Steering geometry - confirmation bias

SteveA said:

Definitely with you on the throttle input here Dances. But lets step back to the question.

Unless you intentionally apply steering forces going into your hairpin, you won't turn at all. Once you have the bike turning you don't continue making steering inputs unless you need to tighten or open the line. When you are not steering, you relax the forces. Exiting the turn you want to hook up and get as much exit speed as possible, so you will be working the throttle, and you may need to make more steering inputs.

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Agreed with the counter steering to initiate and modulate a turn but lets not loose sight of the original post which has to do with geometery and has now drifted into turn dynamics - which is ok.

You can complete a turn with neutral throttle but Alan asked in the context of quickly, so this is not a neutral throttle scenario. In other words, throttle and handlebar inputs are intertwined within the literal context of Alan's question. If one were to enter transition and exit a turn at fixed throttle, the steering sequence is counter steer to shift the center of gravity (of the bike and rider) towards the side you want to turn to and initiate the turn, modulate through steer/countersteer (balance) and then counter steer to get the center of gravity back in the vertical plane with the bike to exit the turn. Even with a neutral throttle funny things happen with the engine outputs due to changes in the effective radius of the rear tire when leaned versus when vertical.

Quick transitions from one turn to the next gets even trickier in that the transition through vertical loads the suspension as opposed to starting a turn with a relatively neutral suspension.

Lots of things happening with turning a bike. I can still remember my father shoving me off on my first ever bicycle ride, it was holy shit, WTF (sensory overload) for about a second and then "magic"; no time to think, just do.

Dances with Shrapnel said:

........Lots of things happening with turning a bike. I can still remember my father shoving me off on my first ever bicycle ride, it was holy shit, WTF (sensory overload) for about a second and then "magic"; no time to think, just do.

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Oh Absolutely....

But what I remember on that equivalent occasion is a series of failures and soggy landings, a break whilst the saddle height was adjusted more appropriately for me (it was my older sisters' bike!) followed by me just riding away and never looking back!

First motorcycle, series of stalls, bumping into a parked car, discussion about throttle an clutch coordination, followed by me just riding away and never looking back!

You have to understand the dynamics to some degree to progress at all, you can get away without understanding geometry, until you want to change what happens!

I have only ever ridden one original 500cc Manx. It was ex-Ginger Molloy. I found that if I got off-line a bit coming out of corners, when I gave it more stick - it self-steered slightly in the correct direction and came back on line. It was extremely confidence-inspiring. I then knew why the top guys used to love them so much. My 500cc Triton was much faster down the straights than any 500cc Manx, but my lap times on the Manx would have been much better. If you have to fight to keep your bike on the bitumen when accelerating out of corners, you cannot be fast. I don't believe anybody ever counter-steered a Manx - it is a modern thing caused by handling which is dictated by extreme engine power levels and fat tyres.

Did I miss something that counter steering is a modern concept dictated by big power and fat tyres???

acotrel said:

I don't believe anybody ever counter-steered a Manx - it is a modern thing caused by handling which is dictated by extreme engine power levels and fat tyres.

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So which way do YOU move the handlebars when you initiate a right hand turn?

Let me answer that for you Alan, on a Manx and pretty much every motorcycle; you push the right handlebar away and/or pull the left handlebar towards you to initiate a right hand turn...........which is counter steering. Not a modern thing but a historic thing supported by the physics, dynamics and kinetics of our motorcycles.

Dances, maybe that would explain the ill handling and crashes, refusing to accept counter steering and pulling the bar into the right while initiating a right hand turn !!!!

acotrel said:

......I don't believe anybody ever counter-steered a Manx - it is a modern thing caused by handling which is dictated by extreme engine power levels and fat tyres.

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You may remember Wilbur Wright, used to play with wings and things, more than a hundred years ago! and skinny wheeled bicycles.....

Wilbur Wright explained countersteering this way:

I have asked dozens of bicycle riders how they turn to the left. I have never found a single person who stated all the facts correctly when first asked. They almost invariably said that to turn to the left, they turned the handlebar to the left and as a result made a turn to the left. But on further questioning them, some would agree that they first turned the handlebar a little to the right, and then as the machine inclined to the left, they turned the handlebar to the left and as a result made the circle, inclining inward.

Lets make it really simple.

Everyone counter steers a motorcycle to initiate a turn, except at extremely slow speeds, like when parking, or riding a trials bike at a walking pace, where one does sometimes actually steer in the turning direction. It has absolutely nothing to do with extreme power levels or fat tires. The physics of it isn't all that complicated, and has been settled science for quite some time now.

Maybe Alan is talking about what happens after the turn is initiated and the bike is already leaned over and moving in an arc. At that point you might need to apply a little steering pressure in either direction for a variety of reasons (decreasing or increasing radius corners, elevation changes, traffic, etc.), but that's not the issue here. We're talking about counter steering for a very short period to initiate the turn, and everyone who rides does it, whether they know it of not.

Ken

Most motorcyclists I have spoken to in the past say they do not counter steer it's very hard to convince them that they do it without realising! As a side note my 750 commando has Yamaha yokes with apprx 40mm offset ,std length shocks and 19" wheels 27° rake frame and the handling is superb ,the steering feels very neutral to me although I'm not a racer

Ive noted the changeover speed on my mountain bike. This is where one stops steering in the intended direction and begins to countersteer instead.
This occurs at around 8 mph on my mountain bike. I'm guessing it's very similar on a motorcycle.

Glen

SteveA said:

you can get away without understanding geometry, until you want to change what happens!

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This ^^^^^^^^

baz said:

Most motorcyclists I have spoken to in the past say they do not counter steer it's very hard to convince them that they do it without realising!

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Agreed, but they are still doing it. There is no other way to start a turn at speed. I think racers might be more aware of it because it becomes more obvious when entering tighter turn radii corners at higher speeds. One of my favorite quotes on the subject is from Randy Mamola. When talking about how to get his bike into a corner rapidly, his description (now politically incorrect, no offense intended) was to just "flick the bitch in", i.e., make a very strong counter steering movement of the bars to snap the bike over into the turn. Some of the riding schools have specific exercises that will demonstrate to even the strongest sceptic that he is in fact using counter steering to initiate his turns.

Seriously, this is not a matter of personal opinions any more, but established fact. I don't think you will find a single scientist or engineer who has studied motorcycle dynamics who will disagree. Nor any modern chassis designer, suspension specialist, or top level road racer.

Ken

Dances with Shrapnel said:

Simple question yet poorly framed. You neglected to mention throttle control (neutral, off, or rolling on the throttle), rather important, don’t you think?

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I presumed that as you ride around corners, you get back on the gas while the bike is still cranked over to accelerate out of the corner. As you accelerate, the rake changes and that determines which way the bike will turn, if it is going to turn at all. The difference in rake is only a fraction of a degree, but it operates the castor effect. With any bike, you can usually consciously steer it, into the direction you want to go. But most bikes have a natural tendency to go one way or the other as you relax and accelerate. Bevel Ducatis are notorious for running wide. So when that happens, riders often take the high line rather than trying to go under other riders when coming out of corners.

The way my Seeley is set up at present, where you put your mind going into or out of corners - that is where it is instantly. All I have to do is sit on the bike, brake and accelerate and allow for it's self-steering. Simple physics dictates that for the bike to turn, the front wheel must precess. The only way that can happen is if a force is applied to an axis of the wheel. Even if you are not conscious of it, even a slight shift in weight will steer the bike if the steering geometry is set up to be very quick. Fortunately for me, Commando engines are not usually savage. However I would not like to ride my bike if it was fitted with separate pipes with megaphones.
I have encountered a few instances where bike have seriously mishandled. When it happens, the problem usually comes from nowhere and extremely quickly and can give the big fright. There are obviously safe limits when you alter the steering geometry. I think my bike is on the limit for steering quickness. Any change to the set-up makes me nervous, you don't need to get it wrong.

acotrel said:

I presumed that as you ride around corners, you get back on the gas while the bike is still cranked over to accelerate out of the corner. As you accelerate, the rake changes and that determines which way the bike will turn, if it is going to turn at all. The difference in rake is only a fraction of a degree, but it operates the castor effect. With any bike, you can usually consciously steer it, into the direction you want to go. But most bikes have a natural tendency to go one way or the other as you relax and accelerate. Bevel Ducatis are notorious for running wide. So when that happens, riders often take the high line rather than trying to go under other riders when coming out of corners.

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Ah, "presumed"; explains everything.

Really not that simple Alan. You also need to consider whether the bike exhibits squat or anti squat characteristics. That is why emphasis on: "you can get away without understanding geometry, until you want to change what happens". One needs to look at and understand the whole of the system, not just one element when trying to sort out a bike.

acotrel said:

The way my Seeley is set up at present, where you put your mind going into or out of corners - that is where it is instantly.

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Now we are getting somewhere; mind control placing something instantly:

Telekinesis with a good measure of Quantum Mechanics.

All kidding aside, I understand what you are conveying here and to me describes a well sorted out bike.

My Seeley might be well-sorted, but I got it right by sheer arse. I used the TZ350 fork yokes because I had them and I knew the bike they came off had 26 degree rake and fairly neural steering. So I took the gamble. I was just lucky that it worked. I only found out about the self-steering bit, because as I practice, I work up to the corners when braking and work at getting on the gas earlier while coming out. The first time it became really apparent, I gassed the bike when it was cranked over half-way around a corner and it did not end up on the grass at the outside of the bitumen. Then I began to use the improvement in handling everywhere. When I was a kid, I simply used to adjust to my bike's handling like everybody else. Most of my racers were converted road bikes. They are usually made so they don't kill people by mishandling - STABLE ! The thing about this stuff is it can make you look like an amazing rider, when it is actually the bike doing it's thing .

You have got to be careful. Many years ago, there was a Parilla 250 production racer brought to Melbourne and one of my friends bought it. It is extremely quick-steering. Everybody who ever rode it has crashed it. It is a lovely thing to ride. However you can be all tucked-in and going like the breeze, then in the next split-second find yourself on the road and not knowing how you got there.

acotrel said:

You have got to be careful. Many years ago, there was a Parilla 250 production racer brought to Melbourne and one of my friends bought it. It is extremely quick-steering. Everybody who ever rode it has crashed it. It is a lovely thing to ride. However you can be all tucked-in and going like the breeze, then in the next split-second find yourself on the road and not knowing how you got there.

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You know, sometimes Alan, I am inclined to ask, just how much alcohol does the average rider consume at a race meeting in the Antipodes?

If you are talking about consuming methanol fuel in your bike, at historic meetings - not so much that you cannot afford it. If you are talking about drinking hooch, it doesn't usually happen. Personally, I am virtually teetotal - I might drink about one gin and tonic per month. But we did have one superbike rider who was getting into the funny stuff in a big way. He even ended up racing internationally. Most of us were glad to see the back of him.
Pretty funny about the guys who crashed the Parilla. I know them all and how good they are, so I would not try to race that bike.

I tried to find that Parilli fork specs but couldn't. If you know might be interesting to reason out its surprise upsets and avoidance.

I have not crashed doing a harsh turn. By far most were just toolling along essentially dead ahead, sane secure as practical on THE Gravel to hit combo of lumps bumps, holes/ridges or completely unknown, fork snatch out from under while holding steady dampened no conscious steering imput to keep going straight 30's mph, mostly low sides but also couple hi sides bike just resonated suspenion to lift few inches up as it pivoted horizontal on our CoG/ about seat height but landing on me still seated holding bars. My impression is 30's was not enough to stay in slight normal/natural/required counter steering so fork was going slightly in/out direct/countering - which feels about identical to the slight wiggles of wind and road texture, until mis-matching tire bike momentum SPLATT.

I've had close calls working up on some daily paved commuting nice mild turns, till surprise sliding counter steered SV650 120 race compound front but able save d/t planned run off turn allowed. Thot might be doing something wrong but after 2nd time few feet terror body got imprinted on what never do again.
I got pretty handy on SuVee with in its limits but would still spill me out the blue behaving sanely. Last time on heated tires from hour of errands sanely spirited throttle/leans, with errands done headed home totally legal, to do 3 lane wide hyw intersection sweeper at 40's instead of 50's with intent to just help lean a tad more to slightly sharpen turn at apex to end up sliding on my L ankle. Had no sense I was pressing luck at all. No grit on road, just surprise combo of fork rake/trail wheel base tire temps lean angle low throttle assist. That was Oct 2016 so finally sunk in no way to prevent these surprised in Ozarks so gave SuVee away this summer.

Commandos have dumped me on sane Gravel travel too, actually more so till I got the knack of em, then were rather better off pavement than moderns by constantly avoiding ever getting out of direct steering, resisting counter steering tendency as can not predict the degree of traction counter steering front requires.

As Al puts it, nothing to learn on hard to control cycles but going slower with more effort not to crash constantly. Must have good tool to to best job - which boils down to trial and error, lots of errors.

Btw an extra long trail can also dolly/caster wheel too at lower but still uncontrollable frequency but tends to give warning first.

In counter steering under hooked up power, the rear tends to lift while front pulling down. This puts twist load through system so best wishes never to twist and shout too much.