Where Rubber Meets The Track - Tech File

Compounds, sizes, tread depth, and spring rates-these are just a few of the variables racers face each week when it comes to dealing with the tires on their vehicles. Tires, in fact, have become one of the greatest determining factors on how you finish in your series. This is especially true in entry-level racing divisions, such as Quarter Midgets, Karts, and Legends Cars.

With the exception of Legends, which put out roughly 125 hp, most of the cars in entry-level divisions have less than 30 hp. The tires on these underpowered vehicles must be watched closely and sometimes altered to make them better than the tires of the competition. I raced karts for approximately nine years and I recall having to prep, cut, and balance the tires to even have a chance at winning a race. When we got a new tire mounted, we would immediately put it on the tire cutting machine, cut half of the rubber off, fill it with 6 ounces of our favorite prep, and leave it in its own personal rotisserie all night to soften the tire. The bad part was every competitive team was doing the same thing.

I remember one year when creosote was the key to winning races. Creosote, however, is a known cancer-causing chemical formerly used on railroad ties and light poles. It did wonders for a go-kart tire, though, and at 14 years old I was using a paintbrush and a plastic cup full of creosote to find that extra edge. Looking back, it sounds ridiculous, but this was the extreme that everyone was using to run competitively on the dirt ovals in the Midwest.

Later, at age 18, I burned the prep into the tires and used MAPP(r) gas because it burned hotter than regular propane. I can recall one incident in which I used a prep that I wasn't familiar with at all. I had heated up the tire to the point where it was steaming profusely, and I applied the prep without any problems whatsoever. But as soon as I touched the torch to the tire, it instantly burst into flames and the tire was fully engulfed. It took two of us to put out the fire.

These are the dangers that every entry-level racing series has had to deal with and address in recent years. Stories were popping up all over with people experiencing chemical burns, trailers being burnt to the ground at the racetrack, people breathing in toxic gases that the prep was emitting, and so on. This is not to mention the cost of cutting the rubber completely off the tire.

Something obviously had to be done. The World Karting Association (WKA) stepped up with rules changes that would not only level the playing field, but also help cut the cost for lower-budget teams.

At every sanctioned WKA event, competitors now present a brand-new set of spec tires for each class entry and have them inspected. The inspectors check the tires' durometer readings (hardness) and temperature, and they conduct a physical inspection comparing it to a legal test tire. If any tire fails inspection, it will cost the driver second-round practice and qualifying for that class. Cutting of the tires is not allowed, and the tires will be inspected when the teams first get to the track, before practice, before qualifying, and before and after the race. Prepping is no longer allowed on the tires and the officials inspect them with what's called the JTR Eagle, a handheld vapor analyzer. It detects chemicals that may have been used.

The spec tires that are used differ between classes, depending on the weight of the class and the horsepower that is pushing the kart. Most of the spec tires, however, are Vega Oval Yellow, Maxxis HT-5, Firestone YGF, or Dunlop DCS.

Legends & Bandoleros
In Legends and Bandolero competition, sanctioned by 600 Racing in Concord, North Carolina, there is a spec tire rule with a tire manufactured by BFGoodrich. These tires are purchased from 600 Racing and are allowed to be cut. The tires will last about 8-10 races. They inspect the tires during the pre-race tech, qualifying, and before and after the race. The Legends tires resemble a regular street tire, but make no mistake, they are made specifically for the Legends Cars and even have "Legends" imprinted on their sides.

The biggest upside with the tire rule for the Bandoleros and Legends series is the cost. A set of tires will cost around $400 and will last roughly 10 races. You will spend $100 to camber-cut the tires. The average tire bill for a whole season is roughly $1,500, which is very reasonable for almost any racing series.

With a spec tire rule, your choices are limited when it comes to tire compounds and brands of tires, but in some cases this can be a good thing, especially if you have never been to the track before and you are not familiar with the type of rubber the track likes. However, there are some variables you can control, such as the size of the tires and the stagger you run on the car. Stagger is the difference from the right-side tires to the left-side tires. A pretty standard stagger setup that we ran on dirt was an inch of stagger in the front and an inch and a half in the rear of the car. The stagger in the front two tires is not as important as in the rear of the car, as the front tires are not connected by a solid axle. The rear tires are the most important because of an axle. If you are getting into the corner very well and experiencing a loose condition at the exit, you might have too much stagger in the rear of the car.

Temperature
Tire temperatures become important as well. Anytime the vehicle comes off the track, whether that track is dirt or asphalt, you need to be recording tire temperatures. These are especially important with drivers who don't have a great deal of experience.

Tire temperatures don't lie. A loose-off condition might stem from the car being tight when it enters the corner. Your driver will have to turn the wheel more to accommodate the tight condition, and the rear end will break out during corner exit. The temperatures will show the tight condition before the loose condition because that is the main problem. You can tell if you are having a tight condition by looking at the tire temperatures. Here is a sample that was taken from a race at South Boston Speedway. The temperatures might be a little more than what you would experience with a kart or a Bandolero, but the same rules apply.

As you can see, three of the four tire temperatures look really good. The RR, LR, and LF are within 10 degrees of each other. But the RF is almost 20 degrees hotter than any other tire. This is indicative of a tight condition. When you loosen up the car, you will more than likely see an increase in the rear tires, but if you start to see a big difference where the RR is 20 degrees warmer, you have gone too far with your adjustment.