MPG ratings

wrote:

> ...Also, using the factory cruise control is a boon to trip economy.
> Especially on the more finely controlled current era vehicles.
>
> Once the cruising speed is reached, the computer will keep the vehicle
> speed highly constant. It'll throttle into the engine going up hills
> (sometimes as low as 15mpg), then trim the throttle back IMMEDIATELY as
> the hill is crested, and then also back out of the throttle going down
> the other side (going into "coast" and the resultant "fuel shut-down"
> modes). If you try to "foot drive" it, we all will try to maintain the
> speed up the hill, but forget to back out once we get to the crest and
> then head downward. The higher speeds reached at the crest and on the
> downslope, before we realize we're going too fast and then back out of
> the throttle, are not as economical by a significant amount as letting
> the cruise do the work. This is highly apparent when you try it both
> ways and watch the "Inst Eco" readings!...

Quite an extensive and thought-out write up.

I am surprised, with all the detail you did go into, that you did not
mention affects of the cruise control downshifting to maintain the
setpoint window on rolling hills terrain - particularly since you
mentioned owning LH cars which definitely do this (to a point of
annoyance at times, though it is better than getting tickets). Of
course it is bleeding off energy that has to be made up when the terrain
levels out and slopes upward again, and that costs gas mileage just like
braking to accomplish the same thing would.

But if you weren't in cruise control, you would be having to either
manually downshift or use the brakes to keep within the same
ticket-avoidance window that the cruise control is attempting. I find
that to really be safe from tickets, I have to take manual control in
some way - usually I use your anticipation technique and move the
setpoint down 2 to 4 clicks (depending on the amount of slope - 1 mph
per click) before starting on the downslope, and I still get the
inevitable energy-robbing downshift, but I force it into play earlier by
dropping the setpoint (and bumping it back up at the bottom of the hill)
- otherwise I find myself at risk of a speeding ticket. Maintaining the
same setpoint and letting it drift upward in speed 5 to 7 mph to gain
fuel economy over the risk of getting a ticket would make as much sense
as running red lights for better fuel economy. So it's another
economy-killing reality that we gladly put up with to reduce/eliminate
insurance rates and fines.

I also find the 'up' (2 mph per click) and 'down' (1 mph per click)
speed settings adjustment to be *very* convenient for some of the
reasons you said and what I added above. If I want to bump up 1 mph,
without even thinking, I click up once, and down once. In extreme cases
(steeper slopes), I manually downshift ahead of time (pretty much the
same effect as lowering the setpoint). And, I find myself with my foot
off of the gas pedal and using the cruise buttons to fine tune my speed
during most of my mostly-55-to-60-mph-40-mile-each-way daily commute
(using the gas pedal only for the occasional stop light and one small
town that I pass thru).

Bill Putney
(To reply by e-mail, replace the last letter of the alphabet in my
address with the letter 'x')