The Bum Steer

[jrandom]

I believe...

Yes, that's what most countersteering discussions boil down to.

[Mikkel]

It's taken me a while to get back to this but since I opened the batting on this topic, I guess I should respond.
Sorry mate but while I see your point, I don't agree.
Firstly, it is possible to ride a bike at speeds which are so low that the gyroscopic forces are so small as to be ineffectual and we have all done it.
Secondly, countersteering can be explained by considering the gyroscopic forces on the front wheel only - that's in fact how I have usually seen it explained. So to evaluate precession's part in countersteering, disposing of the angular momentum of the front wheel only, is all that is necessary. There is still the stability provided by the rotation of the rear wheel and the motor. I know that in many cases, the crankshaft rotates in the opposite direction to the wheels, but it still resists movement in some planes.
(To test this for yourself, try changing down a couple of gears next time a crosswind is buffeting you around.)
A quick analysis of the MAGNITUDE of the forces in play leads to the conclusion that there MAY be something other than precession at work. It takes remarkably little effort to tip in a bike of considerable mass that is also spin stabilised by the rear wheel and the motor.

You say you disagree - except it doesn't really seem so to me.

The part I've highlighted is the only thing I have any contentions with... You say the gyroscopic forces are ineffectual. Not quite so - the gyroscopic forces are present from the second your wheels start turning and from that second they are providing stability. That stability increases with the rotational speed and vice versa. This is why it becomes more and more difficult to ride a bike as you slow down and there's a lower limit for how slow you can ride in a straight line - if it was all TRAIL then this wouldn't be the case. Q.E.D.

For the rest of your post - yes I mostly agree. But I don't find anything there that is in disagreement with what I have already written. You wonder about how little effort is necessary to tip a big bike over using the handlebars - I'd say that's due to leverage and steering geometry. I wanted to chuck a couple of formulas in here for good measure showing how the vectors from the torque applied at the handle bars translate into a roll inducing change of the rotational momentum of the front wheel. But alas, I've grown rusty in the finer parts of classical mechanics and can not be bothered to study my old mechanics book thoroughly now - too close to beer'o'clock as it is.

Anyway - a video probably says more than a thousand words. I'd like you guys to try and explain what happens in this one:

[YOUTUBE]http://www.youtube.com/watch?v=545GwnupKAE&feature=related[/YOUTUBE]

[YOUTUBE]http://www.youtube.com/watch?v=2pYi3-q_IVA&feature=related[/YOUTUBE]

Oh yeah, and please do continue to argue against gyroscopic stability induced by rotational mass!

[Deano]

Here's the true bum steer. Pic included.

[Mikkel]

Can't help myself...

This video shows nicely how the interplay of applied torque and rotational mass pans out:

[YOUTUBE]http://www.youtube.com/watch?v=dCcfKBfmyP4&feature=related[/YOUTUBE]

[swbarnett]

I've been watching and reading all the countersteering threads of late and someone's comment "... if you're getting around corners, then you must be coutersteering, can't be done otherwise ..." has prompted me to post a counter-view on counter-steering.

I got that from a paper in a Physics journal talking about how bicycles steer.

Watch the top racers, watch the best of them Casey Stoner. Their bodies are on the inside of the bike before they tip in for the corner. ... They are pushing the bars up to hold the bike straight waiting for the tip in.

This is the old "pick up the hammer while you're standing on it" theory. You can't push the bars up unless you've got something to push against. The rider is hanging in mid-air.

If unbalanced weight was all that was required to turn then these riders would start turning the moment they shifted their weight and bikes would be a lot more unstable than they are. The reason that they don't is that the gyroscopic force must be counter-acted before the bike will lean. When the rider tips in to the corner they are counter-steering. They're not holding the bike up, they're holding the bars straight. When they relax their arms the bike leans. Possibly in response to this a counter-steer occurs. So, even when you're using your body weight to aid the "tipping in to the corner" counter-steering is still involved.

[MSTRS:Me]

No, not confusing as this explanation was very well worded. However, a lot of earlier explanations were veering on the borderline nuclear physicist theory paper....sorry buys, just my point of view!




I got to admit I really still struggle with a slow tight U turn...can't seem to get the hang of it. However, countersteering on a track day at speed is no longer an issue.

Where could I be going wrong?

Steering a bike in a variety of situations, and at various speeds simply takes practice. The transition between turning the bars and nudging is a fine line, that will be at different points for different bikes/styles of bike. At low speeds (walking pace) your body position on the bike assumes greater importance than at higher speeds when countersteering kicks in.
You say you have trouble with low speed, tight u-turns but have countersteering sorted...so does Yungatart. Perhaps it's a woman-thing?? I suggest you avail yourself of a course at RRRS - Noel (The Stranger) will get you sorted.

[Paul in NZ]

Fark - I don't think of any of this when I'm out for a ride... Its more...

hmm..corner comin up.. hmm wonder if Vickis in the mood tonight? corners gettin closer - christ I could go a beer about now... corners gone cor that was cool... hmm wonder if Vickis in the mood tonight? next corners gettin closer - christ I could still go a beer about now... corners gone cor that was cool... hmm wonder if Vickis got any beer in the fridge? Shit - did I check the tyres? Oh yeah - I was going to do that after I put the beer in the fridge but I aint dead so I guess they are ok... Christ whats that bloody noise? Vicki won't be in the mood tonight if I blow the bike up again next corners gettin closer - christ I'm still thirsty... corners gone cor that was cool... hmm wonder if I can remember all the words from that song... dah dah dum.. no um dum dah argh fug it ..... If I stop and call I could check if Vickis in the mood tonight? corners gettin closer - christ I could stop for a beer at the same time eh?... corners gone cor that was cool... hmm nah - she will hate it if she smells beer on my breath... Vodka - yeah - that could work... nah - best not eh - coffees the go... Yeah - that would put me in the mood eh?

Countersteering? I had a counter once and it didn't steer too well...

[MSTRS:Me]

Yeah Paul - that'd work. Vicki being 'in the mood' is counter to reality, hence the corners go by nicely?? And beer (or vodka) are bought over the counter, so that's working too. And the song in your head...only works if it incorporates a counterpoint rhythm.

[Biggles2000]

Yes, that's what most countersteering discussions boil down to.

Well if you would like to try following me around a few corners with your hands off the bars with out crashing....... which I believe is impossible to do as the bike would simply go straight ahead...... then you are right and you can bum steer. Try it please?

[Mom]

I have played around with weight transfer to make a bike turn when this argument came up long enough ago that you would have still been shitting in your nappies,and the direction changes that could be initiated wouldn't get you around any 1/2 way decent corner

Agreed! but combined with other strategies it helps! and IMO should be also factored into the equation.

It's taken me a while to get back to this but since I opened the batting on this topic, I guess I should respond.

Please do...LOL cant understand a word mind. follow what you are saying, but way too technical for the mere plebs like me on here to understand.

Fark - I don't think of any of this when I'm out for a ride... Its more...

I think a lot of riding is instinctive, and learned by experiencing and/or being taught, nothing to do with mathematics, physics or what have you. If it were about that I would have given up before I even started.

For me it is a combination of what needs to be done to get around that corner. I came back to riding on my sons pathetic scooter. It had fat tyres and cornered like it did not want to!! I did the lean/countersteer/weight transfer thing (albeit at 50kmph) and I was not going to get round without hitting the council formed drain on the side of the road. Stomped on the peg inside peg, and away we went. It is not a science in IMO, it is what you have to do to make the turn, and the skill level you possess to enable you to do it!


Feet steering has to be a factor too!

[Ixion]

Call me an ignoramus if you like, but surely when you move your body weight and cause the bike to tip in without your hand/s on the bars (which I do regularly) the bike itself is countersteering. Just because you are not directly putting the action in through the bars yourself does not mean the action is not happening. I dare, nay double-dare, anyone to successfully turn a bike at speed by using bodyweight only on a bike with locked bars. Oh that's right, Keith Code already did that for us. But still the debate rages on.

Yes. That is exactly correct. For a bike to corner at any speed , the front wheel must be perversely displaced (ie turned a bit right if you want to go left). That is the counter steer mechanism.

Whether you initiate that displacement by pushing the handlebars (consciously 'countersteering'), or by causing the bike to lean over (by weight shift or banging your knee on the tank or whatever) makes no difference.

In the first case the wheel displacement will cause the bike to lean. In the second case , the lean will cause the wheel to displace. It works the same either way round

Conscious countersteering (with the bars) is manifestly not the only way to cause the counter-steer dispalcement . (It may be the best but that's a different argument).

But regardless of how initiated, a bike cannot corner at speed without involving the counter-steer mechanism.

Both parties are correct. Any (highish speed) cornering on a bike is countersteering - but it need not be the rider pushing the bars which causes it.

[dhunt]

I thought I would add to the confusion by quoting a few of the top riders in MotoGP. Taken from the MotoGP: Performance Riding Techniques Book

It's not something for me that you can draw on a chalkboard. As far as counter-steering and body-steering go, I think a lot of riders guess and don't really know what they do or don't understand. I mean, I just try to get around the track as fast as I can!"

Erm, erm, it's just erm, I dunno! It's just natural.

When I'm turning right I push on the right bar. Sometimes if the corner is really fast then I pull on the left one too but not very often.

I think it depends on the speed - at 100mph I definitely counter-steer. I pull a little bit right to go left

I use my body. Push my shoulder to the inside of the corner

Your bike's handlebars, of course, play the big part in steering, but your footpegs help you to steer the bike too.

I have small levers; my arms are shorter so I haven't as much power as Gibernau, so I use my body and legs as well. I move and use a lot of leg like if you were to break a stone.

And here's a summary from the book itself

Putting pressure on the inside footpeg to try to get the bike to turn is a waste of time and effort. Logic should dictate that putting more of your body mass on the inside peg will get the bike to lean, and experimentation in a car park or in a really slow turns would support this theory.
But once your bike gets up to speed and the strong gyroscopic forces from the front and rear wheels come into play, then the only thing that putting pressure on the inside peg will do is make your thighs a bit bigger.

Just leaning into the corner and hoping that the bike will follow is also a waste of time and effort. I'll admit that doing this can give you a slight change of direction, but will it make the bike turn? Will this alone get the bike into and out of a corner? The answer is no. You'd to have the turning arc of an oil tanker for this to work - and that isn't going to be of much use, or very exciting, for a bike.

But even MotoGP riders aren't too sure - or even in agreement with each other - on some of the essential steering points.

Hopefully this helps.

[Forest]

Oh yeah, and please do continue to argue against gyroscopic stability induced by rotational mass!

I don't think anyone here is arguing against the existence of gyroscopic forces.

At least I hope they aren't!

[smoky]

I’ve never heard so much twaddle about a very over done subject in one thread before.
Actually I have but; I think you’re taking things too far out of context – body position is important, counter-steering is important, so is throttle control, where you’re looking, your line, weighting the peg, bla bla bla - get them alright in the same corner and you have the best result.

Some of your comments about counter steering makes me wonder if you even know what it is – and suggest you use it a hell of a lot more than you think

If it didn't work, racers wouldn't be using it (watch the MotoGP slow motions to see it in action).

trust me - they still use counter-steering, I don’t think you can watch a GP racer and actually even see the counter-steer being applied, even in slow motion. So your just guessing at what they’re doing based on your own experience - unless you’ve got a reference to someone riding in a GP who is saying the same as you.

I've been using the technique for a year and perfected it on my daily runs over Paekakariki Hill Rd - there's not a better test.

Well I guess when we're faced with soo much experience - how can we argue against that.

You can tell the obsessive counter-steerers, they're the ones who look like motorcrossers when you're following them on the road - body upright while they push the bike down in a desperate attempt to carver the corner.

Not sure who you’ve been riding with – have you ever read anything that say’s ‘stay upright when you use counter-steering’. Just because you ride with people who do something odd doesn’t mean shyte.

[Ocean1]

I got to admit I really still struggle with a slow tight U turn...can't seem to get the hang of it. However, countersteering on a track day at speed is no longer an issue.

Where could I be going wrong?

And this from an ex dirtygirl. *sigh*

I figure you already know, lean the bike and keep your body weight over the tyre's contact patch. Helps if you load up the uphill peg too, same as in the dirt. In fact I'm embarrased to say I sometimes do it standing up Just seems easier to pretend the Buell's a KT250 No, don't do that, but there might be a clue there about weight transfer eh? And throttle control.

Appart from that, it's just an afternoon in a carpark, making with the little wee circles.