Grumpycat
Veteran Member
Yup, but there is at least one unicorn out there. A 2000 Toyota Avalon with OE 16" wheels maxes MPG around 67 MPH. I drove about (20) 500 mile days in mine to know. It was the damndest thing but 28 MPG at 60 MPH and 30-34 at 70 MPH. Back down to 28 at 75. Miles on odometer divided by gallons purchased at the pump. Yes, on a day with low traffic I held to 60 MPH for 500 miles, I was that curious.Let’s clear one thing up, the slower you go the better mpg you get. I don’t have cold hard facts but most vehicles will probably get the best fuel mileage at about 45 to 50 mph. It’s just physics.
Mentioned on Avalon forums and got a lot of "everybody knows that is impossible!" but several, "me toos, I thought I was going insane."
This car was geared very high. Apparently it grunted at 60 MPH at too low of an RPM for efficiency so much so that the engine efficiency increased faster than wind resistance up to about 67-68 MPH.
The problem is that ICE specific-power efficiency is not linear. If you need 30 HP from a 200 HP engine there is one RPM which uses the least fuel for that HP. There are many RPMs which can produce that HP.
With this same car a bare empty cheap less than 200 pound trailer with nothing but a 4x8 sheet for a bed knocked MPG down to under 20 no matter what speed. Add a motorcycle to the trailer, no change.
The 2nd generation 2004-2009 NHW20 Prius will max MPG at 41 MPH.