"Negative Steering" Please explain. 1

[Tryan]

Could somebody please explain to me the phenomenen called negative steering on a motorcycle? While it has been something I have been aware of and used for about 35 years riding, I haven't found anybody who could explain it!Simply put, when you pull on the righthand side of your handlebars you go left and vice versa! Some people think you are quite strange when you tell them, others are aware of it but can't explain it! Anybody?

 

[Scoobystu]

The front wheel doesn't even have to touch the ground for counter steering to work but it does need to be spinning, as proved by the guy who holds the wheelie record around the Isle of Man TT circuit. In order for him to go round corners he had to fit an electic motor to the front wheel to keep it spinning so that he could coax it round the corners by counter steering. Apparently leaning the bike over was near on impossible because of the gyroscopic effect of the back wheel.

 

[Tryan]

OK, maybe there is a slight gyroscopic effect, which obviously would increase with the speed of the bike,but perhaps no more than 10 percent.I say this because even with his front wheel spinning in the air the same as his back wheel he would probably only have slight "counter steering" assistance! ie.Riding towards an 80kph corner at 80kph, power on enough to get the front wheel up,then counter steer.Would you go round the corner? An interesting slant you've put on this question tho, Scoobystu!Maybe Metalguy can try it on his way home tonight!! Just kidding!

 

[Metalguy]

Don't think so. But I bet that wheelie guy had his front wheel spinning pretty fast!

Here's something else to ponder. It has been demonstrated via very high speed measurements that a gyro, when enclosed in a sphere (IIRC), falls thru air at different speeds when it is spinning fast vs. not. Don't know why, but I found something about it on the net a while ago. I'll look for it if I get time.

I'm in Italy not too far from pisa. Anyone know Galileo's phone number? <g>

 

[Scoobystu]

The guy that wheelied round the TT circuit did it on a modified CR 500 with footpegs on the swingarm and a rear brake lever on the bars. I reckon he would have just had to find his centre of gravity and coast it round. He would have to be going at a fair speed though.

What about the guys who ride supercross and motocross, the guys who are good at jumping can throw the bike sideways in mid-air and then straighten the bike up again by revving the bike and spinning the back wheel. How does that work?

I will try it the next time I do a 40 foot double. Well now that I think about it maybe not.

 

[Tryan]

Your gyro in the sphere made me want to ask was it vertical, horizontal or somewhere in between!! Which then made me wonder whether a gyro knows which way is up, at all!! I re-read ICman's response and he stated that you need gyroscopic effect to right the bike after it leans! I don't think you NEED, gyro effect,I think you have to OVERCOME, the gyro effect to either make the bike lean or to right the bike after it leans, and this can either be by countersteering or counterbalancing! As for that phone no, go to the Pisa museum and find a phone book for somewhere round early 1600...................

 

[Tryan]

Scoobystu,once again an interesting spinoff to the question,and I'm not quite sure what forces are going on in some of the manouvres those guys get up to! I think tho, once you leave the ground the rules change,and while there might be some gyroscopic effects, the supercrossers are simply rearranging the geometry between the bike and themselves! The effect of the back wheel accelerating or braking might be due more to centrifugal forces than gyroscopic!However it's certainly open for discussion!

 

[Mowgli]

Hi,
I'm a motorcycle instructor but when teaching the &quot;push steering&quot; we simply tell them to try it and then demo that it works. Last thing you want them to be doing is physics of mechanics as they cross a parking lot with 34 other novices around.
It is a gyroscopic effect, only taking effect at around 20-25kph. It becomes more pronounced as the velocity increases. I forget the exact law, but it goes something like &quot;.. for each input there will be an opposite and equal reaction 90° out of phase.&quot;
This is best demonstrated by holding the front of the front wheel while stationary, and pushing on one of the handlebars (eg the right). The bike will lean to the right as the front of the wheel wants to stay where it is. Once the lean is initiated, the wheel will fall in (ie lean) and the same pressure will be required to hold it there. As a result more handlebar pressure will tend to make the bike lean in further and pressure on the opposite bar will tend to make the bike right itself.
We have some great slow motion video's of a bike heading at the camera, and the push steering is really evident. When I first heard of this, I sat in the parking lot while a (trusted) friend headed towards me with his bike at 30mph. He would swerve when he got close and watching the front of the bike it became obvious.

 

[okeng]

The motocross/supercross thing is pretty interesting. I've watched guys that are good at that a lot and have never really figured out what all is going on. When you see someone get a lot of whip, they are doing a lot before they leave the ground--I remember watching Guy Cooper's footpegs leave marks on the takeoff face of a jump. I also know I can't do any of it very well. It is pretty easy, however, to change the attitude in pitch while you're in the air. Revving the engine up brings the front end up, (seems quicker with a big 4-stroke), and tapping the back brake brings the front end down really quickly. Tapping the back brake in the air while forgetting to pull the clutch in means you land with the engine no longer running, which is sometimes a good physics lesson all by itself.

Jess Davis

 

[Metalguy]

Mowgli,

You may be a fine MC instructor, but you're incorrect about the gyro effect. At the speeds you mention, any gyro effects would be a few ounces/grams at the most, given the very slow wheel RPM, while the leaning of the bike requires far more-eg, you can easily counter the weight effect of a timid passenger who leans the wrong way.

 

[Tryan]

Okay, lets say your driving down a road doing 60mph in a car and turn the steering wheel to the right to go round a right hand corner, because it has 4 wheels it will simply go round the corner, but in the process it throws a lot more force on the left hand wheels,agreed!!Gyroscopic effect? I don't think so! Now we go down the same road, this time on a motorbike, and approaching the same corner you push on the right h/bar which tries to steer the bike to the left and because of the bikes' momentum, it tries to keep going straight ahead,which effectively results in the bike tipping over, or leaning, to the right! Anyone who races has at some stage had someone cut them off taking the front wheel one way while they're going another, usually resulting in the bike tipping right over! Gyroscopic effect? I don't think so!! Okay, thats 4 wheels and 2 wheels, now lets try 3! Same road ,same corner, 60mph on an ATV with 3 wheels,pull on the right h/bar and the right rear wheel will probably lift trying to tip it over or lean the opposite way , like in &quot;counter steering&quot;!Gyroscopic effect? I don't think so!Just simply momentum and G force!! Yes, of course there is a gyroscopic effect present, but I don't think it has much to do with &quot;counter steering&quot; as much as it sounds like a good theory!

 

[Blackjacks]

Definitely not a gryoscopic effect, try it on a sports bike with a 16&quot; front wheel (less flywheel effect,right?) and a scooter with 10&quot; wheels.

Anybody mention that you can &quot;pick&quot; the bike up out of a bend by applying a turning force into the bend? If it was a gyroscopic force then wouldn't that just lift the front wheel in the air?

 

[Tryan]

There is a gyroscopic action called&quot;precession&quot;{which Mowgli may have been alluding to} which basically means that when a spinning wheel{gyro}, has a rotational force applied to it, ie. turning your front forks,which is working in a horizontal plane, the wheel{gyro} will react by rotating the axle at right angles to the initial force, or in the vertical plane! Now, this translates very nicely to exactly what happens in countersteering!{The example I'm using is a spinning bicycle wheel held out in front of you.Try it,it does work} Jerk it hard horizontally, while it's spinning vertically, and it will react by leaning over from the vertical plane, but move it slowly horizontally and it will not move from the vertical!
So if this is the basis of counter steering then it would only work if you jerk hard on the h/bars, and what about the other gyro on the back that has no forces acting on it! Wouldn't they cancel each other out?

 

[Metalguy]

If you jerk the bars, you best have the front wheel in the air!

 

[evelrod]

Interesting discussion, especially from my point of view , a rider since the 1940's. &quot;Gyroscopic precession&quot;---ya'll need to consult the text again. No body has mentioned that you can steer a bike if the front wheel is fixed. A bit clumsy but it can be done. Try leaning a bicycle while riding without your hands on the bars and see what happens. The front wheel tries to stay straight briefly before leaning into the turn---right out of the text. I have been out of school for a while but I'll just bet you can get all this out of a high school physics book.

Tryan, good ideas except for the spinning wheel example. The fact that the wheel leans when you try to turn it in your hands has a lot more to do with the fact that your hands are hardly &quot;fixed&quot; in the horizontal plain. The very reason a bike is more stable at speed is the difficulty in getting the spinning wheels to deviate from the verticle. Some relation to the shifting of the CG in the horizontal plain and the change in circumferance of the tire from center to side would be interesting.

Thanks guys. Like I said, interesting discussion. &quot;Counter steering&quot; is just something I have always done mechanically without concious thought, until now.

Rod

 

[Tryan]

My last post may have been a bit confusing, but the spinning wheel was just a way of working through the gyroscopic theory put forward by Mowgli!I'm curious Mowgli, why your so sure it's gyroscopic, did you read it in a book? If so, and Metalguy is right, {pity his post was deleted}, then how does this information end up in a book as a fact? Shouldn't all these books be thrown in the bin? Evelrod, I thought I mentioned the fact in an earlier post, that to steer the bike, you have to overcome the force of the spinning wheels.{ I think I may have called it gyroscopic effect} I also think that the profile of the tyre {s}doesn't have anything to do with steering a bike! I think it is a change of the center of gravity and the bike trying to fall over!You could go round a corner by leaving the bike upright and leaning your body into the corner , which would effectively change the center of gravity! The profile of the tyre just makes the transition a little smoother, maybe!! But that could be a whole nuther thread! We are talking about counter steering, and at the end of the day, as has been said by some,it is just something you have to know HOW, rather than Why! If this is the end of the thread, then thanks for all the input, but I hope it's not, cause then all we'll have is those freeloading pirates next door!! Just kidding!

 

[Metalguy]

Let me relate an experience I had with a REAR tire on my ZX10 Ninja. I stupidly put a Metzler ME55 on, hoping to get something that would last a while. The profile was somewhat flat, but the bike did NOT want to lean over. I put up with it for a while, then finally changed it to something with a round profile (a Bridgestone BT56, I think). Night and day difference. So, the profile of even a rear tire has a huge effect on how the bike handles.

 

[evelrod]

This thread is getting a bit long but I'll post this anyway as y'all have managed to get me back out on my old '48 Norton to check all this out. Leaning the bike by whatever means results in a turn only if the front wheel is turned after lean is established in the direction of the turn, HOWEVER SLIGHTLY!!! That means that a bit of counter steer to get the lean angle and then the wheel must be brought back through &quot;straight ahead&quot; and on into the direction of turn. It is so slight a movement at any speed above walking that it has simply gone unnoticed by me for all these years. I just always did it that way without concious thought. I even ran some GP and motocross tapes of various bikes and it is pretty plain to see. It's been there in front of me all the time, I just never noticed.

This is the most activity in this forum I have seen in three years. Thanks all. Let's start another post on the tire profile and coumpound deal. I had a Metzler on a 441 Victor and did not like it then , either.

Rod

 

[obssv]

I'm currently taking sophomore dynamics at Wright State.
Counter steering dynamics is my project for the quarter since I ride a crotch-rocket and counter-steer constantly.
I've read all of your posts and I'm starting to get a bit of a picture. I have an idea I'd like you to consider. Suppose you take a bike and fix the front wheel in line with the rear wheel, stand it up perfectly vertical, attach a cable (of fixed length) to its CoG (CoM?) and then fix the other end of the cable to a fixed point away from the bike. Now, roll on the throttle and watch out. In my mind, the bike can't go in a perfect circle with the front wheel fixed. This seems more obvious if you imagine the wheel base of the bike as high compared with the radius of the circle; the wheels can't be on the circle. So, Countersteering must, somehow, bring the front wheel into &quot;alignment&quot; on that circle. Another thought, is it possible that the front tire being opposed to the actual turning direction produce some opposing force that counteracts the motion of bike?

 

[evelrod]

obssy---&quot;I've read all of your posts...&quot;---Apparantly you have NOT read them all!

Rod

 

[obssv]

I don't understand, did I miss something?