Splash & Go writes:
"Zen and the Art of Rain Tire Maintenance"
Posted by Uptight Motorsports Nerd on September 14, 2010
Viewed 328 times
When the weather is dry racing slicks and street tires work under the same principals. As the tire rolls forward the flexing of the sidewall generates heat. Once we enter a turn, the tread slips on the dry pavement creating more heat from friction. This heat needs to be dissipated and there are two ways to do it.
1. Air traveling over the tire will wick away heat.
2. Rubber scraped from the tread will carry away heat (creating infamous ?marbles?).
Rain changes everything. Water acts as a lubricant and a cooling medium. Lubrication reduces the friction and heat that came with our tread slipping on the pavement. Slick tires cannot handle large amounts of water because some friction is needed to create traction. Street tires and rain tires have circumferential and lateral grooves that direct water away from the tire, allowing the friction needed to turn a corner. Liquids are a more efficient cooling medium than gasses; therefore, water keeps the tire cooler than air would in dry conditions, and a cool tire does not need to shed as much rubber.
It should be understood that the term ?wet? is not an absolute. What we understand as ?dry? is really the absence of moisture (like ?dark? is the absence of light). There are conditions that you cannot hold a [road] race in with any sort of rain tire; a light drizzle is not among them.
The Holy Grail of rain tire technology is oval track racing. For years we have been told that ovals are too fast, too stressful for rain tires. I do not believe this anymore. I?ve explained how rainwater cools tires; this eliminates the heat generated by the stresses of racing on banking. Speed is the real problem. I?ve observed that speeds in moderate rainfall are 80% of their dry counterparts. In an article published about the USGP a few years ago (sorry that I can?t find it now), a Bridgestone engineer admitted to studying the potential for rain tires in the Indy 500 and found that the cars would have a maximum cornering speed of 150 mph. This proves, hypothetically at least, that rain tires would be feasible at the Indy 500 if the dry cornering speed were below 185 mph. Just as well, there aren?t many ovals that force the IndyCars to slow below 190.
Stock cars open a can of worms (or should I say ?night crawlers?) when it rains. Years of avoiding road racing like the plague has left NASCAR with no concept of rain racing. Conditions such as fog on the windshield, rooster tails, and hydroplaning have left people afraid to experiment. Allow me to dispel these fears.
1. Windshields can be kept clear with chemical defogger.
2. Rooster tails are a product of speed and water depth. If water is deep, we wouldn?t be racing anyway (see paragraph 3). It is also worth mentioning that TV makes these look worse than they really are by using wide angle lenses.
3. Hydroplaning is a product of speed, weight, and tire efficiency. The more downforce (and mass) a car has, the more it resists hydroplaning. Open wheel cars have more downforce than stock cars, but stock cars are just as safe because they are heavier. In a straight line, the only difference between downforce and mass is that downforce is not subject to inertia.
Focusing on ovals again, stock cars usually average 80% of their open-wheeled counterpart?s dry speed. For this reason we will lower the safe cornering speed from 150 to 120 miles per hour. Now let?s consider how many ovals on the Sprint Cup calendar have dry cornering speeds below 120 miles per hour.
When road races are factored in, there exists a potential for 12 wet races at 7 tracks each year.
Someone once told me ?rain tires won't work on an oval... banking creates waterfalls and rivers of water.? This is actually bull****. Banking cannot create rivers of water. Rivers are long, narrow, and deep. Water will roll down the banking, yes, but it will never have enough force behind it to knock a car around. This is the concept behind road crown! When it rains at the 24 Hours of Daytona, drivers often admit that the oval section is the easiest part of the track because banking keeps it dry; the infield is Hell because it floods so easily.
The rest is a matter of will. Do enough people (or at least the right people) want this to happen? Do the TV networks hate rain delays bad enough? Does the ticket buying public hate rain delays enough? Do the sponsors want this enough? Do tire companies want to make the investment in technology? To quote Jurassic Park, ?Creation is an act of sheer will.?
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