DIY Electric Car Forums banner
1 - 1 of 1 Posts

72,624 Posts
Discussion Starter · #1 ·
Re: [EVDL] "Compression" slowing force with electric motors?

Another effect that may be more or less important than friction is drag, or
air resistance; it's the force of the air pushing against you as you move
past. As you go faster, it becomes more and more important. In a light,
odd-shaped vehicle like a motorcycle, it is the main force slowing you down.
In an aerodynamic but heavy car, it's not as important as friction until
high speeds.


On 8/29/07, Doug Weathers <[email protected]> wrote:
Martin Maitner wrote:
> > Do you get any "compression" effect from the electric motor
> Nope. When you're not providing power to the electric motor, it just
> spins freely. There's nothing like the compression effect from an ICE.
> In fact, this can be a problem! Electric motors have a maximum RPM
> they can withstand, and it's sometimes possible to exceed this limit if
> you leave the motor in gear going downhill. Since the motor doesn't
> resist being spun like an ICE does, it just spins up really quickly and
> can fly apart before you know it. So don't leave your EV in low gear
> and go downhill unless you've calculated the maximum RPMs and are
> watching the tach like a hawk. Put in the clutch and/or shift to
> neutral. Brakes help, too :)
> > or is gravity the only force slowing the speed?
> Not gravity; friction. Gravity pulls in different directions depending
> if you're going uphill or downhill, and you always get back the energy
> you lose (what goes up must come down), but friction always slows you.
> One of the ways people increase the range of their EVs is to reduce
> friction wherever they can - low rolling resistance tires, reducing
> toe-in, careful alignment, eliminating dragging brakes, putting extra
> air in the tires, streamlining, low-viscosity oils in the gearbox, etc.
> --
> Doug Weathers
> Las Cruces, NM, USA
> _______________________________________________
> For subscription options, see
For subscription options, see
1 - 1 of 1 Posts
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.