【PIRELLI】DIABLOMAN One Point Lesson: “Air Pressure for Track Riding” | News

Here’s a one-point lesson from DIABLOMAN.

Why do you lower the internal pressure when riding on the track?

Riders who participate in circuit track days, etc., should often lower the air pressure before riding. When returning home, please put it back to the regulated pressure.

I think I hear such announcements, but I just kind of do it, and I wonder how low I should go. or why? I think there are only a few riders who know exactly how much they should lower the bar, or who can accurately explain their decision depending on the situation.

DIABLOMAN will tell you! In a nutshell, it is to prevent the internal pressure from rising too high.

Well, that’s right. So why would the internal pressure be too high on the circuit if it is not lowered first?

The reason is that the air inside the tires expands thermally as the tires heat up due to the load on the tires from driving faster than normal on public roads and from heavy braking/cornering/start-up acceleration.

Do you understand? The cold internal pressure is lowered based on the assumption that the rider can put a load on the tire and adjust it according to that level. The amount of reduction is adjusted based on the assumption that the pressure will be lowered to the correct level when the tire heats up and warms up. This means that we need to be careful not to lower the pressure too much before we can properly load/load the rider and heat it up!

So it’s not okay because you made it the same as a fast rider.

The words “cold/warm” are used here to indicate the cold state of the tire before driving and the warm state when the tire is heated up after riding. What is really important is what the values are when the tires are warm during driving.

Also, the value when warming up the tires with tire warmers at the circuit, for example, may drop in winter if the pace during driving is slow, or it may rise further in summer due to high road surface temperature, and the amount of change will depend on the driving pace and rider skill. Therefore, in the top-level category, the internal pressure is checked after two or three laps in the pre-test and adjusted so that the pressure is stable at the proper value during riding.

It also depends on whether the laps are 15 minutes or 30 minutes in a row and the number of runs. The internal pressure does not always increase, and it will drop off after a certain value is reached, but if the motorcycle is run continuously at a high load for a long period of time, it will easily increase. Depending on the situation, it can easily rise by 0.3 to 0.5 bar or more when cold.

In addition, the pressure on the street is set higher by a margin for various reasons, such as to withstand the impact of crossing road gaps and curbs and to withstand the weight of two riders, which is why the required internal pressure is lower on circuits, where there are basically fewer road gaps for a single rider.

DIABLOMAN asks you to be careful not to lower the internal pressure too much because it is dangerous to imitate fast riders and racing tires with different case stiffness, construction, and compounds.

The role of internal pressure is to maintain the round shape of the tire and the profile. If the internal pressure is low, the tire will collapse, resulting in heavier handling and reduced turning ability, as well as increased drag and slower acceleration.

It’s easier to visualize this in the extreme, so imagine a tire that’s been punctured and deflated.
Overinflated internal pressure is akin to a flat tire.

Internal pressure also has the role of gripping the tire by the surface pressure that pushes the tire from the inside to the outside (road surface).

Increasing the surface pressure is one aspect of traction due to load/load, but in this case, the focus is on the internal pressure. Adjusting the internal pressure is similar to adjusting the suspension preload, and the tire can be considered a part of the suspension.

Stiffness due to structure goes hand in hand with spring rate. So, if the internal pressure is reduced too much under certain circumstances, the grip level is actually reduced due to insufficient preload.

It also changes the front and rear height in millimeters as well as the preload. Especially when the pace is not very fast, lowering the internal pressure increases the ground contact area and makes the rider feel more secure and grippy. However, it is just such a feeling, and although the ground contact area has increased, the surface pressure due to the internal pressure has decreased. For the same amount of internal pressure, a smaller ground contact area will result in more surface pressure on the ground surface.

Grip at low internal pressure means that the tire is relying on the rubber compound for grip, which means that the rigidity and surface pressure of the tire are reduced. It means that the motorcycle is running at a speed range that is just about sufficient for that internal pressure.

The ride quality improves as the preload is also removed. However, this is true at slower speed ranges, and the higher the speed range, the less dependable it becomes. This is the same reason why the suspension of a tourer vehicle is fluffy and the suspension of a sport vehicle is stiff. Of course, it is not enough just to have a firm suspension, it is necessary to have a high quality of suppleness in the stiffness.

Riding with a crushed front tire, as it is commonly called, is not similar to riding with a crushed front tire due to low internal pressure.

What is important is that the internal pressure of the tire has an appropriate value depending on the environment in which it is used,

Is it a single rider or a tandem?

Is it for city streets or winding roads at high elevations?

Is it a touring pace at a track day or a racing speed at a high-load circuit?

Is it a racing speed?

How many consecutive laps are required?

It is possible to maximize performance by adjusting the tires to fit the appropriate values depending on the tires used and the rider’s level.

How much to lower the tire or not depends on the type of tire installed, the rider’s level, and weather conditions, so please do so under the advice of someone who has the correct knowledge and can properly assess the situation.

Hmm? Does it depend on weather conditions? Yes, it’s well known that if you take a bag of chips with you when climbing a mountain, the bag will swell up due to changes in air pressure.

Similarly, tires are adjusted at the gas station at the bottom of the mountain, and if you go up the mountain to enjoy the winding road, you may not go flat, but the internal pressure may increase with elevation, but it will not decrease.

In addition, especially during cold weather, front tires, which are affected by cold road surfaces and cold winds at the very front, are difficult to heat and increase internal pressure, and front tires, which have less air volume than the rears, tend to be more severe in heat and pressure retention.

Also, on public roads, the specified air pressure tends to be higher in the rear, taking into account that two people are riding together, but on the race circuit, the front is often set a little higher.

Especially for advanced riders, who abuse the front end of the motorcycle through hard braking, if the internal pressure is reduced too much, the tires will be crushed too much and the front end will buckle and lose its ability to turn.

TPMS, a device that monitors internal pressure and air temperature in real-time while driving, is a standard feature on slightly upscale motorcycles these days and is a very effective way to monitor tire condition. There are two types of TPMS: one is to replace the entire valve and the other is to simply replace the valve cap.

It also has an alert function that alerts the user when the value changes beyond a set value, so it is effective as reassurance equipment since it can notice a flat tire as soon as possible.

I hope you’ll pay more attention to your tires and have a safe and enjoyable motorcycle life!

Original Source. [ PIRELLI Fan Site ]