ALT-3 Gas Mileage and Tires
With fuel prices higher than ever many drivers are looking to make their vehicles as fuel efficient as possible. Understanding a few details about your tires will help you maximize your fuel efficiency. In addition to tire inflation issues, the tire design, size and performance characteristics all contribute to the gas mileage of your vehicle.
The US Department of Energy has announced that proper inflation of your vehicle tires can save you up to 3.3% of your fuel usage. Just think at around $3.00 a gallon that can save you around $.10 per gallon. Many of us drive miles out of our way just to save a few cents a gallon, when the savings are basically free. Just keep your air pressure at the proper value as indicated by the recommended tire inflation sticker found in your car. Inflation stickers are often located inside one of the door frames, trunk lid, or inside glove box.
The air pressure in your tire will determine how much surface area of your tire is in contact with the road. If your tires are under inflated, there will be more rubber meeting the road, and it will take more effort for your engine to roll the tire against this increased friction. Over inflating your tire to maximize fuel economy is not a good idea, as too small of a surface area contacting the road can make for unsafe driving conditions. Also other factors such as transverse winds, curvature of the road, can cause the tire to stray from it's forward coarse, again resulting in more energy required to keep the vehicle operating in it's desired direction. It will also take you longer to brake with over inflated tires.
The tire design and size will impact your fuel economy as well. Simply put a wider tire amy look better, or give more feel of the road, but it will also have more surface in contact with the road, again, more energy is required to turn the wider tire. Thinner tires will be more fuel efficient, however, too Little contact area can lead to dangerous conditions as listed above. The best advice is to refer to the tire inflation sticker, as it will give ther recommended tire size for your vehicle.
Tire size is described by the numbers written on the side of your tire. For example:P175 80R15, P indicates the tire is a passenger tire(LT would designate a light truck tire, and T is for a temporary, spare, tire). 175 is the width of the tire in centimeters. 80 is the height of the tire from the rim to the road as a percentage of the tire width. (175 CM X 80% = 140 CM). The R15 indicates the radius of the tire rim in inches.
Radical changes in the tire size from the original factory size can have hidden effects upon gas mileage. If the overall diameter of the new tire is smaller than the overall diameter of the old tire, the smaller tire require more rotations to travel the same distance as the larger tire.The vehicle odometer will register more miles than you actaully have driven. Thus your MPG calculations will be overstated. The opposite is true for increasing overall tire diameter. You will find your MPG has dropped!
The speed rating of a tire gives the rated maximum speed for the tire. The alpha designation is listed as follows:M 81 mph Temporary ..spare tiresN 87 mph Temporary ..spare tiresP 93 mphQ 99 mphR 106 mphS 112 mphT 118 mphU 124 mphH 130 mphV 149 mphW 168 mphY 186 mphThe trend is for car enthusiasts to buy higher rated speed tires, even if the vehicle is not capable of achieving or maintaining these speeds. This will often lead to a drop in fuel economy as the higher speed tires tend to have better grip, which will require more energy to turn the tire.
AA, A, B or C are the indications used to rate a tires traction. AA is the best and C is the worst. While traction is key to safety, the tires with the highest traction, will also consume the most fuel.
Realistically the performance characteristics will only amount to less than 1 % change in overall fuel economy. Choose the tire that is best for your driving style and road conditions. Radical changes in tire size will give you false fuel efficiency data, and buying tires based on looks alone, will almost always cost you more in fuel.
The majority of the efficiency gains are by keeping your tires pressurized with the proper tire inflation.
