The truth is, we don’t really understand why the swing arm is getting longer and longer.

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実はよくわかっていない「スイングアームが長くなっていく理由」A longer swing arm?

In fact, the swing arm gets a little longer with each run: ......
So why is it that so many vehicles are bragging about the longer swingarm every time a new model is announced? That's the story.
This should be especially true with a sport bike.

Somehow, he said, "Because it's better, right? Iloilo! And even if you understand that, what is that illo? The reality is that there are surprisingly few people who can explain it accurately.
Shh!
Knowing this will help you choose a potential transit candidate and give you a better understanding of the new model announcement article.
What you know will change the way you ride.This is not an exaggeration.

WebiQ is here to bring you a little happiness and motorcycle knowledge.
In this article, we'll talk about why the swing arm gets longer with each model change.
It's all over the place, it's all over the place.

Is it really getting longer?

When new models are announced, you may have seen descriptions such as "swing arm length 10mm longer than the previous model" along with a 0% increase in frame rigidity.
But even a chain adjustment can change that much, and isn't it practically at the margin of error: ......?

Indeed, the change in one generation due to the model change is slight.
But when it starts to build up over the years, the same manufacturer can make such a difference.

It is noteworthy that the swingarm is a percentage of the wheelbase (the distance between the front tire axle axis and the rear tire axle axis).
The YZF-R1 (from 2015) on the upper side of the image tries to close in on almost half of the wheelbase, while the SR (from 1978) on the lower side of the image appears to be around 35% of the wheelbase.
The fact that it took 37 years for the swingarm to get this long as a result of the manufacturer's best efforts to make it longer year after year, is a story that has happened to all manufacturers except Yamaha.

Isn't a long swing arm and a long wheelbase a disadvantage?

Naturally, to be compact and quick to turn, the wheelbase has to be short.
This is easy to understand if you think about it in terms of four-wheeled vehicles, and you don't have to worry about which one is easier to turn, a sports car with a short front and rear length, or a bus or truck with an extremely long wheelbase.
It's the same reason why the Super Sport has a shorter wheelbase than the American.
So simply extending the swingarm would also extend the wheelbase, which would inhibit its sporting qualities.

In other words, you don't want to extend the wheelbase for cornering, but for one reason or another, you want to extend the swingarm, which is a complete contradiction in terms of requirements.

Where do you absorb the longer swing arm?

The history of the evolution of sportbike bodies is how to extend the percentage of the swingarm in the same wheelbase? It is also the history of our pursuit of
The only way to extend the wheelbase, but not the swingarm, is to shorten the first half of the body.
So we have been trying to shorten the body of the car, and technology has evolved to make it shorter.
In other words, there's a reason you want to go that far to make the swing arm longer.

Now, of all the things that precede the swing-room pivot, the one with the largest occupancy is the engine.
This is where the technologies of various companies come together to shorten the length of the engine.
In the past, the crankshaft and transmission shafts (2 shafts) were arranged in a single row, but nowadays, the most common practice is to move one of the transmission shafts up and down and arrange them in a triangle.

Others include pushing the distance between the engine and the front tires to the limit, placing the radiator to the side to push the engine mounting position forward to the limit, and bringing the swingarm pivots and drive sprockets just barely close enough to each other.

The engine itself was designed to be shortened front to back, while the engine was mounted as far forward as possible ...... and all of the shortened bodywork was used to extend the swing arm.

Here's the gimmick! What is anti-squat?

Finally, let's get down to business.
The reason manufacturers want to extend the swing arm that far is because they don't want to lose the anti-squat effect of a well-moving swing arm when you have a supple footing setup that follows the gap in the road!

Well, I don't know!

Desjone!
I'll walk you through it, step by step!
I'm just getting to the point, but it's still a conundrum!

In the first place, a sport bike is better when the tires don't slip and grip and can accelerate at will.
To do this, the suspension absorbs the gap in the road surface andYou can keep your hand on the road at all times.You need.
In other words, you need a "well-moving suspension".

In addition, despite the well-running suspension, it must be able to withstand heavy loads while cornering.
We have been working on suspension settings and suspension installation methods, but the problem is the "force to contract the rear suspension (force to make the body roll backwards)" that is applied during acceleration.
It is especially important to open the throttle to get out of the corner when the suspension has shrunk due to overload and the rear tire is overloaded.

What I mean is: ......
The majority of bikes use chains to drive the rear tires, and when you accelerate, you're pulling on the top of the chain.
Then, as it is, the chain will try to shrink the suspension.

This is very troubling.
The more you open the throttle to get up from the corner, the more the rear tire tries to move away from the road.
When you want more grip by putting too much weight on the tire, it acts in the opposite direction to release the excess weight, which causes it to slip down.

There have been some elite people in the past who have come up with a great solution to it all at once.
After some friendly competition among engineers from around the world, we came up with a great arrangement: 'Place the swingarm pivot, drive sprocket and rear axle in a triangle to solve the whole problem.
That's the arrangement in the diagram below.

Can you see that the drive sprocket shaft (the pink dot on the left), the swingarm pivot and the rear axle are not aligned and are triangular in shape?
This arrangement will cause the following things to happen when accelerating.

    1. The upper side of the chain is pulled as it enters the acceleration regime.
    2. The grip of the rear tires tries to push the swingarm through the rear axle shaft in the direction of the swingarm pivot.
    3. However, the body is heavy and cannot be pushed forward easily.
    4. The power pulling on the chain tries to lift the swingarm pivot upwards (!) to find a place to go.
    5. As a result, the rear of the car lifts up (!!!) when it should be sinking in acceleration G.

What, so it's like ......, but it's true.
The rear of the car doesn't sink while accelerating, but rather lifts up.

This "axis arrangement that prevents the rear from sinking under acceleration" is collectively referred to as anti-squat geometry.
That's amazing, those old engineers, Eli!

Proof that the rear isn't sinking even under full acceleration

Even when you do a wheelie at full acceleration to the point where the rear tire gets dented, the rear suspension doesn't shrink as much as you might imagine, does it?
As a result of the balance between heavy load and perfect balance between the force to shorten the rear by acceleration G and the force to extend the rear by anti-squat effect, it is possible to maintain an excellent position with the three points almost in line and to accelerate.

If you look at the race scene, you can see that the rear of the car never sinks even when fully accelerating exiting a corner.
The front forks are stretched out as the overweight is released under acceleration, but the rear suspension is not shrinking, but is stepping on it.
Sometimes the rear suspension even extends at full acceleration.

When you ride, you will feel the "rear sinking under acceleration", but in fact, most of it is just a misunderstanding of the change in attitude caused by the extension of the front forks.

Why longer swing arms are better.

Did you understand about anti-squat?

By the way, the suspension is always in motion and the rear axle moves up and down among the three points for anti-squat.
The shape of the triangle is constantly changing, especially if the suspension moves well enough to grab the road and not let go.

If the swingarm is short, the all-important triangle can be reversed when the suspension shrinks due to stepping on a gap while cornering.
When the triangles are reversed, the suspension shrinks the more you try to accelerate, which is the worst thing that can happen to you.

How to keep the triangle in position as the suspension moves...
The answer to this question is to lengthen the swing arm.
With a certain amount of length, even if the axle position moves a little, it won't be an inverted triangle.
This is because if you step on the gap and the rear tire moves upward, the longer the swing arm, the less angular change is required.

In conclusion.For the same wheelbase, the longer the swingarm, the more elated you are.

And more!

If you can't make the swing arm longer, but you don't want to step into a gap and create an inverted triangle, you can also increase the angle of the swing arm.
The strategy is to lower the rear axle to a position where it will not form an inverted triangle even if the swing arm angle moves significantly.

You can certainly get the benefits from this: ......
It's another bad thing that happens.
Look at the image below again.


The intersection of the upper orange line showing the upper side of the chain and the lower orange line connecting the rear axle to the swingarm pivot is outside the frame on the left side of the screen.
There is a blue line connecting this intersecting point to the ground point of the rear tire, and the driving force generated by the tire ultimately acts in this direction.

It is important to know what percentage of the blue line penetrates the distance between the body center of gravity and the ground directly below it.
For example, if the blue line runs through 50% of the body's center of gravity, including the rider, then 50% of the driving force is broken down into the force to move forward and the other 50% is broken down into the force to buckle the body (the force to sink the rear).
If the car is going through 100% of the body's center of gravity, all the driving force will be pushing on the center of gravity, so there will be no force to sink the rear of the car at all.

And as you increase the angle of the swing arm, can you see how this blue line rapidly turns upward?
The force to sink the rear, which usually occurs to some extent, is less likely to occur, and the anti-squat effect of the chain is greater, so the force to lift the rear is excessive when accelerating.
The result is a very difficult vehicle to drive.
(A mechanism that allows the swing arm pivot position to be adjusted up or down is used in a very small number of super sports vehicles to solve this problem.

The longer the swing arm, the less the angle change when you move, so this relationship of "where the driving force passes through" is less likely to change significantly.
In other words, the characteristics of the bike are less likely to change with changes in load.
As a result, the characteristics of the body are less likely to change with the curvature and speed of a corner, resulting in more stable handling at all times and in all places.
It's safe to ride, stable and fast.
That's why bike manufacturers are desperate to make their swing arms longer.

Longer swing arm = more stable and fast vehicle characteristics.
In conclusion.For the same wheelbase, the longer the swingarm, the more elated you are.

An easy ride height adjustment can ruin everything.

The anti-squat theory was established rather recently, in the 1980s.
In the 70s, there was still a lot of hesitation, and some bikes had a drive sprocket and swingarm pivot that were coaxial.
I guess I was looking for drive efficiency rather than an anti-squat effect, but it fails spectacularly.

The angle of the swing arm, which is such an important reason, and the length of the swing arm to reduce the change in angle, but as you wise folks have already guessed, if you raise the rear ride height for looks, the above "more! The same thing happens in the same bad situation I wrote about in
The rear ride height tends to be raised for a variety of reasons, such as the ass being up and cool, the rear being up and the caster standing up so it's quicker, the front load being up, etc., but you should know that even the slightest change in ride height can have a very big impact.

Also, the story is quite difficult to follow this time, but even this one is pretty much on the edge.
It's actually much more complicated with a lot of factors involved, so why bother if you're curious?
It's all over the place, it's all over the place.


At the end of the day, I don't deny that what's cool is different for everyone and that you should focus on looks, but please think carefully about what impact it will have and keep it out of harm's way.

 

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