hatchetf15

True story. Florida was very flat. All tricks, including much drafting, were employed. Helped the boredom of an 11 hour drive significantly. And this was only for one tank with obsessive attention. Manual pedal.

My cruise control loves to give it the juice going up the smallest incline, then hunts for the correct speed with gas.

Bomba

This is pretty consistent with the best that I ever got with my 2006 CTT. I got 18.7mpg, calculated properly, not using the on board computer. I typically do this every fill up with all my cars. Refill, calculate gallons against miles travelled.

My current 2008 CTT doesn't ever go above 11mpg, but that's all city driving.

blaino

It's usually right around 55. This was actually one of the main reasons highways, when first built, had speed limits of around 55 as this was the optimal gas mileage during the fuel crisis.

JBI

Yes, true. And the reason that many over-the-road trucks are governed to 60-62 MPH. The fleets know how to stretch a gallon of fuel. I've never heard 40 mph as a sweet spot; I've always heard that aerodynamic drag begins to become a factor around 60 mph. Regardless of how slippery the vehicle or how advanced the powertrain, aerodynamics start to take more power around that speed. How *much* more power depends on many factors - c.d., frontal area, drivetrain efficiency, etc.

OP, you can search for hypermiling if you're into that sort of thing or interested in the techniques. I once had a late '90's Civic HX with taller final drive gearing from the factory and Honda's lean-burn VTEC-E system which was pretty cool. You could get 47 MPG in the summer with it pretty regularly if you learned the feel of the system engaging and disengaging, but if you needed the 'power,' (all 110 hp or so IIRC), you had it -- unlike the DX and LX variants which could get similar mileage but only because their peak engine outputs were 30 or 40 hp less. The EX with it's standard VTEC engine and shorter gearing was always good for about 35 MPG. Getting great mileage can be a pretty fun game; one I no longer feel like playing, though.

Mike Murphy

Aerodynamic drag is proportional to the square of velocity. And most vehicles public the coefficient of friction for aerodynamic drag. The better the number (lower), the faster the vehicle can go and the less affected it is by the drag. Guessing the Cayenne’s coefficient of drag depends on the model and the year, but a 2019 version had 0.34., compared to a Honda Insight of 0.25, versus Ford Ranger of 0.49.

The old 40-50mph range is probably best for the Ford Ranger, whereas an Insight can do much faster speed and get better mileage.

Jfrahm

Thanks for the replies. I will try to get some data at 55mph for comparison, try to see if it offers a significant advantage to 60-65mph.
Hypermiling techniques might help depending on the conditions. If one was on a highway drafting a truck would help a lot but that could cause an issue as in my experience the drafting distance is quite close and you also get a lot of rock chips.

Carrying extra fuel has it's own set of problems, if you know you need it you'll have it and it won't be an emergency. We're talking about fuel that stays aboard inconspicuously for a long time and needs to stay fresh, not smell and not cause fiery death in an accident.
A couple of 1.5L MSR type bottles might work along with the right funnel to get the fuel into the tank. Not a ton of range, maybe 15 miles, but even half that might get you off a dangerous section of highway and to a place where you might get help (if not more fuel).
Kind of a pain to keep fresh also.

Does anyone know if an uphill angle runs out of fuel before a downhill? I think that's the situation in my S8.

hatchetf15

-True. I try to stay just where you get the burble…about one trailer length back. A chip seal surface is definitely not good for drafting behind anything. Just like NASCAR, a normally spaced line of vehicles, with you at the rear, gets a sizable drag reduction. All that said, it’s a giant pain to get an instant 25 mpg for a decent amount of time. Fun exercise.

-Wouldn’t it depend on the pick up locations in the tank?

blaino

Correct, each car is different and depends entirely on where the pickup point is in the tank. Similar reason why some cars show more gas when parked uphill vs. cars showing less gas when parked uphill - depends on where that car's fuel sensor is located.