[Cruzator]

It was but it wasn't all downhill. That run was from the Shell station in Fairplay to the Conoco in Bailey. While a lot of downhill there are two passes (Red Mountain Hill and Kenosha Pass) between them I was above 50 MPG at the top of Kenosha which is about the mid point on that segment. That's why I also posted that I've seen ~60 MPG on "flat" ground for 25 miles.

About a year and a half ago I drove from my home on the south side of Denver to the University of Wyoming in Larimie, WY and back. I took the same route in both directions which eliminated elevation changes in the fuel economy calculations and still ended up on the high side of 55 MPG for the day.

The ECO MT really, really likes altitude and hills. I get 1-3 MPG improvement in overall fuel economy in Colorado than I do when driving the car in the east.

Impressive, Obermd!!! Did you ever get a chance to do a check from Eisenhower to the twin tunnels?

 

[Cruzator]

OK. You guys made me go out and look. I always have mine set on the 500 mile best trip. Here is my best 25 miles . . and yes, mountains play a huge part in it.

 

[Cruzator]

Guess 1 is wrong - our gasoline is generally 10-15% ethanol.


Guess 2, 3, & 5 are probably the reason with guess 2 being the seriously important one. P&G can boost fuel economy by up to 80% when done properly.


Guess 4 is correct for NA engines. The 1.4T engine in the Cruze LT, ECO, and LTZ uses the turbo-charger to keep the air/fuel mixture at the optimum for clean burn.

Agreed. I would go with 2. Lots of downhill miles with very little uphill once crossing over the divide. Basically going from 11,000 feet (or about that) down to 5500 feet. All downhills except for a few stretches. One the other hand, going the other way, I may only get 32 mpg.

 

[Cruzator]

OK. You guys made me go out and look. I always have mine set on the 500 mile best trip. Here is my best 25 miles . . and yes, mountains play a huge part in it.
View attachment 214786

That was the run obermd had me check from the Johnson tunnel (around 11,100 feet) down to the twin tunnels at Idaho Springs (probably around 6700 feet or so). I was actually still pegged passed 99.9, so I drove it to the top of Floyd Hill (probably around 7600 feet)

 

[Cruzator]

In theory higher pressures yield, lower rolling resistance, which equals higher fuel economy. It also creates a stiffer sidewall, that prevents the tire from "leaning" when turning. This improves handling.

There is a point of diminishing returns though. At some pressure, the tire becomes so stiff that imperfections in the road are no longer absorbed by the tire, but instead transferred into the suspension. Harmonics sets up in the suspension and actually causes higher rolling resistance.

Then you also get other negatives of higher pressure. The ride quality suffers, as does straight line traction.

This is definitely not for everyone. Like I said, I understand the theory behind higher pressures and also the consequences of running them. There is definitely a point north of the vehicle manufacturers recommended tire pressure that will give better mileage and handling and a point south of their recommendation that will improve ride quality and straight line traction. It is up to the individual to find what compromises they want to make to get what they want from the car; higher fuel mileage or softer ride.

I have left my tires at the tire manufacturers maximum limits for 85,000 miles and haven't had any complaints. I haven't done any side-by-side mileage tests at lower pressures to verify that I am running the optimum pressure for economy though, so your mileage may vary...


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Bradherr, looks like we are both averaging the same MPG. I run my tires around 45 PSI, in the summer. I tried it around 50 PSI, but I didn't care for the ride and didn't notice much difference in MPG's.