The Science Of Tires: Part Three

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Article By Chris Callen Photos By: Heather Callen

Originally Published In The June 2018 Issue Of Cycle Source Magazine

Last month we picked up on part 2 of our Science of Tires segment where we visited the world headquarters of Metzeler Tires. As usual when I get to do something cool, we had to cut it into another part so we are picking up as we headed into the Dynamic Testing area of their labs.

The Dynamic Test Department:

In contrast to that indoor procedure, on the outdoor track, they have a live action test where they test both wet and dry conditions. On the wet, they have a glass area where a motorcycle passes over cameras underneath. The glass area is covered in a solution of milk and water, and an image of the contact patch is captured as it passes. By increasing the speed, they can change the dynamics of the testing. On the other side of this area, they also provide feedback for dry conditions in a similar manner. As the motorcycle passes, it goes over a computerized mat that reads the contact patch and transfers the image to the computer screen. In the same way, they change the dynamics by varying the speed at which it passes. In all of these outdoor tests, they are factoring in a lot of parameters. Obviously, the weight of the machine and the weight of the rider are the first two. The results of these tests provide a molecular look at how the tires composition and design are utilized. The idea of this testing is to identify the ideal balance of pressure, load, contact patch shape and uniformity. This is an important place to talk about chopper guys and the age-old practice of running a tire at low pressure to give extra suspension. You see, tires today are not made the same way and manufacturers are doing all this testing and research to know how a tires sidewall and contact patch will stand up under a known weight at a known pressure.

When you run a modern tire at a lower than suggested pressure you violate the structural integrity of how the tire was made. It becomes an incredibly dangerous proposition in handling, longevity; the whole deal goes out the window. In the old days tires were basically balloons with tread glued to them; you could do whatever to them and very little changed. Today you are better off running within the manufacturer’s suggested range and taking advantage of their all that their scientific testing provides you. You see. In contrast to car tires, a motorcycle tire is very lightweight in structure so much smaller amounts of influence can affect how they displace pressure. The amount of inflation, the amount of weight, the rim width, all are factors that must be kept in close arrangement to what the manufacturer suggests. If not, failure of the tire will result, one way or another. While the Static Department has to deal with modeling to predict how a tire will react to different road surfaces, the Dynamic track environment has several different asphalt patches that put those models to a real-world testing, and that’s just at the Vizzola test track. Metzeler has many tracks where they test real conditions from all over the world (where they gather this information??). It would be nearly impossible to build a track that would give you all the conditions you needed and if you did, the waiting list to get on it would be ridiculous. While all this testing is going on, the science of tires carries knowledge, and if changes are to be made, this is the time to make them because all of this is happening with prototype tires. That was the next question. What is a prototype tire and what does that mean?

Well, it turns out that the cost of manufacturing a mold to put a single tire into production is enormous, more than we can convert into dollars. To make sure that they have the perfect solution for a new tire, no mold is made until the prototype proves to be perfect. But how do they make a tire without a mold? Well, all tires start the same. There is a given chemical composition that the carcass, side walls, and tread are made from. The three components are brought together and other than the tread pattern that is the tire. Since the tread pattern is so important, especially in modern tire technologies, this is where a company’s true craftsmanship plays out, and their dedication to the process shines through. You see, they may go through a hundred tires in pursuit of a concept and a final prototype. Each one of these needs to have the desired tread pattern and to achieve that they are cut by hand. Yes, that’s right, each one is given a 0.1mm cut outline of the tread pattern by a computercontrolled laser, and the design itself is cut by hand, by one technician with a heated blade. Rarely, they get a special project, a limited-edition tire, where they can show off their artistic abilities, for the most part they are in charge of consistency. I can’t even imagine the number of hours that go into a single tire, let alone to numerous copies that must be exact, during the life of a single concept tire as it travels through testing. We were told that some can take 1 to 3 days depending on the design of the tread pattern and in the end, you can’t identify a hand cut design from one out of a mold.

An Autopsy of A Tire:

The testing they perform on prototypes aren’t over when the outside testing is complete. They actually take the used prototypes and dismantle them to test the compounds on a microscopic level to see how it stands up through the testing. Every aspect of the sidewalls, the belts, and the carcass are rigorously examined as the development of the prototype continues. This again provides an opportunity to review the original compound or structural design. If need be, the whole process starts all over.

And The World Spins Madly On:

So, you might wonder why these manufacturers have so much investment in furthering the science of tires. It comes down to the fact that nothing stays the same. Not only are new models being introduced every year, design perspective changes also. Additionally, the amount of performance we demand from vehicle manufacturers change and the way we drive does as well. It’s a daunting task, to say the least, and requires a company like Metzeler to be ever vigilant as to what comes next. As motocross riders jump higher, go faster, superbike racers brake harder and cut deeper into the corners and touring riders push the boundaries of elements and civilization itself, Metzeler has to meet them at the moment they need a specific tire, of a specific size, and having done all the research ahead of time, they will be ready to provide them with a solution. That’s like a place where a crystal ball might come in handier than a lab coat. In closing, I would like to thank our gracious hosts Salvo Pennisi (22 Time World Record Holder), Piero Misani (5 Time World Record Holder) Gianluca, Diego, Tyler Porter and everyone involved with the Metzler program for not only providing Heather and I with an amazing trip to Milan but for the education of a lifetime as well. Hopefully, this little report will give you some understanding of how much goes into your next set of new skins and why they need to be maintained as much as the rest of your machine’s components.

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