A set of Chicken Hawk Racing...
A set of Chicken Hawk Racing tire warmers was placed on the Burnham Boilers NASCAR Busch North car driven in competition by multiple series champion Mike Stefanik at the Lime Rock Park event in October 2003. Stefanik said it takes four to six laps to get the tires up to proper pressure.
The smart racer looks for the competitive advantage. He keeps his eye on the trends in the sport and strives to be the leader. When the heat is on, the real winner will head for the front.
The idea behind using a tire warmer is a little more complex than meets the eye. The warmer itself is not a confusing piece of equipment, but the tires it heats can be. The benefits of a tire warmer are obvious: It keeps the surface rubber of the tire hot (170-210 degrees F, depending on tire brand and compound). Having the surface rubber hot increases the coefficient of friction of the rubber, increasing its ability to grip the track surface.
More subtle issues become apparent with time and usage of the tire warmers. The benefits include:
* Heat-soaking the carcass
* Eliminating the chance of cold tire incidents
* Saving heat cycles
* Tuning your tires-brand and compound.
* Setting hot pressures and sizing your tires.
A crewmember cleans the tires...
A crewmember cleans the tires already in the warmers. While the surface rubber heating is obvious, the carcass of the tire is picking up needed temperature as well.
The practice of heat-soaking the carcass is almost as important as getting heat into the surface rubber. This means the tire is hot and stable throughout the carcass and inside the tire. Through the use of data acquisition equipment, we have found that a tire with a surface temperature of 200 degrees has about 175-degree heat inside the tire's airspace. This is found by a thermocouple passed through the rim, measuring the inside surface of the tire, actually touching the tire.
A tire's carcass is more flexible when heated to race temperature. It is also more consistent. During actual use, a tire is deformed under braking, cornering, and accelerating due to the forces being applied. Of course, the tire is also part of the suspension, and suspension frequencies will change as the tire is warmed on the track. By warming the tire before the race, the tire will perform much the same at the beginning of the race as it will during the middle. This enables better choice of proper compounds, not to mention the elimination of cold tire incidents. The issue of heat-soaking is why the quality of insulation that a warmer uses is important; you want to drive the heat into the tire, not heat up your garage.
This graph shows the carcass...
This graph shows the carcass temperature as well as the surface temperature. A thermocouple-equipped data logging system provided the inside information through the rim to the computer.
The cold tire accident is certainly more common on sub-50 degree days, but overzealous throttle application can get the same result on a 90 degree day. The tire still starts out cold, especially when selecting harder compounds for higher track temperatures or abrasive surfaces. The cost of an off-track incident can more than pay for a set of warmers, even if you're not destined to be the class champion. Having a consistent tire on all days, in all conditions, takes one more variable out of the equation.
In the words of Michelin Race Tire Director Ron Wood on the use of tire warmers during the summer, "Hey, 90 isn't 190." Have you ever seen the sweltering hot races in Sugo, Japan? The crews apply dry ice to the gas tanks to keep fuel cool, blowers cool off sweaty drivers, and the warmers are always on the tires. In other words, just because you're sweating doesn't mean your tires are hot.
The tire warmers can be used...
The tire warmers can be used without having an effect on other necessary maintenance.
Each time your tire is heated and then cooled, it hardens up. A NASCAR Busch North driver once stated, "Tires harden up when they cool off, just like cookies that come out of the oven and get placed on the counter." A warmer can help avoid this by keeping the tires warm between sessions on the track. A temperature adjustable warmer works better in this case because you can turn the heat down to about 130 degrees F and keep the tires warm enough to prevent them from going through a heat cycle without overheating them.
For example, a team turns the Friday practice days into one heat cycle. The tires go from the warmer to the track and right back to the warmer on a low setting. In this way, six track sessions put the tires through only one heat cycle. We also keep the tires warm between the two races on Sunday, which are normally separated by about 2 hours. This helps get the most life out of tires.