Potential reason for the front end wobbles in GP bikes

[EdouardB]

Hi everyone,

Before I go any further, I just want to say that this is just a theory and I'm not saying this is absolute truth with a Genius hat or anything. Maybe I'm completely wrong here.

Yesterday I rode at a racetrack that has a lot of bumpy 2nd gear accelerations while picking the bike up (for those who know it, Carole in France), and I encountered the same kind of wobbles than in GP bikes: strong ones, and that remain for about 50 meters with a large amplitude.
I thought about it while at the racetrack and determined the reason to be this one:

- when picking the bike up I am countersteering by pulling on my inside hand (some people push on the outside one, but it's harder to do when you're hanging off the bike),
- at the same time my bike was starting a wheelie on the bumps (front end got up very slightly, maybe 10cm),
- the result is that my bars were turning slightly during the wheelie because of the pull on the bars,
- my front wheel lands on the ground while turned
- wobbles after that, and by keeping the throttle wide open it would go away.

Now this is nothing new really, I remember seeing 500 GP riders in assen in 2000 and 2001 who always had the same problem at the beginning of the straight (coming out of the chicane) but I'm thinking this is the exact same kind of behavior than in GP bikes.

This video illustrates what I'm talking about (the wobbles are smaller here, because, well, he's just much better than me - also, notice the fine rear brake use, but that's not the subject today):

https://www.youtube.com/watch?v=lxyNCr-98ZU

I was able to correct the problem by losening my arms when the wheelie starts.

So I'm thinking that maybe in GP bikes what happens is that the rider input to pick the bike up involves counter steering and that this input continues even when the wheel is off the ground maybe? And then the front wheel is missaligned and produces wobbles. Maybe there should be an option to lessen the input when the wheel is up? I don't know.

Also, one thing I still do not understand is why do we have to cut the throttle to kill it instead of keeping it wide open like in real life (which works).

Anyway maybe my theory is misleading but I just figured I should talk about it in case Piboso reads it.

[JJS209]

that sounds for me like "normal" kickback that you get when your frontwheel re-touches the street not in the angle the bike is going - then i get kickbacks on the handlebars, but i think thats a known thing.
so i think you mean something different than i understand here.

[HornetMaX]

I was able to correct the problem by losening my arms when the wheelie starts.

Mark one more against people asking for more steering damping to solve the problem

So I'm thinking that maybe in GP bikes what happens is that the rider input to pick the bike up involves counter steering and that this input continues even when the wheel is off the ground maybe? And then the front wheel is missaligned and produces wobbles. Maybe there should be an option to lessen the input when the wheel is up? I don't know.

In GPB (unless you're using direct steer) when the bike is wheeling the rider puts the handlebar in the middle position, so I'm not really convinced.
Mostly my doubts stem from the fact than on most of GPB tracks we don't have very bumpy turns ... the wobble (which is in fact a weave more than a wobble) seems to happen also on very smooth turns.

Also, one thing I still do not understand is why do we have to cut the throttle to kill it instead of keeping it wide open like in real life (which works).

To kill a weave you're effectively advised to cut/reduce the throttle (and loosen your arms or, at least, avoid fighting the handlebar movements, which would make things worse).
It's different on a low speed wobble, for which cutting the throttle is bad (and for which more steering damping would help).

But again, I think that Piboso already knows what is at the origin of the 3 unexpected behaviours of beta5 (excessive wheeling, low speed wobbles and high speed weave).
So let's cross fingers for beta6.

MaX.

[grimm]

Also, one thing I still do not understand is why do we have to cut the throttle to kill it instead of keeping it wide open like in real life (which works).

That statement isn't entirely true. My wreck in 2008 was proof of that. At the point the rear tire starts following the front, more throttle will only make it worse. The physical forces that happen during a wobble are far beyond anything I can describe with any accuracy, but, giving it a fist full of throttle really isn't what actually causes it to subside, it is merely enough times it didn't go wrong that encourages the idea that is how a wobble or weave is solved. 99.9% of the wobbles I have gotten into were either operator error, or it was surface changes on the tarmac that caused things to go awry.



This is a really good video that convinced me that more throttle isn't really the solution. And over the years new experiences showed me steady roll off, or just plain out steady throttle subsides a wobble or weave exactly like GP Bikes. 

https://www.youtube.com/v/fvsDIq3WwVA

[yoshimura]

between real life and a simulation with a pad, this n are not comparable, there are too many parameters that comes into account.Force of arm, the position of the corp, in thousandth of seconds it takes to react

[EdouardB]

In GPB (unless you're using direct steer) when the bike is wheeling the rider puts the handlebar in the middle position, so I'm not really convinced.
Mostly my doubts stem from the fact than on most of GPB tracks we don't have very bumpy turns ... the wobble (which is in fact a weave more than a wobble) seems to happen also on very smooth turns.

Fair enough - it was just an idea anyway

[EdouardB]

that sounds for me like "normal" kickback that you get when your frontwheel re-touches the street not in the angle the bike is going - then i get kickbacks on the handlebars, but i think thats a known thing.
so i think you mean something different than i understand here.

Of course it's a normal kickback, but what I was saying is that the fact that riders don't keep the frontwheel aligned is mostly because of countersteering and therefore, maybe in GP bikes it was an input problem of this kind. I hope it's clearer now

[EdouardB]

At the point the rear tire starts following the front, more throttle will only make it worse.

You're right, it really depends on the amplitude. Once the rear follows the front it's time to ease off the throttle for sure like you said.
However as long as the wobble doesn't amplify I don't see any reason to cut the throttle so I stay wide open and losen my arms as much as possible. And in GP bikes this never seems to work! Which is strange considering how realistic the game is.

[BOBR6 84]

I thought the wobbles etc are a physics problem with beta5b? Not enough weight on the front or something like that? Which allows violent wheelies too..

Im actually getting used to 5b lol. Id like to see it calmed down a little bit but not completely because in some situations it looks/feels very realistic to me lol.

Id still like to have a steering damper in the setup options though to incorporate into my setup! 
In my mind I get the idea it would dampen the input of the virtual rider on the bars in slow corners.. Even if it has no effect on the laptime, maybe it would stop the bars flapping around like crazy in some corners too?

[HornetMaX]

I thought the wobbles etc are a physics problem with beta5b? Not enough weight on the front or something like that? Which allows violent wheelies too..

Same here.

Im actually getting used to 5b lol. Id like to see it calmed down a little bit but not completely because in some situations it looks/feels very realistic to me lol.

Same here, again

Id still like to have a steering damper in the setup options though to incorporate into my setup! 
In my mind I get the idea it would dampen the input of the virtual rider on the bars in slow corners.. Even if it has no effect on the laptime, maybe it would stop the bars flapping around like crazy in some corners too?

Yes, but at the price of a worse weave.

At the point the rear tire starts following the front, more throttle will only make it worse.

You're right, it really depends on the amplitude. Once the rear follows the front it's time to ease off the throttle for sure like you said.
However as long as the wobble doesn't amplify I don't see any reason to cut the throttle so I stay wide open and losen my arms as much as possible. And in GP bikes this never seems to work! Which is strange considering how realistic the game is.

If only the front is oscillating, then keeping the throttle on should not harm. That's a wobble.
If the rear is oscillating too, then keeping the throttle on is gonna amplify it. That's a weave.

In GPB, when you have this sort of oscillations when picking up at corner exit on the throttle, it's almost always a weave, so just shut the throttle.

The wobble is there only in very slow corners where you typically enter with the throttle shut.

MaX.