TomT
Well-known member
You will often read that someone will say that their fuel mileage dropped when they got new tires and, therefore, the new tires must not be as efficient as the old... Some things to keep in mind in this regard:
1. New, Full-Treaded Tires Generate More Rolling Resistance Than Shallow-Treaded, Worn Tires
Tire rolling resistance gradually drops by about 20% during the life of a tire as the tread wears from its original molded depth to worn out. This can be attributed to the reduction in tread mass and rubber squirm, as well as subtle hardening of the tread compound during years of service and exposure to the elements.
While this gradual reduction in tire rolling resistance and minor increase in fuel economy may be too subtle to register during the tire's life on a tank-by-tank basis, the virtually instantaneous switch from worn tires to new tires (even if they are the same brand, type and size) will typically result in an increase in rolling resistance of about 20%. Since the automotive industry estimates a 10% increase in tire rolling resistance will result in a 1% to 2% decrease in vehicle fuel economy, drivers should expect to experience a potential 2% to 4% decrease in mpg.
2. New, Full-Treaded Tires Travel Farther per Tire Revolution Than Shallow-Treaded, Worn Tires
Vehicles are programmed with their Original Equipment (O.E.) tire's revolutions-per-mile to allow their odometers to calculate the distance traveled. Unfortunately, vehicle odometers aren't 100% accurate and the tire revolutions per mile will change (increase) as a tire's tread wears. This makes the vehicle to appear to travel further for a given unit of energy expended and increases the apparent fuel mileage even though the actual mileage may not have changed. Thus, again, older tires appear to give better fuel mileage than new tires...
While many of these individual differences may seem insignificant, it is easy to understand that when they are added together, the new tires may appear to reduce vehicle fuel economy. It also means that a Toyota Prius appearing to get 50.0 mpg just before replacing its worn-out tires with new tires of the same brand, type and size, might be reduced to registering just 47.25 mpg afterwards, even if all of the driving conditions were identical.
Remember, "your mileage may vary..."
1. New, Full-Treaded Tires Generate More Rolling Resistance Than Shallow-Treaded, Worn Tires
Tire rolling resistance gradually drops by about 20% during the life of a tire as the tread wears from its original molded depth to worn out. This can be attributed to the reduction in tread mass and rubber squirm, as well as subtle hardening of the tread compound during years of service and exposure to the elements.
While this gradual reduction in tire rolling resistance and minor increase in fuel economy may be too subtle to register during the tire's life on a tank-by-tank basis, the virtually instantaneous switch from worn tires to new tires (even if they are the same brand, type and size) will typically result in an increase in rolling resistance of about 20%. Since the automotive industry estimates a 10% increase in tire rolling resistance will result in a 1% to 2% decrease in vehicle fuel economy, drivers should expect to experience a potential 2% to 4% decrease in mpg.
2. New, Full-Treaded Tires Travel Farther per Tire Revolution Than Shallow-Treaded, Worn Tires
Vehicles are programmed with their Original Equipment (O.E.) tire's revolutions-per-mile to allow their odometers to calculate the distance traveled. Unfortunately, vehicle odometers aren't 100% accurate and the tire revolutions per mile will change (increase) as a tire's tread wears. This makes the vehicle to appear to travel further for a given unit of energy expended and increases the apparent fuel mileage even though the actual mileage may not have changed. Thus, again, older tires appear to give better fuel mileage than new tires...
While many of these individual differences may seem insignificant, it is easy to understand that when they are added together, the new tires may appear to reduce vehicle fuel economy. It also means that a Toyota Prius appearing to get 50.0 mpg just before replacing its worn-out tires with new tires of the same brand, type and size, might be reduced to registering just 47.25 mpg afterwards, even if all of the driving conditions were identical.
Remember, "your mileage may vary..."