Tire ataxis An Experiment in Documentation
Disclaimer
This is a writing experiment, not a complete summary of the original document.
This is a non-expert^[Editor: My use case is as a beginner racer with a Spec Miata. I've skipped sections from the original document that include additional information for autocross, banked ovals, etc. Do not rely solely on this version.] attempt to apply the Diataxis framework of documentation to the Hoosier Tire Care & Safety Guidelines.
- This document is intentionally incomplete. It is not intended to replace the original guidelines. Always review the original document before relying on any information in this one.
- The reader assumes all risk to themselves and others and to the longevity and performance of their tires. All Hoosier legalese from the original document still applies.
Introduction
The R7 and A7 have been developed to improve wear and consistency without any sacrifice of performance. In many cases, the performance will even improve over previous models. The new tire models are an evolution in the continuing effort to provide the best tire for racers.
Proper break-in can save you a lot of money.
Proper tire management is a difficult process and will require a lot of work. The benefits from doing it right include greatly increased tire life as well as consistent performance and durability under stress.
To accomplish this almost always requires a second set of wheels.
How to Break In New Tires
Preparation
- Select a proper wheel width for your tire. Hoosier recommends a wheel width no more than +/- 1/2" from the tread width.[Hoosier: Wheel width dramatically affects wear and performance of the Hoosier P-Metric radial tires. It is possible to use narrower wheels than is recommended, but at a sacrifice to shoulder wear and cornering power.][Hoosier: The fact that a tire will “fit” on a rim is not an indication that it will work effectively in that condition. The performance characteristics of the tire can change significantly within the recommended range of application. Mounting a tire on a rim that is outside of the recommendation is not a good idea.]^[Editor: Interestingly enough, the stated tread width of a Hoosier SM 7.5 is 205, but a side-by-side comparison with a Toyo RR in 225 shows little difference in real-world overall width.]
- Mount tires according to the manufacturer's specifications. For new Hoosier racing tires, mount the date code toward the inside of the vehicle.^[Hoosier: Tires without directional arrows can later be remounted in reverse to even out the wear. See details in the Reference section.]
Phase 1: The Initial Run
With higher than normal pressure, start at an easy pace and finish at the maximum tire temp on the last lap, but running no longer than 15 minutes.^[Hoosier: The first laps are critical for setting up the durability and competitive life of the tire. The goal is to have the tire temp as high as possible on the last lap without “shocking” the tire during the warm up laps. The last lap should be at—or very close to—the maximum possible.] For the initial run:
- Find the recommended cold starting pressure for your vehicle:
- Set inflation pressure 3-5 psi higher than you would normally use.
- Limit the first session to 10-15 minutes of running without "shocking" the tire: No wheelspin, late braking, or sliding.
- Do 4-7 laps with each lap approximately 7-10 seconds a lap faster than the previous lap. (See Editor's skeptical commentary on the real-world execution of this under Reference > Hypothetical Lap Times.)
- Bring the car in and allow the tires to cool at a normal rate for at least 24 hours—not "the next day"—or, even better, a week.
Driving Style
Smooth driving yields faster lap times and better tire wear. Drivers who achieve their speed by “tossing” the car run the risk of increased tire wear.
Braking
Develop a sensitivity for the limits under braking. Avoid flat-spotting your tires.
Avoid brake pads that are too aggressive. Aggressive pads make it very difficult to develop good braking feel for threshold braking.
Phase 2: The Curing Process
After completing the initial run phase, the length of time the tire is allowed to set is possibly more important. The barest minimum for the curing process to be beneficial is 24 hours. (Not “the next day.”) Any less than 24 hours is a waste of time. The best situation would allow a week before using the tire again.
Reference
Hypothetical Lap Times (Editor Commentary)
For breaking in new tires, Hoosier recommends "4-7 laps with each lap approximately 7-10 seconds a lap faster than the previous lap" and "finish at the maximum tire temp on the last lap". This seems unrealistic and hard to achieve in real life, because the starting laps look slow enough to get black flagged.
- For a ~2-minute track: 2:28, 2:21, 2:14, 2:07, 2:00 = 11:10
- For a ~90-second track: 2:05, 1:58, 1:51, 1:44, 1:37, 1:30 = 10:15
- For a ~1-minute track: 1:49, 1:42, 1:35, 1:28, 1:21, 1:14, 1:07, 1:00 = 11:16
Due to the doubtful precision of lap times (especially for beginners), the unlikely execution of the recommended process, and the high expense of one session of track time^[Editor: To figure out the true cost of one session of track time: ([cost of a track day] + [cost per mile to get there] + [food and accommodation] + [consumables]) / [number of sessions] = [probably much more than it costs to pre-heat-cycle four tires]. And heat cycling during a session also risks doing it wrong, reducing the life of the tire, and increasing an annual tire budget overall.], vendor heat-cycling seems like a much more cost-effective way to break-in new tires.
Tire Temperature
Temperature Range
Generally, optimum traction will be generated when the pit lane temps show 180-200 degrees for the R7 in road race applications. But for best performance the expected temperature range will vary from track to track.
Temperature Gauge
To get accurate hot tire temperatures, you should use a needle probe. An IR sensor surface temperature device will read cold and this may cause you to miss your hot target temperatures.
Tire Pressure
One characteristic of new tires is the feeling of lower traction initially (when inflation pressures are correct). It is important to resist lowering the pressure to attempt to eliminate this feeling. Dropping the pressure too far may improve the “feel” of the tire however it will also lower the performance and increase the wear rate.
Starting Pressure
Hoosier recommends a starting minimum cold pressure of 26 psi on all DOT radials.
Never drop hot tire pressures back down to cold pressure set points. Tires will be severely under inflated as a result of dropping hot pressures to cold pressure set points which will lead to increased tread wear and possible tire separation. Hot pressures will gradually return to the cold starting pressure as the tires cool off.
Higher Pressures
Higher pressures are needed when the vehicle has limited negative camber, will improve the performance capability, but will require a more sensitive feel to take advantage of the increase.
Air Temperature
For every 10 degrees F increase in air temperature, the tire pressure will gain approximately .7 psi. As Air Temperatures increase throughout the day, so will the Air Pressures in your tires. It is critical to maintain or manage your HOT air pressures throughout the day. Also, keeping the tires in the shade or out of direct sunlight will assist with consistent air pressure settings.
Depending on the morning air temperatures (50-60 degrees), higher cold pressures may be necessary to achieve the HOT pressures sooner.
Compressed Air vs. Nitrogen
Compressed air will cause a faster increase of HOT air pressures while nitrogen will cause a slower increase of operating HOT pressures.
Using Nitrogen, cold air pressure settings need to be started at 2-3 psi higher compared to compressed air pressure settings. Using Nitrogen will offer more consistent air pressure readings, repeatable tire performance and improved overall results.
Chassis Setup
Camber
For optimum performance the Hoosier P-Metric radial tires require about 3 degrees of negative camber. There will be a trade off in maximum performance to maximize wear. Generally, 1/2 degrees less than optimum will result in the best compromise for wear and speed. Less than 2.5 degrees negative can result in excessive wear on the outer shoulder junction.
Spring Rates
Hoosier tires typically offer better performance with spring/shock rates higher than previous brands you may have run.
Rear Engine Vehicles
When matching a race tire to your rear engine vehicle, it is very critical in matching the OE (Original Equipment) rear tire diameter or size to the race tire. Having the same diameter or greater race tire will offer a higher load carrying capacity.
- If a shorter diameter tire is used, the race tire will overheat, overload and eventually fail.
- The same or taller diameter race tire will also offer a higher spring rated tire which will help absorb the shock of forward acceleration, provide higher cornering grip and less wheel spin during corner exit under power. More air pressure (2-3 psi) should also be used in the rear tires with this vehicle configuration.
Independent Rear Suspension
With IRS and proper geometry up front, tire pressures can be reduced from the recommendations listed above. When there is adequate camber gain and good roll control, the Hoosier radial tire will perform very well at the reduced air pressure. This results in a bigger “sweet spot” and easier control at the limit.
When tuning at reduced pressures use the following formula to determine the minimum safe pressure:
- Divide the total vehicle weight, including fuel and driver, by 100 to arrive at the minimum safe pressure.
- ([car weight] + [driver, cooler, hydration] + [fuel]) / 100 = [minimum safe pressure]
- Example: Your car weighs 2,750 lbs. as raced, so 2,750 / 100 = 27.5. The minimum safe (cold) pressure is 27.5 psi.
Extreme care should be taken when tuning at reduced pressure. Tire damage can occur that is not visible to external inspection.
Vehicles equipped with independent rear suspension (IRS) have a distinct advantage over non-IRS cars when using radial tires. This is true for two reasons.
- First, it is possible to setup some amount of static negative camber on IRS suspensions, if needed.
- Second, the IRS geometry can provide the proper camber gain to achieve the dynamic camber needed for a radial tire. This is a great benefit because it then becomes possible to better address front tire grip when the rear of the car can be optimized closer to the tire’s potential.
Mounting Information
Rotational Guidelines for Tires with Directional Arrows
- All Hoosier tires having directional arrows must be mounted so that the tire travels in the direction of the arrow.
- Hoosier tires having directional arrows will have them on both sidewalls.
Rotational Guidelines for Tires without Directional Arrows
- Road racing tires include catalog numbers beginning with 43, 44, 45, 46.
- Every Hoosier race tire has a four character serial code embossed into ONE sidewall of the tire.
- All Hoosier DOT tires will also have two additional codes as required by the Department of Transportation. (Example: J7AB 4AX8 3709)
- In most cases, Hoosier tires used in road race applications should be mounted with the serial code toward the center of the vehicle.
- Once a tire has been run in the proper orientation it is acceptable to remount the tire in the opposite direction to even out the wear.
“Measured” rim vs. “Recommended” rim
In our printed product catalog and on our website tire specifications you will see two columns of information regarding rim dimensions. In most cases, the “measured rim” and the “recommended rim” will be the same. However in the case of DOT tires, the information may appear contradictory.
The reason for the differences lies in the Department of Transportation requirements for publishing tire dimensions on any tire that carries a DOT certification. Each tire size has a specific rim that must be used when taking measurements for tire comparison. This is intended to allow consumers a consistent way to compare tire sizes between brands.
With respect to the Hoosier P-Metric line, the recommended rim size will typically be wider than the DOT standardized wheel.
Speed Rating
The A7/R7 tire model carries a W Speed Rating of 168 mph.
Service Life
Hoosier Racing Tire strongly recommends that new (sticker) tires should be put in service within 2 years of date of purchase. Used (scuffed) tires have a shorter service life than new (sticker) tires. Poor storage and infrequent use accelerate the aging process.
Old tires can fail in use, causing loss of vehicle control and personal injury. Environmental conditions like temperature extremes, exposure to sunlight, electric arc, solvents, automotive fluids, and atmospheric pollutants accelerate the aging process.
Storage: Freeze Warning
Hoosier tires, especially asphalt and hard compound tires, may experience rubber cracking if the tires are transported, crushed, flexed, or stressed when frozen.
To avoid this problem:
- Always store Hoosier racing tires indoors at temperatures above freezing and off the vehicle.
- For long-term vehicle storage or winter transport, always use spare tires not intended for future competition.
- If tires have been subject to freezing temperatures, allow them to warm up to room temperature (about 70° F) for a minimum of 24 hours before the tire is mounted, transported, or flexed.
- If below freezing temperatures are expected, consider shipping tires once more favorable conditions exist.
Do not use tires that have evidence of freeze crack damage.