Shaving Tires for Autocross / Track Use / Competition
One of the reasons radial racing slicks are so effective is because they feature shallow tread depths and their contact patch acts as a single unit. However, any tread design that breaks up the contact patch into smaller elements or adds additional tread depth (required to enhance wet traction) will increase tread block squirm and reduce dry performance. This means that tires typically provide their worst wet traction and their best dry performance just before they wear out. It’s also important to remember that the heat generated every time a tire is driven activates bonding agents in the rubber. As this process is repeated continually throughout the tire's life, its rubber compounds gradually harden and lose flexibility reducing the tire's grip. Therefore, a shaved new tire will provide more traction than a tire worn to the exact same tread depth after being driven for thousands of miles on the road.
Tire shaving is an effective means of permitting more of a tire's performance capability to be realized early in its life. And in many cases, shaved tires used in competition actually have a longer useful life than tires that enter competition at full tread depth.
The process removes tread rubber and reduces tire weight by several pounds. A shaved tire's tread profile will usually result in a slight increase in the width of the tire's contact patch putting a little more rubber on the road. The resulting shallower tread depths reduce the tire's slip angle, increasing its responsiveness and cornering power by minimizing tread block squirm.
Minimizing tread block squirm also reduces heat buildup and the risk of making the tire go "off" by overheating its tread compound. Depending on the severity of overheating, the overworked areas of the tread compound may turn blue, tear, blister or chunk.
So with all of these benefits, the next important questions are: "Which tires need to be shaved? “How far should they be shaved?"
Extreme Performance, Max Performance and Ultra High Performance Summer Tires
Since they are not purpose-built for track use, most of these tires begin with 10/32" of starting tread depth. Our experience is that shaving them to no more than 6/32" of remaining tread depth will provide a noticeable improvement, while shaving them to approximately 4/32" will allow them to run even faster lap times. However in all cases, tread temperatures should be carefully monitored to assure they don’t exceed 210° Fahrenheit and that there is relatively even temperature distribution and wear across each tire’s footprint.
It's also important to remember that once used, all tires will be a little less effective during the next competition season. Therefore we recommend that tires be shaved to a depth that is sufficient to last for no more than one competition season. If it is very important to you to do well in the one event you run a year, running tires shaved to about 4/32" will further enhance your performance.
Track & Competition DOT Tires
The following tires are manufactured with only 4/32" to 4.5/32" of molded tread depth and do not require tire shaving for autocross or track use.
BFGoodrich g-Force R1
BFGoodrich g-Force R1-S
Hankook Ventus Z214
Hoosier A6 Radial
Hoosier R6 Radial
Kumho Ecsta V710
Most other Track & Competition DOT tires begin with 6/32" to 8/32" of molded tread depth. While some tires do not require shaving for dry autocross use, all of them will benefit from shaving to about 4/32" tread depths for driver's schools, track days and competitive track use in dry conditions.
Dry Autocross Dry Track
Michelin Pilot Sport Cup Optional Optional
Michelin Pilot Sport Cup+ / N-Spec Optional Optional
Pirelli P Zero Corsa System Optional Required
Yokohama A048 LTS Optional Optional
Yokohama A048 M Optional Optional
Yokohama A048 MH Optional Optional
NOTE: Depending on the severity of the track surface and layout, vehicle setup and performance, as well as ambient air and track temperatures, Michelin Pilot Sport Cup, Pilot Sport Cup+ / N-Spec, Yokohama A032R H and Yokohama A048 tires can be track driven in dry conditions without shaving.
Air Pressure for Competition Tires
The table below suggests tire inflation pressures for competitive driving. Tires should be reset to normal inflation pressures when returned to the street. These recommendations should be used as a starting point. Pressure can be adjusted to match the driver's preferences. Adjust pressure in 2 psi increments
Type of Vehicle Position Pressure
Front Wheel Drive Front 35-45 psi
Rear 30-40 psi
Front Engine/Rear Drive Front 35-45 psi
Rear 30-40 psi
Rear Engine/Rear Drive Front 35-45 psi
Rear 35-40psi
When racing on D.O.T. approved tires air pressure is a major consideration in tuning the handling of your car, especially in cases where suspension adjustments are limited. The chart below shows some of the changes you can make to change the balance of the car.
Guide To High Performance Handling
Adjustments Decrease Understeer Decrease Oversteer
Front Tire Pressure Higher Lower
Rear Tire Pressure Lower Higher
Front Tire Section Larger Smaller
Rear Tire Section Smaller Larger
Front Wheel Camber More Negative More Positive
Rear Wheel Camber More Positive More Negative
Front Wheel Toe Toward Toe-Out Toward Toe-In
Rear Wheel Toe Toward Toe-In Toward Toe-Out
Front Wheel Caster More Positive More Negative
Front Springs Soften Stiffen
Rear Springs Stiffen Soften
Front Anti-sway Bar Soften (Thinner) Stiffen (Thicken)
Rear Anti-sway Bar Stiffen (Thicker ) Soften (Thinner)
Weight Distribution More Rearward More Forward
To get even tire wear when using D.O.T. tires you must be very careful not to use too low of a tire pressure. The Hoosier Radials can wear unevenly if underflated and seem to work best at much higher pressures, such as the mid 30s to as high as 50 psi. Underinflation will cause a thin ring of wear at the very edge of the tread. The best results on the Hoosiers seem to come when they are properly inflated, on fairly wide wheels, and with a good amount of negative camber. If properly inflated, these problems can be avoided. Probably the biggest adjustment you can make to improve tire wear is the driver. Avoid sliding the tires, locking up the wheels under braking and drive as smooth as possible.
TIRE PRESSURES IN THE RAIN
For both autocross and road racing, increase tire pressures 6-10 psi from what you would normally run in dry conditions. Hydroplaning occurs when a wedge of water develops between the tire and road surface. This wedge can actually lift the tire off the road and eliminate traction. Increasing the pressure rounds the profile of the tire by decreasing the deflection of the tire. This results in a smaller contact patch - narrower and shorter. It also helps keep the grooves in the tread open so they can channel the water out from under the tire.
Getting More Out of Competition Tires
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When developing your vehicle's handling, maximize your:
Wheels - Always use the widest wheel allowed on your car's class, that fits your car and/or is recommended by the tire manufacturer for your tire size.
Alignment-Springs and Sway Bars - Keep our tires perpendicular in corners, try to achieve neutral steer (With power oversteer for rear wheel drive cars)
Shock Absorbers - Can help tune transitional handling
Inflation Pressures - Always use the lowest pressure possible, while higher inflation pressures may enhance responsiveness, they sacrifice traction. If uneven wear begins while at low pressures, increase them.
Tire Tips
Between races, never store tires exposed to the elements on your race car trailer's tire rack or outside your shop, store them in a cool, dry place away from electric motors.
Immediately after every track session, remove debris and inspect your tires for damage and wear. If possible, let them cool while they are off the ground
Your tire's tread temperatures as read by a pyrometer will "never" be even across your tire's tread (Unless you have just completed a successful tuning session on a skid pad.)
Tire pressure increases 1 psi for every 10 degrees in ambient temperature
Shade pairs of tires from direct sunlight between sessions as much as possible. The sun's heat will raise your tire's pressure.
Autocross inflation pressures should be adjusted warm, road racing inflation pressures should be adjusted hot.
For racing or track events, your rain tire's starting inflation pressure should be higher than your dry tires.
Tires are part of your suspension, using lower profile tires is like using shorter, stiffer springs.
Competition Tire Heat Cycling Service
As participation in autocrossing, track days, driving schools and road racing continues to grow in popularity, the tire manufacturers have developed unique DOT-legal competition tires which feature very sophisticated tread compounds. However just like other high performance parts, these tires will provide more consistent performance and last longer if they are properly broken-in.
The first time a competition tire is used is the most important. During that run, its tread compound is stretched, some of the weaker bonds between the rubber molecules will be broken (which generates some of the heat). If the tires are initially run too hard or too long, some of the stronger bonds will also be broken which will reduces the tire's grip and wear qualities. Running new tires through an easy heat cycle first, and allowing them to relax allows the rubber bonds to relink in a more uniform manner than they were originally manufactured. It actually makes them more consistent in strength and more resistant to losing their strength the next time they are used. An important heat cycling step is that after being brought up to temperature, the tires require a minimum of 24 to 48 hours to relax and reform the bonds between their rubber molecules.
Looking at the heat cycling system, it positions a mounted and inflated tire between rollers which apply pressure while the tire is rolled up to speed. It is very important to note that this allows heat to be generated as a result of deflecting (stretching) the tire within its normal operating range. There is no "artificial" heat added (no oven, no forced air, etc). Then they receive the stamp showing they are Tire Rack heat cycled.
we confirmed that in our controlled environment we were able to achieve appropriate and more consistent temperatures across the tire's tread without causing treadwear. All of these are significant improvements over heat cycling tires on our test track. And the 24 to 48 hour waiting period efficiently occurs while the tires are in transit to you. That means the tires are ready to use when they arrive!
The cost of heat cycling is $15 per tire. Hoosier, Kumho and Yokohama all recommend that their competition tires be "heat cycled" before being run in competition.
Breaking In Your Tires
Tires are comprised of many layers of rubber, steel and fabric. Due to these different components, your new tires require a break-in period to ensure that they deliver their normal ride quality and maximum performance. As tires are cured, a release lubricant is applied to prevent them from sticking in their mold. Some of the lubricant stays on the surface of your tires, reducing traction until it is worn away. Five hundred miles of easy acceleration, cornering and braking will allow the mold release lubricant to wear off, allowing the other tire components to begin working together. It is also important to note that your old tires probably had very little tread depth remaining when you felt it was time to replace them. As any autocrosser or racer who has tread rubber shaved off of his tires will tell you, low tread depth tires respond more quickly. Don't be surprised if your new tires are a little slower to respond (even if you use the exact same tire as before). Their new, full depth brings with it a little more tread squirm until they wear down.
NOTE: Be careful whenever you explore the capabilities of your new tires. Remember that every tire requires a break-in period of 500 miles for optimum performance.
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