"Spats are fitted at the front of each wheel arch to further
suppress airflow changes around the tires, which themselves feature a
low rolling resistance compound."

This winter I received an practical lesson on the total uselessness
of the low rolling resistance tires. My wife traded her old Subaru
for a 2014 model, advertised as now being capable of achieving 30+
mpg. The first thing that tweaked my curiosity about the new Subaru
was the fact that before we drove off in our new car, the salesman
walked out and started letting air out of the tires. He said "Keep
tire pressure at 29 psi" (?????).

The good news was that the car did indeed make 30+ mpg. The bad new
was that the car interacted with the highway pavement joints like a
farm hay-wagon crossing railroad-tracks.. and things got worse.... We
could barely get out of our N Wisconsin snow-covered driveway. The
LCD display on the dash would continually display orange wavy tire
tracks as we tried to climb the long hill leaving our yard. A couple
of times we slid right off the road into the snowbanks along the
side. It was almost as if the tires didn't know which way forward
was.

After a couple of days of total frustration I called the Subaru
dealer, who graciously offered to replace the Yokohama plastic tires
with genuine Firestone winter tires. The Subaru is now nearly
unstoppable, goes like a tank through most anything. I have not seen
the gas-mileage display hit 30 mpg since the tire swap, but I could
not care less. It is now April 14th, we still have 2' of snow in our
yard, and a few more inches are predicted for tomorrow night. :(

RBerglund

The prius rides the same way. You feel every pebble in the road.


Paul Lamar

Even the ¨all season¨ tires fitted by the factory do not work in
REAL winter conditions. When you get a dump of snow, especially the
wet stuff, you may as well be on drag slicks. Once the temp drops to
about 5 degrees C switch to winter tires. Steel wheels with the
winter tires is a good plan as the steel wheels are more durable and
cheaper to replace if you slide into a curb. Then once it is warm
again just bolt the original tires back on. Fuel economy is not going
to break records when the front tires are pushing through 2-3¨ of
snow. This from Alberta, Canada. Early last winter, every time it
snowed was 20cm or 8¨.

Dale Davies

Prius- Pfffffft! Clown car.  According to Mazda the 2nd generation Rx-7 (FC) with the sport aero pkg had a Cd of .29!
All of Paul's work w/the TC 20B and his site inspired me to start a thread on rx7club:
http://www.rx7club.com/general-rotary-tech-support-11/high-fuel-economy-mpg-rx7-ideas-1057639/
-Not, much has come of it yet, but one of the members has been getting some amazing MPG's w/a PP'd engine!

-Dan

.25 is better than .29 :)

It is called the coefficient of drag

Aero Drag = coefficent of drag times the frontal area in square feet times the dynamic pressure.

Aero Drag = tire rolling drag at 50 MPH roughly.

Tire rolling drag is linear while aero drag is a square law function.

For example at 100 MPH tire rolling drag is double but aero drag is four times
higher.

Paul Lamar



The Rotary Engine News Letter. Powered by Linux. ACRE NL web site.
http://www.rotaryeng.net. You Tube http://tinyurl.com/beqqxas.
Copyright 1998-2014 All world wide rights reserved.