What is a realistic accuracy & precision of typical MPG measurements when measured by the consumer using the typical method of dividing their tripmeter miles by the gas-pump gallons during fillup?

Close to 100% accuracy if done right. I've done it on long trips. But MPG will vary depending on terrain, weather, wind direction, stop-and-go traffic, etc. So if you want "true" MPG for your car, you have to do it for the life of the car. Once you do it initially, it's kind of pointless to do again except to satisfy your curiosity.

wrote on 7/24/2017 9:46 PM: What was the lowest speed you could use 5th gear in the 75 car?

What is the realistic accuracy & precision of typical consumer MPG calculations (tripmeter miles/pump gallons)

Jul 20, 2017 84 Replies

Rate this thread:

clare 8 years ago

No, because the speed doubling takes only half the time, but 4 time the power. Not necessarilly 4 times the fuel, because the engine may be "on the cam" at the higher speed, running more efficiently.

An example of this was the 1975 Toyota Celica GT. With the 1975 gearing, it was actually most efficient at 80MPH in 5th, as long as you didn't have to change speed or pass anyone. (I got 52MPG at just over 80mph from Waterloo to Kingston Ontario at 2am on a Sunday morning back in 1979-ish.

Didn't work on the 1976 model - same body (and engine) but different gearing

Vote

rickman 8 years ago

What was the lowest speed you could use 5th gear in the 75 car?

Vote

clare 8 years ago

Can't remember for sure, but it was a DOG at 60mph - requiresd a downshift to get anywhere. I think hey geared the 75 GT the same as the 4 speed. I know I was shocked by the mileage on that trip - going out to Kingston to pit crew for Taisto Heinonnen, "The Flying Fynn" and Tom Burgess on the Twin Lakes Rally. Crewsd for him on the Tall Pines and the Blossom too.

I was offered his backup Celica Team car in 1980 when we finished rallying in the navigational rallye series (After finishing 1st, second and third in 3 years we were no longer elligible) and our R12 was not adequate to run competetively in the performance series but I decided to quit while I was ahead, since I was getting married.

Vote

rbowman 8 years ago

I had the misfortune to own a '71 Audi when the 55 mph national speed limit went into effect. The German engineers thought 55 was a very brief period on your way to cruising speed not a speed you'd try to drive.

Vote

dsi1 8 years ago

As it goes, if you want the best gas milage, you should always get into the highest gear as early as possible. You can shift into top gear at almost any speed. Well, I wouldn't do it below 25 MPH.

Vote

Join the Discussion

Have something to add? Share your thoughts — no account required.

Didn't find your answer?

Ask the community — no account required