Race Tire Pressures
by Timothy Kast
Race tire air pressures are often viewed as confusing and contradictory information at both club and national levels. The truth is that air pressures and the measurement of the same is a simple, safe and sane science. The disinformation is usually the culprit here as there is no chicanery or track-side voo-doo involved. The air pressures used in most roadrace paddocks are usually the result of what works on what track, where and why.
Tire inflation adhesion on race day is a combination of ambient temperature, weather conditions, and past experience at that particular track. This is then sifted down to whos going fast with what pressure in what compound using all of the above mentioned criteria. The set pressures of the day listed at the major tire manufacturers tent are the culmination of these guidelines. Tire manufacturers spend a great deal of money and time on this note keeping research to be able to post the days pressures, so feel confident that these figures represent very possibly the best setting for maximum safety and adhesion. Feel free to fine-tune if your riding skill and crew find it necessary, but generally speaking, those race day pressures will be the setting to adhere to. Other race day challenges will present themselves to command your attention, so its best not to cloud the day with unnecessary fiddling. Set it and forget it. The time saved worrying will make you a more relaxed and approachable individual, and your crew as well as those around you will love you for it. Being a successful racer often means not losing track of who and what you are.. come race day when the pressures on.
How does tire pressure affect my tires?
Tire pressure affects the contact patch; it also affects the way the tire corners. Together, these affect the manner in which the tire grips.
How will this afftect my traction?
Sure, the bigger your contact patch is, the better the tire will grip on a dry day. but too low of a pressure could result in the bike being unstable, or squirrelly in a corner. Going to high with our air jpressure will give a smaller contact patch and a joucyh, rough ride because the tire cannot do its job and grip properly. You must maintain the delicate balance between all these factors working in harmony; contact patch, stability, ride and grip. Get all those right then you are ready for your next topic.
Tire temperature is affected by:
1. Air and track surface temperature
2. The construction and compound of the tire
3. Your motorcycle and suspension set-up
4. Your style of riding
5. Your top speed and lap time
6. Your cold pre-race starting pressures
7. Your attitude and expertise
D.O.T. approved tires in racing compounds offer excellent grip within a broad temperature range. These tires are constructed in a sturdy manner generally to absorb the loads common to everyday street riding. What you gain in a wide temperature range and versatility, you will lose in individual tailoring both of the rider and the track you will be racing at. If the manufacturer does not offer different coumpounds of a D.O.T. approved tire, this leaves you no other choice than to try a different brand name D.O.T. approved tire in hopes of finding a hotter or colder tire to cure your particular traction malady.
At tracks such as Daytona with its high banking and the heat generated because of its fast corners and radical degrees, require a specific counmpond and construction. You can then change slicks with compound and construction easier than you can with D.O.T. approved tires, but conversely you lose the versatile feel of a race compound street tire in the process.
If you are having trouble with your tires, you can usually illustrate your problem areas with more practice. Practice makes you more confident aboard your machine at speed; that will in turn give you the knowledge to select your tires more carefully and theres really no honest substitute for that. Practice, confidence and knowledge will start you on that hallowed stroll to the victory podium.
How should I set my tire pressure?
Reasonably knowledgeable individuals (R.K.I.) know that in truth the only thing that a tire pyrometer is, is an expensive thermometer. Factory teams go after more than just pyrometer readings. Was the air pressure set at the recommended number before the rider went out? Was the tire properly scuffed in? How many laps did it take to properly scuff the tire in? What was the cold durometer reading of the tire before the rider went out? What is the ambient temperature? Then you can factor in that remaining pyrometer reading to provide you with that all important background information. Oh yes, did I mention altimeter and humidity, too? See, and you thought it was easy to be a tire guy.
Start with the recommended pressure of the day. If you dont know, ask your race tire representative. If you feel like you need to alter the setting from what was recommended, use a plus or minus setting of only 1-2 pounds. Avoid any major setting increases or decreases as that will only muddle your original setting reference point. Any major setting change (anything above or below five pounds of air) would indicate a failure to have dialed in your suspension. Grip is more finite while all your chassis components can be adjusted more easily. Factory sponsored National Superbike and Supersport riders all run 1-2 PST within the recommended daily pressures. This is common knowledge and the posted chart is regularly referred to, when in doubt.
Speedway air pressures are higher than other tracks to counter heat-related decomposition of the tires and the tremendous centrifugal forces slamming the same tire. As mentioned nitrogen is used (it doesnt heat up) to retain a constant air temperature despite the speeds, heat and the pounding the exterior of the tire is taking. Since speedways use the higher velocities of bike and rider, caution should be exercised with personal fine-tuning of your air pressures other than what is posted for the day.
Road courses are where you can more fully utilize all of the tire; however, the tire is less likely to heat to proper consistency of adhesion quickly. Road courses with their wide expansive sweepers and slow corners will allow more frequent adjustment of the pressures, but there again choose the posted popular norm on race day.
A word concerning rain tires is necessary considering most riders and mechanics do the opposite of what is needed for the tire to work. The carcass of the tire needs to be firm to retain the tread patterns natural ability to force rain water out of the sipes to provide traction. Thusly, raising the air pressure 2-4 pounds over normal slicks, rather than lowering it, is mandatory. This enables the rain tire to grip through the water to the tracks surface; instead of the pattern collaspsing from lack of air. Rain tire patterns are also designed to disperse the rain water from the tire gripping surfaces. The design and the low durometer rubber of the tire provides the bite.
The home team
Part of the mystery surrounding air pressures has something to do with the folks who sell and mount the tires. You see, due to the immense crush of everyone wanting their tires at once, not every tire guy can stop and tell you all the information that goes into making the educated decisions of what air pressure toun at what track, where, when and why. To someone unfamiliar with the machinations of race tire technology, it might seem like the SWAG method (scientific wild assed guess) we discussed in Race Tire Primer (another article by Tim - ed). I assure you that this is not the case and perhaps in a future issue of NP Online I can show racers how to keep a log book of their own different air pressure settings to refer to.
Remember, always keep a rubber sealed metal valve stem cap on your valve stem. Vaya Con Dios!