On 3/10/2012 7:29 AM, Bruce Richmond wrote:
The National Academy of Science discusses LRRT issues here:
For reference, the Prius OEM Bridgestone tires provide an estimated 3%
lower rolling resistance, with the tradeoffs being a wear rating of 160,
which is about half the 300-400 one sees on even performance tires (even
other Bridgestones) providing far better wet and dry traction, braking
and cornering performance.
The relevant part would be:
The impact of emphasizing one performance objective (such as low
rolling resistance) over other performance criteria is inconclusive.
Some studies have shown that tires with low rolling resistance do not
appear to compromise traction, but may wear faster than conventional
tires. Another study in 2008 by Consumers Union and summarized by
Automotive News (Automotive News, 2008) concluded that there may be a
reduction in traction, because of low-rolling-resistance tires, that
increases stopping distance. The study is not rigorously controlled,
and other influences may confound the results. The response by one
tire manufacturer, Michelin ( Barrand and Bokar, 2008), argues that
low-rolling- resistance tires can be achieved without sacrificing
performance factors by balancing the design and manufacturing process
variables. Tire makers are continuing to research how to get optimal
performance (including fuel economy) without sacrificing other
criteria such as safety or wear. Goodyear points out that performance
tradeoffs between rolling resistance, traction, and tread wear can be
made based on materials and process adjustments, which also affect
cost (Goodyear Tire & Rubber Company, 2009).
That pretty much backs what I said, the end result depends on more
than just the rolling resistance. I also noticed in there:
The opportunity to improve fuel economy by reducing rolling resistance
is already used by OEMs to obtain better EPA numbers, and so
original equipment tires tend to have lower rolling resistance than
consumer-replaced tires because typical values for the coefficient of
rolling resistance (ro) values differ between them (NRC, 2006). This
represents an interesting value tradeoff. The OEMs are more interested
in getting low-rolling-resistance tires to show improved fuel economy,
and people buying replacement tires are more interested in low cost
and durability. Therefore the total opportunity for fuel consumption
reduction is defined by the fraction of the tires on the road that
falls into each category. Education of the public on the subject of
low-rolling-resistance tires for replacement tires and the continued
introduction of tire pressure monitoring systems, which is discussed
below, may help improve in-use performance of tires for fuel
I would read that to say LRRT are a good thing which the public should
be educated to take advantage of.
On 3/10/2012 2:22 PM, Bruce Richmond wrote:
I would say the observed results on the Prius Bridgestones make it an
open and shut case for big compromises.
I would say that is a sampling of only one of many possible.
On 3/10/2012 5:25 PM, Bruce Richmond wrote:
Got any of your own? Or will it be <crickets>?