Graph: mpg vs mph

This week I had a trip to Dallas and back (200 miles each way) that showed the effect of wind on mpg. Driving to Dallas, 80 mph much of the way, with a steady 15-ish mph headwind I had a very low mpg of 24.7. On the return trip with calm weather, same speeds, I averaged 31.3.

I had also just topped off my tires to 36 psi.

craigo said:

This week I had a trip to Dallas and back (200 miles each way) that showed the effect of wind on mpg. Driving to Dallas, 80 mph much of the way, with a steady 15-ish mph headwind I had a very low mpg of 24.7. On the return trip with calm weather, same speeds, I averaged 31.3.

I had also just topped off my tires to 36 psi.

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I've been running 38psi lately at the urging of the forum. Compared to 34psi, no difference in mileage has been noted over several tanks of fuel.

craigo said:

This week I had a trip to Dallas and back (200 miles each way) that showed the effect of wind on mpg. Driving to Dallas, 80 mph much of the way, with a steady 15-ish mph headwind I had a very low mpg of 24.7. On the return trip with calm weather, same speeds, I averaged 31.3.

I had also just topped off my tires to 36 psi.

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With calm weather you still couldn't beat the EPA fuel economy highway rating at 29/26/33 combined/city/highway for a FWD CX-5. (Yeah, it's hard to beat EPA highway rating with 80 mph ⋯)

yrwei52 said:

With calm weather you still couldn't beat the EPA fuel economy highway rating at 29/26/33 combined/city/highway for a FWD CX-5. (Yeah, it's hard to beat EPA highway rating with 80 mph ⋯)

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I'd say it's impossible, unless maybe going downhill The high speed test only gets above 70 for 45 seconds, and 80-ish for about half that: https://www.fueleconomy.gov/feg/fe_test_schedules.shtml

So, today I made a run to my old place of work. About 60 minutes one-way, and a route I drove for 15 years, 5 with my ex-Impreza CVT. I was filling up every 4 days. I spent most of those 5 years finding the best way to get great mileage in that Impreza. In the winter (20f) I'd get 28 mpg, in the summer (70f) I'd get 34 mpg. With today's temp (50f), I estimate I'd get 31.6 mpg.

At the end of the trip, I put almost 12 gallons into the CX-5, and calculated 28.35 mpg over the whole tank. (That's with a lot of hooning, a couple dozen 0-70ish WOT runs). The 'Average MPG' gauge in the cluster showed 28.0 mpg. The Fuel Economy panel in the touch screen showed that I got 33.3 mpg for today's trip. When the FE monitor has the same number of miles as the trip meter, they both show the same mpg, so I'm reasonably confident that I got 33 mpg actual. This is 20% 0-35 mph city, 20% 65 mph interstate, and 60% 55 mph county road stop-and-go every couple of miles to 4 miles.

As I expected, from city driving, where I clearly got better mileage than I was getting in the Imp, the CX-5 is getting fantastic mileage. (The Imp's CVT is awful on mpg when it's cold. It's got something around 7 quarts of oil in it, and it takes a long time to warm up). Both cars have Michelin X-ice 3's on them.

I get this kind of mileage by accelerating very slowly, keeping highway speeds down (I drive 65 on interstates, and 55 on county highways), and coasting to stops.

cx-500 said:

The point was actual data. As far as your statement that it's 'happiest 60-65', I don't know what you mean. It clearly isn't more efficient there. You might have a point if mileage dropped off drastically after that, but it's a clear, linear drop. If drivers need to reclaim time, it won't cost them hugely to drive faster. If they have the option, driving slower won't drastically save them money.

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my 528i gets the same MPG whether I'm going 100 or 160KM/h. it feels more efficient and peppy going 120km/h at 2500RPM because of the extra torque.