Any vehicles stand out as being exceptionally efficient at higher speeds?

[jamesqf]

Originally Posted by wdb

"...the power needed to push an object through a fluid increases as the cube of the velocity."

In short, if you're looking for a vehicle that gets better gas mileage at 70 than at 60, you are not likely to find it.

I don't think that was the question (though my Insight does get better mpg at 50 than at 35). Rather, if you are constrained to travel at a certain high speed, what vehicle(s) will get the best mpg?

I think that's going to come down basically to CdA plus tires: a small car with good aero, and LRR tires.

[SoobieOut]

There is always the famous TOPGEAR test
BMW M3 Beats Prius in Fuel Economy Test

Where a BMW M3 had better fuel economy than a Prius on a closed track. However the Prius was maxed out on speed and the BMW was barely taxed.

I think alot of economy at high speeds depends on gearing and where the engine/drivetrain was designed to operate.

A 1974 law (in the US) instituted a national speed limit of 55 miles per hour (a compromise between efficiency and speed). But as the oil crisis abated, the law was amended to 65 miles per hour in 1987 and finally repealed entirely in 1995, ceding the power to set speed limits back to the states. Now, many states have speed limits that exceed 70 miles per hour on interstates, and some stretches in Texas and Utah have limits as high as 80.

So older cars from the 70's and 80's may be designed for 55 MPH best fuel economy.

[Vekke]

I think the only real option in the US is 1.9 TDI and from those cars the estate wagon has better aero. Ofcourse if you want to take the rough road and modify your CD to 0.2 any small petrol engine car would do fine.

Look from these forum a topic from my seat cordoba wagon and check its fuel economy.

[drmiller100]

above about 60 mph the vast majority of fuel used is to push the car through the air.

Effective Frontal area is king. Effective frontal area is actual frontal area and form drag.

so you want a REALLY narrow, short vertical height car which is REALLY tapered very well at the back. Sounds like you need one of my reverse trikes, or Ken Fry's cars.

[redpoint5]

Originally Posted by jamesqf

I think that's going to come down basically to CdA plus tires: a small car with good aero, and LRR tires.

That, and gearing. My car has an extremely low Cd that is comparable to a Prius or Insight, but I'm screaming at 3000RPM @ 70mph down the highway. That's nearly 4300 RPM @ 100mph!

If I could figure out how to change the ratios or final gear, I would.

My guess is the Insight would be extremely efficient at 100mph compared to most any other car.

[Ladogaboy]

Sometimes, I'm just forced to ask why? Is it really so bad where you are?

That being said, I don't want to impose my values on you. However, physics isn't so kind. No matter what, you are going to pay a penalty for wanting to go faster. I'd say, given that the variables also include time, you should assess how much time would be saved by 55 mph versus 65 mph versus 75 mph etc. You said 5 hours, but that doesn't give us a good idea of distance. Are you saying roughly 300 miles? More? Less?

Anyway, in my opinion, you'll want to first assess how much time you're actually going to save by going 10 to 20 mph faster.

[serialk11r]

Okay just ran some numbers with my Lamborghini example...
The Aventador has 7L, and spins at 2860rpm at 60mph. A Toyota Celica GT-S had about the same rpm for 60mph, but with 1.8L. This means we're asking the mighty 7L engine for only 1/3 of the torque that we're asking of the 1.8L engine, which is IIRC less than 25% of its available torque. The Aventador then is running at <10% peak BMEP...I think it's possible that 70mph could be better than 60mph in this car, despite the higher power requirement, because the engine efficiency is so much higher.

I don't know why people ignored my example, because the OP did ask for cars that got their best mpg at higher speeds.

[NeilBlanchard]

The higher the speed, the more aerodynamic drag matters. The AeroCivic is case in point.

[MosersMopars]

My former 1996 Dodge Grand Caravan (same model until 2000) would get the same average economy on a 55mph trip as a 70 mph trip. It was modded to 27 MPG. It had the 3.3L v6, 4 speed auto, and 15 inch wheels, also a roof rack. Had to make sure the tire size was correct, and I'm sure some aero mods would have helped too. My 3.8L GC would get terrible mileage over 55 with all other options identical, though it didn't notice a 1 inch tire height difference. Note that these two engines are in the same family, but have drastically different personalities. The 3.3 likes to rev, the 3.8 makes TORQUE. I only miss those vans when I'm at the pump.

[jamesqf]

Originally Posted by redpoint5

My guess is the Insight would be extremely efficient at 100mph compared to most any other car.

Yeah, considering that you need a long downhill or good tailwind to hit 100 mph :-) Or with MIMA you can use the electric assist to get there for a minute or so. It does get about 40 mpg IIRC.