Pondering My Practical Limit on Fuel Economy

Codyroo · Feb 6, 2012

I think you should be getting better MPG's at your cruising speeds as well.

When I'm only seeing 50 mpg or so on the highway, it usually involves going into a headwind or a head/crosswind.

Also, it does not appear that you have low rolling resistance (LRR) tires on the car. This can impact your MPG's greatly (F8L can tell you all you'd like to know about that).

If and when it comes time to swap tires, try a set of LRR tires, you might be pleasantly surprised.

SageBrush · Feb 6, 2012

Google Wayne Brown's website on the Prius. He has performed accurate work demonstrating the effect of wind on fuel economy, and it is not pretty.

We might guess that a round trip would cancel out the wind effect, but this is not the case.

kneedraggin · Feb 8, 2012

I second that on the wind playing a major factor in fuel economy. Here in Los Angeles we have a very "hilly" commute and even at times going down a rather large downgrade on the freeway I have to be accelerating down the hill to even keep my speed constant while when the wind in behind me I have to keep it in B mode or apply the brakes the whole way down to not be majorly speeding so you can obviously imagine the times where the wind is behind me on my commute I avg way better mpg. So you just might have yourself ending up in headwinds most of the time therefore impeding your fuel economy and unfortunately there are no "tips" for driving against the wind. Mother nature always wins that one;-) lol

Fred T. Jane · Feb 8, 2012

F8L said: ↑

Here is your GenIII video.

http://priuschat.com/forums/gen-iii...max-mpg-driving-techniques-youtube-video.html
Click to expand...

Thanks a lot!

fotomoto said: ↑

This.

You are only a few miles from the gulf that generates nearly constant on shore winds. And then add in nearly constant a/c use. And finally, the EPA hwy mileage is 48 not 50. I have yet to meet any EPA mileage figure in any car, even after the new revisions, but I get the closest with the Prius.

I'd suggest resetting Trip B daily for each leg while monitoring the daily wind forecasts. I see a huge difference between head and tail winds here along the gulf coast.
Click to expand...

Well, Monday here was going and returning. There was a brisk wind on the way back:

The oldest 5 minutes of data was me driving at 64 mph. Note how it is consistent on the ride back... riding into the wind.

On Tuesday I forgot to reset it, so that's my MPGs for the round trip. I rode about without the AC on at all. The mileage numbers in the chart on the way back was because I was behind an 18-wheeler the entire time. You safety folks can rest easy; the 2-second rule was in effect.

Tonight, I fueled up after riding about, and here was the last 15 minutes of driving. You can clearly see when I was driving 55 mph (10 min mark) and then when I was driving 64 mph:

As you can see, the mileage is consistent, but what I know is absolutely killing my MPGs is the first 3-4 minutes as the engine is warming up, which leads me to my relentlessly dumb question:

I've found Ken's post on the stages of warm up, and I understand that it varies by outside temperature, but how long should the warm up process take if I am driving about in 40-55 degree weather at start-up? For the first 4-5 minutes I'm only averaging in the mid-upper 30s mpg. I've tried to accelerate both briskly and slowly, as well as accelerating throughout with the ECO leaf on, and there's no change.

Thanks for the discussion folks!

[edit] The last pic was when I fueled up this evening. The actual MPGs was 47.7 MPG for that 404-mile tank.