Everyone perceives the sense of grounding differently.
I believe that ground contact describes the feeling of being confident that the tire will grip. This is a venerable problem for riders, and most of us have used or heard of it, but different people seem to have very different images of it.
Some may vaguely define ground contact as the feeling that the car will grip or the feeling of security that it is not likely to slip. Others may define ground contact as the response of the tires when braking, applying traction, taking a corner, or applying a load. Others define ground contact as the way the tire slides at the limit.
None of these are wrong, and I consider all of them to be included in the grounding factor. But it is also undeniable that they are not in the realm of sensory impressions.
I'm looking at changes in self-aligning torque.
So what I have been focusing on is the response that hangs on the handlebar grip. In fact, ground contact is often mentioned in reference to the front sensation.
As the tire withstands centrifugal force and bending force is generated, not only the tire but also the tread surface is distorted, so that the ground surface is left behind on the inside rear side. This may be difficult to understand, but at any rate, consider that grip occurs largely on the inside rear portion of the ground contact surface.
This causes the tires to generate self-aligning torque that reduces the misalignment angle (slip angle) between the direction of the tire and the direction of travel, and tries to restore it to its original position. This torque is then transmitted to the handlebar grip.
In a situation where firm grip can be demonstrated, the response changes linearly when attacking a corner. Therefore, you can have confidence in attacking. We believe this is one of the major elements of ground contact. If you are approaching the limit of your grip, the response will tend to head down.
However, there are pitfalls in this concept as well. If we mistake what is caused by steering effort for a response, we can suddenly lose the response or slip down.
Therefore, I have not only this big picture, macro view of the response, but also a micro, micro view.
Since the bike is constantly changing direction in small increments and the road surface is not a mirror surface, this response is changing in small increments. Therefore, by feeling this waveform, we can grasp the sense of ground contact. If these minute changes are not enough, the sense of ground contact will be weak.
And the viscoelastic feeling transmitted from the tire may be the basic element of ground contact.
This kind of ground contact is also the ground contact that is supposed to be sported. But tires convey a sense of grounding even when they are just rolling.
Tires made of rubber are viscoelastic. Like an elastic spring, it not only flexes in response to load, but also has a viscous element that sinks and returns in a jiggle. The tire flexes at the ground contact point, returns to its original position, and then flexes again after one lap.
Moreover, the road surface is not a mirror surface, and the flexing sensation is always felt. At that time, if it is a proper tire, the flexing has a viscoelasticity that is typical of rubber. This is also the sense of ground contact.
In extreme cases, a tire whose rubber has deteriorated over time has significantly lost its viscoelasticity, and a sense of ground contact cannot be expected. Since the entire tire is covered with rubber, rubber deterioration greatly affects not only the tread but also the overall flexing sensation.
In any case, under poor conditions, the tires cannot be expected to flex, and a sense of viscoelasticity cannot be conveyed. This is what alerts the rider to an abnormality in the sense of ground contact.
This means that in order to grasp the feeling of being grounded, the entire body, not just the arms, must be relaxed. On a cold day, the sense of ground contact tends to be less. It may take some experience to correctly determine whether this is because the tires are really hard or whether the body is just stiffened by the cold.
