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Downhill technique: Flairing one's knee

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Road Cycling “It is by riding a bicycle that you learn the contours of a country best, since you have to sweat up the hills and coast down them. Thus you remember them as they actually are, while in a motor car only a high hill impresses you, and you have no such accurate remembrance of country you have driven through as you gain by riding a bicycle.” -- Ernest Hemingway

Downhill technique: Flairing one's knee

Old 03-10-20, 03:43 PM
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79pmooney
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Originally Posted by Robert A View Post
Please explain why the rider's weight should be on the outside pedal and not the inside one. Is there a benefit to shifting one's weight to the outside of the turn?
If you have your weight on a pedal and that pedal is down, you are basically hanging yourself from the BB, effectively your weight is acting on the bike as if it were lower than the bottom bracket. Outside pedal is strongly preferred because at high lean angles there is on danger of the inside pedal scraping. If you descend with your cranks horizontal, now your weight on the BB is acting right through the BB, not acting as if it were lower.
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Old 03-10-20, 03:55 PM
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Originally Posted by tyrion View Post
It's good semantics. It's useful and accurate to call this countersteering. Even if you're not moving the bars past the straight-ahead alignment to change lean angle*, you're still moving them in the opposite direction of your desired lean angle change.

*I think at high speeds you are usually moving the bars beyond the straight-ahead alignment to increase lean, but at slow speeds you might not. This is much easier to analyze on a motorcycle where you can explore this physics for hours on a winding road or a track.
I once had to bring a doubter with me on my BMW. Hands off the bars, then pull backon the left grip with one finger, bike goes right. It's easier to see on a stable machine that's going 40 or so. What you're doing is moving the wheels out from under the CG. Once one is in a corner, I think if a bicycle's geometry is perfect, one could take one's hands off the bars and continue on your line. But many bicycles aren't perfect and so we see bikes which will oversteer and understeer. I have not confirmed this latter conjecture however, nor am I responsible for your mishaps in attempting to do so. I did have a riding buddy go completely off the road on the outside on a brand new custom bicycle, well known local builder, because it badly understeered.

I've been on a bicycle which oversteered, a relatively new Giant. A friend lent it to me to make a long somewhat technical descent and I had a heckuva time with it. I remarked on it later and the owner had no idea what I was talking about. We get used to how our bikes handle.
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Old 03-10-20, 03:59 PM
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Originally Posted by Jack Tone View Post
What a great thread! I want to play, too. The ONLY way to initiate a turn on a two wheeled vehicle, at slow OR fast speed is to countersteer.
Not entirely true. You can use an outside force to initiate a turn. I used such a force when a Jeep pulled a right turn on me when it was right beside me as I was going straight through the intersection. We got so close the jeep wheel nudged my fork, initiating the lean I needed to make the turn.
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Old 03-10-20, 04:01 PM
  #54  
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Originally Posted by tomato coupe View Post
Are you stating that your bars will turned to the left during the entirety of a right hand turn?
What is to be gained by continuing this? Do you think you're going to change my mind? Somehow convince a guy that's been racing for the last 24 years that he's wrong about how to go fast on a bike? I'd be happy to post a shaky GoPro video of me descending a 3600' mountain at 1.5-minute pace off of the record (that I hold).

If you don't think you countersteer through corners, fine. You don't. I've never ridden with you, and chances are slim that I ever will, so I can't show you what the rest of us are talking about.
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Old 03-10-20, 04:41 PM
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Originally Posted by Cypress View Post
What is to be gained by continuing this? Do you think you're going to change my mind? Somehow convince a guy that's been racing for the last 24 years that he's wrong about how to go fast on a bike? I'd be happy to post a shaky GoPro video of me descending a 3600' mountain at 1.5-minute pace off of the record (that I hold).
I have no doubts that you have a lot of race experience. But, that doesn't mean you are correct with the physics of this. I have a lot of physics experience, and I also rely on the what I have taught by my coach, who has a lot of racing experience at the highest level.

If you don't think you countersteer through corners, fine. You don't. I've never ridden with you, and chances are slim that I ever will, so I can't show you what the rest of us are talking about.
You didn't answer my simple question: "Are you stating that your bars will turned to the left during the entirety of a right hand turn?"

If your answer is no, then we have no disagreement. If your answer is yes, then I'm going to state that you are wrong.


These things have been studied, and they have been measured. Below is a measurement of a right hand turn followed by a left hand turn, where the third plot is the angle of the handlebars. You can clearly see counter steering as a downward spike at about 15 seconds, with the bulk of the right turn (region marked by the arrows) occurring from about 25-55 s. During the turn, the handlebars are turned to the right, in the direction of the turn. (In this case, the angle is about 8° for a turn radius of about 9 m at a velocity of about 11 mph.) You can see counter steering again at about 75 s for the left hand turn, with the bulk of the turn ocurring from about 90-130 s.
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Old 03-10-20, 04:44 PM
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Originally Posted by Robert A View Post
Please explain why the rider's weight should be on the outside pedal and not the inside one. Is there a benefit to shifting one's weight to the outside of the turn?
Originally Posted by 79pmooney View Post
If you have your weight on a pedal and that pedal is down, you are basically hanging yourself from the BB, effectively your weight is acting on the bike as if it were lower than the bottom bracket. Outside pedal is strongly preferred because at high lean angles there is on danger of the inside pedal scraping. If you descend with your cranks horizontal, now your weight on the BB is acting right through the BB, not acting as if it were lower.
I always thought weighting the outside pedal improved traction by keeping the CG over the tires.
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Old 03-10-20, 04:54 PM
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Jobst was convinced that the knee flare was just habit, didn’t contribute to the bike’s control. I believe in the whole countersteer thing because it has been proven,but visualizing it is hard.
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Old 03-10-20, 04:57 PM
  #58  
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Originally Posted by tomato coupe View Post
Are you stating that your bars will turned to the left during the entirety of a right hand turn?
That is absolutely the case. Countersteering does not just initiate a turn, it maintains the turn. Quit countersteering and the bike will straighten up.
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Old 03-10-20, 05:03 PM
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Originally Posted by DaveSSS View Post
That is absolutely the case. Countersteering does not just initiate a turn, it maintains the turn. Quit countersteering and the bike will straighten up.
The handlebars must be turned in the direction of the turn after counter steering initiates the turn. That is easily proven.
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Old 03-10-20, 05:03 PM
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Originally Posted by tomato coupe View Post
I have no doubts that you have a lot of race experience. But, that doesn't mean you are correct with the physics of this. I have a lot of physics experience, and I also rely on the what I have taught by my coach, who has a lot of racing experience at the highest level.


You didn't answer my simple question: "Are you stating that your bars will turned to the left during the entirety of a right hand turn?"

If your answer is no, then we have no disagreement. If your answer is yes, then I'm going to state that you are wrong.


These things have been studied, and they have been measured. Below is a measurement of a right hand turn followed by a left hand turn, where the third plot is the angle of the handlebars. You can clearly see counter steering as a downward spike at about 15 seconds, with the bulk of the right turn (region marked by the arrows) occurring from about 25-55 s. During the turn, the handlebars are turned to the right, in the direction of the turn. (In this case, the angle is about 8° for a turn radius of about 9 m at a velocity of about 11 mph.) You can see counter steering again at about 75 s for the left hand turn, with the bulk of the turn ocurring from about 90-130 s.
Speed is a factor here. At higher speed you need more lean for the same turn radius. As the bike leans, the tires act like rolling cones and provide the turning forces and less handlebar turn is needed for the same turn radius. At higher speeds you can actually be turning right with the handlebars turned slightly left.

Last edited by tyrion; 03-10-20 at 05:08 PM. Reason: changed "arc" to "turn radius"
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Old 03-10-20, 05:10 PM
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Originally Posted by tyrion View Post
Speed is a factor here. At higher speed you need more lean for the same arc. As the bike leans, the tires act like rolling cones and provide the turning forces and less handlebar turn is needed for the same arc. At higher speeds you can actually be turning right with the handlebars turned slightly left.
You can calculate the steering angle if you know the lean angle, the turn radius, and the wheelbase of the bike. Speed only comes into it via the lean angle, and there is no lean angle that causes the steering angle to go negative. (This all assumes the back wheel isn't skidding.)
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Old 03-10-20, 05:20 PM
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Originally Posted by tomato coupe View Post
You can calculate the steering angle if you know the lean angle, the turn radius, and the wheelbase of the bike. Speed only comes into it via the lean angle, and there is no lean angle that causes the steering angle to go negative. (This all assumes the back wheel isn't skidding.)
I don't know how you get that. Lock your handlebars straight ahead and lean the bike to the right and it will turn right because of how the tires interact with the road. If you want to turn slightly less right you have to turn the handlebars to the left.
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Old 03-10-20, 05:31 PM
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Originally Posted by tyrion View Post
I don't know how you get that. Lock your handlebars straight ahead and lean the bike to the right and it will turn right because of how the tires interact with the road. If you want to turn slightly less right you have to turn the handlebars to the left.
Here's some easy experiments: Lock your handlebars straight ahead with some tape. Push the bike, lean it to the right, and see if it turns to the right. Lean it to the left, and see if it turns to the left. Next, lock the handlebars a little bit to the right, lean it to the either side and see which way it turns. (Obviously, you should push the bike, not ride it.)

Last edited by tomato coupe; 03-10-20 at 05:40 PM.
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Old 03-10-20, 06:04 PM
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Many amusing responses above. Calculations don't mean squat. Take a motorcycle training course. My instructor was a motorcycle cop for over 20 years. He knew how to turn a bike. Push on the right side to turn right (counter steer). Quit pushing and the bike will straighten up. I passed the course, bought a motorcycle and took it up and down twisting mountain roads with little experience. His instructions were absolutely correct. A bike won't turn unless you're pushing on one side of the bars. Otherwise it will go in a straight line. At very low speeds, the steering is normal - turn the bars right to turn right.
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Old 03-10-20, 06:17 PM
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Originally Posted by DaveSSS View Post
Many amusing responses above. Calculations don't mean squat. Take a motorcycle training course. My instructor was a motorcycle cop for over 20 years. He knew how to turn a bike. Push on the right side to turn right (counter steer). Quit pushing and the bike will straighten up. I passed the course, bought a motorcycle and took it up and down twisting mountain roads with little experience. His instructions were absolutely correct. A bike won't turn unless you're pushing on one side of the bars. Otherwise it will go in a straight line. At very low speeds, the steering is normal - turn the bars right to turn right.
The techniques for riding motorcycles and bicycles are not identical, largely because rider weight is dominant when riding a bicycle, but cycle weight is dominant when riding a motorcycle.
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Old 03-10-20, 06:26 PM
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I've actually ridden 3 motorcycles that were lighter than I am. I do feel that most, if not all, techniques are similar.
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Old 03-10-20, 10:14 PM
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Originally Posted by Carbonfiberboy View Post
It moves the CG to the inside, which reduces the bike's angle of lean slightly, which may or may not improve adhesion, depending on a whole host of things.
.
This - if you look at racing motorcyclists cornering hard, they don't just drop their inside knee, they shift their whole body over, so their ass is hanging off the seat on the inside. By shifting their center of gravity to the inside, that can keep the bike as upright as possible and maintain maximum grip in the corner. Cyclists can't do that - if the outside pedal is down and their outside leg is at close to full stretch, they couldn't shift off the saddle even if they wanted to, but their inside knee drops and I imagine they shift as much body weight to the inside as possible to achieve the same thing - move the COG of the rider/bike combination to the inside, so that the bike can be held as upright as possible to maximize grip.
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Old 03-10-20, 10:51 PM
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Originally Posted by Litespud View Post
This - if you look at racing motorcyclists cornering hard, they don't just drop their inside knee, they shift their whole body over, so their ass is hanging off the seat on the inside. By shifting their center of gravity to the inside, that can keep the bike as upright as possible and maintain maximum grip in the corner. Cyclists can't do that - if the outside pedal is down and their outside leg is at close to full stretch, they couldn't shift off the saddle even if they wanted to, but their inside knee drops and I imagine they shift as much body weight to the inside as possible to achieve the same thing - move the COG of the rider/bike combination to the inside, so that the bike can be held as upright as possible to maximize grip.
How does that improve grip? The lateral pressure on the tires should be the same regardless of how the rider leans, or am I missing something?
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Old 03-10-20, 10:56 PM
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Originally Posted by 79pmooney View Post
If you have your weight on a pedal and that pedal is down, you are basically hanging yourself from the BB, effectively your weight is acting on the bike as if it were lower than the bottom bracket. Outside pedal is strongly preferred because at high lean angles there is on danger of the inside pedal scraping. If you descend with your cranks horizontal, now your weight on the BB is acting right through the BB, not acting as if it were lower.
At no point did I suggest that the inside pedal should be down.
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Old 03-10-20, 11:51 PM
  #70  
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Originally Posted by tomato coupe View Post
The techniques for riding motorcycles and bicycles are not identical, largely because rider weight is dominant when riding a bicycle, but cycle weight is dominant when riding a motorcycle.


Largely because a motorcycle is propelled forward by xxx horsepower, and a bicycle is propelled forward by 1/xxx horsepower.
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Old 03-11-20, 12:04 AM
  #71  
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Roll downhill, put out a knee, see where the bike wants to go... that's why it's done. In fact you can to a large extent steer by just moving the knee in or out.
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Old 03-11-20, 07:15 AM
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No one has claimed that bicycle and motorcycle steering is identical, but the basic principles of how the steering works are the same. There is no need to flare a knee when proper steering technique will accomplish the same thing. I've ridden the same winding mountain roads on both bicycle and motorcycle. A motorcycle takes a lot of deliberate effort to turn and is much more tiring. One big difference with a motorcycle is the ability to ride at higher speeds both up and down a mountain, so the need for constant countersteering is obvious.

All the talk of what road racing motorcycle drivers do is irrelevant. That won't be discussed in any class geared toward safe riding techniques on city streets and highways. Race coarses are often made with special asphalt that creates better traction and they won't have sand on the road like a real winding mountain road. Motorcycle or bicycle riding in the mountains requires a careful watch for rocks and sand at all times.
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Old 03-11-20, 07:50 AM
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Originally Posted by DaveSSS View Post
That is absolutely the case. Countersteering does not just initiate a turn, it maintains the turn. Quit countersteering and the bike will straighten up.
I don't agree. When riding a bicycle we're basically "falling" constantly on one side or the other. What we do to avoid hitting the ground is using the handlebar to constantly put the bicycle under us. For example: if you fall to the left, you turn left to put the bike again under you. You have to mantain this equilibrium to avoid falling off the bike. This is why it's so difficult to do a track stand (because you can't constantly steer the bike under your). This means that it's impossible to ride a bicycle in a real straight line (it can be really narrow, but not fully straight).

When you enter a right turn you first countersteer to move the bike that sits under you to the left (which means you start falling to the right, since you moved the bike left, but your body kept going straight because of inertia). As you start the turn, your mass will pull you outwards, so what you do to avoid kissing the ground is use the handlebars to keep the bike in a delicate equilibrium that equals the centrifugal force that's pulling you outwards while you turn, with the gravity that's pulling you to the ground. As you exit the turn, you just steer harder to the right until the bike is under you again.

This means that it's impossible to counter steer the whole turn unless your rear tire is partially skidding. In a tight turn, you probably countersteer only to enter the turn, while on a wide one it's possible to countersteer partially through it, but not during the whole turn.
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Old 03-11-20, 08:29 AM
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Originally Posted by Robert A View Post
How does that improve grip? The lateral pressure on the tires should be the same regardless of how the rider leans, or am I missing something?
MotoGP racers lean off the bike in corners to keep the inside peg from dragging on the ground. The suspension also works better when the motorcycle is more vertical which helps a bit with traction. Motocross racers don't have the problem of the inside peg dragging so they actually lean to the outside of the corner to make the bike lean more than the rider. I watched a few fast bicycle decent videos, and they seem keep their bodies pretty much aligned with the angle of the bike, so I'm not sure how relevant the motorcycle leaning comparisons are. I did see a number of cyclists flare the inside leg, but only on tight corners. Looks to me like their leg just naturally does that as they look around the corner with their outside leg down.
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Old 03-11-20, 09:39 AM
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Originally Posted by kingston View Post
MotoGP racers lean off the bike in corners to keep the inside peg from dragging on the ground. The suspension also works better when the motorcycle is more vertical which helps a bit with traction. Motocross racers don't have the problem of the inside peg dragging so they actually lean to the outside of the corner to make the bike lean more than the rider. I watched a few fast bicycle decent videos, and they seem keep their bodies pretty much aligned with the angle of the bike, so I'm not sure how relevant the motorcycle leaning comparisons are. I did see a number of cyclists flare the inside leg, but only on tight corners. Looks to me like their leg just naturally does that as they look around the corner with their outside leg down.
There's also a fundamental difference between motorbikes and bicycles. In a bicycle, most of the mass is the rider, while on a motorbike, most of the mass is on the motorbike itself.

This affects cornering because more mass means more inertia, and in this comparison, mass is placed at vastly different locations, which affect the CG among other things.
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