Limit cornering on bikes

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Erunanethiel
Erunanethiel
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Joined: Sat Oct 26, 2013 9:17 am

Limit cornering on bikes

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In a steady state limit cornering cornering situation, a bike shouldn't be able to stand back up because it has to countersteer into the turn, momentarily carving a tighter line than before. But if it is at the edge of traction, it can't.

This has been bugging since I realized this. Because you know, as most of us here thinks feeling you are right at the edge of traction in a corner is almost better than sex.

But also those MotoGP riders don't seem like they are holding back espically during qualifying.

I would like to know you guy's thoughts.

Tommy Cookers
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Re: Limit cornering on bikes

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centrifugal force 'stands up' the bike whenever the rider allows less lean than hitherto
CF is the equivalence of the force situation whenever the bike is travelling on a path that's not straight

Erunanethiel
Erunanethiel
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Re: Limit cornering on bikes

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Centrigual force is balanced by gravity since the bike is leaning. You need to increase the "centrifugal force" by steering into the turn momentarily so that it will not be cancelled out by gravity. That steering into the turn bit requires grip that the tire doesn't have in reserve.

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Tim.Wright
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Re: Limit cornering on bikes

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Perhaps the driver moving slightly more upright is enough to upset the gravitational vs centrifugal force balance and let the bike right itself.

Gyro effects will also always be trying to stand the bike up too.
Not the engineer at Force India

Jolle
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Re: Limit cornering on bikes

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The normal state of a motorbike is straight on standing up. In a corner it takes effort to stay in the curve. The gyro effect of wheels take care of that.

Modern(ish) bikes look to turn in quite well trough well balanced geometry, although the big sport bikes with their ultra wide tires, take quite a bit weight shifting to have a steady corner.

probably if you search a bit, there are clips on YouTube where riders fall off their bike mid corner in a race, with their bike straighten up and heading for a barrier :P

Tommy Cookers
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Re: Limit cornering on bikes

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Jolle wrote:
Fri Feb 21, 2020 8:12 pm
The normal state of a motorbike is straight on standing up. In a corner it takes effort to stay in the curve. The gyro effect of wheels take care of that.
Modern(ish) bikes look to turn in quite well trough well balanced geometry, although the big sport bikes with their ultra wide tires, take quite a bit weight shifting to have a steady corner.....
I hope that the following doesn't sound like any disagreement ....

the gyroscopic moment is a tiny fraction of the 'toppling' (due to lean angle) moment
ie 2 - 4 deg of extra lean was required to 'overcome' the gyroscopic moment
according to Royal Enfield's (Tony Wilson Jones) tests c. 1959
gyroscopic moments can be regarded as dampers in roll - and in yaw

Moto GP machines etc have reduced gyroscopic moment in choosing engine rotation direction opposite to wheel rotation
'effort to stay in the curve' is determined by steering geometry including front (and rear) tyre geometry
results opposite to the above ideal are possible

I still don't understand the OP's question
or some of Moto GP machine behaviour seemingly apparent on a normal lap

johnny comelately
johnny comelately
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Re: Limit cornering on bikes

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The normal state of a motorbike is on its side

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Airshifter
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Re: Limit cornering on bikes

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When really cranked over, simple weight transfer of the rider or allowing the bike to straighten up is simple. You can't confuse "steady state" limits and compare them to very short term, almost instantaneous, limits.

Erunanethiel
Erunanethiel
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Re: Limit cornering on bikes

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Tommy Cookers wrote:
Sat Feb 22, 2020 11:07 am
Jolle wrote:
Fri Feb 21, 2020 8:12 pm
The normal state of a motorbike is straight on standing up. In a corner it takes effort to stay in the curve. The gyro effect of wheels take care of that.
Modern(ish) bikes look to turn in quite well trough well balanced geometry, although the big sport bikes with their ultra wide tires, take quite a bit weight shifting to have a steady corner.....
I hope that the following doesn't sound like any disagreement ....

the gyroscopic moment is a tiny fraction of the 'toppling' (due to lean angle) moment
ie 2 - 4 deg of extra lean was required to 'overcome' the gyroscopic moment
according to Royal Enfield's (Tony Wilson Jones) tests c. 1959
gyroscopic moments can be regarded as dampers in roll - and in yaw

Moto GP machines etc have reduced gyroscopic moment in choosing engine rotation direction opposite to wheel rotation
'effort to stay in the curve' is determined by steering geometry including front (and rear) tyre geometry
results opposite to the above ideal are possible

I still don't understand the OP's question
or some of Moto GP machine behaviour seemingly apparent on a normal lap

Yes tthe bike is leaned "2-4" degrees more to overcome the gyroscopic moment, so gravity is pulling down just as much as the gyroscopic and "centrifugal forces" are trying to flip the bike the other way. This means the rider needs to steer into the turn momentarily, to decrease the lean angle.

Jolle
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Re: Limit cornering on bikes

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Anyone that rides a bike knows you have to push is to stay in a corner. There is no curve where it’s balanced. If you straighten the steering, the bike will erect itself again, due to the gyroscopic effect of the wheels. With clever frame geometry this push is very light, but you keep a pressure on the inside clip-on the whole way trough a long corner.

There is so much more to motorbike dynamics then a centrifugal force and gravity. Rear tyre width, cords, engine configuration, frame flex, on/off throttle etc etc all play a big part. That’s why you need more then one bike...

Greg Locock
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Re: Limit cornering on bikes

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If you straighten the steering your nose will kiss the tarmac.

Erunanethiel
Erunanethiel
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Re: Limit cornering on bikes

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Jolle wrote:
Sun Feb 23, 2020 2:47 am
Anyone that rides a bike knows you have to push is to stay in a corner. There is no curve where it’s balanced. If you straighten the steering, the bike will erect itself again, due to the gyroscopic effect of the wheels. With clever frame geometry this push is very light, but you keep a pressure on the inside clip-on the whole way trough a long corner.

There is so much more to motorbike dynamics then a centrifugal force and gravity. Rear tyre width, cords, engine configuration, frame flex, on/off throttle etc etc all play a big part. That’s why you need more then one bike...
Maybe you should stick to 250cc

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Andres125sx
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Re: Limit cornering on bikes

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I think rider gravity applies from the wheel footprint, it´s not directly the gravity, gravity causes a turn from the wheel footprint, what means he can change this moment at will while changing the distance from the footprint moving around the bike. This changes the balance and the tendency of the bike to keep turning, increase the turn or straighten the bike

Or that´s what I guess, I´ve never studied the effect

J.A.W.
J.A.W.
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Re: Limit cornering on bikes

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Well, the easy way, if you've got an adjustable steering damper on your bike,
is turn it up to max-resistance & feel the difference...

Or even more extreme, lock the steering head in fore-aft position,
& attempt to get it to turn, sans the ability to effect rotation about its axis.
Dr Moreau sez..
"Who breaks the law... goes back to the House of Pain!"

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SectorOne
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Re: Limit cornering on bikes

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Jolle wrote:
Sun Feb 23, 2020 2:47 am
Anyone that rides a bike knows you have to push is to stay in a corner. There is no curve where it’s balanced. If you straighten the steering, the bike will erect itself again, due to the gyroscopic effect of the wheels. With clever frame geometry this push is very light, but you keep a pressure on the inside clip-on the whole way trough a long corner.

There is so much more to motorbike dynamics then a centrifugal force and gravity. Rear tyre width, cords, engine configuration, frame flex, on/off throttle etc etc all play a big part. That’s why you need more then one bike...
I don´t think thats right. A spinning wheel does not automatically want to stand straight up, it just means it wants to stay in its position meaning the faster you spin the wheel the harder it is to influence a direction change.

Thats why carbon wheels and counter rotating cranks are so good, they make the bike easier to flick from side to side.

Erunanethiel wrote:
Fri Feb 21, 2020 12:39 pm
In a steady state limit cornering cornering situation, a bike shouldn't be able to stand back up because it has to countersteer into the turn, momentarily carving a tighter line than before. But if it is at the edge of traction, it can't.
but maybe when you do the opposite of counter steering to stand the bike up you increase the front contact patch but also increase the diameter of the front wheel causing you to turn less?
"If the only thing keeping a person decent is the expectation of divine reward, then brother that person is a piece of sh*t"