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Turning - a bike analogy - Page 2

post #31 of 77
Originally Posted by epic View Post
Sorry... I needed to change a poopy diaper... I'm sure you wanted to know :

Anyway, Davis talked about how he'd rather be above the bike with the bike angled beneath him so hat if it skids, he is still with it. Some people corner with the bike up and the body leaning away while some will have thier bike and body closer to the same angle. This is where we need some Ron LeMaster stuff (we'll have to substitute Graham Watson). I'd like to see what Paolo Salvodelli does. How does it compare to Nicolas Vouilloz?

Compare to motorcycles - a road racer leans his body in farter than he can lean his bike. A motocross rider seems to go more the Davis Phinney route.
Oh, man, sorry to hear that.
Did you see a Doctor about it ? I'm sure there are treatments avalaible.
post #32 of 77
One more thing, bikes don't have sidecut. Why does tipping them make them turn?
post #33 of 77
Thread Starter 
Originally Posted by epic View Post
One more thing, bikes don't have sidecut. Why does tipping them make them turn?

Because the wheels are not edges, but are shaped, so, in a sense, a bike does have a sidecut.

Tip the wheel over and you have the base of the wheel with a radius R, and the side of the wheel (which is now in contact with the road) having a radius of < R. For the wheel to stay in shape, the base of the wheel will travel a further distance than the side, so it turns.
post #34 of 77
Thread Starter 
I may possibly want to retract my previous answer, having just gone off to search for info!

"A bicycle does not turn by cone or gyroscopic effects it turns by tracking. A tilting bicycle turns sharper than an upright bicycle. You can steer a bicycle no-handed by tilting because the trail effect makes it track. So, even though the cone and gyroscopic forces are there, it's the much more powerful tracking forces that steer a bike. And this time no stupid jokes.

Thankfully, when riding a bike we don't have to think about any of these things, calculating the various effects, making countless adjustments distracting us so much we are oblivious to the passing scenery, not to mention the odd bus in our path. Most of these things happen below the radar. Otherwise the expression, "it's like riding a bicycle" would have an entirely different meaning. These effects are more like autopilot or power steering. So, hats off to physics and bicycle designers, we thank you. "

Worth reading, maybe...
post #35 of 77
I'm going to have to weigh in on the side that says the wheels act like cones when tipped. This model works pretty well.

A 2nd order model would include the deformation of the tire and the angle between the tire rolling straight along its circumference and the direction it is being stretched in (which depends on how far it is turned from straight ahead) and the forces generated therein.

You can add more slip angle by turning into the turn with the handlebars, provided you are "hanging off" with more mass low down inside the turn. Hence it is possible to turn tighter even though your motorcycle can't lean any farther.

"Trail", the distance between the contact point of the tire/road and the point where the steering axis would intersect the road produces a stabilizing force which makes the bike want to go straight. Trail can become negative (and destabilizing) if you come down hard on the front wheel after taking too much air (very exciting 180 kph).
post #36 of 77
Fox, the countersteering IS the tipping. As you push the inside bar forward, the wheel turns away from the intended turn and the bike topples toward the turn. Interestingly, during the turn, if you want to adjust, or tip/topple less, you turn the bars the other way--either by pulling back the inside bar, or pushing forward the outside bar. It's kind of like what Ghost says. If you countersteer to start the turn, you've got to "un" countersteer to stop overturning or to finish.

All that stuff above about what Keith Code did with the fixed bars is apparently true. It all started when he and others tried to get riders to turn JUST by leaning, and they got scared silly and cheated. So apparently Code set up a bike where the cheating wasn't gonna happen.

As far as leaning in or out, here are two thoughts.
1. Bruce Bowlin a great ski teacher, m/c rider, great friend told me: "It's just like skiing. When you think there's gonna be a chance that the rear wheel is gonna slide, you lean out. When you think it's gonna hold traction you lean in." Perhaps simplistic, but there are some really cool applications in skiing and riding here.
2. Lee Parks, author of Total Control, told me that hanging off to the inside is done when the outward pull of the turn exceeds the downward pull of gravity, and that the main reason for it is clearance.

Managing both ideas, I tend to lean out when on dirt or when going really slowly, and I tend to hang in on the twisty pavement (that part is so much fun, and I probably exaggerate it too much).

On skis it's similar, I counterlean or angulate less when the platform is good and solid and supportive, and more when it feels skittery.

Phillipe's thought about it depending on the bike is a good one. Lee Parks told me that, with my bike (R1200GS) it probably doesn't matter very much which you do most of the time.
post #37 of 77
Originally Posted by Ghost View Post
Re Kieth Code: I believe he actually constructed a motorcycle that had the steering welded straight to illustrate that body english alone was not very effective at turning a bike that couldn't be "steered".
Originally Posted by epic View Post
One more thing, bikes don't have sidecut. Why does tipping them make them turn?
As Mr. Code's experiment suggests, tipping alone doesn't make bicycles turn. We do turn the front wheel, but less than we might think. A camera looking directly down on the bicycle from above would show this. The turning of the front wheel replaces the sidecut, in some sense.

That's MY story, anyway.

We might note also that a "flat" in-line skate requires some steering effort, whether conscious or unconscious; a rockered in-line skate corresponds to a decambered ski and will arc a turn simply by being tipped.
post #38 of 77
OK, we have been here before, in this classic discussion:
The debate is whether the "permanent reverse camber" (aka "rocker") of an ice-skate, inline skate, or grass ski causes it to carve or "track", or whether it merely facilitates pivoting.
post #39 of 77
I believe that Code's experiment suggests that the tipping is caused by the countersteering of the front wheel.

But Epic's question is really good. And I believe (but am not a good enough rider to know) that most m/c riders attribute it to the pressure at the tipping. As you load the front wheel, and tip the bike, the pressure down on the wheel compresses more on the side of the wheel to the inside of the turn, while less pressure arrives at the outside. This causes the wheel to, more or less, take the shape of a cone with the pointy side inside. Roll a cone shaped coffee cup across the floor and see what happens.

In short, pressure forward with tipping causes a coning of the wheel that makes it change direction.

Now I'm not an expert in this so please don't hold me to it. But I think it's close.
post #40 of 77
Originally Posted by Martin Bell View Post
OK, we have been here before...
The debate is whether the "permanent reverse camber" (aka "rocker") of an ice-skate, inline skate, or grass ski causes it to carve or "track", or whether it merely facilitates pivoting.
Both, I suspect. And, as noted, the "cone effect" from deformation of the wheels/tires will have some effect as well.

When a rockered in-line skate is tipped far enough, bearing compliance and wheel deformation will allow the front and rear wheels to come in contact with the pavement. The resulting four contact patches define some kind of curve. And, of course, the untilted skate is easier to steer than one with the wheels set flat, so it's easier to pivot. We note, however, that at least on pavement, pivoting must be done progressively and smoothly, since the willingness of an in-line skate to skid on pavement is minimal, although possible.

Ice skates accomplish the same thing through deformation/melting of the ice. More than a single point is in contact, and a curve is defined, although it's short enough to modify easily by steering.

Back to bicycles - the "cone effect" may contribute (more so on a mountain bike, with lower tire pressures), but any time the front wheel is not perfectly straight, the tangents defined by the contact patches of the two tires define a curve (an infinite number of curves, actually, assuming both contact patches have a non-zero length).
post #41 of 77
A little thought experiment for you:
With the bike tipped, say to the right, draw a line with a grease pencil where the rubber meets the road on the right side and on the left side of the tire. Now notice that the left line has a longer circumference than the right one, just like a cone with the pointy end on the right side.

That is the main mechanism for turning with a leaned bike. If you lock the steering straight ahead and lean the bike way over it will turn. Good luck overcoming gyroscopic force and inertial on a motorcycle at speed. Counter-steering works by "kicking out" the bottom (where the rubber meets the road) to the other side to start the lean. When enough lean has been dialed up, the steering is adjusted to balance the forces in the turn (let's not get into the centrifugal/centripetal arguments).

You adjust your cm so that you are balanced on the bike in the turn. If you are straight up, not hanging off, going faster requires more lean (or banking), and going slower requires less lean. If you want to turn tighter, but are not going fast enough to balance that lean angle, you counter weight the bike and lean to the outside while the bike leans in. If you want to go faster but not lean the bike in more you hang off.
post #42 of 77
Originally Posted by Ghost View Post
You adjust your cm so that you are balanced on the bike in the turn. If you are straight up, not hanging off, going faster requires more lean (or banking), and going slower requires less lean. If you want to turn tighter, but are not going fast enough to balance that lean angle, you counter weight the bike and lean to the outside while the bike leans in. If you want to go faster but not lean the bike in more you hang off.
Would you change anything if the amount of tire grip changed? Pavement vs. dirt/gravel? Relate this to skiing ice vs. packed powder.
post #43 of 77
Originally Posted by bud heishman View Post
Would you change anything if the amount of tire grip changed? Pavement vs. dirt/gravel? Relate this to skiing ice vs. packed powder.
Weems called it correctly. With no grip, the g-force isn't there for a full lean, you would be more angulated; you are going around at a slower speed (cm doesn't need to be as low and inside), and you would be ready to follow the bike around in a drift and stay on top of the slide. I guess you would also have a foot ready to act as a runner on the inside. I stand to be corrected though; I was never a flat track racer, just a squid.

Although, racking my memory, I seem to remember sliding around paved corners while hanging off. Sliding on pavement is a pretty dangerous game to play though; should the tire suddenly regain grip on pavement you will be flipped up over the bike in a high side.
post #44 of 77
But wait there's more!

Having understood the coning model. Consider turning a bicycle by leaning without touching the handlebars. The two tires are at two different points on the circle, and forces stretching the rubber as the tire rotates will turn the tires so that they are each rolling in a tangential direction to their contact points.

Turning a bike in at this point will cause the forces acting on the front tire to move the contact patch in. Turning the bike out will cause the forces acting on the front tire to move the contact patch out. I'll call this a "steering" force, it's probably the "tracking" force wtfh mentioned. Consider this effect separately from the "coning". Since these steering forces act on the bottom of the bike the resulting torque (force times distance from) about the cm will alter the lean angle and thereby change the radius of the turn, UNLESS you use gravity while moving your cm to balance the torque. If you do compensate with your cm then it's steering, not counter steering.

Effectively you can have more of this tracking force making a tighter turn (more steering angle) IF your cm is far enough inside the turn. If you steer less into the turn (steering closer to straight) while having your cm not so far inside the turn, you get a wider turn.

Balancing the steering force with you cm and adjusting (blending?) the amount of coning and "steering" is one degree of freedom in bike riding.
post #45 of 77
I think Ghost is really right on with this. It's complex, but it's really fun to ride and imagine this stuff happening. I just finished a 4000 mile trip and although I obviously don't think about all this stuff, and nor do I ride all that well, I really developed an intuitive feel for the tires, and their grip on the road. It seems like it's as if either Code or Parks (or both) said: it's about managing traction. That can be done at a very much sensory level as well as a mechanical one.
post #46 of 77
Originally Posted by learn2turn View Post
The way I see, when I'm in a turn, it's the last little bit of "steer" in the turn I'm in that helps me enter the next turn. That's the analogy to turn the handle bars left to go right. Then, once I'm in the next turn, I steer my skis in that direction.

Try this sometime, when you are in a left turn, at the end of the turn, instead of being lazy letting the radius fade away, tweak in just a touch of extra rotary to the left. Your CM should pass across your line of travel at which point your get on your other edges and go smoothly, and rather passively, into a right-hand turn.

I find when I do this, I get rid of the flat spot between turns. I actually get into a right turn quicker if I actively finish the left turn than if I don't. Makes for way more control.
Isn't this the movement that Bud's been discussing in his Rotary Movement/Turn Completion thread?
post #47 of 77
I thought the analogy of the bike move is a "preturn"?

You can similarly put yourself out of balance momentarily to get your wheels around an obstacle (e.g., pot hole). You don't have time to set up a proper turn around it, but you can throw your wheels around it and let you CoM continue roughly straight ahead. After the obstacle you bring your wheels back under you. You can do this skiing too.
post #48 of 77
The double-cross under!
post #49 of 77
MTBINg related only

I have found that most of my turns on dirt involve very little steering into the turn and sometime counter steering. ANother fun thing I like to do is make SL type turns on pavement to the point the rear wheel is skidding out. and use the rebound from the suspension to get the bike back underneath me.
post #50 of 77
Originally Posted by ssh View Post
Isn't this the movement that Bud's been discussing in his Rotary Movement/Turn Completion thread?
I'm not convinced it is, as countersteering IS the tip. I think learn2turn is talking about a prior move. The motorcycle analogy hear is that, as you start to lean in to the left in preparation for a left turn on pavement, you push the right grip right so the inward learn doesn't start the turn prematurely. Then when you're ready for your "turn-in", you countersteer to start (push lift grip forward).

The analogy only goes so far, and the steering on a bicycle or motorcycle is really misunderstood. (I think.)
post #51 of 77

Well, I don't mean to sidetrack from the current discussion but I would offer another perspective on why a bicycle 'turns' when it is tipped over. I don’t disagree with the material above but would suggest someone go look at a bike and carefully inspect the pivot mechanism above front fork.

Specifically; inspect the angle at which the front fork assembly passes through the frame. I think you’ll find that on most bicycles and motorcycles that angle is just off-vertical (having a small amount of ‘backward lean’ of the rotational axis of the rotating assembly).

This off-vertical-angle-of-axis is what causes the front tire of a bicycle to ‘turn’ automatically when the bicycle is tipped to either side. Draw a line directly along this axis and you’ll find that it hits the floor somewhat in front of where the tire is centered on its contact with the floor.

When the front tire is manually turned it actually pivots from an axis that is off-center of the tire’s contact point. The tire therefore “pushes its heels out” when it tries to turn (it pivots from a point in front of its actual contact center causing the back portion of the contact zone to be skidded a bit). This off-center relationship means that when the bike is tipped the top of the tire will want to ‘fall’ to the side on its own because its CM is also above the actual axis of rotation. The front tire will therefore turn to the side of its own accord.

This is easily provable: Simply hold a bicycle vertically by hand and tilt it to the side. The front wheel will turn.

(Not all bikes have this feature, though I’d bet 99.9% of modern street bikes do. Not sure about ‘trick bikes’ or Mountain Bikes. Very old bicycles didn’t have this feature and were very hard to ride because of the lack. Also, handle bar configurations can muck this up by revising the CM location in relation to the axis.)

This off-vertical axis feature makes it much easier to coordinate redirection of the front wheel with tipping motions. Essentially, the front tire ‘steers’ automatically to support tipping actions of the rider. Designed properly (axis angle, frame height and length, tire diameter, handlebar, etc taken into account) a tipped bicycle will automatically try to ‘turn’ a slightly tighter radius than necessary to laterally support the bike against Centrifugal Force for a given angle of tilt and a given speed.

This design feature creates bikes that ‘try not to fall over’. The more they tip over at typical speeds; the tighter the front tire tries to ‘over-steer’ into the turn thus righting the bike again. You can see this when a bike is launched down a small hill without a rider. The bike seems to repeatedly self-correct for a while (until it goes too slow or hits something).

All this applies directly to skis also. I suspect this is the design element that makes ‘Beta’ skis so cool. A ski can be designed such that for a given skier’s performance level its sidecut will try to turn a tighter radius than the probable skier-tipping-pattern will normally require for lateral balance at the probable speeds designed for.

OK, I know that seems a bit of a stretch… but have you ever wondered why certain skis seem to ‘turn really well’ for you but not your friend? Why a certain ski seems to ‘turn by itself’ or seems to ‘come right back under you’ so easily? It’s a matter of the ski’s sidecut/flex pattern being well-matched to your own CM height, typical degree of angulation in your style and the typical speeds at which you make you typical turn radii.

post #52 of 77
I'm not sure about our theory. On a motorcycle there are measurements called "rake" and "trail". The rake is the angle of the steering column, and the trail is the distance between the point you mentioned (where a line from the steering column would touch the street in front of the wheel) and the middle of the contact patch of the wheel. Apparently, they both contribute to make the front wheel act like a castor on a grocery basket. Apparently the igher the rake angle and the longer the trail distance, the more the bike is liable to go straight, and the more difficult it will be to turn it in.

I'm kind of new at this, but if I've got it right, it would tend to be the opposite of what you're saying.
post #53 of 77
Well, nutz Weems. Why couldn't you have posted those terms (rake and trail) earlier?

After spending so much time trying to come up with a 'good way to say it' and then messing around quite a lot more with my text to get my ideas readable - then you go and post those two terms.

By poking your terms into Google along with 'bike' and 'wheel' I found: this page on the Dynamics involved. Look down under "Trail" and you'll see some better-worded statements than mine. Basically, when the bike tips, the front wheel steers into the turn thus re-righting the bike to some degree. (depending on proper design).

I also found this page which talks a little more about your terms.

I could'a just searched and linked earlier if I had those danged terms earlier...! But thanks though - I've never heard those terms before, heck never even imagined someone would assign a 'name' to simple little measurement like that. Guess it makes sense in a way. Defining names for critical offsets and angles like that I mean.

Hmmm... but how did you get 'opposite' from my text above?
I re-read what I wrote above and still get what my brain thought it was dumping out earlier.

Bikes want to go straight when upright and want to straighten out on their own when tipped because the front wheel wants to steer into a tighter radius than the current degree of system-wide CM-tilt can accommodate, thus re-righting the bike. The key ingredient is the CM-offset from the pivot axis of the front tire & fork assembly (as further modified by greater 'fork offset' - another new term for me. I had no idea what to call this in my initial post. Thought about 'curvy-forward-prongs' but that just didn't sound professional enough for me ).

post #54 of 77
Wow! It sure sounds like it must be hard to ride a bike! Almost as hard as skiing sounds. Luckily, we and our bodies are pretty smart. A 5 year old can ride a bike without ever having heard of trail, rake, countersteer, the cone-effect or anything.
post #55 of 77
No need to get compicated. Remember that a bike in motion will have a force on the contact patch. The bikes with the longer trail will self correct more because the force acting on the tire at the contact patch is farther behind the axis of rotation giving a greater torque.

You are quite correct in that the geometry would cause the steering to rotate when the bike is tipped, but the overall effect is that a longer trail will make the bike want to turn less not more. A longer rake is somewhat like greater turn radius and more stability at speed.

Thought experiment: Consider turning a unicycle, or a bike in a wheelie. No rake and trail complications there.
post #56 of 77
I guess it might seem complicated depending on how granular we look at it. Perhaps it would help if I clarify the relationship.

Mechanical interactions and forces that cause the Front Wheel to automatically turn 'too far' for a given tilt-angle of the bike will result in the overall bike turning less.

The material is not saying that the bike will be more turny with tipping, the material is saying the front tire becomes more turny with tipping - which causes it to 'steer into' the turn so much that it drives the bike back upright.

Kinda counterintuitive I suppose, but this is where its lateral stability comes from. This mechanical relationship corrects tipping with the auto-creation of 'excess' centripetal force. It also 'pushes' the tire's contact patch laterally - from behind the axis of rotation (a torque to re-steer the tire back to 'straight' as the angle of bike-tilt decreases, another self-correction attribute).

This is also why there is a practical limit on the amount of sidecut a ski can have. Too much, and the ski will always over-turn for the given state of lateral balance.

I did consider a unicycle a number of ways. This 'auto-correction' mechanism cannot apply to a unicycle because the axis of rotation will always be right thru the center of the contact patch. As you say No rake; No trail.

Turning a unicycle seems like it would depend more on rider-induced steering than anything else at lower speeds. At higher speeds (with some banking) this would still be true but I think 'tire-mwushing' covers it up.

Imagine your unicycle with a thin (1/10th mm) very hard tire. Or imagine riding on just the rim. I think the rider would have no choice at all: manually turn (rotate) the rim of the unicycle when changing direction - or fall over.

Analysis of rounded-over rubber tire interaction with the road is pretty cool too, but I'm not sure there's much analogy with skiing in that.

I think the way bigger skiing implications are in the changes in lateral balance adjustments a skier will need to make depending on the sidecut of the skis.

post #57 of 77
Fox ..... now take the training wheels off and repeat all of the suggested exercises.

post #58 of 77

Angulation on a bike!

Hi Wear The Fox Hat!

Great post! Just a week ago, I was in a triathalon and was noticing that I was using angulation at each turn. I havn't been on a bike for a couple of years and was suddenly reminded just how much turning a bike resembled skiing. I always use the analogy of long leg, short leg like pedaling a bike when teaching skiing, as well as tipping and turning, but angulation/counterbalancing is there too!

post #59 of 77
Originally Posted by Ghost View Post
Balancing the steering force with you cm and adjusting (blending?) the amount of coning and "steering" is one degree of freedom in bike riding.
Boy, I think you could substitute "carving" for "coning" and "skiing" for "bike riding" and be pretty close?
post #60 of 77
Thread Starter 
OK, so there's a lot of good thoughts here (far more than I was expecting!)

Does anyone know of any top road cyclist who has taken up skiing?
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