# Re: [EVDL] co-efficent of drag

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Re: [EVDL] co-efficent of drag

how do you figure co-efficient of drag after I put fender skirts' front and rear ; smooth skinned the bottom for aerodynamics ' and found a way to reduce the drag from the vacuum in the rear between the tail lights ?
----- Original Message -----
From: Jeff Shanab<mailto:[email protected]>
To: [email protected]<mailto:[email protected]>
Sent: Sunday, August 12, 2007 3:29 PM
Subject: Re: [EVDL] Roll-down test to determine rolling and aero coefficients

Thanks. My rig is so inefficient I really need to look closely at this
and give it a try. The first question I have is if the relation ship is
linear enough to use rolling to a stop as a point. Maybe slowing to
5,10,15,20 mph would give a better indication of the rolling
resistance?. It seems when I push a car that it takes more force to get
it rolling that to keep it rolling. like static and dynamic coefficients
of friction.

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Re: [EVDL] co-efficent of drag

From: FRED JEANETTE MERTENS
> How do you figure co-efficient of drag after I put fender skirts
> front and rear; smooth skinned the bottom for aerodynamics and
> found a way to reduce the drag from the vacuum in the rear between
> the tail lights?

You can use the technique outlined in a recent previous email describing the roll-down method. However, what you really care about is the end result -- does your EV use less power to drive at any given speed?

So, all you need to do is drive on a particular route at a particular speed, and record the power used. Do it a number of times, in both directions, etc. (For instance, use your regular daily commute or other drive you regularly make).

Now make one change (fender skirt, belly pan, tire pressure, or whatever), and repeat the test to see what change it produced. Again, your results will be more accurate if you repeat the test several times. Often, a small change produces such a small result that you need to repeat the test many times to be sure you aren't just seeing random changes.

--
"Excellence does not require perfection." -- Henry James
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Lee A. Hart, 814 8th Ave N, Sartell MN 56377, leeahart-at-earthlink.net

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