I Car low average speed vs aero drag relation

AI Thread Summary
Driving exclusively on country roads at speeds of 100-120 km/h results in a low average speed reading of 40-48 km/h due to the way average speed is calculated over longer trips, including periods of lower speeds or stops. The discussion highlights that average speed is determined by total distance divided by total time, which can be skewed by driving conditions and idling. It is noted that aerodynamic drag becomes less significant at lower average speeds, leading to confusion about the relationship between average speed and the need for good aerodynamics. Participants emphasize the importance of resetting average speed counters to get a more accurate measure during consistent high-speed driving. Overall, the average speed reflects driving habits and conditions rather than just the maximum speeds achieved.
Jurgen M
I drive car only at country roads allways at speeds 100-120km/h, no city and no idle time-heating engine etc.

Why computer allways show very low average speed , 40-48km/h?I allways have feeling that this speed is too low because I allways drive way faster then this. Indeed all my friends have low average speed, max 55km/h.

Math says this is same that you drive car at 40km/h all the time,so average speed implies that aero drag is not importnat, because drag is irrelevant at 40km/h speeds.

So how can we describe average speed/aero drag relation, can we conclude that car with low average speed don't need good aerodynamics?
Math says yes, but my logic say no, because I drive car mostly from 100-120km/h..

Is anyone here with average speed 100km/h or more?
 
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First of all what average speed? Of a trip? Since your last fuel refill? Since the first time driven (when the car was bought)?
My car measures average speed for a trip which is usually 900km, this roughly translates to 14 days (I reset trip when I refuel). Of course I cannot drive 900km for 14 days at 100km/h, so it's logical that the average speed will be way lower than that.
Average speed is usually computed with distance over time, I don't see what aero drag have to do with this simple calculation.
Have you tried reseting the average speed counter when you start doing 100km/h and read the average speed before you fall under 100km/h?
 
Jurgen M said:
Math says this is same that you drive car at 40km/h all the time,so average speed implies that aero drag is not importnat, because drag is irrelevant at 40km/h speeds.

So how can we describe average speed/aero drag relation, can we conclude that car with low average speed don't need good aerodynamics?
Math says yes, but my logic say no, because I drive car mostly from 100-120km/h..
No, it's not the same. If you drive 80 km/h for half an hour and wait at a red light for half an hour, you will not get the same energy spent as if you would have driven 40 km/h for an hour. It requires 4 times the amount of energy:
$$\frac{E_{80}}{E_{40}} = \frac{F_{80}d}{F_{40}d} = \frac{F_{80}}{F_{40}} = \frac{80^2}{40^2} = 4$$
And that is assuming the car is not idling and consuming fuel when at rest.
 
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Motore said:
First of all what average speed? Of a trip? Since your last fuel refill? Since the first time driven (when the car was bought)?
My car measures average speed for a trip which is usually 900km, this roughly translates to 14 days (I reset trip when I refuel). Of course I cannot drive 900km for 14 days at 100km/h, so it's logical that the average speed will be way lower than that.
Average speed is usually computed with distance over time, I don't see what aero drag have to do with this simple calculation.
Have you tried reseting the average speed counter when you start doing 100km/h and read the average speed before you fall under 100km/h?
My average speed is allways about 40,50km/h, last 800km,last 5000km or last 10 000km..
I didnt try that,but speed must then be above 100km/h..

jack action said:
No, it's not the same. If you drive 80 km/h for half an hour and wait at a red light for half an hour, you will not get the same energy spent as if you would have driven 40 km/h for an hour. It requires 4 times the amount of energy:
$$\frac{E_{80}}{E_{40}} = \frac{F_{80}d}{F_{40}d} = \frac{F_{80}}{F_{40}} = \frac{80^2}{40^2} = 4$$
And that is assuming the car is not idling and consuming fuel when at rest.
Yes that make sense.
 
Jurgen M said:
My average speed is allways about 40,50km/h, last 800km,last 5000km or last 10 000km..
My car has also the average speed from when it was bought till now, which is about 53km/h for 170000km. And it won't change much, because I use my car for driving in cities, conutrysides, when there is congestion, road works, highways, ...
To me it seems logical that it will settle around a particular average speed.
 
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