MPG result after long road trip

That is about what you would expect at those speeds and a heavy foot.

 

Assuming 7.5% (positive) error in the displayed mpg, your actual mpg would be around 36.

215/50R17 tire size is not a typo? That would have an O.D. roughly 2% more than stock 15" 195/65R15, even more than the optional 215/45R17.

 

wow, that's brutal, but probably correct under the conditions you stated. regular tyres, easy foot and 55 mph would net you 55-60 mpg.

 

Speaking of brutal: Toyota suggests 33/32 psi pressure (front/back) for the optional 215/45R17 size. That's what we have, and I've set ours at 34 psi all around, of late.

Your tires, assuming the size you post is not typo, are slightly higher profile, so a bit more forgiving, but not by much. Low profile tires at 50 psi are going to give a very rough ride. I wonder too, if it takes a toll on wheel bearings and suspension components.

 

If not a typo, that would add a 2% negative component to the display error (and pump computation error, for drivers doing that), because the odometer would be reading that much lower than it should.

 

From my limited experience in a Prius I would say the main culprit is speed. At a rate of 75-80 mph you're more than likely going to be using more gas than electric to maintain that speed. As far as I can tell no one has yet figured out how to make mpg go up as speed increases. It is the one, simple, mechanical fact.... the faster you push any care, the more gas the engine will drink.

 

if we could only drive in a vacuum.

 

In all fairness, getting 38 mpg over a long haul at 75-80 mph is pretty darn good.

 

what would corolla/yaris get?

 

I wouldn't think it would get that kind of gas mileage.... then again, I don't think a corolla/yaris can go that fast.

 

If you have a GPS accurate to 0.1 mile, compare the miles over a +10 mile distance with a tripmeter. This will give the error factor to calculate the true MPG. At 10 miles, the least significant digit is the unit 0% off. Go 100 miles and you'll have 0.0% accuracy. But getting readings exactly on the 10.0 or 100.0 GPS setting is usually inconvenient.

For other distances you'll need to do some math to scale the offset.

Bob Wilson

 

With oversized tires his mileage is even worse.

 

Careful... GPS has a problem with corners/curves due to its sampling rate. Lots of curves could make a difference always in the same (shorter) dimension. However, 0.1 mile accuracy seems reasonable.

 

At speeds over 70 mph even driving with load doesn't help that much. To get better fuel efficiency at speeds over 70 mph - the only hypermiling technique I know that works is for a smaller vehicle to slipstream/draft closely behind or from the side of a very big profile vehicle like a 18 wheeler or a tour bus - but because this technique poses several serious safety concerns and challenges it is not recommended and normally avoided. Driving solo -at speeds over 70 mph, a high MPG vehicle design benefits mainly from having a small frontal surface and an aerodynamic exterior, e.g. 1st generation Honda Insight or a Honda CRX-HF. .

 

Ah higher speeds, you want to minimize aerodynamic effects but this is tricky:

• partially close bumper inlet - at speed there is plenty of cooling air some of it could flow around the car instead. BUT you need to monitor all temperatures, engine, inverter, MG1 and MG2 to make sure there is enough cooling air.
• front air-dam - a modification that reduces the gap under the front bumper so less air gets entrapped under the car
• tire air-dams - a modification that flows more of the air around the front tires to minimize energy loss
• windows up or small crack - using AC may be more efficient with less energy loss than cabin-air pass-through
• moon caps - minimize air flow through the wheel hubs
• rear wheel well covers - minimize air flow through the rear wheel well
• boat-tail - a structure that tapers to keep the air flow laminar but may obscure license plate attractiong highway patrol 'interest'
• fold the side mirrors - risk highway patrol 'interest'

Bob Wilson

 

Bob's points drive home my conviction: just lift off on the gas pedal a little.

 

That's about right....with my cargo box on the top fully loaded and four adults in the car and a heavy foot, I average 33 mpg going from Salt Lake City to Los Angeles thanks to the descents. Going to SLC from LA...is sad.

 

Small boat trailer with a small 'Jon' boat. It will be easier to load, unload, and a more aerodynamic. Just put the boat 'stern first' and cover with a tarp. Add stiffener ribs to the cover and you'll get even better MPG.

Bob Wilson