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Quick Turn Clarification


jps600rr
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I have a question to clarify the quick turn in, the bike is flicked quickly to high lean angle,

and a split second later the throttle is opened, this leads to an overall higher speed through

the turn because the bike is leaned over a lot at the start of the turn, and you cannot start the throttle opening until the bike is leaned Also you set you lean angle at the turn point for the whole corner?

 

I find that a quick turn is acheived by hanging off, and pushing the bike away keeping in a straight

line, and then just let it drop, but I usually find that I increase the lean angle as I reach the apex.

at the end of the turn I have a higher lean angle compared to my lean angle entering the turn.

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Hey tfc600,

 

Quick turn in is acheived by quick counter-steering.

 

For me, hanging off prior to turning in eliminates needing to shuffle about on the bike while turning in. Changing all the weight distribution or center of gravity at the same time that I am trying to turn the bike is distracting for me. Having the center of gravity preset and stable makes the turn in easier and more confident for me.

 

As for lean angle(s), I have heard it said that there is a two step process to the "turn in" itself. The counter-steer to drop the bike over and then a slight adjustment to acheive final carving angle. But, I am less than completely clear on that. I just know that the faster you counter-steer the handlebars, the faster you get turned in. And the sooner you get to final carving altitude, er, final lean angle, the faster you can go.

 

I'll have to let someone else take the other lean issues.

 

Cheers,

R

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How quick (or how hard) can you countersteer, without losing the front?

I deliberately countersteer, but too, would like to turn in faster.

 

In Twist II, Keith talks about the average roadrider versus the pro racer, in terms of how long it takes them to go from upright to full lean angle, I don't have the book with me right now, but I know its about a second for the pro's.

 

Just how hard are they pushing that inside bar? What are the limits? when you crash?

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Hey Alan,

 

Technically, the limit to how fast a rider can counter-steer is defined by how hard one can push/pull on the handlebars.

 

The limit to the amount of force that the front tire can take is based on the amount of available traction at the front contact patch. On a TZ250 with hot race rubber, that limit is going to be pretty darn high IMO.

 

At high speeds, more effort is required to turn a bike in and I will actually brace the counter-steer push all the way from my feet. And will even pull on the other bar as well.

 

Honestly, I have never over-steered myself into a crash by flicking the front out from under me so hard that the bike lost traction from the flick.

 

I suppose it is possible if one is quite strong in an off-camber corner or limited traction conditions like rain or a slippery surface or cold unscuffed new rubber.

 

Bottom line, in my opinion, you can flick pretty darn fast on a 250. The bike can probably flick faster than you or I can...LOL.

 

 

R

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Hi Alan,

 

Counter-steering is a skill riders develop confidence in with practice and incremental increases in effort. However, since I can't offer a scale for effort, perhaps I can offer a scale for time...

 

The average street rider's turn in time is around ONE second.

 

I believe students get right down to a HALF second.

 

I would say that a fast racer's turn in time is around a QUARTER of a second.

 

Is that better? At least it is a real scale and a target to aim for. Let me know what you think.

 

Good luck,

Bill

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Hi Alan,

 

Counter-steering is a skill riders develop confidence in with practice and incremental increases in effort. However, since I can't offer a scale for effort, perhaps I can offer a scale for time...

 

The average street rider's turn in time is around ONE second.

 

I believe students get right down to a HALF second.

 

I would say that a fast racer's turn in time is around a QUARTER of a second.

 

Is that better? At least it is a real scale and a target to aim for. Let me know what you think.

 

Good luck,

Bill

 

That's about what I thought, I guess the faster you can turn, the entry speed can increase? I am a very lazy turner! need to work on that too. I will have a very busy day on the track in a couple of weeks, but I'm listing the things that I want to work on, then them out one at a time. 1. Quicker turn in 2. Increase throttle sooner on exit. 3. etc etc etc.....

 

Oh, off subject I know, but my buddies and I are in constant conflict over when accelerating out of a corner, does the rear rise, or squat?? any thoughts?

 

Sorry it's off subject.

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Hey Alan,

 

 

Quick "turn in" or "flick" allows a bike to use less lean angle for a given speed and corner.

 

The longer it takes to get to max or final lean angle, the later a bike begins to actually carve the radius of a corner and the more lean angle will be required to complete an effectively tighter radius.

 

A slow "turn in" deepens the effective turn point by the distance traveled while executing that slow motion "flick". This prevents the novice from realizing how much speed they could carry as they must use excessive lean angle to get through the rest of that corner which leads to premature dragging of bike parts and the perception of being "fast". The "quicker flicker" drags nothing on the same machine, at the same speed, in the same corner.

 

 

As for the rear squat vs rise argument...

 

(I am going to disregard tire growth under extreme acceleration as I feel it is a secondary issue.)

 

While acceleration does transfer weight to the rear, the triangular relationship of the swingarm pivot to the rear axle and the angle of chain pull from the front sproket will determine what and how much effect acceleration will have at the rear suspension.

 

From a side view, the drive chain applies forward force to the rear end of the swingarm which forms a lever with the fulcrum located at the swingarm pivot. Ideally, the swingarm pivot would form a straight or nearly straight line between the front sproket and rear axle (at sag with rider) to minimize affecting the rear suspension under acceleration.

 

When the swingarm pivot is above a line drawn between the output shaft and rear axle, the forward force of the drive chain will also apply a downward force (angular moment referent to the pivot) to the swingarm (and try to extend the rear suspension) under acceleration. Whether or not the rear of the bike actually goes up or not, the downward force applied at the rear of the swingarm impedes compression of the shock. While (the bump in) the road is pushing up on the shock, the chain is pulling down on the shock, effectively making the rear suspension stiffer or harder. (This will also affect traction and tire wear.)

 

(If the swingarm pivot were below the line between front and rear sprockets, the chain pull would try to compress the rear suspension and impede rebound.)

 

All the motocycles I've ridden fall into the first non-ideal category of the rear getting harder (or attempting to rise) under acceleration.

 

Kawasaki were experimenting with adjustable eccentric swingarm pivots on their superbikes to sort out the ideal geometry 10-15 years ago. I recall some talk of this "idealized" geometry research being incorporated on production sport bikes.

 

Note: Trying to change the rear geometry with rear ride height or spring pre-load will affect the front geometry and the proper functioning of the rear shock.

 

 

A last off-topic thought about swingarms and chains...

 

The rear axle describes a vertical arc through the travel of the suspension which means that the rear axle will be at its furthest point from the countershaft when the rear suspension is compressed in line with the swingarm pivot and output shaft. It is best to adjust chain slack to accomodate this level of compression of the rear suspension. Or you could end up breaking your chain on the first lap of a 24 hour endurance race that you should have won... :angry:

 

 

Of course, Keith Code has written extensively on these topics in his The Twist of the Wrist series as well as on this website. (And I am sure he could give you a simple yes or no straight answer to the question of squat vs rise. :P )

 

 

Cheers,

Bill

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For anyone who cares, my last post of cobbledy-gook has been somewhat edited for clarity and brevity. Thank you for your patience during this time of personal difficulty. :blink:

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Wow!

 

Ummm, I'm gonna have ta print that and sit down with a coffee (or a cold beer) and study that reply.

 

That reply was quite amazing and I think the bike rises? that's what I'd been led to believe. Can you mimick this by puttting your front wheel against a wall and then letting the clutch out?

 

(I will read it again)

Why do commentators (including ex pro racers) talk about rear squat when accelerating from a turn.

 

Bill, we need you in NZ for some coaching. :)

 

Actually next weekend when I go to the track there is a training day on the saturday. We are practicing all day friday, training day sat and racing on sunday.

 

Time for new pistons soon after that lot!

 

Cheers Bill.

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Alan,

 

Keith posted that same front wheel against the wall example on another thread here. It does isolate the relative action well. Maybe I can do a search for it and copy/paste it in.

 

I can't comment on the words of commentators or ex-pro racers.

 

However, the feeling of weight bias to the rear combined with the front getting light or "coming up" under acceleration could contribute to the perception of squat. The "up against the wall" example would remove it from the equation, which then begs the question of whether or not the rear weight bias under accel can overcome the angular moment created by the chain pull at the rear of the swingarm. My gut feeling is a big NO. Even a few hundred pounds of weight will be overcome by the horsepower being applied there. How much does a horse weigh? :P

 

That said...

 

With the front wheel against the wall, I think the rear would perceptibly rise to the naked eye.

 

 

It is my opinion, finally, that the pertinent point is the effect on the rear suspension. Regardless of whether the rear appears to rise or not.

 

 

Thank you very much for your kind words. I'd like to think I'd make a good coach anywhere. But, NZ is good. ;)

 

Thank you Keith for your years of dedication to sorting it all out and writing it all down. And providing a forum for relationships like this.

 

 

Cheers,

Bill

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I'm an engineer, not a racer, but the rear squatting thing under accelleration is not so difficult to understand and really not complicated. Acceleration merely transfers weight from the front to the rear. A lot of acceleration produces a wheelie and then you have 100% transfer. The weight transfer compresses the rear suspension resulting in squat at the rear and rise at the front.

 

The opposite happens when you decellerate using the front brake. The front dives and the rear rises. 100% transfer results in a stopie.

 

If you push the front tire against a wall the rear should squat and the front rise also.

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I'm an engineer, not a racer, but the rear squatting thing under accelleration is not so difficult to understand and really not complicated. Acceleration merely transfers weight from the front to the rear. A lot of acceleration produces a wheelie and then you have 100% transfer. The weight transfer compresses the rear suspension resulting in squat at the rear and rise at the front.

 

The opposite happens when you decellerate using the front brake. The front dives and the rear rises. 100% transfer results in a stopie.

 

If you push the front tire against a wall the rear should squat and the front rise also.

 

And if you push the front tire against the wall with the engine running and start to let out the clutch, does the rear end squat? That's the easiest way to start to understand the effect of engine power on the rear during acceleration.

 

(And NO, it does not squat.)

 

There are multiple forces that you have at your disposal to use to your advantage. You can argue the physics until you are possibly convinced on how to do it completely wrong, or you can start with some basic theories and ideas and see how they work when you are actually riding a motorcycle.

 

Theory without application is worthless, but a lot of fun in the off season. ;)

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I'm an engineer, not a racer, but the rear squatting thing under accelleration is not so difficult to understand and really not complicated. Acceleration merely transfers weight from the front to the rear. A lot of acceleration produces a wheelie and then you have 100% transfer. The weight transfer compresses the rear suspension resulting in squat at the rear and rise at the front.

 

The opposite happens when you decellerate using the front brake. The front dives and the rear rises. 100% transfer results in a stopie.

 

If you push the front tire against a wall the rear should squat and the front rise also.

 

And if you push the front tire against the wall with the engine running and start to let out the clutch, does the rear end squat? That's the easiest way to start to understand the effect of engine power on the rear during acceleration.

 

(And NO, it does not squat.)

 

There are multiple forces that you have at your disposal to use to your advantage. You can argue the physics until you are possibly convinced on how to do it completely wrong, or you can start with some basic theories and ideas and see how they work when you are actually riding a motorcycle.

 

Theory without application is worthless, but a lot of fun in the off season. ;)

Dang. I was wrong in that the front doesn't rise because the wall is compressing the forks due to the trail angle. This may give the impression that the rear is rising and the front squatting, but the weight should transfer toward the rear wheel. I now also see that the rear wheel traction has the effect of unloading the rear shock and spring which may totally counteract the loading of the rear shock from weight shift to the rear.

 

I was overlooking the suspension geometry.

 

So I concede, you're right. :blink:

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Hey Tim,

 

Specifically, it is the drive chain force being offset to the swing arm.

 

A picture is worth a thousand words.

 

Sit down on the ground next your (or any) bike and look at the angle of the top of the chain compared to the swingarm. They aren't parallel. With the pivot acting as a fulcrum, the chain applies angular moment to the swingarm.

 

Being stationary against the wall effectively isolates this by removing weight transfer due to acceleration. Even if the forks compress while the bike is stationary, any forward weight transfer or "unloading" at the rear will be scientifically insignificant. Probably less than 1%.

 

Well, that's getting better, eh? Pretty soon I'll be able to say it in one sentence of plain english.

 

 

Racer

 

 

Then again if the chain rides on top of a chain guide over the pivot...oh man I gotta go look at a bike. I'm starting to psych myself out...lol.

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OK...if you search the word squat on the forum, it results in a thread titled "weight transfer...does the rear really go up?"

 

In that thread, the last post is by Keith and he relates the story of Eddie Lawson and the chain rollers and almost verbatim what I said just above.

 

Good kid that Keith. Taught him everything he knows... :lol:

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Again on the rear squat v rear rise issue:

 

Today at work I had a discussion about this with 2 colleagues ( I work at a Triumph dealership) they thought I was raving mad to think that a bike rises on acceleration

 

As it happened we had a bike on the dyno machine being put through its paces .......and guess what....the bike was clearly rising as it was accelerating!

 

They both looked at me in disbelief...... I, on the other hand.....looked at them with a smug grin!! B)

 

Bill I printed out your theory for them to read, it made sense to them to, kinda ;)

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Hey Alan,

 

Excellent example!

 

I was going to mention the dyno but didn't think that most folks had access to one or even the experience of ever having seen one in action to be able to relate to it. But yes, that is a perfect example and since the forks are already tied down it further isolates the action by removing the forward force against the wall as a variable that might lead to confusion.

 

You should have bet your mates a little sponsorship money. :D

 

Anyway, aren't you supposed to be at the track? Or is that next week?

 

Cheers,

Bill

 

PS: My "theory" as it stands needs serious editing IMO. :P It boils down to the chain not being parallel to the swingarm. And it isn't really MY theory. Just an observation... made before by others like Keith Code. ;)

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Something to think about - the counter-steer means to go right you are turning the wheel left. So now think about where the front wheel is going and hwere is can skid when you "flick." The "quick flick" is caused by the wheel going left. Once you are there, the wheel then returns along its path, straight and then right to lift the bike up and exit.

 

If you "flicked" so hard as to break the front free, you'd likely be doing that when you turned left to "flick" (assuming a right hand turn.) The skid would be caused by the relative angle of the front tire to the direction you were moving in. In this example, it was moved left of the movement of direction. When you turn the wheel straight as thebike leans over, you are decreasing the angle and hence ending the "front wheel flick skid." Think of skidding a front wheel drive car on ice. Same thing somewhat but the end of the flick is the resolution of the skid.

 

Now you say, sure I flick the front skids and when I turn the wheel straight I'm still goingt straight because the skid did not let the bike turn. Not so. The movement of the front wheel to the left is what leans the bike right - go play with a bicycle wheel if you have never expereinced this. The front wheel's contact with the road means nothing. But what about turning won't you still go straight? Sure, if the skid never ends. Your bike is turning because of the displacement of the CG relative to the bike's direction (more or less - a diagonal from the rear contact patch roughly 2/3rd up the front suspension.) Does this mean you can corner with the front wheel skidding? No, because as soon as you are leaned over and "turning" the front needs to oppose the forces that want to send you flying off on the tangent. The skid resolves it self - to the extent you can make it skid - by virtue of your susbequent actions in the corner.

 

If any of this makes sense to you, you'll realize that you can "flick" the front free and it will unskid when you end the flick because the reason for the limited skid is over in an instant.

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Hey jrfuisz,

 

 

If the front wheel was skidding, wouldn't there be hundreds and thousands of little skid marks on the pavement at the turn in point of a corner? I might be pushing a tad, but, in any case, I think the friction at the contact patch is an anchor for leaning the bike.

 

 

The "bicycle wheel" experiment you refer to demonstrates something called "gyroscopic precession".

 

Essentially, if one applies torque to the axis of a spinning body, mass or wheel, the axis will deflect at ninety degrees to the plane of rotation and applied torque. In plain english, when you steer right, the spinning wheel will lean left.

 

Step one: Grab a bicycle wheel and spin it up and hold it in your hands by the axle. Step two: Move it around and have fun.

 

You will notice that when you turn the wheel right, it leans left. If you turn the wheel left, it leans right. This is precession.

 

The precessional force is significant. Consider the mass of a motorcycle wheel compared to a bicycle wheel, multiply by say 30 mph or more and you are talking orders of magnitude.

 

Of course a motorcycle is more massive than a wheel and there is forward momentum and inertia and another gyroscope at the rear...

 

I haven't been able to work it all out in my head yet. It may be too complex to do without some more study.

 

 

 

As for your statement:

 

"Your bike is turning because of the displacement of the CG relative to the bike's direction (more or less - a diagonal from the rear contact patch roughly 2/3rd up the front suspension.)"

 

I'm not quite clear what that all means.

 

But, I think the traction at the front wheel is important no matter where the leaning force comes from.

 

 

Racer

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Some more of my thoughts on the above issues.

 

The rear rising during accelleration is due to frame (swingarm) geometry. Although there is weight transfer to the rear, it is more than offset by the torsional bending tending to rotate the swingarm downward. Force causing the bending is the horizontal traction force at the rear wheel.

 

The quick turn is (in my humble and often screwed up) opinion, initiated by gyroscopic precession. When force is applied to turn the wheel left the precession force causes it to respond by immediately leaning to the right and this is what initiates the turn to the right.

 

Also note that there is physically no problem with going from a straight line to a turn instantaneously. The limitation is in the ability to quickly lean the bike. Hard countersteering accomplishes this.

 

(I think that's pretty much what racer said above)

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I should clarify - I don't think you can turn the front wheel fast/hard enough to make it skid. Even if you could, you'd be correcting right away so it appears to be a fear issue. I think that is why Code tries to get you to flick as hard as you feel comfortable with.

 

As Code says, the faster you flick the less you need to lean (less wasted road of sorts.) So if you can flick fast, you can run deeper and extent the straight. I suspect the best late brakers are really also great flickers. They can get the bike turning with less road. If you can flick fast, you can pick a later braking end point and pass the slow flickers in the corners.

 

For those of us who don't get to the track, in a panic situation when you come in hot, it appears you need to think fast flick to save as much road as possible.

 

One thing in skidding - I'm my mind - a skid on a cycle is dictated by speed and lean angle. That being said, if you flick to a lean angle and a speed that the wheels can't hanle, you'll skid. Then the issue is balance etc., and whether you are backing the bike in - dirt track style, which is always a fun thing to learn to do on a small dirt bike at least. BUt even then, assuming your balance is good, the bike will naturally deal with the skid, you just need to turn out of the skid when you've scrubbed enough speed.

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Hey Tim,

 

 

We seem to be on the same page regarding squat vs rise. However, I don't quite agree with your description of the why. Even though I am far from an expert in physics, I will try my best to explain and illustrate what I think are the mechanics of it.

 

 

In a nutshell, the driving force is the chain, and the resistance force is the contact patch.

 

When considering movement of the swingarm due to acceleration, the amount of resistance to rotation at the rear contact patch acts like an anchor point. If you make a line drawing with two lines, one for the swingarm and another line drawn from the contact patch to the axle, the chain pulls forward and down on the middle (axle) due to the offset of the chain from the swingarm. Linear force is applied by the chain at an included angle (inside the angle of the two lines) at the end of the swingarm to the degree that the rear wheel provides resistance.

 

If the bike were suspended off the ground the swingarm would still pull down under acceleration. The effect would be most observable in first gear from a dead stop. The mass/stationary inertia of the rear wheel would provide some resistance for the linear offset chain to pull against in direct proportion to the mass of the rear wheel (or mass distribution of the rear wheel for physics experts). The more massive the wheel, the more effect the chain would have on the swingarm under acceleration.

 

 

Back on the ground, the mass of the rest of the bike on the contact patch provides major resistance for an even more effective anchor point, so to speak, allowing the offset chain to pull still more on the swingarm at an angle. If I simply pinned the chain to the end of the swingarm it would do the same thing. Due to resistance at the rear wheel, the chain is being variably pinned to the swingarm under acceleration. The chain force is divided between rotating the wheel and what "spills over" or is released through swingarm rotation or deflection. The more acceleration, the more resistance, the more swingarm deflection. As the wheel spools up, the resistance drops and the chain force on the swingarm declines.

 

 

So that covers the normal bike with an offset chain.

 

 

In the parallel chain scenario:

 

 

If the chain is parallel to the swingarm rather than offset, the force/reaction will be entirely rotational at the rear wheel (axle) with no offset linear component from chain pull. And, technically, the bike is now more efficient.

 

Hang the bike back up in the air. Will the resistance of the mass of the wheel still provide an anchor for the chain to pull the swingarm down? No. There is no offset.

 

Back on the ground, the entire chain force is applied parallel to the swingarm at the top tooth of the sprocket to rotate the wheel or rotate the swingarm and bike up and around the axle. (Wheelie.)

 

The radius of the sprocket is a lever for the drive force of the chain. The radius of the wheel is a lever for resistance.

 

With the front end (up against the wall) held down and back with infinite resistance, and without the offset angle of the chain acting on the end of the swingarm, the length of the lever for the chain force to act becomes the RADIUS OF THE SPROCKET (approximately three inches) for a force acting parallel to the swingarm attempting to either rotate the wheel or rotate the swingarm and the entire bloody bike up around the axle (wheelie). (As opposed to the chain force acting on a lever the length of the swingarm pulling DOWN against the shock while up against the wall.)

 

In this scenario of a parallel chain up against the wall, the rotational force applied to the three inch lever of the sproket would break the chain, break the sprocket or spin the tire before creating lift in the rear.

 

Only by the pivot coming up could the swingarm go down, and in that case, the chain is no longer parallel to the swingarm and it is again an offset linear component.

 

 

 

phew :blink:

 

 

 

I will edit for clarity and brevity. I know there is much redundancy and wordiness. Especially in the second half. But, I think it is essentially coherent if not cohesive enough for now. I am sure there is a chapter somewhere in Twist of the Wrist (if not a single paragraph) that spells it out better. :P

 

 

 

 

Cheers,

Racer

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Racer,

 

I agree. As I stated earlier, I am an engineer (structural) and analysing force systems is something we do routinely. It really isn't necessary to bring out all the details of the forces in the chain, sprocket, swing arm, etc. If you just look at the forces acting externally on the bike (wheels) then you can visualize how the bike will respond. If the bike is stationary and pushing on a wall the front wheel has the bike weight component acting upward vertically thru the center of the axle and the wall is pushing backward horizontall also through the center of the front axle. The extra horzontal force compresses the forks and the front squats. The rear wheel also has the weight component pushing vertically up thru the center of the rear axle, but now has an additional horizontal force at the contact patch which is equal to the force pushing on the wall at the front.

 

The horizontal force at the rear contact patch tends to rotate the swing arm downward causing the rear of the bike to rise.

 

If the bike is free to accellerate forward (not against a wall), the only difference will be that the front will rise, instead of squat, because there is no horizontal resisting force on the front wheel, and there is the overturning moment caused by the inertia of the bike thru the center of gravity of the bike acting rearward. This overturning moment unloads the front wheel and the front rises as the forks expand. The rear rises also because the forces acting on the rear of the bike are similar to the situation when the front is pushing the wall.

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