1. PF Contest - Win "Conquering the Physics GRE" book! Click Here to Enter
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Is countersteering a necessity?

  1. Apr 20, 2010 #1
    Hi Guys,

    We're having several debates on aspects of motorcycle turning and leaning on my bike forum, so I popped along here to see what you guys think.

    If anyone's bored or interested enough to join in, you'd be most welcome, but our arguments do tend to get a little scrappy. :redface:


    I've had a good search and read, but haven't found the exact question I'm looking for.

    To make a motorbike turn right, do you have to countersteer left?

    Can the rider lean right, causing the bike to lean right, then turn the handlebars to the right and take the corner? Or does he subconciously countersteer left when he leans?

    What about riding with no hands? Does the rider leaning right cause the wheel to countersteer left 'automatically'?

    Last edited by a moderator: Apr 25, 2017
  2. jcsd
  3. Apr 20, 2010 #2


    User Avatar
    Homework Helper

    No, you can just steer right, and the bike will turn right, until it falls over onto its left side. Countersteering is used to lean a bike into a turn, once leaned, you steer inwards to actually turn the bike. During the leaning process (roll) you only need to keep the steering a bit outwards to continue leaning further inwards while also steering inwards. Steer inwards just enough and the turn will be "coordinated" and the bike will hold it's lean angle. Steer inwards too much and the bike will straighten up.

    The radius of a turn is mostly a function of the angle between the front and rear tires. If you were to draw a line extending from the axis of the front and rear tires, those lines would cross, usually underground since the bike is leaning. If you extend a vertical line from where those lines cross to the surface, then that point on the surface will be the center of the circle the bike tries to follow. Deformation at the contact patch will tend to make the actual radius a bit larger than this, depending on the cornering forces. The fact that the contact patch is on the side of the tire as opposed to the center also has some effect.

    Depends on the bike. Note that the steering geometry (trail) on most bikes is setup so that leaning the frame of the bike causes the front tire to steer inwards, enough to self correct if the rider is not hanging off to one side, making the bike stable. A rider can turn hands free by leaning inwards, which leans the bike outwards, resulting in the front tire steering outwards, an indirect method of counter-steering. You need to be above some minimum speed for the steering geometry to work. Gyroscopic forces at high speeds dampen this corrective response, and around 100mph, it's virtually gone, let go of the steering ahd the bike tends to hold a lean angle as opposed to straigtening up, and body leaning produces virtually no steering reaction. Normally only race track drivers are aware of this. Some sport type (racer replicas) motorcycles tend to be neutral steering (small amount of trail) and will not respond well to body leaning at any speed.

    Keith Code's "no bs" bike with a second set of fixed and non-steering handle bars apparently has a small amount of trail (and perhaps a steering dampener, which would be "cheating"), used to convince riders that body leaning can't be used to steer that particular bike, but he admits that his dirt bikes (lots of trail on these) can be easily steered by body leaning or just shifting weight on the pedals. For the bikes that can be steered hands free, the focus is on leaning the bike in the direction you want to steer, not the rider's lean angle (that's just one method of leaning the bike, standing on the inside pedal does the same thing).
    Last edited: Apr 20, 2010
  4. Apr 20, 2010 #3
    Hi Jeff,

    Thanks for your help.

    I'm still a little unsure, though.

    What I'm trying to get at is; is this possible:?

    The front wheel is pointing straight ahead, and the bike is travelling in a straight line.
    The rider leans right.
    This causes the bike to lean right.
    The front wheel either 'automatically' or by rider input turns right, and a stable right turn is achieved.

    Is it possible for this to happen, without any countersteering input whatsoever?
  5. Apr 20, 2010 #4


    User Avatar
    Homework Helper

    It's a uni-track vehicle, the center of mass can't shift instantly, it needs a lateral force from the tires to move (accelerate) laterally. If the rider leans right while the front wheel is pointed straight ahead, then the rider generates an internal force to the left on the bike, as well as a counter-clockwise torque (viewed from the rear) onto the bike, both of which cause the bike to lean to the left and steer the front tire left (directly from the internal left force and indirectly due to the lean and trail). This unbalances the bike, causing it to straighten up, then lean right, after which the front tire will lean right. Depending on how far to the right the rider is leaning, the bike may self correct, or the rider may have to straighten up or lean left to recover from the imbalanced state. Note it's possible to hang off the bike by body leaning, but then apply steering inputs to keep the bike going straight, a maneuver commonly used by motorcycle racers when setting up for a turn. In a S turn sequence you'll often see both the bike and the rider leaning and shifting weight in the same direction, at the same time, upwards then over to the other side, where it clearly requires a lot of counter-steering input to perform this manuever.
    Last edited: Apr 20, 2010
  6. Apr 20, 2010 #5
    If everything is perfectly balanced, all the rider can do is change the relationship between the position of his personal c of g and that of the bike. He can't affect the c of g of the rider/bike system without introducing an outside force unless he first unbalances the system - by countersteering.
  7. Apr 20, 2010 #6
    Thanks, guys.

    So the answer is yes, it is a necessity. You can't turn without it.
  8. Apr 20, 2010 #7


    User Avatar
    Homework Helper

    You can't lean without countersteering. You can turn by simply steering in the direction you want to turn, but it imbalances the bike, and depending on the amount of angular inertia on the roll axis, you don't get much lateral force. If this is a short abrupt maneuver, you can use this method to avoid pot holes, much quicker than normal countersteering. You simply steer the tires out from under you to clear the pot hole, then quickly recover once past the pot whole, with minimal net lateral movement of the center of mass.
    Last edited: Apr 20, 2010
  9. Apr 20, 2010 #8
    I think this explains why some accidents happen, because despite your instincts telling you the opposite, you have to initially turn towards the danger to miss it.

    Perhaps it's also responsible for the accidents that some bikers have on their own, when they enter a corner too fast, panic, and go in a straight line.
  10. Apr 20, 2010 #9


    User Avatar
    Homework Helper

    If it's a pot hole, you can simply steer away from it, then recover balance afterwards. Your simply trying to steer the tires away from the pothole, not shift the center of mass laterally. If it's a car or other tall object you're trying to avoid, you need to countersteer to lean away, then mostly likely to keep from running off the road you want to pass that object with the bike vertical and not leaning either way.

    If you conciously countersteer for long enough that you associate lean angle with cornering, then the instinct transitions to one where your instinct is to countersteer to lean away from obstacles.

    Also countersteering is more about the torque you apply to the handlebars. Even while leaned over, you should learn how to adjust the lean angle with countersteering torque, outwards to increase lean angle, inwards to decrease lean angle. It's sort of like flying a plane, except the bank angle is controlled by countersteering torque (without any body movement if you really want to learn this). Then you learn to anticipate where the bike will be in a second or so into the future for a given lean angle and speed. The next tricky part is to look ahead in the turn, perhaps 90 degrees ahead on a long freeway entrance, where you're visual feedback on your current position and lean angle is from your peripheral vision.

    Well since braking while leaning applies an aft force to the side of the front tire, that can cause the front tire to steer inwards, which straightens up the bike. Depending on the bike, you have apply more countersteering torque to the handlebars when braking in turns, and also remember to relax on the bars once you stop braking.
    Last edited: Apr 20, 2010
  11. Apr 21, 2010 #10
    Motorbikes are tricky little buggers, aren't they.

    Fun though.
  12. Apr 21, 2010 #11

    jack action

    User Avatar
    Science Advisor
    Gold Member

    Let's try an explanation of the process.

    First, how a tire creates lateral force.

    There is only two ways a tire can create a lateral force: either, you give it toe (steering in the direction you want) or camber (leaning in the direction you want).

    You could steer a bike the same way you steer a car, i.e. with toe change. But if you do so, the lateral force generated will create a moment forcing your bike leaning outward which will have two effects:

    #1: The moment due to the lateral force will be unbalanced (meaning the bike will tend to lean outward more and more)

    #2: The outward leaning means also outward camber that will counteract the toe change which will tend to straighten your path.

    So lesson learned: Just for #1, you can't steer a bike without leaning inward. Furthermore, by leaning inward, you induced inward camber which means you need less toe change.

    How do you lean in the direction you want?

    Well, you have to create a moment. One simple and obvious way is to shift the CG of the bike on the side you want to lean (like changing the driver's position).

    The other one is less obvious, but it is to rotate the axis of rolling component. What is clear to everyone is that whenever you change the velocity of a component you need a force to be applied. But this is true in magnitude as well as direction. And when you change the direction of a rotating wheel, you change the direction of the velocity of each of the parts (say every molecule) of that wheel. You can feel that force when you push the handle bar. That force creates a moment on the bike that forces it to lean on one side. It just so happen that if you want to lean on one side by creating such a moment, you must turn the "wrong way", hence countersteer. If the front wheel was spinning backward, you wouldn't have that problem, since everything would be reverse and you could steer the "right way" to induce lean in the direction you want.

    Is countersteer necessary? Theorically, no. Any moment that will induce lean will work. But with high speed rotating wheels at your disposition, it's really a simple solution.

    So, at high speed, if you want to turn without countersteer, you're leaning because you're shifting your weight on one side. If you steer in the direction you want to go at the same time, then the two moments created will work one against the other, which means the bike will tend to stay straight (depends which moment is the greatest, which depends on the wheel rotating speed and how far the driver changes its position).
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Similar Threads - countersteering necessity Date
Photovoltaic Cell- P-N Junction Necessity Oct 11, 2014