I've hopefully got a 540+ trip coming up tomorrow/Thursday, mostly highway, so I'm keen to test the cruising economy of my car. I'll probably stick to around 65 MPH, even though the limit is 70 and most people do 80. There's a 50/50 chance I'm going, as there's a car show and I've been promised free tickets, which havn't yet turned up...
"sweet spot" always seems to imply trade offs and for fuel economy, this is no different.
I think for most vehicles, the highest fuel economy is achieved at cruising speeds of (well) below 55 mph. On the other hand, drivers desire to drive (well) above 55mph due to time, safety or "fun to drive fast" reasons.
For me, its just drive AT the 55-65mph speed limits.
Results are in, I did about 12 hours of driving over 600 miles. I tried to stick to 70 Mph, and was getting 72 MPG at this speed with cruise on. My average was 65 Mpg by the time I got home, but I was hammering it on the way home to get back before midnight as I have work today. I'm still pleased with 65 mpg given how aggressively I was driving for the final leg of the journey.
Most cars have a "sweet spot" cruising speed, a balance of speed and economy. It was long thought that 56 MPH was the best speed to cruise at for optimum economy, but I'm not sure that still stands today. A slower speed and you will be using more throttle and take longer to reach your destination, a higher speed means higher revs but less throttle, there will be more wind resistance but it will take you less time to get there.
As I don't use highways very often, I'm just wondering what kind of cruising speeds people stick too for best economy? 60, 70, 80 MPH, or anywhere in between? Are there any mathematical calculations you can do to help work it out?
I've wondered the same.
In the tips section, user Preload says, "Find the cross point of the Torque & Power curve of your engine and try and ride/drive close to this area, it will generally give you the best MPG."
Personally, I thought one's best MPG, at least with a manual trani, is the slowest the car can go in top gear without lugging the engine. I don't have a scan gauge, so I can't test my theory.
If I did that though, I'd be cruising at about 43 Mph, that's when the shift up light appears on the dash when accelerating in 4th. It would take forever to get anywhere and could be dangerous on the highway with traffic travelling almost double that! I generally stick to 70 now, as long as the road is flat and theres no headwind, I tend to get late 60's to early 70's mpg wise. I need to experiment more but with my current wheels, one has a flat spot which gives a terrible wheel wobble above 70, the joys of buying second hand stuff...