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Steering a bike
Ever thought about how much you need to actually turn the handlebars of your bike to go round corners?
Suppose you come up to a bend at, oh, sixty mph, then by how many degrees do you turn the steering... well, today I went and found out. I stuck a twig on to my instrument cluster at the middle of the handlebars with insulating tape so that when I turned the steering the end of the twig would sweep over the dash and give some idea of how much I was turning the bars. No, scientific it wasn't, but it showed that I was not turning the bars AT ALL. Not a sossidge. Agreed, I must have been doing something to get round the bends, but I didn't seem to be steering it round. Mind, it's quite different at low speed, roundabouts etc. And reverse steering too, that's something else again. Just thought I'd mention it, that's all. John ------------------ Johnefyn |
It's called Counter Steering.
At low speed, more steering input is needed. As you speed up, the required input is reduced until you actually need to turn the bars very very slightly in the opposite direction of the direction you want to go. The amount of counter steer & the point at which you need to apply it varies from bike to bike. Most of us to it wothout even realising it anyway. I had a dramatic intro to counter sttering on my first fast bike (Jota, the five barred gate of the bike world lol). Flying up a dual carraigeway at about 100mph. I decided to realy attack the long sweeping left hand bend up ahead. I was on the inside lane & gave the bars a good tug to the left..... To my surprise & horror, the bike turned right quite sharply, shot across the outside lane, came close to ramming the Armco barrier at 90mph. Taught me a huge lesson. |
This is a fasinating post.
I belong to a road bike club and we do a counter steering course to make people aware of the way it works. It is wonderful when people ride thinking about it and it improves their cornering no end. It is complex but basically I understand that the front wheel acts as a gyroscope (remeber the way a bicycle wheel acted as a kid when you span it holding the axle and it felt it had a mind of its own). As you press lightly on the opposite bar the gyro acts to lean the bike and you move onto the smaller diameter of the rear and front tyre this like a rolling cup makes you go around in a cirle. the more you lean the bike by pressing on the bar the smaller the circumfirance and so the tighter the turn. Thats why bikes have rounde cross sections to their tyres. Espcially fast turning sports bikes. At very low speeds you will steer normally but anything over 15mph you instinctivly countersteer until you think about doing something else like the previous poster. Better explaination here:http://www.msgroup.org/TIP048.html Charlie |
Hi Steve
Soon after passing my test, a long long time ago, I was riding my little Honda 185 along a twisty country lane with my girlfriend on the pillion when we met a car coming the other way, just on a corner, 10mph or so. Following a brief panic I duly swerved and we got past ok. But it worried the shit out of me that all I could remember after, and in absolute crystal detail, was of briefly steering TOWARDS the approaching car. It took me a couple of years to realise that I was counter steering, and that that is really the way we all steer at low speed when we need to turn quickly. Until this dawned on me I was convinced that, deep down I was suicidal and that I had a latent desire to kill both my girlfriend and myself. Funny how we learn to ride a bike, steering and balancing in all these different ways and not knowing exactly what it is we learn (how many riders appreciate the notion of counter steering- yet we all do it)(and come to that what do I know about the gyroscopic forces involved with steering a spinning wheel?) So, as in so many things, don't think too hard, just do it. And, yep, my wife and me- we're both still here! ------------------ Johnefyn |
Hi John
you should notice that if you push the inside of the handle bar in the direction you want to turn it goes that way...in fact you are steering the bike the other way ie pulling the opposite bar towards you. There is no dramatic turning of the wheel but you are having sufficient impact on the gyroscopic forces to produce a result. You can use this to make quick evasive turns at low speed by pushing on one bar then quickly pushing on the other. If you can get a small bicycle wheel on an axle, spin it holding the axle ends then try to move the spinning wheel from a vertical axis. It takes quite a large initial effort then you have apply effort to stop it toppling over. If you look at some photos of bike racers cornering at high speed you can see clearly that the front wheel is pointing away from the direction of the turn..of course the extreme version is the high speed power slide. Some people have suggested that using countersteering can have a negative effect on front wheel grip in corners and weight transfer and weighting of the footpegs gives a better result...but I find that you would have to be going pretty hard, already well into the turn or being quite violent on direction changes for it to have much of a negative effect. You would also notice that in very very low speed turns, such as tight carpark figure of eights, you lean away from the bike, so its like you are pushing the bike down, quite the opposite to a normal or high speed turn where you lean into the corner. But at least its not as confusing as trying to ride a sidecar!!!!!! cheers alec |
Hi Simmo (Alec)
Or a tricycle! I was on a 'Star Riders' instructor's course many moons ago (are they still going?) and one of the other instructors who was a motorcycle dealer turned up with a Honda 3- and 4-wheel ATV on a trailer, you know, like farmers have as runabouts on their farms. Well, talkabout laugh, we laughed ourselves silly. Thing was, we'd just been doing slow riding on our own bikes through/around the traffic cones on the yard, so we were all in the two wheel mode and found it all but impossible to change the whole mindset to handle the three and four wheelers. Hey- this thread's got awfully inteletchiwul all sudden (and why not.) I did know that I wasn't moving the bars a lot but until the Twig-and-tape experiment I really didn't realize how little. Braindead: thanks for that, it's going to take just a little while to digest the contents of the site you mentioned, there's a whole lot of heavy stuff in there. As for gyroscopes, I've never been able to get my mind around those, despite having tried. On the subject of the gyroscopic action of the wheels, I wonder what would happen if you could mount a wheel geared to spin in the opposite direction to the roadwheel and mounted side by side with it so as to cancel the gyroscopic effect; perhaps it would end up behaving like the ski you mentioned? My brain hurts John ------------------ Johnefyn |
The mounting of wheel spinning in an opposite direction would have the effect you suggest. Thats how balancing sg=hafts work in agines to produce a 90degree our of phase wave to cancel out the vibration.
The trick is not to think about why it works but to practice how it works on the road/ rack. Cheers Charlie |
Hi Charlie
You've got me there. I didn't know that the gyroscopic effect came into balancing out vibrations, I just assumed that a balancer shaft merely produced an equal and opposite vibration to cancel out the source of the vibration. Where can I read up on that- is it mentioned in the website you just mentioned- as I said, my brain's already hurting with that one! Thanks J ------------------ Johnefyn |
They do exactly as you say produce oppostite viabraitions, but they also conter act the gyroscopic affect of the spinning parts, Have you ever rode a transverse twin like a Guzzi or a BMW Honda CX they lean over to the right when acceleration to stop this many are fitted with balance shafts that conteract the movenment to help them run starighter.
Charlie |
I thought balance shafts were primarily to cancel out vibes? Plenty of bikes run balance regardless of crank layout, makes for a smoother ride but adds to the mass that needs to be moved, thus affecting how fast the engine can spin up.
Plenty of big singles run balnce shafts, my DR600 had two. I thought their mass was calculated to cancel out or equal the mass of the conrod, piston & a percentage of the cranks weight? BTW no BMW twins have ever had a balance shaft fitted with the exception of the new 1200GS. A more common way of cancelling out torque reaction is have a contra-rotating gearbox. This spins the opposite way to the crank. Having alternators/generators contra-rotate has a similar but reduced affect due to lack of mass. [This message has been edited by Steve Pickford (edited 10 November 2004).] |
Hi Charlie
I would say that the lurch you get on blipping the throttle on a transverse engine (mine's an '82 Boxer) is due to torque reaction rather than a gyroscopic effect. In all honesty, though, I must admit that other than when stationary and blipping the throttle I've never noticed any adverse effect due to this; whether that's because my little botty is not sensitive enough, sweetie, or whether it's simply because I've always lived with it.(R51/3, R60/5, R100RT, R100RS) Having said that, though, it is true that the revs shoot up a lot more quickly when the bike is in neutral than when its in gear and actually driving the bike, so it does seem that the amount of lurch is to do with the rate of CHANGE of rpm rather than the actual rpm. Um, yes. I think. Cheers John with the hurting brain ------------------ Johnefyn |
Steve,
1. lol? 2. BTW? J. ------------------ Johnefyn |
Quote:
btw = by the way iirc = if I remember correctly afaik = as far as I know stfu = shut the *** up There are a few others I can't remember at the moment. |
Steve
Ah, now I see. Thanks. Going back to your comments re balancing of the crank etc. I came across another application of that sort of thing regarding balancing steam locomotive coupling- and connecting- rods. These had to be balanced because the mass of these rods going up and down as the wheels went round resulted in a vicious hammering action on the rails. The coupling rods connecting the driving wheels together were balanced relatively easily by having balance weights on the wheel rim, the thing was, with coupling rods both ends went up and down and around with the wheel. The case of the connecting rod, however, is different because only one end of this rod actually goes around with the wheel, the other one simply sliding backwards and forwards as it is pushed and pulled by the piston, and in this case like you said, only a percentage of its weight was balanced out. I think I remember that was something like a third of its weight, though I would have thought it should be more like a half. If anybody is particularly interested perhaps Marks' Standard Handbook would tell us, I could dig it out. It seems to be the same principle as that of a bike engine, albeit on a different scale. Anyway, when you think of the size of the rods on one of the big locos then you can imagine what a hell of a beating they could give the rails when thrashing about doing a ton. John PS just read your letter again Steve. Yes, I'm sure you are correct; the mass of the piston should be included with that of the conrod and it is a percentage of that total that is balanced. J ------------------ Johnefyn |
Uhh, Guys,
The gyroscopic effect of your front wheel has a limited amount of effect on turning (countersteering). I did the calcs a while ago. Remember, there is an equal or greater gyroscope in the rear, called your rear wheel. It takes a bit of energy to make that lean over. The basics of how it works (and a lot easier to understand than a gyroscope) is to remember that a mass in motion wants to remain in motion. The mass of a motorcycle can, for this purpose, be thought of as a point mass somewhere near the center of your bike. That point wants to go straight. Imagine a bike standing still on ice, if you held the center of the bike in one place and slid the tires to the left, the bike would fall over to the right. Now if you are moving and you turn your handlebars counterclockwise (to the left) the center of the bike wants to go straight ahead but the bottom the wheels) go left, forcing the bike to lean to the right. Now that you are leaned over, you are turning to the right. Now, the gyroscopic effect is VERY useful in keeping a bike stable. Ain't physics grand! ------------------ CT_Bob@juno.com |
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