Tech Tips

Tech Tips are internet source articles accumulated for your reading pleasure

Driving Suits - What does the SFI Rating Mean?
Helmet - What does Snell, ANSI and DOT mean?
Why is tire temperature important?
What is "Toe In" or "Toe Out"? and Why is it important?

Driving Suits - What does the SFI Rating Mean?

All Driver's Suits Are Not Created Equal - Unraveling the SFI Rating Mystery (from the Northstar Motorsports web site) Many sanctioning bodies are beginning to require an SFI rated driver's suit, or at least the regulation may have language somewhat like this: "A one piece fire retardant driving suit is required. (Two layer or one layer plus fire retardant underwear minimum -- three layer or the special two layer with SFI rating of 3.2A/5 strongly recommended.)" What exactly does all this SFI stuff mean anyway? There are two materials that are used extensively in the manufacture of driving suits, Proban and Nomex. Proban is a cotton-based material that has been chemically treated to make it fire retardant. This treatment diminishes with washing. It is used primarily in single layer economy suits although there has been a disturbing increase in manufacturers using it to manufacture inexpensive multi-layer suits. Nomex is a permanently fire retardant Aramid fiber that is manufactured by Dupont. It is woven or knitted into material by one of several mills in the U.S. Since it is inherently fire retardant its protection does not diminish with time or washing like Proban. The Proban suit may initially look like a bargain but the life span of the Nomex suit often doubles or triples that of Proban with proper care. Worse yet, it is impossible to tell when Proban has lost its ability to protect the wearer in a fire. That is why Northstar Motorsports only sells multi-layer suits made from Nomex, and we highly recommend either a three-layer suit or a two-layer suit with an SFI-5 rating for all types of racing. The SFI Foundation is a non-profit organization established to issue and administer standards for specialty/performance automotive and racing equipment. SFI tests a long list of products including gloves, suits, neck braces, restraint systems, shoes, underwear and window nets. The SFI standards program is funded by participating manufacturers paying for development and administration through licensing and/or unit charges. The SFI specification for driver's suits, Spec 3.2A, rates how long a driving suit will offer protection from second-degree burns in an approximation of a raging gasoline inferno between 1800 and 2100 degrees. SFI ratings are calculated in calories per unit, area per time of exposure. Basically it gives the buyer a rating system to judge any suit's relative protection capabilities. The following table gives an approximate time until second-degree burns will occur based on the SFI rating of the driver's suit: 3-2A/1 = 3 Seconds; 3-2A/5 = 9.5 Seconds; 3-2A/10 = 19 Seconds; 3-2A/15 = 30 Seconds; 3-2A/20 = 20 Seconds

Helmet - What does Snell, ANSI and DOT mean?

There are three primary helmet ratings: Snell, ANSI and DOT. The standards are set to provide acceptable levels of head protection in the event of an accident. Snell rated helmets can be divided into Special Application (SA) and Motorcycle (M) ratings. The impact protection for these two ratings are generally similar. SA helmets are specifically designed to meet the requirements of an individual who is restrained within a motor vehicle and needs flammability and sharp object impact protection. M helmets are designed to protect individuals who are not restrained and may come in contact with many different shaped objects. Many clubs will accept either the Snell M or SA standard for autocross activities and non-racing track events. Some clubs will accept the ANSI or DOT ratings. High speed racing events generally require the Snell SA rating. Check with your club on their requirements and rating year. Beginning in January 1999 many sanctioning bodies updated their helmet requirements to the SNELL SA 1995 rating. The message is: If you're still racing with a SNELL SA 1990 or older helmet, it's time for a new helmet. The SNELL SA 2000 helmets are now fully available. In most cases these new helmets contain significant safety advances over their predecessors.

Why is tire temperature important?

UNDERSTANDING TIRE TEMPERATURES (from Northstar Motorsports) It is the combination of proper inflation and chassis alignment that gives your tires optimum GRIP on the racing surface. But how do we know what pressures to run and do we set them cold or hot? And once we have the tire pressures set properly, how can we tell if the car's alignment has the proper amount of camber? These are but a few of the mysteries that can be answered by taking temps and pressures. First, tire temperatures are meaningless, or nearly so, after a "cool down" lap. To obtain meaningful data, the driver needs to complete a hot lap and come directly into the pits where the crew immediately takes the temperature of each tire in three places (outside, middle and inside). Begin with the most important side of the car -- left side tires for a predominantly right hand track and vice versa. Rear tires first in a rear or mid-engined car and front tires first in a front engined car. Record the tire pressures before you go out (cold) and then after you come in off the track (hot). Do this after you record the temperatures since the temp drops much faster than the pressures do. The objective is to get the tire to work effectively across the entire face of the tire (all readings the same). In reality this will probably never happen, but you should shoot for no more than a 20*F spread across any one tire. If the center temperature is higher than the average of the inside and outside temps, the tire is over inflated -- try reducing the pressure in 2 lb. increments. If the middle temp is lower than the average of the inside and outside temps, the tire is probably under inflated -- try increasing the pressure again in 2 lb. increments. Once the pressures are set correctly, then look for major differences in temperature side to side. If the inside temp is always significantly hotter than the middle or outside, the chassis may have too much static negative camber adjusted into it. Caution: This reading can also occur if you take the temps after a cool down lap when you have not worked the chassis hard enough to effectively use the full face of the tire -- in effect you have driven on only the inside edge of the tire due to the static negative camber in the chassis alignment. Don't mistake this for too much negative camber, try taking the reading immediately after several hot laps. If the outside temperature is consistently hotter (by more than 10*F) than the inside, try dialing in a bit more negative camber. Once these pressures and camber are set optimally, then look for differences in temps of the front tires compared to the rears. Again, they will never be the same due to engine placement and drive wheels, but differences in temps can confirm your "seat of the pants" feel about how the car is handling. Does the car push (understeering) in many of the corners -- then the front tires will probably be hotter than they should be due to the excessive slip angles that generate the push. In this situation try experimenting by softening the front sway bar (if it is adjustable). If the car feels loose (oversteering) and that is confirmed by the rear temps being considerably hotter than the fronts, then try softening the rear bar. Remember to first try to adjust the end of the car that is not handling optimally. Only then, when you are out of adjustment on that end should you try an adjustment on the other end of the car. Tire gauges and pyrometers are only two of the important tools to help you get the most out of your car's handling.

What is "Toe In" or "Toe Out"? and Why is it important?

Toe in or Toe out? That is the question. First, lets define what we mean by toe. It is the difference in the distance between the front and rear edges of the rims on one axle. If the distance at the front is larger than the rear, then the alignment is said to be toed-out, and if the distance at the rear is larger than the front, thats toe-in. This is relatively easy to measure and to adjust. It requires not much more than a tape measure, or an alignment rack, and then loosen the jam nuts on the tie rods and adjust the rods. Having said all that, what does toe-in or toe-out do to the way a car handles. Generally the rule of thumb is that more toe-in increases understeer and more toe-out increases oversteer. However, with modern cars, especially race cars with independent front and rear suspensions, there is another effect on handling. Most manufacturers recommend a chassis alignment which contains a small amount of toe-in. This will give the best possible stability at speed; the car will not have a tendency to wander. And the small amount of toe actually pre-loads the wheel bearings to make turning more instantaneous. But what does toe-in do to the handling of a race car. As soon as you turn the wheel, the front tires initiate the turn and the rears simply follow. Therefore, what happens at the front wheels will determine how the car responds to the initial steering input. When cornering, the outside tire requires a larger turning radius than the inside tire. In other words, the inside tire has to turn more sharply than the outside tire to get the maximum combined cornering force. With a car that has toe-in, the inside tire is constantly turned in, and it is fighting the outside tire and detracting from the total front cornering power. This reduces the ability of the front end of the vehicle to turn into the corner. However, by having the front wheels set with a small amount of toe-out, the instant you turn the wheel, the action of the inside tire turning more sharply than the outside tire already exists and the car turns into the corner like it is on rails. Once the car gets turned into the corner, then the weight starts to transfer from the inside to the outside, thus minimizing the affect of the inside front tire. Also then the rear tires are contributing to the overall cornering power while the suspension components (springs, shocks, roll-bars) are reacting according to their designs and settings. So if your race car just doest like to turn in, and you feel as though you have to literally throw the car into the turn to get it to turn in, try a small amount of toe-out, rather than the conventional toe-in. You will lose a little amount of straightline stability, but the car will certainly turn in much better.