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Low Rolling Resistance Tires

It's time for new tires on my VW Jetta TDI commuter cars.  I have two identical black '99.5 Volkswagen Jetta TDI 5 speed sedans that I use for my 70 mile daily commute.  I alternate between the two cars, running biodiesel and fleet maintaining them to keep them on the road.  This might be a little nutty, but I have names for all my cars.  The two Jettas are "Hansel" and "Gretel"  It's an easy way to tell them apart and all my cars are a part of the family!

I bought Hansel first with about 250,000 miles on him but with a brand new timing belt and water pump.  He currently has over 300,000 miles and runs perfectly.  Gretel was purchased 6 months later with 220,000 miles and a brand new AC system.  She now has over 260,000 miles and is in great condition.

Now that both vehicles are due for a new set of tires, I'm doing the research to pick the best replacement tires for my driving conditions.  I want to maximize mileage but I also am concerned about safety.  My research has focused on tires with low rolling resistance.

Rolling resistance related to car tires is a way to describe the energy wasted to make a tire roll when loaded with the weight of an automobile and it's contents.  It can also be expressed using the Rolling Resistance Coefficient (RRC).  What makes a tire have lower rolling resistance?  It is a combination of tire weight, materials and tread pattern.  Based on the Department of Energy's research, up to 15% of fuel consumption in a passenger car is used to overcome rolling resistance.  For heavy trucks, this can be as high as 30% of fuel consumption.

For my Jetta, picking a tire with a very low coefficient could improve fuel mileage by up to 3%.  That may not seem like much but could account for between 1-2 mpg.  Assuming that the tires last around 45,000 miles, that could save approximately 60 gallons of fuel.  That doesn't sound like much but it adds up if everyone chooses an LRR tire over standard.

Here are some important considerations:

• Rolling resistance isn't the only consideration when choosing the optimal tire for fuel efficiency.  Make sure with any tire you choose that you inflate them to an optimal pressure.  Most tire shops will tell you to inflate your tires to 32 psi for passenger cars no matter what the maximum pressure rating.  For tires with a maximum pressure of 44 psi, I run them at 40 psi to lower the rolling resistance and improve fuel economy.  However, if you live in an area that gets snow or lots of rain, you need to balance safety with fuel efficiency.  Higher tire pressures reduce the traction of the tire in inclement weather.  If you have your tires inflated to a high pressure, consider reducing some of the pressure on rainy days for better traction.  This can be done with a tire pressure gauge.
• Most new vehicles will have low rolling resistance tires installed from the factory since they help with meeting Corporate Average Fuel Economy (CAFE) standards.  They are also not always more expensive than most medium price brand name tires.
• Hybrid vehicles will also have low rolling resistance tires installed to maximize fuel economy
• Picking the stock replacement tires is always a safe option to get a LRR tire.
• Some online tire sites now list tires with a LRR flag for those that have a low RRC value.

For my search, I used tirerack.com.  I entered my vehicle year and model and looked for tire options listed as "LRR."  For my Jetta, here are the LRR tires listed currently on Tire Rack:
(tire size: 195-65-15)

1. Yokohama dB Super E-Spec (Grand Touring Summer)
2. Bridgestone Ecopia EP422 (Grand Touring All-Season)
3. Continental ContiProContact (Grand Touring All-Season)
4. Kumho ecowing All Season KH30 (Grand Touring All-Season)
5. Michelin Energy MXV4 S8 (Grand Touring All-Season)
6. Pirelli P6 Four Seasons Plus (High Performance All-Season)
7. Firestone Affinity Touring (Standard Touring All-Season)
8. Goodyear Assurance Fuel Max (Passenger All-Season)
9. Pirelli Winter 210 Snowcontrol Serie II (Performance Winter/Snow)
10. Michelin X-Ice Xi2 (Studless Ice & Snow)

Since I planned on buying and getting them installed locally, I called a local tire shop to see if they had any of the LRR tire models in stock.  They had the Pirelli P6 Four Seasons Plus tire in 195-65-15 size for my Jetta.  According to the specifications and Pirelli description, they use a new manufacturing method they call ELRR or Extra Low Rolling Resistance.

Here is the description of ELRR from the Pirelli website:

"The tire's internal structure includes twin, high tensile steel belts reinforced by spirally wrapped nylon to enhance handling by stabilizing the tread area. The P6 Four Seasons Plus features Pirelli's Extra Low Rolling Resistance (ELRR) system that integrates belt, sidewall and carcass compounds and components to reduce weight and rolling resistance, while optimizing overall integrity."

I had these installed on Gretel and will test them and report back on ride and fuel mileage.  I'll have to admit though, I don't keep as close track on fuel mileage since I fill up from a Jerry can of biodiesel and it's hard to keep track.

Now I also need to make a tire choice for Hansel soon.  Help me choose the next set of tires.  Should I go for a second set of Pirellis or is there a better option for fuel efficiency?

Research Links:

Department of Energy Page on Low Rolling Resistance Tires

Wikipedia: Low Rolling Resistance Tires

Presentation: California Energy Commission - Fuel Efficient Tire Program

Hyper-Miling Forum

UK Hyper-Miling Forum

TDI FORUM Post on Low Rolling Resistant Tires