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Re: (ET) Ariens AMP Mower
On Fri, 15 May 2009, Jeffrey Tickner wrote:
On Thu, 14 May 2009, Christopher Zach wrote:Since my diesel car is a manual
transmission, I put it in neutral to coast
First want to clarify that I wrote that above.
My VW diesel actually shuts off fuel to the engine completely when I take
foot off the pedal so I don't have to shift to neutral, it's actually more
efficient and there's very little engine drag since there's no throttle
plate. This took some getting used to and this is also why some trucks have
the 'jake brake'
It's only more efficient if you want to slow down. THere is considerable
engine drag (mine is also a VW diesel). Try getting up to some speed on
flat ground, and then releasing the pedal - see how quickly you slow down.
THen do the same thing with putting the car into neutral. Your
deceleration is much slower.
If you *want* to slow down, then definitely keeping the car in
gear is the more efficient option, since fuel is shut off to the engine
(provided RPMS stay above about 1,100 RPM, at which point the ECU starts
sending fuel to the engine to keep it from stalling). But, if you do not
want to slow down, that additional engine drag while in gear will
ultimately mean more fuel will be burned - since you will have to burn
additional fuel to get the car back up to speed, and the efficiency of the
engine (25-43% depending on RPM) will mean that you have to burn a
considerable amount of "extra" fuel to regain that lost kinetic energy.
Whereas if you put it in neutral, you lose far less energy.
I've tried both approaches quite a bit, and consistently get
better overall fuel efficiency with the approach of putting it in neutral
Plus in NH shifting into neutral to coast is illegal.
Yeah, one of the dumber laws we have. I can understand not putting an
automatic transmission vehicle into neutral to coast - shifting back into
drive while moving is generally not good for the transmission, and can
cause significant "hiccups". But, it's just plain silly to say you can't
do that with a manual transmission.
I think this is similar to regen only when you step on the brakes to
no drag when 'coasting'
However on my E15 with Alltrax I like the regen because when I go down my
big hill it helps maintain my speed, on a tractor I don't want to
When going down steep hills in my VW, and I don't want to speed up, I keep
the car in gear. My point is - since it is more efficient in any vehicle
to be able to coast when you want to, I think it is a design flaw to have
regen kick on as soon as you release the accelerator. Unfortunately, one
of the big reasons our vehicles are as inefficient as they are is because
of designers continually opting for the choice that makes the vehicle
slightly more user friendly at the expense of a considerable loss in
efficiency. Hopefully, people who would be interested in buying an EV
would be willing to put up with the inconvenience of needing to rest their
foot on the brake to get regen to kick on, if it meant allowing a more
efficient vehicle overall by allowing pure coasting when desired.