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Tires, Brakes, Wheels And Things That Go Bump In The Night At The Race Track… By Keith Olcha So an instructor, who shall remain nameless, spins out at Motorsport Ranch in the June Drivers Education event. He comes in to the black flag station and we chat. Later in the day he come up to me and says: "Good news. I know why I spun. My right rear tire had 51 pounds of air pressure in it!" Well that's just dandy. The tire is rated for a maximum of 44 pounds, and in a 911 of that particular weight, he should have had about 41 pounds hot in the rear tires after a run session. Another instructor, who also shall remain nameless, corded two Hoosier DOT racing tires by running them under-inflated for two run sessions. You’d think instructors would know better. Well, they did once, and then they got lazy. Fortunately nothing happened with either driver or their cars, but it never hurts to review safety items again. Let's remember three very important areas of safety: 1) Proper tire inflation, tread surface wear, and lug nut torque 2) Brake fluid level, cleanliness, and air-bleeding 3) Brake pad and rotor wear. Safety belts, seats, and airbags work after you get into trouble. The three items above, when properly maintained, keep you out of trouble. The four tires on your car, and the palm-sized contact patch they maintain with the ground is all that connects your car to the track. It's not a relationship to abuse. Let's start with item number one above- the tires. Tires are filled with air, and it's this air which maintains the tires structure and conformity to the road. The tread contact patch rubber creates friction against the road surface that allows acceleration, braking, and turning to occur. Air pressure varies greatly with outside temperature and heat generated from the friction. You should check your tire pressure at least twice per day, once first thing in the morning, and again after lunch. Street tires generally should have 2-3 pounds more than the factory pressure when cold before a run session under the theory that they need to be stiff to avoid rolling over on their edges, and that they will increase 4-6 PSI during a 25 minute run session. Keith Olcha and his RS America. However, if the rear factory recommendation plus 2-3 pounds would exceed the maximum inflation (found by reading the tire sidewall) don't add air to the rear tires. Also, most manufacturers recommend high under steer-inducing pressure differentials between front and rear tires. A good example is my Boxster. The factory pressure is 29 Front, and 36 rear. On the track, that would have the rear about 42 pounds in hot weather after a 25-30 minute run session. I, along with others, have found that with street tires starting at front 32 pounds (3 lbs over as mentioned above) and rears at about 34 PSI works very well with minimal sidewall rollover and decreases under steer. With DOT track-tires such as Kumhos, Hoosiers, and Yokohamas, those manufacturers have specific pressure recommendations that can be found on their websites, or The Tire Rack's website. For example on a 911- a Kumho V700 Victoracer should be 1 pound for every 100 lbs in the front and 2 pounds more in the rear. So if your 911 is 3000 pounds, a cold inflation starting recommendation is 30 pounds in each front tire and 32 pounds in the rear. Kumhos like a hot maximum pressure of 36-39 pounds. So depending upon your driving style, the track, and outside temperature in that same 911 above, you might start 28 F 30 R or 32 F 34 R for the desired outcome—but not 51 pounds! Lug nuts should be torqued to 90 lb-ft. There's no need to discuss why tires need to stay on the car, is there? And what about the second item, brake fluid? Brake fluid is the hydraulic fluid that converts foot pedal pressure through vacuum assist (in most all newer street cars) into caliper and drum pad pressure so the rotors/drums slow down. Where does all that momentum or movement of the wheel turning go? It turns into heat and goes into the air, the rotor, the tire, wheels, and the brake calipers. After several minutes of heat, it is easy to boil the accumulated moisture (water boils 212 degrees) that has been absorbed by the brake fluid in the caliper. Once that happens the resulting boiled water yields air bubbles, which creates space and thus the dreaded "soft, ineffective" brake pedal. The only solution is to brake less and let the brakes cool down and "bleed" off the air-bubbled fluid in the calipers. How do you keep your brake fluid fresh so that doesn't happen? Bleed the brakes twice per year with fresh fluid and keep your master-cylinder topped up with fresh fluid. What about brake pads and rotors? You can use up an entire set of pads in one weekend DE at a track. Always start with more than _ pad material remaining. Change your rotors every 2-3 sets of pads, or better yet—measure them for acceptable remaining thickness. Porsche has very clear specs for that. On some rotors, it's stamped right on the rotor. So check your car over after every run session, for tire cuts and abrasions. Brake fluid and pad wear twice per day, and inflation pressures twice or three times per day. And have fun. By the time you read this we will be accepting registration forms for our September Drivers ED at Motorsport Ranch. 19