How Far Can a Motorcycle Lean in a Turn?
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This is essentially the biggest factor. And more important than the surface is the material. When properly warmed (notice how they always prewarm the tires in bags before any race) that stuff is basically chewing-gum.
I've worked in F1 and several circuits including the one featured in the article (Jerez) and I remember the walls in the paddock totally splattered of tire material at the end of the day. Some days I'd even go back to home with small pieces stuck in my clothing.
That's the reason why engineers must wear glasses and helmets sometimes.. https://dfp2hfrf3mn0u.cloudfront.net/879/87936_1.jpg
This was Rabat's rain tire after finishing 2nd last weekend on a track that was mostly dry by the end of the race.
If the suspension is not properly set up for compression and rebound, guess what? Materials mean nothing if the tire is not in contact with the ground. And there are some bumpy tracks out there...
Note this is opposite to what many road oriented motorcycles use - progressive rate springs and linkages are often used to allow "more supple" suspension around normal riding circumstances while still having enough suspension force to deal with bumps while overloaded or leaned over hard. Race bike don't have to have any consideration for rider comfort "suppleness" or bumps/potholes. The sole purpose of the suspension on a race bike is to maximise the tire's contact to the track.
Modern climbing shoe rubber is another example of amazing friction. As Charles Cole (Five Ten founder) explained to me, you need both maliability and high shear strength so the "plugs" of the rubber that extend into the depressions in the surface do not tear off.
The rider leans off the bike to the inside of the turn, and since the rider weighs ~30-40% of the bike+rider mass, this moves the center of mass quite a long way to an even higher angle than the lean angle sensors on the bikes frame indicate - the rider moving makes the discrepancy worse not better.
The left/right curvature of the tires (mostly that big fat ~200mm wide rear one) means that the location of the contact patch between the tire and the road also moves towards the inside of the curve. This means the frame lean angle sensor is over-reporting the angle somewhat. This moves the discrepancy back the other way.
Another thing to consider though. Nobody assumes the rule of thumb that "the coefficient of friction is always between zero and one" applies to sticky tape (which it quite obviously doesn't), but a hot motorcycle racing slick has that same tacky stickiness to it that duct tape does. Look at any bike that runs into the gravel traps. It's tires come out _covered_ in gravel that's quite clearly stuck to them at a coefficient of friction greater than 1. It's perhaps non-obvious, but it shouldn't be too much of a surprise that tire "stick" like that to the track surface as well as the gravel on the runoff areas...
[1] Little pieces of discarded rubber
Went looking just now and found better explanations online than the last time I tried, years ago, but I have yet to see a satisfactory analysis of the physics. Many of the explanations claim that counter-steering is only done temporarily to begin a lean, only for "setting up" a turn, and then switches to normal steering. After a lot of experimentation, I'm pretty convinced counter-steering is actually always happening on a bike, but relative to the turning radius of your lean, not relative to straight, which makes it a little subtle and harder to demonstrate. If anyone knows where a solid analysis of the physics is, I'd love to see it!
It's the new Monty Hall puzzle. Or "does 0.999... === 1?"
I guess the difference with a motorcycle is that it simply can't be steered effectively any other way at speed... So you're not going to find any biker who says this doesn't work ;)
I haven't ridden motorcycles nearly as much as bicycles, but my sense is that motorcycle tires/wheels are so much more massive that at normal highway speeds they really do have the gyroscopic effects that everyone mistakenly believes are present in bicycle tires/wheels. When these effects cannot be counteracted by increased steering force, steering requires precession/counter-steer. So there is sort of a progression from low-mass systems that must be steered to stay upright to high-mass systems that must be tilted to steer. It's not clear whether these are really different phenomena, or just two values that have an inverse relation.
I would call the back and forth "balancing", and not counter-steering. You go back and forth in order to keep your center of mass positioned, on average, over the line that connects your two contact points with the ground. But I think you're continually counter-steering while you balance! (Unless you are leaning really fast back and forth, but that's not how we ride bikes, right? We steer to balance...)
Counter-steering (in my mind- this is not necessarily generally accepted) is always an instantaneous effect where you steer the front wheel to the left of where it is, in order to turn more right than you're currently turning. I think that you are always counter-steering, even on a bicycle.
My theory is that if you put any inline two wheel vehicle, regardless of motor or mass, into a constant speed, constant radius right turn, then the stationary position will be the front wheel is steering to the right a bit. Now is where counter-steering comes in. In order to increase your turning radius, or straighten out and stop turning, you steer into the turn by pushing forward on the left side of the handlebars. In order to decrease your turning radius, or turn tighter, you push on the right side of the handlebars, thus steering the wheel more left than it currently is. For this second part, your front wheel might be steering right of center the entire time, the critical bit is that you're steering left of where you were in order to tighten your right turn.
I think counter-steering is going on at all times, even while you're swinging back and forth balancing on a bike. In fact on a bike its a lot easier to experience counter-steering when you're coming out of a turn than when you're going into one. I think this is what people mistake for steering right to turn right. You do steer right, but it happens after the turn started, you always turn into the turn in order to straighten out. It just happens so quickly and automatically its hard to notice its there.
What do you think, sound plausible? The implications of this would mean that mass & gyroscopic effects don't have much to say about counter-steering specifically, they just change how much you can turn by leaning vs turn by counter-steering. With bigger bikes, you can't do much by leaning. (I think I'm just repeating what you said here.) But I also think we use a lot more counter-steer than lean on bicycles, and just don't know it!
As you say, we're repeating each other. Still, I think I understand this topic better now than I did before.
The science museum demo I mentioned is done with small wheels. Even smaller than your average bicycle. The gyroscopic effect is quite significant. Do this at home: Put handles on the side of a bicycle wheel. Spin it (doesn't need to be that fast). Now try to turn it. You'll know what I'm talking about once you've done this experiment.
That said because bicycles are smaller, your mass is larger, and they're typically not going as fast the effect of moving your center of mass e.g. is a lot larger and counter-steering is less noticeable. On a motorcycle there's no way you can't notice it and it was only after I started riding motorcycles that I was more aware of this on the bicycle. Once you go back from your motorcycle to your bicycle you will do this more consciously at speed... I agree with your description of this as some sort of continuum, with less mass, speed and smaller wheels the relative weight of the different effects changes. Clearly on a stationary motorcycle or bicycle counter-steering isn't going to do much :)
And yeah, counter-steering is relative to your lean angle, however at slow speeds if you're leaning then you need the throttle to take you out of the lean otherwise you'll just fall over... At speed it's easy to flick the bike quickly from side to side just by counter-steering both ways...
I didn't stay bicycles stay upright because of gyroscopic effects. I said they are more stable at speed and that I'm pretty sure that's due to gyroscopic effects because all else is equal. Do you think bicycles and motorcycles are more stable or less stable at speed and why? None of your very interesting links (I did see one of them before) add any relevant information.
A quote from your link supports what I said: "It is almost certain that gyro effects are important at the initial stage of steering manoeuvres."
You say: "the gyroscopic effects that everyone mistakenly believes are present in bicycle tires/wheels."
It looks like other cycling instructors teach this too:
http://www.bamacyclist.com/articles/QuickTurn.htm http://www.bikexprt.com/streetsmarts/usa/chapter5a.htm http://www.bikeforums.net/advocacy-safety/295623-quick-turn-...
Maybe the idea is that the size of the necessary movement for a very fast turn is outside of the range of a typical cyclist's unconscious reflexes. So for a gradual turn you can sort of do what feels natural, but for a quick enough turn you need special practice. That might match up with motorcycle instruction practice fairly well if we expect that motorcycle turns are more likely to need to be fast enough to need the rider to perform a counterintuitive movement.
For example: when you steer to the left while having lots of forward momentum, the contact patch of the front wheel wants to go left, so the bike starts rolling to the right, around its centre of gravity. Gravity itself, along with suspension, keeps the bike in contact with the ground even as it rolls over.
Once the bike is rolled over into a lean, it will start falling over, but if you leave it at that, it won't simply fall on its side. The steering geometry (specifically, front-loaded steering geometry, you can look it up separately) wants to steer the bike back upright again, by steering into the turn slightly.
Depending on how much it's steering into the turn, the bike will either turn quickly and come upright through the same mechanism as counter-steering, or it will turn smoothly in a circle if the steering exactly counteracts the centrifugal ("fake") force. And if it's not steering enough into the turn, then the bike will eventually fall over.
Counter-steering while leaned over in the steady state will increase the angle of lean, meaning later, more steering into the turn will be required to maintain lean angle, which will cause the described circle to tighten. Steering more into the turn while leaned over will cause the bike to straighten up.
Additional bonus: the width of the front tyre has a large effect on how much the bike straightens up when using the front brake. When leaned over, braking with the front has a torque effect on the steering axis: the contact patch is off to the side of the tyre, and if you've got a wide front tyre, it'll have leverage over the steering. Braking will cause the road to push back on the side you're leaned over on, which will cause steering into the turn, which will straighten the bike up. Steering geometry probably also affects straightening up on front brakes, but I've always noticed it far more on big bikes than ones with narrower, higher aspect ratio front tyres.
By centre of gravity, to be clear, I meant the roll axis running through it. I used the word rolling precisely to refer to the roll axis.
Gyroscopic effects definitely complicate things - steering takes more effort at speed - but the fundamentals of counter-steering is that it rolls the bike due to torque from a reaction of the road against the angle of the front wheel.
(FWIW, I don't own a car and use motorbikes as my main form of transport; I do about 15k a year, a mix of city commuting and long distance touring. Smaller, lighter bikes are easier to apply extreme countersteering to, and I do often in the city, so I'm well aware of what actually happens when I steer harshly, which exaggerates the effect of everything described. For example, sharply countersteering upright will push the front of the bike into the air.)
The situation at high speed is fundamentally different from the situation at low speed. Try this experiment (this became quite long, but I wanted to make the explanation as explicit as possible to avoid misunderstandings):
1. Put a pebble in the road as a marker and ride towards it quite slowly, like jogging speed. As you approach the pebble, initiate a sudden countersteer to the left. What will happen is that the handlebars will turn slightly to the right, the contact patch will move to the right, and the bike will roll to the left as it rotates around the CM. Your front tire will likely pass to the right of the pebble.
This is the situation you describe: at low speeds, the force from the contact patch makes the bike rotate around the CM, which initially moves opposite to the direction you are trying to go. (It has to, the contact patch force is to the right, and that's the only lateral force affecting the bike initially.)
2. Now try the same maneuver at quite high speed. (Do it in a wide parking lot or something so you don't run off the road, obviously...) What you will find is that unlike in the first situation, when you countersteer, the handlebars are pretty much rock solid. Even though you attempt to turn them to the right, there is no appreciable motion. Because the wheel doesn't turn, the contact patch continues basically a straight line. However, the bike still leans over and starts turning to the left. You'll now find that the wheel will run over or pass slighly to the left of the pebble.
This behavior is impossible to understand without the gyroscopic effects. If the bike still rotated around the CM, the contact patch would still move to the right, actually by a larger amount if you think that it takes a larger force to overcome the stability of the spinning wheels. If that was the case, the front wheel would still pass well to the right of the pebble, but it doesn't.
What is missing in this case is the effect of gyroscopic precession in a fixed gyro. With the front wheel spinning rapidly, the attempt to turn it right when countersteering will not rotate it around in the steering direction, it will cause the wheel to rotate orthogonal to the applied torque, in the roll plane, taking the whole bike with it. If the bike was suspended in the air, it would just rotate around its center of mass, but because friction prevents the contact patch from moving laterally, there is a resulting force with a magnitude that keeps the contact patch stationary. Note that unlike in the slow-speed case, where the force from the contact patch acts to the right, it now acts to the left. The resulting motion is one where the bike rotates around the contact patch, moving the center of mass in the direction of the lean. This motion looks quite "magic" if you're not aware of what the gyroscopic precession does.
Without the precession, you wouldn't need to go very fast until it would be impossible to turn the bike at all. If you just imagine that the gyroscopic effect makes the bike resist leaning over, you'd need to develop a larger and larger contact patch force to the right as you went faster and faster. This would make the bike track further and further to the right as you attempted to turn to the left, which is exactly the opposite of how a bike really behaves.
Hope that explanation helps.
How do braking forces play into this, and do you know what kinds of speeds we're talking about? A soft front tyre (i.e. lower than normal pressure) has a dramatic effect on handling at street / city speeds - the extra rolling resistance makes the steering want to steer further into the turn, causing a countersteer upright. So you need to fight the steering to maintain line. But of course when putting a bike on track, you run with lower pressures as a matter of course - and I know from anecdotal experience that it is possible, on track, to brake while leaned over a bit hard enough to start lifting the rear, something that would require an immense effort to avoid straightening up at street speeds.
You've given me something to think about, but unfortunately I won't be able to solve the problem without either learning a lot more mathematics, or playing with models...
If your wheel is turned right 10 degrees, and you're in a steady state right turn, then setting the wheel to 5 degrees right is counter-steering that will quickly increase your turning radius.
This is the bit that makes it a little harder to convince skeptics -- steady state of a right turn is steering right. What "counter-steering" means is how you steer relative to steady state. Yes?
Great anecdote - the first time I rode on a quad bike was after I'd bought a motorcycle. I felt pretty confident and got going at a decent speed. I then had to turn for the first time... imagine my surprise when the bike went the WRONG WAY. WTF. Because of the handlebars and my muscle memory, I tried to counter-steer into the turn and nearly stuffed myself into a huge tree.
Luckily, I somehow managed to get the rational non-automatic part of my brain working quickly enough to avoid it, but it was a bit too close..
Take Moto GP for instance, they lean a lot more (by training, lack of fear and other factors) than a street rider would. Part of this is tires. They use tires that are more rounded and don't really have a noticeable sidewall.
I have Michelin Pilot 3's on my bike and I feel safer leaning more with then the stock tires that were on the bike.
As a side note, my bike is more upright than most, so this has a lot to do with my ability to lean. I feel very comfortable leaning farther on a bike where I am not already leaning really far forward to begin with.
Note: I have a 2012 Triumph Street Triple. My wife has a 2012 Triumph Daytona Ultra sport. Mine is more upright, hers is a significant forward lean.
Coming back up again is the tricky part.
Kinda like falling out of a skyscraper doesn't kill you. It's the sudden stop at the end that does.
(But I'm not defending the joke :)
For instance, my motorcycle's tires are not race tires, but street tires. The bottom of the tire only goes up the "side" for a limited distance. If I lean too far the side of my tire no longer touches the ground
Also, the lean angle would have to be related to the foot peg size. My current foot peg is quite long--even for mild lean angles somestimes I can feel the road scratching on my boots and the foot peg.
I am not a physics person, but it would seem that the change in diameter that corresponds with the change in angle might change the effective CoG. Can anyone tell me if this is correct?
Bikes slide while leaned over and electronic traction control.
How far could you lean one of these bikes over without the computer helping? :)
You can still lean an all-mechanical bike with ordinary tires quite a ways. When I would be turning through very long curves on freeways and so I would get back fatigue from the fake force (the one that's trying to make the bike stand up vertically again), requiring me to sit on the upper side of the bike to keep it leaned over with less effort. I have a very slim build so this is a trick that might not be familiar to most male riders.
And they certainly leaned those over:
It works for bicycles too!