# How to calculate speed, distance, and watt hours.



## IamIan (Mar 29, 2009)

gsmith191145 said:


> What I want to know is at what speed I will get 60 miles.


It will vary with driving conditions.

Temperature , wind speed , humidity , etc.

If you have a need to travel 60 miles ... I would suggest first determining what the worst reasonable case ( highest energy conditions ) would be that you need those 60 miles of range.


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## major (Apr 4, 2008)

gsmith191145 said:


> Ok my car will do 250wh/mile. 120VDC system
> 
> 20 lead acid 232ah batteries.
> 
> ...


At the speed you use 250 Wh/mile. Or is this a trick question 

Higher speeds use more energy; lower speeds use less energy. And then stop & go....not easy to figure.


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## gsmith191145 (May 1, 2011)

I think I figured it out. I measured amp draw and voltage while driving at different speeds. I did notice that in 2nd gear I got a better watt hour per mile than while driving in 3rd.


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## mizlplix (May 1, 2011)

Hey major: "Higher speeds use more energy; lower speeds use less energy. And then stop & go....not easy to figure."

I would think that slower car speeds with higher motor speeds willgive best milage. True/not true?


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## major (Apr 4, 2008)

mizlplix said:


> Hey major: "Higher speeds use more energy; lower speeds use less energy. And then stop & go....not easy to figure."
> 
> I would think that slower car speeds with higher motor speeds willgive best milage. True/not true?


Hi miz,

I was speaking of vehicle energy requirements. The best (most efficient) motor speed depends on the particular motor. You should design your system, or select the driving gear such that the motor is operating at reasonable RPM for efficiency (which can be a sizable range) and for self ventilation.

Regards,

major


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## Overlander23 (Jun 15, 2009)

Generally, the most efficient speed is between 35-45 mph. This is the speed at which air resistance hasn't had a change to exponentially run away into significantly higher and higher drag loads.

Above this speed range, air drag takes over. Rolling resistance is pretty much the same at any speed. 

But... that's verrrryyyy generally. Of course, it all depends on your particular vehicle and drivetrain setup.


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