

Opposite lock is in GPbikes too, when people back it in on the brakes the rider automatically keeps the front wheel tracking the direction of movement.

Yes, but only because the player is pushing the stick to lean the bike.
In GPB it countersteer because you tell him to lean the bike.

MaX.

The virtual rider has a control for yaw, too.

Yes, but the players hasn't. What is the "target yaw" ? Aligned with the bike's velocity vector ?

The only way I can try to slide the rear is: put weight on the front (i.e. offload the rear) and ... ask GPB/MXB to lean: there's no other input one could use.

When "powersliding" I can understand (on the angle, open throttle, rear loses grip and slides out, virtual rider countersteers to fight the yaw movement), but entering a corner (as in MXB) that's not what happens, no ?

MaX.

[EdouardB]

I'm pretty sure this is what's called "opposite lock" the same thing used in car drifting and speeway to hold the car or bike in a semi spin while the back end slides.

Yes I was talking exactly about opposite lock - let's agree on this term

[EdouardB]

Also I would like to say something about sliding the rear end on an MX bike because it can be difficult for some people to realize if you only have been on pavement or haven't ridden motocross.

Sliding the rear of a motocross bike under acceleration is very much a basic motocross skill (1) and happens very often (2). What i'm saying is that it should be quite easy to start and easy to maintain in a simulation.

1) How easy? Well, to be honest, even though I can ride motocross OK having ridden for many years, I was not at all the fastest kid at the racetrack - more towards the middle/ back of the pack on a good day . And even at my level sliding the rear was very easy, even on long slides, and even on a small bike like an 80cc. In fact I don't know any average motocross rider who cannot slide the rear of the bike. It's just a very basic skill. It is much easier than in road racing because the way tyres are made and the way the grip level of the track is much lower, the sliding is very smooth and not violent like in road racing, especially when the grip "comes back" - you see many more high sides in road racing than you do in motocross. In fact the term is never used in MX.

2) I also want to point out that it happens extremely often. In fact, in real life, the majority of corner exits are done with the rear slightly sideways.

I just felt like saying all this because in my opinion I think this is very much a big part of motocross and should be part of any good simulation.

Pic of a very very typical cornet exit to illustrate:

[HornetMaX]

Sliding the rear of a motocross bike under acceleration is very much a basic motocross skill (1) and happens very often (2).

Easier or harder than on road bikes ? 'Cause road bikers says the same: sliding the rear on the throttle should be fairly easy.

From what I see, it is more frequent (and likely easier) in MX. What do you think ?

MaX.

[PiBoSo]

Opposite lock is in GPbikes too, when people back it in on the brakes the rider automatically keeps the front wheel tracking the direction of movement.

Yes, but only because the player is pushing the stick to lean the bike.
In GPB it countersteer because you tell him to lean the bike.

MaX.

The virtual rider has a control for yaw, too.

Yes, but the players hasn't. What is the "target yaw" ? Aligned with the bike's velocity vector ?

The only way I can try to slide the rear is: put weight on the front (i.e. offload the rear) and ... ask GPB/MXB to lean: there's no other input one could use.

When "powersliding" I can understand (on the angle, open throttle, rear loses grip and slides out, virtual rider countersteers to fight the yaw movement), but entering a corner (as in MXB) that's not what happens, no ?

MaX.

The virtual rider tries to calculate if the bike is under or over-steering. In case of under-steer, it steers more, the opposite in case of over-steer.
So it's not true that counter-steering only happens when initiating a lean. It also happens in case of steady lean and over-steer.

[𝖙𝖋𝖈]

So when oversteer occurs, the rider steers less.. essentially does that mean no matter how hard we try we will never be able to control a slide as we will be fighting against the automated rider response which is trying to bring it under control?

[HornetMaX]

The virtual rider tries to calculate if the bike is under or over-steering. In case of under-steer, it steers more, the opposite in case of over-steer.
So it's not true that counter-steering only happens when initiating a lean. It also happens in case of steady lean and over-steer.

That's very interesting. Can you define exactly (I mean in technical terms) what you call under/over steering ?

Is it what's called "steering ratio" in the Cossalter book (ratio between the effective and kinematic steering angles or, identically, between kinematic and real radius of curvature of the trajectory) ?

MaX.

[EdouardB]

Sliding the rear of a motocross bike under acceleration is very much a basic motocross skill (1) and happens very often (2).

Easier or harder than on road bikes ? 'Cause road bikers says the same: sliding the rear on the throttle should be fairly easy.

From what I see, it is more frequent (and likely easier) in MX. What do you think ?

MaX.

Much, much easier on a motocross bike. Most road bikers I've seen who say "it's very easy to powerslide the rear" were either World level riders (and I believe them) or the local guy who's never been on a racetrack and who has no clue how to do it but likes to think he's a world champion...

[EdouardB]

And when I say "slide the rear" I don't mean the occasionnal movement of the rear tyre in road racing (that happens often). I'm talking about the rear really stepping out and going very much sideways, with a good amount of opposite lock.

Can anyone do something similar to this picture on a road bike? A few stunt guys maybe, but not many people. Sliding is pretty easy off road. You can even goof around with it, it's really not that difficult.

[Phathry25]

I am surprised to see that the rider tries to correct slides. He is no good at it, that's for sure. Lol. I have to wonder if it's him or the tires though. Really you shouldn't be able to fully spin up the rear tire under normal riding conditions on a dirt bike in decent dirt. 

I guess a good test on the user side would be to do a burn out in game and see how much force is puts through the front forks and compare to a real world example.  Would I be wrong in saying that unless you go to the extreme of nuts on the gas tank and head over the front fender you're probably just going to end up pushing the front tire along the ground in real life?

[𝖙𝖋𝖈]

I think the important thing here is the contact surface and weight.

GP bike, big surface area on the rear tyre, flat road surface, lots of grip. The thing that causes the loss of traction is the power of the bike and the rider position - which remember isn't so much forward and backward center of gravity as the seat is very short.

MX bike, knobbly tyres, soft uneven track surface, good grip with weight on the back end (i.e under acceleration) but due to the uneven track surface and the rider standing (or even bouncing on the seat) with most of their weight on the footpegs (center of the bike, forget center of gravity for a moment) the bike is frequently under fast changing different levels of weight on the back end, and when the back end skips about on the terrain and the knobblies don't dig in so much, the tyre looses traction.

When you factor in center of gravity, shifting weight forward or sideways just enhances the effect. It's probably relatively easy to control as it doesn't take much to let off the throttle even for a second, and shift your center of gravity and weight to get the rear tyre to dig in and regain traction. You can do that on a GP bike of course, but there is no soft track to dig in to or catch the back end, which I guess is why once it's gone it's gone.

Of course this is also relevant to a GP bike or any bike for that matter, but it's nowhere near the same scale as offroad.

MaX is now going to tell me I'm completely wrong 

[Phathry25]

You are grossly underestimating how much a GP bike slides around on a track.  Obviously it's not at huge angles, the speed won't allow for that, but trust me they are sliding just as often as a motocross bike.  Why else would the two best riders in the world (Marquez and Rossi, sorry Jorge) use dirt track as one of their biggest training tools?  You say that riding a dirt bike on dirt and a GP bike on asphalt couldn't be more different, but this picture begs to differ.



I realize this isn't motocross, but with the definition of the tracks we currently have it's probably a closer representation to what we have than real motocross. 

As far as inputs at the handle bars go, what we're actually controlling in the game, the two are remarkably similar.  When you get into the throttle on a motocross bike and the rear tire starts to spin a little bit, to prevent it from sliding out you stand the bike up a little bit to combat it.  Watch a GP rider when they turn the throttle on, the bike comes up just a little bit to keep the rear wheel in check.  It's sliding.  Yes the body positioning is wildly different, yes you need to do other things to control the bike through the bumps and ruts and use the clutch a whole lot more, but at the handle bars the two are indifferent as far as I am concerned.

And that's my unsolicited $0.02

[PizzaChet]

You are grossly misunderestimating how much a GP bike slides around on a track...~...And that's my unsolicited $0.02

Ftfy. Been waiting to hear from you. This needed bike logic. Doesn't it just come down to grip level and the weight/geometry of machine for differences in simulating? Sure sounds simple, but so does putting a guy in a rocket and shooting him into space.

[HornetMaX]

MaX is now going to tell me I'm completely wrong 

I won't as most of what you said makes sense (but don't help a lot in understanding the differences). I would just have put amongst the factors corner speed and bigger lean angles for road bikes (even if they are closely tied to the level of grip) .

As far as inputs at the handle bars go, what we're actually controlling in the game, the two are remarkably similar.  When you get into the throttle on a motocross bike and the rear tire starts to spin a little bit, to prevent it from sliding out you stand the bike up a little bit to combat it.  Watch a GP rider when they turn the throttle on, the bike comes up just a little bit to keep the rear wheel in check.  It's sliding.  Yes the body positioning is wildly different, yes you need to do other things to control the bike through the bumps and ruts and use the clutch a whole lot more, but at the handle bars the two are indifferent as far as I am concerned.

Hmmm ... that 's strange: lets say you have a left turn so the bike is leaning left. You give a bit too much throttle and the rear starts to pop out.
Now you're saying that the rider stands the bike a bit to counter the rear sliding. But to do so, the rider would have to turn the handlebar lest (i.e. push right end of the bar).
This would be the opposite of what the "drift" guys are saying, no ? They would turn the bar right (push left end of it) if I understood it correctly.

For a road bike, I'd say that if turning left you lose the rear, you want to lean even more the bike left and you do this by turning the bars right.
If you turn them left and stand the bike up, you go high side.

To me you see they stand the bike because they are preparing to end the turn: go on  the fat part of the tire as early as possible and open wide. That's why they decide to slide into a turn, so that the bike is already pointing in the right direction at exit, just stand it and pin it (in that order, not the opposite).

Just found this on a bike physics book (THE book to have if you are into this stuff, V.Cossalter, Motorcycle Dynamics):

".. with an over-steering motorcycle, if the force needed for equilibrium overcomes the maximum friction force between the tire and the road plane, the rear wheel slips, but the expert rider, with a counter-steering maneuver, has a better chance of controlling the vehicle equilibrium and avoiding a fall" (page 113, paragraph 4.3, you have it on google books: http://books.google.fr/books?id=rJTQxITnkbgC&pg=PA105&source=gbs_toc_r&cad=3#v=onepage&q&f=false).

First video example I can think of (@1.24):

https://www.youtube.com/v/_OhvhjpkhiU#t=84

And that's my unsolicited $0.02

Unsolicited maybe, but much appreciated. By me at least

DISCLAIMER: I don't post often here so most of you do not "know" me. I ride only road bikes and on public roads, mostly within the limits (ouch). So I have zero track experience on road bikes. On MX bikes I have, if possible, even less experience. But I try hard to understand the physics of all this (not that that will make me a better rider, of course). So I definitely can be wrong.

MaX.

P.S.
I'm still veeeery interested in having Piboso's reply to my previous questions (exact definition of over/under steer and "steer more").
I'd surely have to mull it over (and it's almost 2am here now), but I'm under the impression that the virtual rider trying to even out over/under steering may be a bad idea: when a rider wants to slide into a turn, he does not want the bike to have zero over/under-steering ...

In a limit case, 90deg right turn (going north, turn to east) where you enter with the bike (and the rear tire) pointing to east and the front tire poiting nord (rear sideslip = 90 and front sideslip = 0), i.e. fully sideways, the whole concept of under/over steer is not even defined: the kinematic turn center is the rear contact patch ...

[PizzaChet]

You would lean into the turn more and counter-steer while standing the bike up more, like speedway riders. I thought.