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Weight related steering inputs - discussion

Discussion in 'New Riders and Riding Tips' at netrider.net.au started by zenali, Sep 21, 2008.

  1. #1 zenali, Sep 21, 2008
    Last edited by a moderator: Jul 13, 2015
    {Mod: Split this discussion on physics of weight based steering and bike inputs away from it's original thread - flux's tips for making a bike dance}

    I'm quite happy to try both techniques and go with whatever works for me - when I reach that skill level. :)

    But on the topic, have you looked at Code's "No B.S. Bike"? He modified a bike to add a second set of handlebars fixed to the frame to completely remove any of the normal handlebar steering inputs.


    The idea is that you can do all the weight shifting and leaning you like without adding steering inputs into the mix. He was trying to determine how much of the lean used to turn the bike is the result of weight shifting and leaning on the part of the rider, and how much is the result of counter steering.

    There is a video on YouTube where you see the rider actually moving from one side of the bike to the other, not only removing the weight from one peg but actually swinging the entire leg over to the other side of the bike.


    It is worth a look.

  2. What are you trying to say? Weight shift is not relevant? The point is not what initiates a turn we all know that counter-steering changes your line but this is more for those who know that already. Not meaning to be short with you but this thread is not about the basics but for advancing those techniques and learning how to manage your self to aid in bike control. if the only way to steer a bike is the front wheel- how can i change the bikes line with the front wheel skimming the ground , or off the ground for that matter?
  3. Push on the inside peg to get the bike into the corner. I did some digging with google and it would seem that a few racers agree with this (Schwantz most notably). Mid-corner do what you want. Depends on how long the corner is. There's a reference to Scott Russell sliding the rear at wheel by weighting the inside peg (to invoke a power slide) and the outside peg (to bring the rear back into line). When apexing/exiting, weight up the outside peg.

    You and I seem to be in basic agreement, aside from weighting up the inside peg on entry.
  4. I've been lurking in the thread from the start and zenali is right. Some of what Flux is saying about weight is controversial. Where weight is placed on a bike makes very little difference to the bike.

    Where MASS is placed makes a difference.

    Bikes don't "fall over" due to weight placement - in simple terms, they lean in a corner in response to centrifugal forces. Now I know it feels like the bike falls more easily in the corner when my inside peg is weighted, but that's only my perspective and I don't think that that is actually true. But it works.

    Carry on :popcorn:
  5. #5 [FLUX], Sep 22, 2008
    Last edited by a moderator: Jul 13, 2015
    I'm familiar with Code's no B.S. machine. I've even sat on it when it was there at Phillip Island two years ago. Not ridden it though.

    (Partially) irrelevant to this topic. Getting the bike off vertical requires counter-steering to initiate a direction change. That is not being debated here, and I've not said one thing against it. In fact if you go back and read my opening post you'll find that every single point that I put down mentions techniques that may be used to maximise counter-steering effectiveness.

    Let's not get off course here.

    In the video though, note how the bike did change course when the rider weight shifted. Small, yes, but it did change course. The bike moved maybe 2m off course over a 40m distance. That's from vertical though. Do it when the bike is already leaned over and the effect is more significant because gravity always acts in the downwards direction. When you're upright, straight down is straight down into an upright bike, so very little happens. When you're leaning, straight down means "dragging" the top of the bike into the corner more.

    Think about it though. Even if you only believe the video and don't believe anything I say, then if you're turning some corner, do you think that exiting the corner 2m tighter at the exit due to weighting could possibly be beneficial? Is 2m insignificant? 2m is half a lane width.

    Weighting does have a progressively stronger impact the further you lean, and as I said above, it forms a complementary tool to the more powerful counter-steering mechanism for modifying a bike's direction.
  6. A friend would share :roll:

  7. So you've done it, you feel it, you see it working, it works, and yet you still don't believe it. May I ask: Why?
  8. Its time like this that a pic speaks more. I had to re read twist of the wrist over and over again before I mean what he meant by pivoting the outside peg. Its like I-get-it-then-i-dont- many time, then i understood it and I forgot it. I re-read it and I think kind of get it again. Using it as a pivot does not mean putting weight on it. The weight is always put on the inside peg. Its like a bottle opener where the pivot is at the end, load in the middle and the force at the other end.

    Twist of the Wrist does not teach you how to hang off (at all) but it does require you to do it to apply all the other techniques.

    I ride mc19 (CBR250R) on the track and because its has rearsets has lower clearance than the mc22, I have to hangoff more.

    The process of look-lean-push-hanging-off which if done correctly, will be 1 smooth motion.
  9. Vinnie, don't roll your eye at me :) you know I've said loads in other threads - go and have a look you lazy sod.

    I base my views on extensive perusal of articles at msgroup and lurking in the CSBS forum where these topics come up again and again and again.

    Anyway, start here:
    steering http://www.msgroup.org/Articles.aspx?Cat=4
    handling in a curve http://www.msgroup.org/Articles.aspx?Cat=5

    I don't disagree with the OP. The best thing you can do for your bike is to "get out of the way".

    I don't agree with weight loading having any impact on steering.

    I tend to take the Steve Brouggy line on weight steering - that despite a rider's view point (which is a heavily biased and potentially flawed frame of reference) all the poking and prodding somehow ends up producing more counter steer. The rider is just not aware of it. Plus, a body can't act on itself so how does a system, travelling in a certain radius and speed increase centrifugal force by changing the application of it's weight while keeping it's CoG unchanged??? Doesn't make any sense in terms of physics.

    Anyway, the effort to get the no bs bike to veer of course is massive compared to an efficient countersteering input - and riders that pursue that style of riding just end up massively fatigued by the end of the day.

    erewego, if you could break down pivot steering for me, i'd be grateful. Of all the KC stuff, this one simply doesn't compute. I know it's driving towards producing a quick counter steer, but since your body has several contact points between the outside peg and the inside bar, I can't logic how extra effort on the outside peg allows you a harder counter steer. The instructors on the day resorted to the "try it and see what you find" method of explanation, which said to me they didn't understand it either.

  10. Weight is mass x gravity. Gravity is a directional vector. Therefore weight has a direction of force, whereas mass by itself does not. "Weight" really mean a force (F) in physical terms. F = Ma. M = mass. a = acceleration (gravity) in this case. Where mass is placed affects the weighting on the bike. Correct me if I'm wrong here Rob.

    Very simplistically, if carrying all your weight on the pegs, a bike can be viewed as a rudimentary see-saw. It has two pivot points in a straight line, which effectively forms a single side-to-side pivot point. If you stand on a 40cm high see-saw with your feet 30cm apart either side of the pivot point, are you going to tell me that it's impossible to put all your weight on one foot to make the see-saw rock one-way, and then shift all your weight to the other foot to make the see-saw rock the other way?

    Bikes fall into a corner because their weight has been thrown off-center. Counter-steering is the most effective way of achieving that. Bikes stop falling further because you stop counter-steering, and the bike's steering geometry corrects and turns the front wheel into the corner (which is what makes the bike turn) and so provides the necessary centripetal acceleration to prevent the bike from falling on its side. The traction of the tyres provides the necessary anchor point to make that work.

    Are you saying that, much like the see-saw, if the rider places all their weight on the inside peg that this will be of no assistance in helping the bike to tip into the corner?

    You then go on to say this:

    So it works, but you don't believe it, is what you're saying. So you believe that I'm wrong, and zenali is right, even though simple physics supports what I'm saying, and when you try it, it works.

    Explain that one to me.
  11. I was referring to your bag of popcorn :p
    Thanks for those links tho :wink:
  12. I agree with the peg pivot helping you double spring your weight to get out of the way of the bike.

    A see saw is a poor analogy for a bike. And on the analogy directly, are you sure you CoG has not shifted therefore tipping the seesaw? And even if it is perfectly fixed and all you're doing is changing the relative height of your two support points, what difference does that make to the overall system???? I would encourage you to take the measure of your conviction onto CSBS or msgroup and argue the physics of your analogy there. It will receive robust review.

    Anyway, the bottom fundamental physics line is this: if you do not change the position of your mass with respect to the bike/rider system, it does not matter where in that system the weight of your mass is supported. :idea: No change in mass position, no change in the weight force it has on the system.

    And before someone pipes up with the hoary chestnut, you do NOT lower the CoG or vary it in ANY way buy putting the weight in the pegs (or a peg) versus weight in the seat. THAT is simple physics.

    In regards to your other comment, I know what I perceive, but I know my frame of reference is flawed. I might think loading the inside peg is the ruling variable that helps the bike lean over further, but I'm not wholistically aware of every aspect of my interaction on the bike. It could be an involuntary countersteer, or counter counter steer by pulling on the outside bar or a fraction of destabilisation that the bike interprets as a steering input... bottom line though, I know to be suspicisios because physics doesn't support the observation. (See above)
  13. Whoa there! Who said that the human body is acting on itself. No one said that!

    The human body moves independently of the bike (within limitations of the ability to still hold onto the bike). The rider's body has gravity acting upon it at all times. The rider is not acting on himself. The rider instead uses his ability to move about relative to the bike to allow gravity to provide the necessary force to act upon whole and affect what the whole is doing.

    Where I think a lot of the misunderstanding lies is because everyone thinks of it in terms of a bike riding along in a straight line. As I said before, when the bike is upright, gravity is straight down, and no matter what the rider does the forces are all straight down.

    When the bike gets off vertical, then that's when things change.

    To those who doubt this, please explain the following scenario, and I write this 'cos I had the same argument elsewhere, and this is the scenario that I put forward that trumped them. They still stubbornly refused to believe it, yet could not find fault with the scenario.

    Rider is going around a corner at a 45 degree lean angle, sitting fairly upright. The rider now "drops down" to the inside of the corner and weights up the inside peg more (or the outside of the seat 'cos it's off vertical and is now inside the tyre pivot point line). When the rider "drops down" he's momentarily decoupled his vertical force vector from the bike, and the bike will track wider to compensate. The rider then accelerates downwards towards the ground due to gravity. When the rider regrips the bike, the kinetic energy gained from his "fall" gets reapplied to the bike and the bike has to turn tighter to compensate for this. Effectively the act of falling (which tracks the bike wider) balances out the acting of slowing/recoupling (which tracks the bike tighter). The bike ends off at the same lean angle that it started with. Everyone's happy. Here's the clincher though. The CoG of the bike+rider is now different. It is now closer to the inside of the corner than before. The bike is going to turn tighter than what it started out at before the rider dropped his mass.

    If the bike is vertical though, it's all different. If the rider moves one way, the bike moves the other way, and it's a net zero effect. If the rider drops down, the CoG is just dropping down in line with the gravitational vector, and so nothing happens.

    When you get off vertical though, things change, as the gravitational vector is no longer in line with the changes in CoG.
  14. weight has am impact on steering for me. Maybe not directly, but it affects it to a degree. if the front is overloaded, it steers really stiff. But is that what we are talking about? or are we talking about shifting weight to the change the center of gravity?

    I will try to see if I can explain the pivot thing. I've got to go back and read it. thats one point that I've never really got until i did something one day and wondered if its what he meant. then I went back to re-read it and thought it sounded like it. I've since forgotten it. which means that its probably not that important anyway.
  15. #15 [FLUX], Sep 22, 2008
    Last edited by a moderator: Jul 13, 2015
    The see-saw analogy works, because it is not a frictionless system, and neither is a motorcycle. The reason why the see-saw can be made to tip in one direction or another is because the friction of the pivot joint offers some resistance, allowing the see-saw rider to move their weight from side to side.

    Motorbike tyres are the same. They are not frictionless (something which everyone who rides is very thankful for). The tyres form the pivot point, but they resist pivoting to some degree. This allows the rider to move their weight about on the bike thereby allowing gravity to take sway to cause the local system to rotate.

    To those that doubt that bikes can be steered with weight alone, then take a stab at explaining this:


    Wheelies on the back wheel, hands in the air, making the bike do figure-8's.

    Anyway - I'm out. It's real. It works. People make it work all the time.

    Don't want to fight about it. Try it. If it works for you, then good.
  16. By body I mean the bike/rider system. If the CoG is unchanged, then a change in weight support location does not impact on the bike. If all you do is push down on a peg harder, then the force applied there can't result in a change since a body (global sense) can't impact on itself by application of a force inside the system. You can't push yourself over for example.

    Weight shift - means moving mass around.

    Peg loading - means putting more force on a peg.

    Pure peg loading does not impact on the system. Peg loading in conjuction with mass shifting will have some kind of impact.

    Regarding the decoupled kinetic energy thing, one flaw is that you say that the bike's lean angle remains the same. That's not possible if your mass is now further inside for the same turn radius. If you've tightened the turn, then you must have made a steering input.


    Plus kinetic energy??? The potential energy difference between the two body positions is not that great. How much Ek are you generating? Anyway, how can kinetic energy impart a force on the system such that it generate more centrifugal force which results in more lean and a tighter line???? It just doesn't make sense - even if it feels like it does on bike. (see flaw self perspective comment earlier)

    Attached Files:

  17. You've misunderstood my example. Think about it more.

    As for peg weighting. Just try it Rob.

    If it works for you. Good. Eh?
  18. One wheeled steering is not the straw man trump card for your concepts flux.

    Lean does not equal turn. See link in previous post.

    The seesaw analogy is flawed. Get the bike rolling and vertical and load up a peg. If there's no change to YOUR CoG you wont get any lean on the bike (as you suggest in a see saw analogy). And if you do get some lean, you've probably countered it with a shift of mass the other way, i.e., the system CoG hasn't changed, otherwise you'd fall over.

    I double dog dare you to take these concepts to msgroup.
  19. one day riding along i tried putting pressure on the pegs and it did help lean/move the bike.

    now i read this thread it makes a lot more sense to me.

    if i put more weight on right peg i lean right
    left peg - left.

    but i cant really test it on the road as it would be extremely unsafe to lean the bike over that far..

    good thread tho, thanks guys.. :)
  20. How about some responses Flux rather than on message posting. eh? :)