Welcome to Netrider ... Connecting Riders!

Interested in talking motorbikes with a terrific community of riders?
Signup (it's quick and free) to join the discussions and access the full suite of tools and information that Netrider has to offer.

Yet Another Steering Thread

Discussion in 'New Riders and Riding Tips' started by nikku, Jun 28, 2006.

  1. Yeah I know, steering, particularly countersteering, gets done to death regularly. So ignore this if you're not interested :p

    I've just been thinking about basic steering forces, stuff that most of you will already know from experience. Just writing down my thoughts as a newbie :grin:. For brevity I'm stating everything as fact, but everything is really "I think..." - and "he" is gender-neutral :)

    This is not really about countersteering, if countersteering is understood to mean "the act of getting the bike to lean at the correct angle". This assumes that the bike magically gets to the correct lean angle, so countersteering can be ignored.


    So, first of all, there are two distinct processes by which a bike can turn:
    1. Turning the front wheel. For example, on a tricycle, or when slow maneuvering; there is no lean.
    2. Leaning the wheels. For example, on a monocycle, or when leaning the bike by shifting your weight without touching the handlebars.

    During any turn, centrifugal force will "push" the bike towards the outside of the turn. This acts upon all parts of bike and rider equally (by mass).
    However, because the bike has traction at point of contact with the road, the contact patch acts as a hinge upon which the bike rotates. In the absence of any other forces, the bike will topple over to the outside.

    So in (1), without leaning the bike, the rider must lean to the inside, pulling the bike with him in the opposite direction around the contact-patch hinge.
    [Note that on a physical bike it's a bit more complicated, because simply turning the front wheel when stationary will move the centre of gravity of the bike to the outside of the wheel line. So when moving the rider has to lean this amount to the inside, plus an additional amount to counteract the centrifugal force. Since this technique is used in slow maneuvering, the additional rider lean to counteract the centrifugal force will be relatively small.]

    In (2), the bike and rider lean together to move the entire combined centre of gravity to the inside of the turn. There are now just two forces acting on the bike: gravity pulling the bike to the inside around the contact-patch hinge, and centrifugal force pulling the bike to the outside around the contact-patch hinge. To be stable, the two forces must add up so that the rider and bike feels just one force pulling straight down the rider's back and bike into the ground. Then (as long as you maintain traction :)) the forces are just like riding in a straight line, except you happen to be curving.

    Finally, you can of course combine (1) and (2).
    Since (2) is just like riding in a straight line, exactly the same forces as in (1) are added, and in the same way. The front wheel can be turned into the curve, and the rider must lean (only now it's called "hang") himself out of line with the bike, further into the curve, to offset the additional centrifugal force.
    [Note that in this case, unlike slow maneuvering, the centrifugal force from turning the wheel can be greater, requiring a greater rider lean, or hang.]


    So yeah, that's what I've been thinking about lately :)
  2. Let's not forget slow-speed (walking pace) manoevers like feet-up full-lock u-turns.

    At these speeds centrifugal force is so weak that the bike's natural tendency is to fall INTO the curve. Thus the skilled slow rider counterbalances by leaning to the OUTSIDE of the turn, letting the bike drop in lower and reducing the turn radius while maintaining balance.

    It's a lot harder than quick stuff, but much easier to practice and teaches you a lot about balancing the weight of a bike using your body position.
  3. Good point. I'd even been trying that (not very gracefully :grin:) and completely forgot to write it in!
    When I was writing that, I was thinking of slow-speed as being bike upright, turn handlebars. But of course you can lean the bike in addition to reduce turn radius even at slow speed, as you say!
  4. I don't mean to burst your bubble, however, even when you turn the bars at low speed the front wheel actually leans - this is caused and intended by the rake angle - If you do a google on countersteering you will find a coulpe of good documents that illustrate the dynamics.
  5. Noooooooooooooooooooo, not another steering thread. I think I'll steer clear of it :LOL:
  6. Thanks Mithel, but I don't see what bubble has burst :)
    The front wheel will lean due to rake, and I guess that lean would contribute to the turning, but (intuitively) that could only be a small part of the steering force from turning the front wheel. Wouldn't the majority come from the change in direction that the wheel is pointed?
    And I have read a couple of good explanations of countersteering, and the previous couple of discussions here that I've been around to read have been interesting. :)
    I was just sort of turning the idea over in my head, in my own words.


    You know one thing I like about this place? The terrible puns :LOL:
  7. just a quick reply from work, so i haven't read the whole post...

    i've found that number 2 is virtually impossible on anything bigger then a 250cc. i've tried riding no-hands on various bigger bikes and leaning does nothing (even for small corrections in direction). i've also tried jerking the bike to one side using my legs and leaning at the same time.

    counter-steering tends to be a lot more deliberate (and requires more force) on a larger bike. especially at higher speeds, it is a very definite push on the inside bar

  8. It should be noted that the act of counter-steering merely unbalances the bike in order to get it to lean. Once the bike is leaned over to where you want it, and you stop pushing on the bars, the front wheel actually does self correct and turn very slightly into the corner much like how a car steers. Since the bike is leaned over on an angle, the amount for which a bike needs to turn the front wheel into the corner is less than is required on a car, but rest assured, bikes do turn corners by the front wheel turning into the corner, at all speeds.
  9. Interesting Cathar, I'd read that some bikes understeer, some oversteer, and some neutral steer when going through a curve with steady throttle and no handlebar input. Am I understanding you correctly, are you saying all bikes oversteer? Or am I getting terms mixed up?

    Thanks all for linking the articles, I had read them so I know this thread is nothing new, but I just wanted to get it out and sort of test my understanding I guess.

    So anyway, I do have a related practical question, which might be more interesting than the same old same old :)

    Assuming the same stable curving line, at the same speed, with the same bike and rider, my understanding is that the bike and rider can be stable in a continuum of positions which will all result in the same curve. At one extreme the bike is leaned far over with rider in line with the bike (ie, (2) from my original post), at the other extreme the bike is more upright with the rider hanging off the inside (ie, (1)+(2) from my original post).

    My question is, do you reckon either extreme is "better", or why would you choose one or the other?
    I've read, for example, that hanging off the inside can be useful on uneven surfaces (trails, I guess), since the bike will be more upright and have more clearance.
    On the road, would either be easier? Safer? Better on the tyres?
    My guess is that traction, at least, would be pretty much the same, since ultimately the same mass is generating the same centrifugal force against the same contact patch (hmm, or would it be the same contact patch, since in one situation the bike is more upright?)

    Just wondering... :)
  10. This was dis-proved years ago, when Keith Code used a modified Kawasaki ZX-6R with two sets of bars, one being mounted to the frame so that the forks could not be rotated at all (and thus the front wheel unable to turn)
  11. Leaning the bike with no hands on the bars is surprisingly effective at turning the bike. As you mentioned the effect is less noticeable on 250cc+ bikes, but its still definetly there and a major force.

    I've gone around some very tight bends on a CB250 with no hands from start to finish, simply idling in a high gear and adjusting my bodyweight to get through the turn. The only problem comes in changing direction, which is hard to get a really quick reaction out of the bike in a set of S bends. I guess that why they invented handlebars in the first place :p

    It may require more force on a larger bike, but I'm sure you can still significantly control a bike of any size this way.
  12. Out of the two extremes:
    1. Rider is line with bike gives you a better control over the bike on the road. It's simply more comfortable and an easier position to ride from and therefore safer. You can react quicker and swerve quicker from a position ready atop the bike. The grip on your tyres is easily sufficent for most road situations, so even though this position offers a smaller contact patch (closer to edge of tyres), theres still a lot in reserve if you're riding at a decent pace.
    2. The bike upright, with rider hanging off. I can offer some personal experience on this matter. A while back I bought a 20 year old 500cc sports bike, which I'm fairly sure was still on its original tyres when I bought it, or at least 10-15 year old ones. Needless to say, woefull grip on the tyres. They had tread, but they were hard as a rock. Being well short of $$ as usual, I rode around on these tyres for several weeks. I found the only way to ride the bike was to hang way off it, even going into slowish corners. Even a tiny lean angle gave the feeling that the tyres were going to slide, so I had to ride it with almost zero lean angles, using just my body weight to get around bends. I could actually still go at a decent pace riding like this though, it was just very tiring and scary to ride.
    So if conditions are slippery, due to rain, oil, dust or whatever, then hanging off the bike is the way to go. Doesn't necessarily need to be hanging off, but if you're getting scared, just try putting a little more weight than usual on the inside of the corner.

    It's interesting comparing the riding styles of modern GP riders to those of decades ago. Modern GP riders ride by putting their knee down, hanging off the bike as much as possible. Whereas if you look at an old-school rider like Mike Hailwood, they sat upright and inline with the bikes. Supposedly the main reason modern GP riders put their knee down is purely as a feeler, to gauge how much lean angle they're getting, and there is no reason if someone was to go out and compete using the old Hailwood style of cornering that they would be any slower or have less grip. So I guess both styles must offer roughly equal grip. Contradicts what I just posted, but interesting none the less.
  13. Mouth, Keith Code's experiment proved it, not disproved it. With Keith Code's bike, the bike was totally unable to turn. I talked to him directly about it when he was here in January.
  14. Yes, but regardless of whether a bike under or over steers with no handle-bar input and a steady throttle, it is still steering and not going in a straight line. It is turning because the front wheel will turn into the corner.

    What you're describing is the effects of differing steering geometries where a different setup will effect the degree of neutrality of the steering when there is no rider input. A correctly setup geometry will steer a fixed radius cornering line with a steady throttle and no bar input on a smooth surface from the moment the rider stops providing input. Some bikes which are not correctly setup will begin to understeer or oversteer once the rider stops providing input, and so require a constant rider input to keep them on the intended cornering line but the bike is still turning in any event.
  15. Doesn't TOWT state that steering occurs from the back wheel?? That once the bike is leaned you don't even need a front wheel any more???
  16. TOTW Chptr 13 Steering - Steer for the Rear
  17. what os TOTW???

    ___ _____ Two Wheels??
  18. Twist of the wrist.

    Message too short my arse.

    Sorry Nikku.. :p