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Cruise Control Less Efficient?


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11 replies to this topic

#1 JT95

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Posted 15 March 2005 - 04:15 PM

Took a road trip yesterday in my 95 LSi wagon. I've used my cruise control on the big road many times, though I don't always use when traveling. I live in a fairly flat part of our state, but my parents live in a hilly area, which is where I drove to. I set the cruise at 70mph, but noticed that the car downshifted a lot when I got to hills--not monster mountains or anything, just your regular interstate hills. The RPMs at 70mph are usually right under 3,000, but on the hills the engine frequently kicked to 3,250 and often 4,500 until hitting the cap of the hill. On the way home I didn't use cruise control, and although the mph sometimes dipped by a couple on the bigger hills, my RPMs stayed level at 2,850.

Anybody else had similar experiences w/ their Sube cruise? I assume the rounds of hitting the higher RPMs killed any dcent gas mileage on the trip down. My only other cruise control experiences are with V8 engines and, obviously, V8s don't huff up hills the way a 4 banger can. Normally, my Legacy cruise control works fine, but it seemed to downshift excessively on this hilly road.

#2 Tiny Clark

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Posted 16 March 2005 - 01:10 AM

I'm always turning mine on and off over here on the autobahns, otherwise I get that downshifting as well. I just disengage it when I see the speed start to decrease going up hills.

NEED MORE POWER!!!

#3 Martinjmpr

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Posted 16 March 2005 - 12:00 PM

I believe cruise control is much less efficient in hilly country. I usually turn mine off until I get into the flat lands. It's just that the cruise control is "dumb" and can't really plan to efficiently use the engine's power. So the CC holds the vehicle right at the set speed, even when engine speed drops due to the slope, causing the tranny to downshift.

On moderately flat roads, though, I think CC rules. It allows me to set an efficient speed and not fluctuate up and down.

#4 mtsmiths

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Posted 16 March 2005 - 12:58 PM

Don't you just love it when you're cruising along at a dead-set speed and some bozo in the other lane who can't maintain relative speed in a bucket gives you 'stink-eye' (or worse) because he thinks you're playing speed games.

#5 Tiny Clark

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Posted 17 March 2005 - 02:08 AM

The worst thing about cruise controls is people don't speed up to pass a car on the interstate if someone is behind them travelling at a faster rate. Maybe they forget they can still use that skinny pedal on the right with CC engaged.

The sign in most states that says "Slower Traffic Keep Right" is a law, not just a suggestion. They will ticket you on the autobahn for impeding traffic. :)

#6 SubaruLegacy2003

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Posted 17 March 2005 - 09:05 AM

The problem with cruise control is it can't see the hills coming, you probably speed up just a little before the hill, allowing you to maintain your momentum while one the CC senses the speed drop it has to go too far to catch up....

#7 mtsmiths

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Posted 17 March 2005 - 01:07 PM

The sign in most states that says "Slower Traffic Keep Right" is a law, not just a suggestion. They will ticket you on the autobahn for impeding traffic. :)

Tiny, the average American couldn't get a license in Germany if he bribed the examiner. And wouldn't live for a year if he did.

#8 frag

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Posted 17 March 2005 - 01:23 PM

Tiny, the average American couldn't get a license in Germany if he bribed the examiner. And wouldn't live for a year if he did.


Make that «average north american driver...»

#9 mtsmiths

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Posted 17 March 2005 - 02:29 PM

Make that «average north american driver...»


But, but frag, whatever happened to L'audace! Toujours l'audace!

#10 frag

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Posted 17 March 2005 - 02:49 PM

But, but frag, whatever happened to L'audace! Toujours l'audace!


Exactly! That's why most of us here would'nt pass a driver's test in any civilized country. A stock car racing license perhaps?
By the way, in case it should mean something, we are of exactly the same age. Just old enough to stop taking things too seriously.

To return to the main subject, could it be remotely possible that the cruise control is taking the right decision and that we should rev more when we go up a steep hill instead of putting all that stress on a laboring engine?

#11 mtsmiths

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Posted 17 March 2005 - 03:05 PM

By the way, in case it should mean something, we are of exactly the same age. Just old enough to stop taking things too seriously.


Not only that, but have you noticed that we have almost exactly the same number of posts?

Could you be my evil twin? Nah, not a Quebecois, never happen.

Actually, I have contemplated retiring (should that 'ever' become an option) in Canada. I'm an enrolled member of a trans-border Indian nation (Wyandotte in the lower forty-eight - Wendat up your way - fragments of the old Iriquoi Confederacy) ... and you can't keep me out!

Heh, Heh, Heh ... eh?

#12 Ranger83

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Posted 17 March 2005 - 08:32 PM

The cruise control does not know what's coming. And it attempts to hold the speed within a narrow range. I have a V6 Honda Accord and my gps says it hold +/- 0.3 mph. The Subaru doesn't do as well - more like +/- 1 mph. You don't have any extra momentum so whe your speed drops, the cruise control feeds throttle and may initiate a downshift - even if you're about to crest the hill.

Take a tip from the truck drivers, who take it easy up the hills and let
'er roll down the hills.

I was towing a 23' keellboat (about 3,000 lbs on the trailer ,and a lot of wind resistance) with a Ford van from Ma to FL when I learned this. Trying to maintain 75 mph, Iwas getting around 11 mpg. Hitting 89 downhill and sagging to 70 uphill got me over 12 mpg.




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