Consumer Tires and Wheel Knowledge

Reading A Tire Sidewall Passenger Tires (P-Metric) Figure 1 Winter Tire Designation Your tire has very useful information molded into the sidewall. It shows the name of the tire, its size, whether it is tubeless or tube type, the maximum load and maximum inflation, the important safety warning and much other information. Shown below is the sidewall of a popular "P-metric," speed-rated auto tire: P215/65R15 95H M+S "P" stands for passenger P Metric Sizing "215" represents the width of the tire in millimeters "65" is the aspect ratio of height to width – so in this example the sidewall height is 65% of the tire width "R" means radial construction "15" is the rim diameter in inches "95H" is the load and speed index. This description means the load index is (95) and (H) is the speed rating. Some speed-rated tires may include the speed symbol immediately before the "R" instead of showing a service description. ( i.e. P225/60HR16) "M+S" means it is an All-Season Tire suitable for Mud and Snow. The Mountain Snowflake symbol is the designation that the tire meets the RMA definitions for use in severe snow conditions. The maximum load is shown in kg (kilograms) and in lbs (pounds), and maximum pressure in kPa (kilopascals) and in psi (pounds per square inch). The letters "DOT" certify compliance with all applicable safety standards established by the Department of Transportation (DOT). Adjacent to this is a tire identification or serial number. This serial number is a code with up to 12 digits that are a combination of numbers and letters. The last characters are numbers identifying the week and year of manufacture. (Example: "1501" means fifteenth week of the year 2001.) Load Index The load index is an assigned number ranging from 0 to 279 that corresponds with the load-carrying capacity of a tire. Most passenger car tire load indices range from 75 to 105 ---although some passenger tires carry more. The Load Index on any vehicle needs to be maintained in order for the tire to be capable of carrying the maximum load of the vehicle as designed by the manufacturer. Speed Rating The speed rating of a tire indicates the speed category (or maximum range of speed) at which the tire can carry a load under specified service conditions. It also is used to provide the expected steering response engineered into the vehicle by the manufacturer. The Original Equipment (OE) speed rating should be followed whenever possible. Often times, the desired replacement tire is not available in the OE speed rating. (i.e. When selecting Winter Tires) In this case the highest available speed rating is the desired replacement. If the replacement tires are different in speed rating than the OE tires then the maximum speed capability of the vehicle is limited to the lower speed rated tires, and the handling characteristics of the vehicle will be compromised, at all speeds. Note: If the OE recommended speed rating is not followed, it can often times lead to accelerated or abnormal tire wear. Winter Tires Always Install 4 Winter Tires Often times when changing to winter tires, the OE speed rating may not be available. In these instances, it is acceptable to purchase a Winter Tire with a lower speed rating than the OE speed rating, so long as the consumer understands that the maximum speed of the vehicle is going to be limited to the speed rating of the Winter Tire, and that a lower speed rating will also result in a different steering response from the vehicle. Often times when changing to winter tires, the OE speed rating may not be available. In these instances, it is acceptable to purchase a Winter Tire with a lower speed rating than the OE speed rating, so long as the consumer understands that the maximum speed of the vehicle is going to be limited to the speed rating of the Winter Tire, and that a lower speed rating will also result in a different steering response from the vehicle. Understeer & Oversteer The reason you always want the best performing tires on the rear of the vehicle, is to ensure you do your best to eliminate any oversteer situation. So regardless if the best tires are by tread depth, or tread type (Winter tires), the best 2 tires should always be on the rear. The reason you always want the best performing tires on the rear of the vehicle, is to ensure you do your best to eliminate any oversteer situation. So regardless if the best tires are by tread depth, or tread type (Winter tires), the best 2 tires should always be on the rear. Understeer is the condition that while driving the front wheels lose traction and are unable to turn the vehicle in the desired direction. This will cause the front of the vehicle to push out on a turn. The natural driver response to this situation is to lift off the throttle and apply brake as required to get the vehicle to respond. A common example of understeer would be trying to take a turn to quickly for the road conditions, and having your vehicle push out on the turn, and the driver having to lift off the throttle and apply brake to get the vehicle to turn in the desired direction. Oversteer is the condition that while driving the rear wheels lose traction while the front wheels grip. Oversteer is a more dangerous problem for the average driver than is understeer, because there is no natural driver reaction that will result in the driver regaining control of the vehicle. The most common result is that the driver is caught off–guard when this happens, and a collision or accident will be the result This is why the best tires must always be mounted on the rear of the vehicle, to try to prevent any occurance of oversteer. Tire Disclaimer & Warning The OE Load Index must be maintained at all times to provide sufficient performance to carry the weight of vehicle as designed by the manufacturer. The OE Speed Rating should be maintained at all times to maintain the handling characteristics of the vehicle and the maximum speed capability of the vehicle. If the desired speed rating is not available in the tire being purchased, then the highest available speed rating would be the desired fitment. All 4 tires on a vehicle should be of the same speed and load index and of the same tread pattern and tread wear. Tires with the most tread should always be mounted on the rear axle of the vehicle, regardless of Rear Wheel Drive or Front Wheel Drive application. Warning: If the replacement tires are different in speed rating than the OE tires then the maximum speed capability of the vehicle is limited to the lower speed rated tires, and the handling characteristics of the vehicle will be compromised, at all speeds. If the replacement tires are a lower load index than the OE tires, then the maximum load capability of the vehicle is limited to the maximum load capability of the tires. If dissimilar or mismatched tires are mounted on front and rear axles of the vehicle, then the dissimilar or mismatched tires could result in loss of control of the vehicle. Active Green + Ross do not endorse the operation of any vehicle in an unsafe or unlawful manner since property damage, personal injury or death may occur.

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