Inside Tire Tech Teaser

I recently attended a seminar hosted by Paul Haney, noted tire expert and author of the book “The Racing & High-Performance Tire”. Here are a few highlights which may make you want to investigate further and as I would recommend, read the book! Tires are almost universally recognized as the most important part of the racing equation beyond the driver. Despite this fact, they are usually the most neglected and misunderstood. There is so much misinformation and mystery surrounding these devices that a variety of conflicting tire facts can be gathered at any track event by just interviewing crew chiefs.

Basically, the job of a tire is to cause the car to uniformly change direction or speed. The art of tire design took a huge step forward in the 1900s when, thanks to advances in rubber compounding, the pneumatic tire became available. The advent of belted and radial tires in the mid 20th century allowed sidewalls to become shorter, providing the driver more control due to the decrease in sidewall flexing. Synthetic rubber technology from the 1990s on has significantly improved durability and grip. The modern tire is far superior to that which was available even 20 years ago.

Rubber is a unique material because it has a high coefficient of friction. The coefficient of friction of wood is around .75, whereas that for rubber is over 2.0. The respective coefficients are found by experiment. Two important components of rubber friction are momentary molecular bonding (within the rubber itself) and mechanical keying, which is related to the surface, in this case, the track. Therefore, a new unworn paved aggregate penetrates deeper into the tire. Since the points of the material are sharper, there is a more acute contact angle. Both of these effects create increased mechanical keying. As a track ages, two things happen: the peaks are worn down so that the sharp points don’t penetrate as much and there is less contact angle.

As we stated above, there are many myths associated with tracks and tires:
· Oil and rubber make the racing line slippery when the track is wet. Not true! The rack surface on the line is polished; it’s rounded and penetrates less into the tread. Off line, the surface is unworn, sharper and gives more grip. This is intensified by using softer, more pliable rain tire compounds.
· Laying down rubber makes a track faster. Another untruth! In reality, a clean track surface has more grip. This is why we often see drivers pass over the track during warm up or practice. Dust is a lubricant between the rubber and aggregate, so the cars are blowing the dust away from the line and into the debris to clear the track. An interesting aside: have you ever noticed that drag strips have a rubber coated area on the start? That is not for grip. It is there to provide the drag tire manufacturers and racers with a consistent material across the country at each venue. Otherwise there would have to be a different setting and tire for each track.

In summary: Rubber is a unique viscous and elastic material. How friction (grip) is generated is very complicated, it is sensitive to operating temperature and gets softer at higher temperatures, within limits. Important point, it is sensitive to load and rate of loading, so more grip when loaded, less grip when loaded rapidly, read…be smooth. Surface texture also has a great affect on grip - those faster times we all have been seeing at VIR won’t last! Rubber changes with time, heat cycles, UV exposure, etc. Another important point, never allow your track tires to remain below 32ºF for any period of time and store them in black plastic garbage bags if possible.
There is much, much more to say, but to find out more you should read the book, The Racing & high performance Tire by Paul Haney. Also, if you have a chance to attend a seminar or webinar on the topic, you will find it interesting and fascinating. Check Motorsportreg.com for webinars. See you at the track!

 

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