The Bum Steer

[Mikkel]

At what speed do you consider a bike to behave “normally” with regard to control inputs. In other words using other than lateral body movement alone to maintain ballance and affect course?

How much vertically stabilising force do you suppose gyroscopic precession is contributing at that speed?

You did indeed not read my post I see.

My argument was that the guy who made an attempt at counter-rotating weights to cancel out the gyroscopic effect of the wheels didn't do it properly...

If he had, he would indeed not have been able to ride the bike in a straight line (or most likely not at all)... As such, the conclusions derived from his study of the behaviour of such a bike would be without merit.

It has nothing to do with speed or how the bike reacts to steering input - simply the fact that if you completely eliminate the gyroscopic effect of the bike it's not going to be rideable (at any speed).

[James Deuce]

Which was exactly my point, I cannot countersteer with no front wheel contact but I can alter the direction of the bike.



For steering/turning alone with no counter steering I agree, but the simple physics are that the rider must make up on average at least a third of the total weight of both rider and machine, and being perched on top of the "lever" moving your weight will influence the direction of the bike.

I think Grubs reference to the racers is maybe a little misguided in this instance, He has made no mention of how the riders distribute their weight with their feet. Although they have there body mass weighted to the inside of the turn most of their weight will be on the outside footpeg, just ask #34 (Kevin Schwantz)

The dynamics of a Unicycle are vastly different to a Bicycle. Yes, you WERE countersteering as a kid on a bicycle, but the amount of force to turn a bicycle is tiny compared to the force required to turn a motorcycle 15 to 20 times heavier and 10 to 15 times faster. So tiny it is indistinguishable from the subsequent lean that feels like it was generated by moving your body weight.

[jrandom]

to overcome gyroscopic precession for a two wheeled, tandem in-line vehicle you HAVE to turn a wheel opposite to the direction you want to turn to initiate a lean in that direction... To steer you HAVE to countersteer once you are traveling at more than 10-25 kph depending on motorcycle geometry.

Presumably, the fact that I can steer a bike around corners as it rolls in gear downhill doing 50-60kph with my hands off the bars, using my hips and knees and waving my upper body about, is because gyroscopic precession isn't the be-all and end-all of the matter.

In other words, the bike can still be steered with weight re-distribution only, it's just that as it goes faster, the gyroscopic force gets greater, and eventually the weight redistribution required to steer it without changing the gyroscopic force direction becomes quite high, so it's imperative to push on the handlebars.

I also note that as I steer it by moving my body weight around, the bars naturally flop in a countersteering-like manner. What's the story with that then?

[James Deuce]

Presumably, the fact that I can steer a bike around corners as it rolls in gear downhill doing 50-60kph with my hands off the bars, using my hips and knees and waving my upper body about, is because gyroscopic precession isn't the be-all and end-all of the matter.

In other words, the bike can still be steered with weight re-distribution only, it's just that as it goes faster, the gyroscopic force gets greater, and eventually the weight redistribution required to steer it without changing the gyroscopic force direction becomes quite high, so it's imperative to push on the handlebars.

I also note that as I steer it by moving my body weight around, the bars naturally flop in a countersteering-like manner. What's the story with that then?

Try doing it at 260km/hr.

It depends on the amount of mass required to overcome the force generated by rotational inertia. As you've noticed the bars will turn away from the direction you are travelling

The danger to the myth that counter steering doesn't work and can be ignored is that people will now go out and try to change lanes on the motorway by shifting their weight. You can precisely steer a motorcycle with the bars or you can fuck about try to turn your bike with your knees.

Your choice. I can't see why people would chose imprecision over precision when it is already a dangerous business, riding a motorcycle.

[MSTRS:Me]

I also note that as I steer it by moving my body weight around, the bars naturally flop in a countersteering-like manner. What's the story with that then?

Think of the steering head being a hinge-pin...you are sitting on one half of the hinge...if you push that half in one direction, it's opposite half will turn in the opposing direction. Once the turn is initiated, the front of the bike will fall back into line with the rear and stay there, until you again apply some counter force to change things.
Simple.

[skelstar]

I also note that as I steer it by moving my body weight around, the bars naturally flop in a countersteering-like manner. What's the story with that then?

It'd be the 'impulse' of you shifting your weight that makes it steer. Hinge-like re: MSTRS's post.

I can steer myself all the way down the lower-half of Belmont Hill just with shifting weight (agressively) around... not regularly, just for fun.

[jrandom]

Try doing it at 260km/hr.

Exactly. That's my point. Countersteering isn't the only way to turn a motorcycle. If you hang enough weight off the side, the motorcycle will turn that way. More speed requires more weight or a longer lever, etc. 260kph means that you have to push on the bars, because you simply don't have enough weight or a long enough lever to turn the bike any other way.

By the way, in response to your 'precision' comment, I like to roll down hills in top gear pretending to paddle a canoe with both hands because it looks silly and is fun.

Which is what the whole motorcycling deal is supposed to be about, after all!

You won't catch me not using countersteering on a racetrack, though. (Or while changing lanes on a motorway, for that matter.)

[MSTRS:Me]

It'd be the 'impulse' of you shifting your weight that makes it steer. Hinge-like re: MSTRS's post.

I can steer myself all the way down the lower-half of Belmont Hill just with shifting weight (agressively) around... not regularly, just for fun.

Major Drive? You won't do it on the other roads on the hill...Pomare/Wairere/Park/Hill

[James Deuce]

You're perpetuating the myth that counter steering is pointless, or at best conditional, with your attitude, which means I can't respect that opinion at all. I get vastly more fun from dialling up the correct angle of lean for a given speed and corner radius so I don't have to correct, or I can precisely modify a line, than I ever would from taking my hands of the bars, where the throttle, clutch, and 90% of my braking lives.

[skelstar]

Damn, I meant Kelson Hill. Yeah and I meant upper-half. Heh... post lunchtime.

[Forest]

You did indeed not read my post I see.

My argument was that the guy who made an attempt at counter-rotating weights to cancel out the gyroscopic effect of the wheels didn't do it properly...

If he had, he would indeed not have been able to ride the bike in a straight line (or most likely not at all)... As such, the conclusions derived from his study of the behaviour of such a bike would be without merit.

It has nothing to do with speed or how the bike reacts to steering input - simply the fact that if you completely eliminate the gyroscopic effect of the bike it's not going to be rideable (at any speed).

You should read the article I just linked on trail.

Motorcycle stability comes from trail, not from gyroscopic effects.

[MSTRS:Me]

Presumably, the fact that I can steer a bike around corners as it rolls in gear downhill doing 50-60kph with my hands off the bars, using my hips and knees and waving my upper body about, is because gyroscopic precession isn't the be-all and end-all of the matter.

Try doing it at 260km/hr.

Exactly. That's my point. Countersteering isn't the only way to turn a motorcycle. If you hang enough weight off the side, the motorcycle will turn that way. More speed requires more weight or a longer lever, etc.

The greater the speed that the wheels rotate at, the greater the gyroscopic effect that needs to be offset. Problem with weight-shift alone is that it is too waffly and imprecise to be universally useful. Even at legal, but high, speeds.

[Ixion]

How does that explain wheelies around corners or circular wheelies were the front wheel has no contact with the ground?
Off the general direction of topic but I'd like to hear your explanation.

Edit: sorry for crappy picture, but usefull to expalin my point

The "wheelie" context is actually irrelevant, because you have effectively turned your motorbicycle into a motor unicycle.

That changes things greatly, because you no longer have the bicycle issue of the front and rear wheels needing to follow different arcs.

You steer a unicycle by ackerman angle, like a car. Watch a unicycle rider sometimes , he doesn't corner by leaning over.

One thing that causes confusion is that people believe that leaning a bike over in itself makes it go round a corner. Not so. You can lean bike over until it's handlebars touch the ground, but that in itself will not make it deviate from a straight line.

Try it. Walk beside your bike. Now, lean it over (I suggest toward you), but hold the bars straight ahead. Keep walking. Are you going in a circle? Thought not. It would be quite hard to push the bike to the gas station if it were not so.

Why a bike corners when leaned, is because the countersteering thing works both ways, once you have enough momentum for the gyroscope business to work. Turn the bars , and the bike leans over. Lean the bike over, and the bars turn. In either case what initiates the actual turn is the displacement of the front wheel contact patch.

You can turn without consciously initiating the turn by countersteering. Ride along with a heavy weight on the tank. Now hold the weight out to one side. The bike will lean over because of the offset CoG. That will turn the bars, an initiate a turn. Providing of course the bars are able to turn.

If the bars are locked, you won't turn, no matter how hard you lean. You can test this, I did it once. Tie a rope from each end of the bars back to the saddle tree (works best with wide bars). That should lock the bars so they won't move either way. Now get at the top of a hill and roll down it. Try to turn by leaning over. Won't work. Will hurt.

A good rider can maintain some degree of control by moving weight about in this fashion. Some degree. Sort of.

However, I do agree with the original poster, in that in some cases novices become obsessed with counter steering.

For normal day to day ridsing, no one should need to think about it. The only times you *need* to think "COUNTERSTEER" is if you need to dodge something, or you misjudge a corner and end up in the poo, and need to tighten up hard.

Of course, both those situations may be life and death ones, which is why training and mentoring courses concentrate on them.

[Deano]

I also note that as I steer it by moving my body weight around, the bars naturally flop in a countersteering-like manner. What's the story with that then?

I found the opposite, the bars tend to tip in. This is on a 50km/h downhill gentle curve using body weight shift alone, hands off bars.

[Ixion]

You should read the article I just linked on trail.

Motorcycle stability comes from trail, not from gyroscopic effects.

It's the gyroscopic effect that causes a bike to turn in an arc when leaned over. It's trail that resists that to a greater or lesser degree . More trail,. more resistance to falling over, more stability.

Zero trail (vertical forks) the wheel will tuck under immediately and fall over . Infinite trail (horizontal forks) the bike will never turn. Somewhere in between is a good medium, for varying values of medium