Crash Analysis?

[Sykes92]

So I came across this vid of Marc Marquez wiping out during a turn. What exactly happened here? I thought maybe too much lean angle, but I cant really tell if his bike starts scraping the road. I thought bikes couldnt "fall over" at speeds of over 10mph, so long as they dont scrape the road or lose contact with the road because of ice/rain/oil/gravel. Anyone who can set me straight with some knowledge haha?

Link to original page on YouTube.

[allanoue]

He lost traction on the back tire. You can see a long trail of rubber at :07. Just a bit too much throttle.

[Sykes92]

Originally Posted by allanoue

He lost traction on the back tire. You can see a long trail of rubber at :07. Just a bit too much throttle.

Oh, crazy. I didn't even notice that skid mark.

[CC Cowboy]

That's what happens when you let kids ride million dollar motorcycles.

He tucked the front end. You will always see "skid marks" from the rear wheel.

The lose of traction was the front tire.

[allanoue]

Originally Posted by CC Cowboy

That's what happens when you let kids ride million dollar motorcycles.

He tucked the front end. You will always see "skid marks" from the rear wheel.

The lose of traction was the front tire.

Why/how did he tuck the front end?

[CC Cowboy]

Look closely (and often, I had to rewind many times) and you will see he is still trail braking and tucks the front.

[adouglas]

@CC Cowboy, Please define what happens when the front wheel "tucks." I've seen the term used a lot but never seen an actual definition. @Motofool, o wise master of the laws of physics, are you monitoring this thread?

Is it that the front wheel locks? That's implied by the observation that he's trail braking.

I imagine that a tuck works like this:

- You're leaned over, which reduces available traction.
- The limits of front traction get exceeded somehow...
------too much braking causing the wheel to lock,
------increase in lean angle beyond the limit of traction,
------too much weight shift to the rear through acceleration
- The front slides to the outside of the turn due to centripetal acceleration
- When the front slides, the bike falls over like a drunken sailor

If the front slides while NOT cranked over it's not as much of an event.

Is that right?

[alex.s]

watch his front suspension. he is braking very hard into the corner and simply lost the front. the reason? there could be a million reasons. the simplest one was that he simply didn't have as much front grip as he though he did


also, you'll never lose the front under acceleration unless you let the brakes off too quickly (which still isn't acceleration, its letting the brakes off too quick)

[CC Cowboy]

Originally Posted by adouglas

@CC Cowboy, Please define what happens when the front wheel "tucks." I've seen the term used a lot but never seen an actual definition. @Motofool, o wise master of the laws of physics, are you monitoring this thread?

Is it that the front wheel locks? That's implied by the observation that he's trail braking.

I imagine that a tuck works like this:

- You're leaned over, which reduces available traction.
- The limits of front traction get exceeded somehow...
------too much braking causing the wheel to lock,
------increase in lean angle beyond the limit of traction,
------too much weight shift to the rear through acceleration
- The front slides to the outside of the turn due to centripetal acceleration
- When the front slides, the bike falls over like a drunken sailor

If the front slides while NOT cranked over it's not as much of an event.

Is that right?

Front wheel doesn't need to lockup, just travel slower the the speed of the bike causing loss of traction. Other than that you got it down (pun intended) except acceleration part, and drunken sailor (actually goes down like a young girl on the third date).

[Sykes92]

Thanks guys! I am still very new to the physics involved with bikes so every bit of information is greatly appreciated; especially if it helps prevent an incident down the road (pun intended)

[Motofool]

Originally Posted by adouglas

@.........Motofool, o wise master of the laws of physics, are you monitoring this thread?

The detail that shows the front tuck is at 0:38.
When the rear tire slides out, the steer naturally turns toward the outside of the turn (under-steers).
When the front tire slides out (tucks), the steer naturally turns toward the inside of the turn (over-steers).

Here is a great article written by our Misti:
http://www.motomom.ca/the-limit-expl...tion/#more-856

Rough explanation to our curious apprentice and protegee (the OP):

There are two parts of our bike that define our well-being: the frontal and rear contact patches of the tires.

Basically, those are the frontiers between two different materials (molecular structure) and they are in contact in a dynamic way, each particular portion kisses each other for fractions of a second at a time.

Dynamic means that there are two main things acting over those surfaces: movement and forces.

The molecular structures determine how much the billions and billions of electrons get attracted to each other: that is called coefficient of friction (there is a number for each combination of materials).
The roughness and softness of the surfaces determine how much each is ingrained into the other and grabs.
The combination of both plus the forces acting perpendicularly to the surfaces is what we call traction.
Certain tire (and pressure) over certain surface under certain perpendicular force (weight+suspension effect) can resist only certain amount of lateral forces (in any direction) before it slides (sideways) or skids (forward).

While moving over a straight line, there are only forces and movements in the vertical and longitudinal directions: weight support, suspension effect, accelerations and decelerations (braking).

While moving over a curve (rotational movement), there are additional forces and movements added to the ones mentioned above: lateral ones generated by the natural resistance of any mass to be deviated from a straight movement (centripetal acceleration).

Because it is the only one of both that is directional, the frontal contact patch is the only one responsible for forcing the bike to follow a circular movement against the natural tendency explained above; hence the lateral force and slip (the rubber gets twisted and each following portion to occupy the contact patch position lands off the pointing direction of the steer and away from the center of the turn).

The above also happens for cars' and trucks' tires.
The geometry of the steering mechanism of cars and trucks is designed in a way that they tend to return to a straight line naturally.
For motorcycles, taking advantage of the natural lean, the geometry of that mechanism is designed in a way that the bike (if properly set up) tends to stay on the chosen curvilinear line naturally; hence, the advice of staying light on the steering bar.

As a result of that design trick, when the frontal contact patch is overwhelmed by the lateral forces and reaches its limit of available traction for the conditions of that instant, it lets go offering little resistance to the slide and the weight of the bike takes over and over-steers the bar (the bar more or less remains in the same position for the rest of the slide).

Note how the body of the bike makes contact with the track and pivots the rear tire up (and the front tire) in the air, instant after which the natural resistance of any mass to be deviated from a straight movement takes over and both, rider and bike, follow a straight line.

Management of traction is the name of this game, being your front tire the weakest link.

[Sykes92]

Originally Posted by Motofool

The detail that shows the front tuck is at 0:38.
When the rear tire slides out, the steer naturally turns toward the outside of the turn (under-steers). When the front tire slides out (tucks), the steer naturally turns toward the inside of the turn (over-steers)...

Here is a great article written by our Misti:
http://www.motomom.ca/the-limit-expl...tion/#more-856...

Rough explanation to our curious apprentice and protegee (the OP):...

Management of traction is the name of this game, being your front tire the weakest link.

That was probably the most awesome explanation of anything I have ever heard in the history of ever. You went really really in depth. Thanks! I appreciate that

[Motofool]

Originally Posted by Sykes92

...........of anything I have ever heard in the history of ever............ Thanks! I appreciate that

The history of ever has been a short time for you, Cameron; you are just a baby opening your eyes to this awesome world.

Stay so curious and alert and questioning and you will hear and see much better things.

You are welcome

"You must understand the whole of life, not just one little part of it. That is why you must read, that is why you must look at the skies, that is why you must sing and dance, and write poems and suffer and understand, for all that is life.
A consistent thinker is a thoughtless person, because he conforms to a pattern; he repeats phrases and thinks in a groove.
Freedom from the desire for an answer is essential to the understanding of a problem." - Jiddu Krishnamurti

[Motofool]

Originally Posted by Motofool

..........For motorcycles, taking advantage of the natural lean, the geometry of that mechanism is designed in a way that the bike (if properly set up) tends to stay on the chosen curvilinear line naturally; hence, the advice of staying light on the steering bar...........

I have found this picture that shows a bike with neutral steering geometry (zero over or under-steering tendencies):



Other bikes need a steady pressure to counter-act the above mentioned tendencies (tires' section and pressure are the major, but not the only factors for those tendencies to show up).

Any additional unconscious tension over the handlebar just puts unnecessary additional lateral forces on the frontal contact patch.

Sometimes that unconscious tension only happens when the pilot does not have a totally relaxed grip and the front suspension hits a road or track bump or valley that requires a slight momentary adjustment of the steering direction (healthy thing that the bike of the picture would do naturally without the resistance of the pilot).

[cbinker]

Too much front brake.

[csmith12]

Originally Posted by alex.s

watch his front suspension. he is braking very hard into the corner and simply lost the front. the reason? there could be a million reasons. the simplest one was that he simply didn't have as much front grip as he though he did

Originally Posted by alex.s

also, you'll never lose the front under acceleration unless you let the brakes off too quickly (which still isn't acceleration, its letting the brakes off too quick)

I don't believe the transfer of load between front and rear is instantaneous, so I would think there is a we bit o time for one to loose the front during acceleration in there somewhere. However, once the weight has been managed, you can wheelie the exit or totally lite up the rear (it witch case, the front better darn well hold lol).

Food for thought....

[alex.s]

Originally Posted by csmith12

I don't believe the transfer of load between front and rear is instantaneous, so I would think there is a we bit o time for one to loose the front during acceleration in there somewhere. However, once the weight has been managed, you can wheelie the exit or totally lite up the rear (it witch case, the front better darn well hold lol).

Food for thought....

you are right. this is actually what caused my last crash. hard and fast trailed turn in and right into the gas before letting it settle... just too fast on the transition between front wheel and rear wheel and they both overloaded from the lean angle

[EsrTek]

Moto- That dude is nuts in that pic!!
I read that before that a bike should do that, but have never seen anyone actually do it.
The skeptic in me wonders if that is just 1 pic in a series of pics, and the next one would show the rider ejecting himself from the bike :P

[rojoracing53]

Originally Posted by Sykes92

Thanks guys! I am still very new to the physics involved with bikes so every bit of information is greatly appreciated; especially if it helps prevent an incident down the road (pun intended)

We racers aren't physicists ether, we just magically make things with 2 wheels go really fast with methods we ourselves don't fully understand.

Or what CC said

[rojoracing53]

Originally Posted by alex.s

also, you'll never lose the front under acceleration unless you let the brakes off too quickly (which still isn't acceleration, its letting the brakes off too quick)

This is mostly right 95% of the time but I've accomplished that 5% a couple times it can be done. For reference both times were probably well over 100mph so nothing you'll ever get with a 250.

[alex.s]

Originally Posted by rojoracing53

This is mostly right 95% of the time but I've accomplished that 5% a couple times it can be done. For reference both times were probably well over 100mph so nothing you'll ever get with a 250.

i've done it with the 250.

i'm a pro crasher

[JA-Moo]

Once the lean angle wanted is reached, and your center of gravity is correct, as long as your speed is pretty much consistent, the bike will stay at that lean angle. Any kind of steering input will change the lean angle, so you are not actually "steering" if you are in a constant arc.

[csmith12]

Originally Posted by alex.s

i've done it with the 250.

i'm a pro crasher

I went down under WOT as well. It sucks....

[Motofool]

Originally Posted by EsrTek

Moto- That dude is nuts in that pic!!
I read that before that a bike should do that, but have never seen anyone actually do it.
The skeptic in me wonders if that is just 1 pic in a series of pics, and the next one would show the rider ejecting himself from the bike :P

Eric,

The bike is as perfectly balanced in that picture as it can be while rolling hands-off in a perfectly vertical position.

It is difficult to see, but as soon as we start cornering, our weight and the weight of the bike don't point vertically down as when we are standing on our feet.

The bike and our body act as if gravity was coming from an inclined direction rather than from a vertical one.
If you had a plumb hanging from any part of the bike, you would see the thing taking an angle.

For that very reason, we must lean the bike, aligning the points that support our weight (contact patches) with that inclined direction from which gravity is felt coming while cornering.

We cannot lean too much or too little, we lean what we have to for keeping the balance (just like we cannot stand more or less vertically on our feet).

We do choose the speed with which we take a curve, and then the necessary lean angle comes naturally for a new state of balance.

Link to original page on YouTube.

Link to original page on YouTube.