Prototype gp500 physics model

[EdouardB]

Tracey, have you ridden the 1000 on GP bikes a lot? I think they have the right amount of powerslide. I'm strongly against putting more powersliding in for those bikes.

Also, I (respectfully ) disagree with your comment "To an extent and to a degree powersliding and rear wheel steering is an integral part of the skills required to get a racing motorcycle round a race track at a competitive pace and lap time."

In over 100 trackdays, I've never seen a rider in front of me do a huge powerslide like you see in motogp or in video games. Including race winners. I've seen a lot of guys slide consistently at the exit of a turn, but it was more a wobble than "rear wheel steering" or a long powerslide.

Also, in the 500, very very few people actually managed to powerslide without crashing. Maybe 5 riders maximum per year. When I went to see the Assen 500 qualifications in 2000 and 2001, I remember only 4 or 5 riders doing proper powerslides: Rossi, Biaggi, Capirossi, Barros, and sometimes Checa.

So I think the amount of powersliding in GP bikes is fine.

[HornetMaX]

You seem to have the knack for picking controversial subjects. Big bang engines ...

My understanding of them is that their main difference with respect to screamer engines is not in the power delivery curve (they dyno stuff, power or torque vs RPMs).
Their main advantage is in the fact that the unevenly spaced firings allow the tire  more time between firing groups and it seems (not everybody agrees and the one that do, can't really explain why) that is beneficial.

Simplifying to death, it is as if over 1 second, a screamer fires 4 pulses (each of amplitude 1) spaced 0.25s.
A Big bang (extreme case, totally non real) would fire one big pulse of amplitude 4, and then nothing more. More realistic, could be 2 impulses of amplitude 2, spaced by 0.5s.

Notice that Little/Medium/Big/Giant bang, this does not affect the engine output in terms of delivered toque/power (assuming airbox and exhaust are retuned): the dyno chart is roughly the same. A big bang engine is not more powerful or more torque-happy, except in Yamaha's marketing speeches.

Now if we all agree the effect of big bang (or irregular firing) is that, then no, this cannot be simulated properly in GPB, as it would require a tire model much much more sophisticated than the current one (which is already plenty for a game). A rough workaround would boil down to give the big-bang bike slightly better tires. But who likes rough workarounds here ?
And as far as I've read, the real reasons of why a big bang is beneficial are still a non fully clarified subject.

MaX.

P.S.
EdouardB, I love you !

[EdouardB]

Love you too, Hornet

The point of a Big Bang is not to change the maximum torque or anything (it does not). It just makes the micro variations of torque on one cycle much smaller because of a better repartition of the accelerations of the 4 pistons at every rotation. Because after a certain RPM the torque transferred to the rear wheel comes much more from the inertia of the rotation than from combustion (confirmed by GP engineers Frits Overmars and Jan Thiel on numerous forums).

This video explains much better (Crossplane is basically an inline big bang): https://www.youtube.com/watch?v=V_e_gC99Ql0

[EdouardB]

As for how easy the big bang 500s were compared to the screamers, it's been confirmed by many GP riders.

And as for the difference between a 500 and a four stroke, like Kevin Schwantz says: "a four stroke alone is easier than a 2 stroke with traction control"

[HornetMaX]

Hmmm ... that video is what I call "yamaha marketing speech" (*), designed to make people by an R1 just because it has a crossplane something inside, and that sounds very cool.

The explanation relating to inertia/combustion torque is the one put forward by Masao Furusawa (Yamaha, at the time).
But along this he said that the crossplane advantage was in the fact that with irregular firings, the "combustion signal" was "less masked" by the "inertia signal" and hence more likely to be felt by the rider. That's one theory, the other is the one that relates to the tire preference for irregular firings.

None of the two theory has been ultimately proven to my knowledge. By this I mean that it is indeed possible that the riders prefer this or that (or event that they are faster with this or that), but I'm not sure somebody knows really why. Ducati more or less admitted they were trying big bang just to see if it works any better, without knowing why it should or should not work better.

People sceptical about the explanation argue that the inertia/combustion torque pluses are smoothed by the final transmission flexibility and damping (which does exist, for sure).
Also it seems that Michelin didn't ever notice a difference in tire wear between a big bang and a screamer ...

MaX.

(*)
In the video: "Paradigm shift" ? Big bang/irregular firing has surely been used way before the M1 in racing bikes .... 

[girlracerTracey]

Tracey, have you ridden the 1000 on GP bikes a lot? I think they have the right amount of powerslide. I'm strongly against putting more powersliding in for those bikes.

No but I will do. Everyone is telling me they are easier to powerslide so I'll give them a proper go.. 

Also, I (respectfully ) disagree with your comment "To an extent and to a degree powersliding and rear wheel steering is an integral part of the skills required to get a racing motorcycle round a race track at a competitive pace and lap time."

In over 100 trackdays, I've never seen a rider in front of me do a huge powerslide like you see in motogp or in video games. Including race winners. I've seen a lot of guys slide consistently at the exit of a turn, but it was more a wobble than "rear wheel steering" or a long powerslide.

I'm not talking about "huge" powerslides though as I explained in my post. But on many circuits on certain bends racers will often use a bit of rear wheel steering to adjust their trajectory onto the straight and up to the edge of the track..in full racing conditions.

Also, in the 500, very very few people actually managed to powerslide without crashing. Maybe 5 riders maximum per year. When I went to see the Assen 500 qualifications in 2000 and 2001, I remember only 4 or 5 riders doing proper powerslides: Rossi, Biaggi, Capirossi, Barros, and sometimes Checa.

Fair comment. It wasn't an easy thing to do. But taking up your definition of "proper" powerslides..many other riders did rear wheel steer but to a much less pronounced degree. Simon Buckmaster on the RS500 Honda used rear wheel steering. I think they all did, but to a much lesser degree. Possibly not as visible from the track-side.

So I think the amount of powersliding in GP bikes is fine.

That's fair enough. I hear what you are saying. 

Can anybody direct me to a gpbikes' video where a 500cc bike is rear wheel steering on the power? I would be very interested in having a look at this..out of genuine curiousity.

grT

[girlracerTracey]

On the controversial subject of 500cc "Big Bang" engines I found the following article which sort of confirms what my understanding was..

http://ultimatemotorcycling.com/honda_nsr500_motogp_racing_history/

"A big surprise arrived in 1990 was the advent of the 'Big Bang' engine. In this configuration the firing of each cylinder was offset 90°, meaning that instead of each cylinder firing at 90° intervals, each set of two cylinders fired 180° apart. The slight reduction in maximum power that resulted was more than offset by the improved torque characteristics caused by the increased amplitude in combustion torque waves. Traction during acceleration was markedly improved.

This was a major turning point in engine development, and the NSR's engineers experimented with various firing orders and crank angle/ignition timing settings. As the bikes became easier to ride, lap times began to drop. Usable power became more important than maximum power. Chassis upgrades included such trick parts as expansion chambers and other parts made of titanium, helping to reduce machine weight by more than 15kg.

Around this time another gifted rider appeared on the scene. Mick Doohan had been battling with Yamaha's Wayne Rainey and Suzuki's Kevin Schwantz, finishing 3rd in the championship in 1990 and 2nd in 1991. His time had now come.

By the time 1992 rolled around, a new 68° irregular firing order was being used. Each pair of cylinders fired simultaneously at 68° and 292° intervals. The resulting irregular combustion torque wave shapes delivered markedly superior traction. And just by chance, thanks to the crank phasing, the 112° V angle cancelled out the theoretical primary vibration, eliminating the need for a balancer shaft. For the first time since 1986 this allowed a return to a triple-shaft engine, and a more rigid and precise engine structure. This new engine had a unique exhaust note, leading observers to call it a 'screamer' engine. In the bike's first outing, the rain-sodden Japan GP, Mick Doohan rode the 'screamer' to victory. This win was especially impressive because prior to the screamer engine the NSR500 was difficult to ride in the wet."

[girlracerTracey]

One last thing from me on this..

I found this article which makes quite interesting reading on the subject of rear wheel steering from past to present:

Marquez and the science of slide

By Bob Gray
Image by Repsol Media

http://www.bikesportnews.com/features-detail.cfm?featureid=160

"Back in the days of 500cc Grand Prix racing, spinning the rear wheel as you exited corners was an essential skill. These days, we don't see it much, with a few notable exceptions. Why is that? Are electronics to blame once again, or is there some other reason why riders favour backing it in over sliding it out?

We've seen many different approaches to cornering on a motorcycle over the years. Knee-up, knee-down, hanging-off and sitting bolt upright and, of course, Mick Doohan's unique 'all of the above' approach. And to be fair, each method works in one way or another. However, there's one style of cornering that has simultaneously terrified and amazed racing audiences for as long as most people can remember – sliding the rear end. So why are so few riders doing it these days?

Take two very different riders like Jorge Lorenzo and Marc Márquez. It is well known that Yamaha bury tiny rails in the track before each MotoGP round, which is why Lorenzo's bike never gets out of line. On the other hand, Márquez doesn't mind lighting up the rear at any opportunity. It's important to recognise that this is only our perception, though. Watch closely and you'll notice that he doesn't drift the rear out of every corner. It's not like watching a speedway race. And that's important, because it suggests that it's something he's choosing to do. If it was down to a lack of grip, everyone would be spinning. If it was his riding style or it was something to do with the bike, it would happen at every single corner.

So what makes bikes corner? Leaning for a start, but that isn't the exclusive reason. What about steering; everyone knows about counter steering and how it is used to make a bike turn. Geometry? It's true to say that changing the set-up of a bike changes the way it corners, but a bike that is badly set-up or designed still goes around corners – it just does it slower. In fact, bikes corner for all of the above reasons, and more besides, which is partly why it seems such an unapproachable subject.

Let's start by looking at steering. Most bikes have a steering range of ±20–35°, but it's rare to use that much in 'normal' riding conditions. In fact on a normal road ride it would be unusual to use much more than ±15° – and that's pulling out of junctions. On track, it's even less. If we ignore the fact that bikes lean for a moment and just look at the steering, what happens when you turn the bars? The front wheel points in a different direction to the frame and rear wheel plane and leans slightly. If we slowly push the bike forwards it's easy to appreciate the fact that the bike is going to move in a circle because the front wheel is steering it to.

The radius of that circle can be found by drawing an extended line through both wheel spindles in the direction of the turn. The point where the two lines cross marks the centre of that circle – the point about which the bike will turn. It's worth emphasising that this only holds true at very low speeds, and only when the bike is upright. It's also important to recognise that while we may be pushing the bike at a constant speed as far as the speedo is concerned, the bike's velocity vector has changed because it's accelerating towards the centre of the circle. It has to be.

Newton told us bodies in motion carry on in a straight line unless some force causes them not to.
In this case, a force generated at the front tyre by the steering is pushing it sideways. We can work out how much acceleration there is by squaring the velocity and dividing it by the radius of the turn. If we look at a real world example, the radius of the ridden line at the apex of Donington's Melbourne loop (not the track itself), is about 20 metres. And at the apex of that turn you can expect a true speed over ground of around 49km/h. To work out the bike's lateral acceleration at that point we square the velocity (in metres per second) and divide by the radius v2/r. That works out as an acceleration of 9.262m/s2, which we can turn into g by dividing it by 9.81m/s2, which works out at 0.94g.

But if you've watched bikes cornering at the Melbourne loop you'll know they're really on their side – and there's a good reason for this. At less than walking pace, a bike can turn without any perceivable lean angle simply by turning the steering. Any faster though and the bike wants to fall 'out' of the corner. This is because it's balanced above the tyre contact points. If something causes them to accelerate sideways, they move out from under the bike and it appears to fall the other way.

Sticking with the Melbourne loop example, the contact points are trying to accelerate towards the inside of the corner at 9.262m/s2. But there's no lateral force trying to push the bike's centre of mass to one side too. So to create that force we lean the bike into the corner. As the bike's centre of mass is no longer above the line drawn between the contact patches, the bike tries to fall that way. The 'falling force' is proportional to the centre of mass's horizontal displacement from the contact patch. In other words, the more the bike leans, the more it wants to fall. This is good because the faster we go, or the tighter the radius of turn we make, the more the tyres try to accelerate away from under us. It follows then that the more cornering force we generate at the tyres, the more we need to lean to balance it out.

We can work out the lean angle based on the lateral acceleration of the tyres and the vertical acceleration caused by gravity by finding the arctangent of the lateral acceleration (in g). In the case of the Melbourne Loop bike that works out at 43.23° (Tan–1[0.94] = 43.23). So in order for our bike not to flip out of the corner, it needs to be leaning at 43.23°. This might sound low if you've ever watched a bike go round the Melbourne Loop, but the 43.23° we're talking about is not measured through the plane of the wheels, it's measure on a plane coincident with the combined centre of mass and both tyre contact points.

This happens because when you lean a bike over the contact point moves away from the centre line of the tyre towards the edge. In reality, this means that unless we were riding on thin discs of metal, the lean angle between the centre of mass and the contact points will always be less than the lean angle through the bike's chassis. And the wider the tyres, the worse that gets.

While we're on the subject of lean, there are two more things to consider. The first is that when we lean, the force that causes the tyres to accelerate sideways is no longer caused by steering with the bars (actually it is a little bit, but not like when the bike was upright) – it's generated by camber thrust from the tyres.

Camber thrust comes about because the tyre deforms as it's pressed into the track surface. Viewed from the rear, the distance from the outer edge of the contact patch (closest to the edge of the tyre) to the wheel spindle will always be less than the distance from the inside edge to the wheel spindle. As the tyre has to turn with the wheel, this means the edge of the contact patch with the larger radius is going to try to cover ground per wheel revolution more quickly than the edge with the smaller radius. And the only way it can attempt to do this is to turn about some axis.

The axis it tries to turn about is actually the same as if you replaced the tyre with a cone that hit the floor in the same spot as the contact patch. And if you imagine where the point of that would be, that's where the tyre would like to rotate around. But it can't. Not least because there's another tyre at the other end of the bike trying to do the same thing, but also because for the lean angles we deal with, the radius of that turn would be impossibly tight. So what happens is a massive compromise that creates slip within the contact patch itself and that is also part of the reason why tyres tear up in the way that they do.

From a riding point of view, though, the speed you go round a corner is limited by grip, which is controlled by the tyre and the surface it's rolling over. In order to get round a corner, we need to generate enough lateral acceleration for the bike to follow an arc that keeps us on the track and out of the gravel. Most of the cornering force comes from camber thrust created by leaning, which is good as the bike needs to lean over in order not to be flipped out of the corner. The steering will turn slightly into the corner based on the lean angle, geometry and tyre size, and that also creates some input.

When things go well, we hit the line we want. But it's important to recognise that, even though you don't feel it, the bike is slipping slightly all the time. So, although you're on the right line, the bike is trying to turn on a tighter one but is slipping out to the correct one. As you get close to the tyres' grip limit, the amount of slip increases and you get the sensation of drifting off line. If the grip at one wheel suddenly increases faster than the other you begin the process of what can become a high- or low-side.

If we go back to the question on sliding or not, the question really becomes, how do I get the bike where I want it? The simple answer is to steer it like anyone else, but racers sometimes need to hold a tighter line – to get the bike lined up for the next corner, for example. This is where rear-wheel steering comes in. Because when a bike is really wheel steering, things almost work backwards.

Think about it like this: although the steering angle at the bars reduces the faster we go, the front wheel of our bike still has some input when we corner because it points into the corner. As the rear end drifts outwards, we actually end up with a negative steer angle at the front (because the front wheel is pointing in the direction of travel it is negative compared to the plane of the rear wheel). However, the rear wheel is now pointing and leaning much more in the direction of the turn – and has more weight on it because we've applied power to get it to spin. The weight, angle and camber of the rear wheel mean it's responsible for the majority of the lateral acceleration, which is also now linked to the normal rotation of the wheel as that's pointing towards the inside of the turn.

When exiting a corner and holding a tight line ready for the next one, having the rear wheel sliding out means much of the cornering force is controlled by the throttle (rather than leaning and using the bars). It risks a crash, of course, and gives the tyre a harder time, but if a rider feels the time/effort saved is worth it, that's what they'll do.

As for which is faster... that's a tricky question, especially these days when there are tens of thousands of pounds of technology being used to prevent the rear wheel sliding. The simple answer is that it depends on the rider – not their talent, their confidence. They have to be sure of both the chassis and engine, and to be confident that the advantage outweighs the consequences. That's the most likely reason we don't see it as much as we used to. It's hard to get the engineers to disable systems that work so well, because by leaving them on and riding at the controlled limit of adhesion means all the other factors can be managed effectively over the course of the race. It takes a confident rider to argue against that."

[JamoZ]

When is the GP Bikes novel coming out? 

[BOBR6 84]

"Back in the days of 500cc Grand Prix racing, spinning the rear wheel as you exited corners was an essential skill. These days, we don't see it much, with a few notable exceptions. Why is that? Are electronics to blame once again, or is there some other reason why riders favour backing it in over sliding it out?

better tyres.. more grip, better brakes, brake harder and deeper with slipper clutches etc

think on the 2stroke 500s they tried to allways be in the powerband.. so if you give it a fistfull its gonna spin up.. whats the saying? its not who gets on the throttle first that wins its who gets on full throttle!!  my rear tyre slides and steps out when im racing, darley moor is all stop, start, so its hard on the gas out of slow corners.. it happens. not highsided yet but its coming lol

[EdouardB]

Hornet, fair points. I agree about having the whole thing being dampened by the transmission.

Tracey, you too ! I see a lot of power slides in motogp though. Overall, the point I wanted to make is that a powerslide should be easier on a 4 stroke compared to a 2 stoke.

fuck it, everyone has valid points these days :-P

Tracey, give the 1000 a try fast ;-) show us a picture of you playing them to prove it (never mind that comment)

Doohan's case is interesting because he went away from the big bang engines and won while criville struggled. I think its really a rider's preference thing.

I remember Christian Sarron telling me though that the big bang he tested for Yamaha in 93 was much easier than the screamers he used in racing in the late 80s. But it could be from other factors as well... Tyres, better Cdi with smoother valve controls, etc...

[HornetMaX]

The slight reduction in maximum power that resulted was more than offset by the improved torque characteristics caused by the increased amplitude in combustion torque waves.

The above sentence does not explain why "increased amplitude in combustion torque waves" leads to "improved torque characteristics".
And the reason is that nobody seems to know for sure.

By the way, "improved torque characteristics" is extremely vague. What does it mean ?

I found this article which makes quite interesting reading on the subject of rear wheel steering from past to present:

That article is one of the few that does not make gigantic blunders trying to explain how things work on a bike. Kudos to the author !
Everything he says, from 1st line to last, is explained in precise terms in the book I mentioned (Motorcycle Dynamics, V.Cossalter).

Steering like this is faster or not ? I think it depends a lot on the technical characteristics of the bike.
On some years it has been more or less mandatory, on some other years it was better to avoid it.

To do it on corners where an error can make you a vegetable surely requires extreme confidence and predictability.
And in terms of predictability, today's bikes are light-years ahead than 500cc bikes. In the 500cc races I recall, there were no more than 4 riders
doing it for real at a given one time.

MaX.

[Allen]

Tracey, have you ridden the 1000 on GP bikes a lot? I think they have the right amount of powerslide. I'm strongly against putting more powersliding in for those bikes.

Also, I (respectfully ) disagree with your comment "To an extent and to a degree powersliding and rear wheel steering is an integral part of the skills required to get a racing motorcycle round a race track at a competitive pace and lap time."

In over 100 trackdays, I've never seen a rider in front of me do a huge powerslide like you see in motogp or in video games. Including race winners. I've seen a lot of guys slide consistently at the exit of a turn, but it was more a wobble than "rear wheel steering" or a long powerslide.

Also, in the 500, very very few people actually managed to powerslide without crashing. Maybe 5 riders maximum per year. When I went to see the Assen 500 qualifications in 2000 and 2001, I remember only 4 or 5 riders doing proper powerslides: Rossi, Biaggi, Capirossi, Barros, and sometimes Checa.

So I think the amount of powersliding in GP bikes is fine.

As someone who raced 2/350 machines in the 80s (TZs and Rotax 256 engined) I can say without any doubt it is a lot easier to feel yourself sliding a bike on the exit of a corner than to see another rider doing it in front of you (unless you happen to be the poor sod following a nutter who is taking a long look over their shoulder whilst leaving a black line on the road... ). Modern tyres are no different, they get maximum grip when slipping around 5% and that 5% is what you feel through your arse cheeks...

[HornetMaX]

As someone who raced 2/350 machines in the 80s (TZs and Rotax 256 engined) I can say without any doubt it is a lot easier to feel yourself sliding a bike on the exit of a corner than to see another rider doing it in front of you

Just to be sure I get your point right, you mean that it's easier to control a slide being on the bike (for real) than watching it sliding (like in a simulation) ?

MaX.

[Allen]

As someone who raced 2/350 machines in the 80s (TZs and Rotax 256 engined) I can say without any doubt it is a lot easier to feel yourself sliding a bike on the exit of a corner than to see another rider doing it in front of you

Just to be sure I get your point right, you mean that it's easier to control a slide being on the bike (for real) than watching it sliding (like in a simulation) ?

MaX.

I mean it's easier to feel IRL than see it and it's certainly easier to control IRL than it is in a sim with no haptic feedback (although if the traction control is set to give 5% slip, it should always happen anyway). As soon as I feel the bike start to move I would be adjusting the weight I'm putting on the pegs and bars and shifting around to keep things rolling without having to back off the throttle... which is reserved for those moments when things have got really out of shape!