Hybrid Car Review

Low rolling resistance tires are often touted as being very helpful when you want to help conserve fuel. By some estimates, up to 6% of your fuel bill could go away if you have low rolling resistance tires.

But what are low rolling resistance tires and how can you find them next time you want to replace your tires?

What are Low Rolling Resistance Tires?
First, the definition: Low rolling resistance tires are just what you think they are. They provide less resistance (less friction) when rolling along than other tires do. In other words, how easily do they roll down the road? Energy is continually being wasted through heat between the tire and the road, within the tire and between the tire and the rim.

Keep in mind that rolling resistance is not the same as grip, or how well a tire 'handles' the road. Although the two can be related, it is not a one to one relationship and you don't necessarily have to lose the grip to improve your rolling resistance.

As a simple rule, the harder a tire is, the less rolling resistance it will have. Which is why making sure your tires are properly inflated is so important. No matter what type of tire you have, the best thing you can do for fuel economy today is to check your tire pressure.

What kind of difference does resistance make?
Although there is no hard and fast rule, a 10% reduction in tire rolling resistance should improve your fuel economy 1 to 2% (according to a study by the NREL). But the number varies widely by tire and vehicle type.

How is rolling resistance measured?
The Society of Automotive Engineers measures rolling resistance by measuring the force needed to roll a tire against a dynamometer at a fixed speed of 50 mph (test procedure SAE J1269). SAE J2452 promises better results by measuring at different speeds, but SAE J1269 is the golden standard. Rolling resistance can typically vary 20 to 30% even among tires of similar size type and level of performance.

How does it affect me?
It is estimated that rolling resistance can account for 15% (stop and go driving) to 25% of a cars resistance to moving. So if a low rolling resistance tire improves your vehicles rolling resistance by 20%, your fuel mileage can be improved 3 to 5%.

Let's say you drive 15,000 miles a year at 20 mpg. That's 750 gallons a year. A 4% improvement means you save 30 gallons a year or $90 (at current fuel prices: $3). That's enough to justify paying extra for a low rolling resistance tire, as long as it's duration is the same as a similar tire, but with higher rolling resistance.

California adopts the first fuel efficient tire law
Joe Nation (D-San Rafael) sponsored law AB 844 back in 2003. In July 2008, the law will go into affect, mandating labeling and fuel efficiency standards for all replacement tires sold in California. The law directs the California Energy Commission, in consultation with the California Integrated Waste Management Board (CIWMB), to adopt and implement a tire energy efficiency program of statewide applicability for replacement tires for passenger cars and light-duty trucks.

According to the CEC AB 844 can be considered as consisting of three implementation phases:

Phase I, the Energy Commission shall:

1. Develop and adopt a database of the energy efficiency of a representative sample of replacement tires sold in the state, based on test procedures adopted by the Energy Commission.
2. Develop and adopt a rating system for the energy efficiency of replacement tires that will enable consumers to make more informed decisions when purchasing tires for their vehicles.
3. Establish requirements for tire manufacturers to report the energy efficiency of replacement tires.

Phase II, the Energy Commission, in consultation with the California Integrated Waste Management Board (CIWMB), shall adopt and implement:

1. A tire energy efficiency program for replacement tires designed to ensure that replacement tires sold in the state are at least as energy efficient, on average, as Original Equipment (OE) tires on new passenger cars and light-duty trucks except to the extent that the Energy Commission determines it is unable to do so in a manner that:


• Is technically feasible and cost effective
• Does not adversely affect tire safety
• Does not adversely affect the average life of replacement tires
• Does not adversely affect the state effort to manage scrap tires


2. Consumer information requirements for replacement tires for which standards have been adopted.

Phase III, the Energy Commission, in consultation with the CIWMB, shall:

Review and revise the program, including standards, as necessary not less than once every three years.

As a side note, it seems that manufacturers like Michelin have been helping to craft the rules.

Where do I find low rolling resistance tires?
That's the rub right there. The original tires on your car probably are low rolling resistance tires. Car manufacturers, especially with the public emphasis on environmental friendliness and fuel economy, want to get the best mpg rating they can from the government. An easy way to improve their rating (every little bit helps!) is to make sure the tire on the original vehicle is a low rolling resistance tire.

But replacement tires are another story. As of now, there are no requirements for tire makers to indicate how fuel efficient their tires are, and so they don't. There have been some independent tests done (see the pdf from greenseal for their recommendations) but until July, 2008 when California's new rules are adopted, you may need to contact the manufacturers for more information.

Do you know where to get more information on tires? Let me know in the comments. I'm sure everyone will appreciate the knowledge.