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When the steering wheel is turned and the turning motion is completed, if the hand is released, the steering wheel automatically tries to return to the vicinity of the center. This phenomenon is mainly due to the casters provided in the suspension mechanism. It is the result of factors such as camber, kingpin angle and scrubs interacting with each other. In other words, an automatic restoration mechanism that tries to return to the center position is provided, which helps maintain and stabilize the straight running state.

However, when it has a deviation in the thrust, it keeps going straight while always correcting the deviation, and it is running in an unstable state that always needs correction.
If the vehicle is disturbed by the unevenness of the road surface, the balance will be lost and the driving direction will be disturbed and a correction steering wheel will be required so often. Repeat this several times, that is, the handle causes a hunting phenomenon near the center and wobbles.

Also, when starting and stopping, weighted movement occurs with respect to the front axle, so if there is a shift in the thrust, the amount of countersteering will always change and a correction rudder will be required. Since it starts to move, it is necessary to hurry and steer in the opposite direction again.
Exactly the same phenomenon is repeated every time the vehicle starts and stops. The amount and direction of the thrust shift is the same, so this phenomenon follows the Laws of Physics.

Most drivers would have given up because of the disturbances caused by the fraudulent road surface on the left side of the road, but that's not the case.
When the thrust does not shift, you can drive Extremely stably and comfortably. This is a feeling that you can not verbalize unless you actually drive a Zero Thrust Car and experience it.

The decision of zero thrust is whether you can take your hand off the steering wheel and stop?
Can you be nervous when you enter the tunnel during the daytime driving?
Can you take the cigarette out of the box, hold it and divert your eyes to ignition?

Looking at the mass and support structure of an automobile from a Physics point of view, there are many elastic bodies from ground contact to heavy objects, and it can be said that all of them are always in an antagonistic relationship. If you let it collapse, the antagonism will collapse, and all the other parts that were antagonizing will displace and cause position movement according to "the law of action & reaction".

From another point of view, that the weight 200 kg or more from the tire to the engine & transaxle mount to arm and link bush supports through movable and eligible floating materials. You will be forced to make precision mechanical adjustments in a floating environment with viscoelasticity supported by rubber materials.

Ordinary small cars are about 1.5 tons. It is necessary to move this delicately to loosen and tighten bolts and nuts such as 17mm and 19mm while considering the position movement due to friction. Under 1G conditions, a 4-post lift is available. If necessary adjustments are made, the tension friction on the tire contact patch will change as described above, so the vehicle must be moved back and forth to release stress on the tire surfaces. The driver's seat has a balance weight of 60 kg burdened, so moving vehicle is performed by human power with gear neutral. The measuring device that is manually performed is removed and installed each time repeatedly. It consumes physical strength, but the concentration of energy cannot be resolved. It is a different dimension of the battle with oneself, which is completely different from the periodical maintenance work such as regular inspection and parts replacement.

Such barren work unknown when to finish can be solved at once by installing only one adjustment mechanism! It is the introduced a thrust trim adjustment mechanism! Although the purpose and concept are different, MB company's luxury model 4WS mechanism is currently adopted in it. It is true that it costs money to introduce the trim, but it is equipped with a meaningless idle stop system for a while with the intention of the Government. On the other hand, this is an indispensable device at any rate, and if it is mass-produced, the cost should be reduced.

As an airplane pilot always make trim adjustments after takeoff and climb without exception, so a car driver can also make thrust adjustments so that he can drive safely and comfortably under the load conditions at that time. I do wonder why they don't do it? I'm sure that the engineers in this field should know about this truth and fact, they do not take action because the automobile users never argue about this critical problem.

As mentioned before, it is impossible and hopeless to keep the thrust angle at Zero degree by measurement and adjustment.
The captain of a light airplane that does not have an automatic device by a computer, adjusts his trim according to his own feeling, and in the case of an airplane that flies horizontally, the opponent is air and must be balanced three-dimensionally. On the other hand, in the case of vehicles, it is friction with the road surface with slipping resistor and is balanced on a two-dimensional plane.
To be honest, I took a sneak peek at the measurement and adjustment of the thrust while considering them, and when I actually went into the scenery, there were many uncertainties, and I had an incredibly furious difficulty in the working. And it was not something that an outsider amateur could do, far from reality!
As a result of more than 20 years of insistent and repeated trial and error, I have experienced more than 10 different cars while that time and finally came close to be able to do something like that recently.
When measured several hours after the start of the measurement, I also took several years to figure out why the data was deviated so much, but this was mainly due to spot deformation of the tires parked in a place for long period of time. I learned that this effect could be dealt with by increasing the tire pressure for convenience.
Even if the thrust angle is brought to zero at that moment from the state where it exists, he has all kinds of bushes, including the release of pressure displacement and the change and wear of the tire ground surfaces, and other fluctuations occur, which cannot be achieved only by one measurement and adjustment.
It's a barren world that has to be repeated endlessly.

All industrial machine products are made while allowing a certain error. There is a tolerance for each component machine element, and there is an assembly error in which errors are accumulated as a result of assembly. This latter error is a variation of the product and is set as a tolerance value. The smaller the tolerance value is, the higher the precision of the machine will be, and the higher the cost will be. This tolerance is stipulated in detail in the JIS standard as a machine element.
An automobile can be regarded as an industrial product that combines many mechanical elements, but it is employed many rubber parts for tires, axle arm connections and engine support parts for the purpose of vibration and sound insulation.
As for the rubber material used, often used NBR, IIR, etc., but it is inevitable that it will be deformed and deteriorated due to aging and continuous pressurization.
In addition, there are physical characteristics peculiar to rubber, which makes it difficult to adjust and maintain the desired value of the axle.
Among the characteristics, viscoelasticity and pressure displacement and the hysteresis characteristics associated with them, the displacement quickly recovers when the external force is removed. However, there is some residual strain, and it takes time to recover as it's original figure. It shows two-step or several-steps deformation recovery characteristics.
In addition to the product variation due to the assembly tolerance as a machine mentioned above, the existence of many built-in rubber parts makes it difficult to measure and adjust the wheel alignment of an automobile and maintain the set state.

I'm happy to be able to enjoy ASO regular concert # 94 for the first time in two years tonight.
I was very impressed to find that the instrument being played was visible near at hand because the seat was in the center of the front of the first floor.
In the first half, Liszt's symphonic poem Les Preludes showed a well-balanced balance of his rhythm harmony melody and remarkable progress over the years in his ASO. I appreciate the conductor, Kazufumi Yamashita!
In the 4th movement of Mahler Symphony No. 5 in C sharp minor in the latter half, there was a rare harp performance, and the sound of a large, large-capacity stringed instrument that I listened to for a while with a wonderful tone was unique and peaceful~.
I'm looking forward to the autumn concert, thank you!