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Old 17-02-17, 09:00 AM   #51
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Default Re: Cornering

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Then there's the excentrifugal forz
Explain that if you can
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Old 17-02-17, 09:07 AM   #52
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Default Re: Cornering

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This isn't quite right - the front wheel acts as a gyroscope, so by forcing it to rotate with the handlebars you are causing the wheel to roll (gyroscopic precession), tilting the bike. The centrifugal/centripetal forces just stop you from falling over when both tilted and cornering as the forces exactly match the forces from your CoG being off the centre-line.

I've always assumed that it's called counter-steering because you need to turn the handlebars the opposite direction to the way you would at a low speed - I challenge anyone to do a 180 turn in a road with counter-steering (at least with a sensibly heavy bike).
There is actually more than one effect at play here.

The gyroscopic effect means that the rotating wheel wants to keep rotating in the same plane and will continue to do so unless a force is applied (the rotating wheel wants to maintain status quo and keep bike upright), by turning the the front wheel relative to direction that the bike is traveling a sideways force is applied through its rolling contact patch that transfers through the CofG of moving mass which is quite a distance above the tyre contact patch, this makes the CofG move sideways and rotate the bike relative to the fixed tyre contact patch. It is mainly (non-existent as we now know) centrifugal force acting through CofG that pushes the bike over. Gyroscopic progression may play an important part initially when the axis of the gyroscope (front wheel axle) is turned, it is important because it is the quickest thing to take effect, but not the biggest force in the grand scheme.
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Old 17-02-17, 09:35 AM   #53
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Default Re: Cornering

I disagree, the centrifugal force wants to push the bike back upright ...

The difference in the circumference between the inner and outer edge of the contact patch will cause the bike to turn in an arc. This causes a centripetal force through the contact patch, but because the centrifugal force is through the CoG, it will cause the bike to tilt back upright. But, this potential rotation is exactly balanced by the downward force due to the CoG no longer being above the contact patch - so you have gravity pulling the bike towards the road and the centrifugal force pulling it upright.

Looking at it a different way, you can't lean the bike when you're not cornering and you can't corner at speed without leaning the bike. The two forces counter each other exactly. (If they weren't exact, then the bike would tilt until a new equilibrium is reached.)

At speed, you can initiate a turn using the gyroscopic effects of counter-steering, or by moving your weight off the CoG, or a combination of both, but it's just the lean of the bike which determines the radius of the arc you're turning.
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Old 17-02-17, 11:17 AM   #54
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Default Re: Cornering

I don't think there yet exists a full working theory of 2 wheeled bike physics. It's a bit like the three body problem where there isn't a satisfactory solution yet.

Of course that could be because it's mainly bikers who are interested in solving it and they like to disagree a lot
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Old 17-02-17, 11:21 AM   #55
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LOL!
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Old 17-02-17, 11:58 AM   #56
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Default Re: Cornering

They still aren't 100% sure how Aircraft wing aerodynamics work<grin>
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Old 17-02-17, 12:00 PM   #57
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Old 17-02-17, 12:43 PM   #58
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They still aren't 100% sure how Aircraft wing aerodynamics work<grin>
All I know is that if you fit the wings on upside down the plane won't leave the ground easily. But you can fly a plane upside down if you have the correct angle of attack (tail lower than front of plane).
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Old 17-02-17, 01:18 PM   #59
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Default Re: Cornering

Have done a bit of trawling today and found this little nugget about counter steering, complete with some videos of actual handlebar and bike movements. It's a beginners guide so even I didn't have any trouble grasping what the guy is trying to tell his readers.

http://www.obairlann.net/reaper/moto...rsteering.html
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Old 17-02-17, 01:34 PM   #60
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Default Re: Cornering

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Originally Posted by daktulos View Post
I disagree, the centrifugal force wants to push the bike back upright ...

The difference in the circumference between the inner and outer edge of the contact patch will cause the bike to turn in an arc. This causes a centripetal force through the contact patch, but because the centrifugal force is through the CoG, it will cause the bike to tilt back upright. But, this potential rotation is exactly balanced by the downward force due to the CoG no longer being above the contact patch - so you have gravity pulling the bike towards the road and the centrifugal force pulling it upright.
Which is exactly the physics behind hanging off the inside of the bike. In doing so you move the COG to the inside so that it continues to act in a plane straight down to the contact patch with the road. With a typical 180 section rear tyre the contact patch is effectively 90mm (or thereabouts) to one side of the centre of the tyre. The 200kg odd of the bike is still above the centre line so by hanging your 90kg or so 180mm off the bike you effectively bring the COG back above the contact patch and brings things back in balance.

Obviously I've generalised a whole lot with the figures there, but hopefully keeping it simple makes it easier to understand. Now you see why skinny little runts like Marquez pretty much have to climb off the bike mid corner where lardy chaps like Crutchlow just have to shift their knee....

To take the principal further this is also why you get above the bike when you are expecting or controlling a slide. Here you want to be using some of the "grip" available to hold the bike down into the corner so that when you lose this grip it wants to pick itself up (the centrifugal force) rather than low siding the tyres out from under you.
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