[TestDrive]

Originally Posted by PA32R

I developed one for my LR3, a small write up on it is at Adventures in Fuel Economy, Energy Use, Physics, and Life: The best speed for fuel economy.

Its limitations are obvious, as anyone who reads the blog entry will see, but I think it's in the ballpark.

It seems worth hi-lighting the The How Stuff Works article mentioned in your blog - What speed should I drive to get maximum fuel efficiency?

Your conclusions are a bit theoretical, but seem to agree with my drive tests using a 1994 Ford Escort LX Wagon (1.9L SOC & 5sp MT) on 150.5 mile daily loop. (If you're curious about: location, distance between stops/turns, elevations and etc. click here for a google map)

This is a contract haul route for a local newspaper. I leave at 1:15 AM and complete the loop by 6:15 AM. Because this section of the country is such low population, other than wild life and the occasional escaped cow or horse, I practically own the road during these hours. On a typical night I may see five or six vehicle traveling either direction on the first leg of the route. From point B to the last turn before point K, I seldom share the road with even one other vehicle. From K to the end of the loop, I see something like 6 to 8 other vehicle depending on the day of the week.

Point B is a relay pickup point - another vehicle brings the papers to me there. When the papers arrive at Point B on time, I can drive as slow as 32 mph and still complete the route on time. When the papers arrive later, I sometimes have to drive as fast as 65 mph. If I drive the route at fairly stead 37 mph (drive with load for a few obvious hills, EOC to 13 stops, Engine Running Coast through 19 turns and use quite modest acceleration (0 to 30 mph in about 20 seconds - hitting all five gears), I average 49 mpg. If I accelerate more aggressively, my average mpg is worse. If I "ACCELERATE WITH LOAD" (Yeah, I coined the term just now), mpg can go as high as 54 mpg.

"Accelerate With Load" means - Shifting to the next higher gear as soon as it is at all possible to accelerate without engine knock.

Consider for a moment the upshifting recommendations in the 1996 Ford Escort Owners Manual (Don't have a manual for my 1994. 1996 is the oldest manual available at https://www.fleet.ford.com/maintenan...ls/default.asp)

Upshifting
For normal acceleration, you should upshift at the following speeds:

.......... 1.8 Liter Engine ..... 1.9 Liter Engine

1 to 2 ........ 11 mph ............... 12 mph
.............. (18 km/h) ............ (19 km/h)

2 to 3 ........ 24 mph ............... 22 mph
.............. (39 km/h) ............ (35 km/h)

3 to 4 ........ 34 mph ............... 31 mph
.............. (55 km/h) ............ (50 km/h)

4 to 5 ........ 43 mph ............... 42 mph
.............. (69 km/h) ............ (68 km/h)


For cruising, you should upshift at the following speeds:
.......... 1.8 Liter Engine ..... 1.9 Liter Engine

1 to 2 ........ 10 mph ............... 11 mph
.............. (16 km/h) ............ (18 km/h)

2 to 3 ........ 17 mph ............... 17 mph
.............. (27 km/h) ............ (27 km/h)

3 to 4 ........ 29 mph ............... 25 mph
.............. (47 km/h) ............ (40 km/h)

4 to 5 ........ 39 mph ............... 35 mph
.............. (63 km/h) ............ (56 km/h)

If you use the second - cruise -shift table and accelerate aggressively, the engine knocks. If you're on level ground and accelerate lightly/moderately, the upshift indicator light more or less matches the second shift table. If you accelerate extremely lightly - as if there were a raw egg between the sole of your shoe and the accelerator pedal and you'll lose a $100 bet if the egg cracks - the upshift light indicates an upshift somewhat sooner than the table. If I up shift at the points denoted by the indicator light when using such minimal acceleration, I can still accelerate in that next higher gear - with out producing engine knock at a rates of acceleration slightly more aggressive than dictated by the raw egg parameter. Actually, it's possible to shift well before the indicator light designates and continue accelerating (as if raw egg under foot) in the next higher gear without engine knock. eg.

• Shift from 1 to 2 at 9 mph
• Shift from 2 to 3 at 13 mph
• Shift from 3 to 4 at 17 mph
• Shift from 4 to 5 at 23 mph

That's what it takes to go from 49 mph to 54 mph with all other parameter the same as indicated above.

A couple of notes of caution for anyone contemplating attempting this technique.

• Turn your radio off! Engine to knock can cause serious damage. You need to be able to hear what's going on.
• You need a deserted or very lightly traveled stretch of road. Otherwise, rest assured some idiot will rear end you. Not to mention, it would be pretty discourteous to drive this way in the midst of traffic.
• If it's not illegal in your state, drive in stocking feet - no shoes - when you first attempt this.

FWIW My 94 Escort is essentially unmodified. Tires are the next taller profile than stock (odometer reads under by 6.5%). The only areo modes are a crack in the front bumper (kamakazi jackrabbit = increased drag) and missing plastic grill (kamakazi pheasant = increased drag). Tire pressures are as indicated on door post. Run of the mill TropArtic 5w30 oil. Generic ATF in the tranny.