Does Cruise Control Really save Gas?

[Spazdog]

If I'm in gas saving driving mode, I can save more gas with my right foot than the cruise control. Cruise often will drop my car to 5th gear going uphill does not allow me to build up momentum going downhill.

Feels really funny going down some steep hills. I wonder what all it's doing trying to hold that speed. As far as I can tell it's not connected to the brakes. Maybe it's cutting the fuel.

Driving "light with the right" can annoy other drivers too. Building up momentum going downhill and then letting the uphill section bleed it all back off to save gas does lead to some inconsistant speeds.

But I still like cruise control. Won't own a car without it. It does lock in a set speed and prevents unwanted delays by law enforcement. (mostly....I did get a ticket for 57 in a 55 zone one time. When I count all the times I went 2-3mph over right through the speed trap without the cop even looking up from the radar or lidar gun at me I think it is a fair trade off. Gotta' be at least 200:1 now, no ticket to ticket ratio)

 

[CharBaby]

CC can save gas if you set it at a more reasonable speed than compared to not using it at all. It holds a more constant speed than we as humans can do for long periods of time. We tend to speed up gradually on the highway when traveling long distances with out realizing it.

I mean, don't set it a 85 mph on the highway and expect to get better MPG than cruising at 65-70 mph w/o CC. It ain't gona happen!

When using CC on a long trip especially in a 4cyl auto, if I see the road incline or if we're driving through mountainous areas, I add throttle on my own as not to have the tranny down shift(even w/CC enguaged). Otherwise, on it's own while using the CC, the tranny will down shift and there goes you MPG.

You really have to know how to modulate the throttle while using CC. I'm pretty good at it, even when driving for hours on end. I get as good as possible while using CC and modulating the throttle. Much better than my wife for example. Her driving style nets poorer MPG in all situations than I do because she excelerates a little harder and brakes a little later than I do. I sometimes have a neck ache after driving with her. But she is a good driver just the same...Never an accident or speeding ticket in ~40 yrs of driving...EVER!

She's the girl driving the "getawaycar"

JK!

 

[DreamerGT]

Originally Posted By: Craig in Canada
As someone already said, if you're one of those drivers that exhibit poor throttle control, surging on and off the throttle even when you're trying to maintain speed on flat ground (I simply can't believe how many of these people are out there) then cruise control will save you money.


My wife is one of them :facepalm:

 

[eljefino]

It's a mental thing to expect ever increasing pitch from your engine noise. (And CVT noise bothers many.)

It's like a record sounds okay at 47 RPM but really dragging at 43.

 

[brianl703]

Originally Posted By: rshunter
Caterpillar had a cruise system for their on-highway engines that would mimic fuel saving techniques. It would allow a truck to lose a few MPH on climbs, and gain a few on hill descents. It achieved clearly measurable improvements in fuel efficiency.


Years ago I saw a data sheet for the chip that Ford used in their cruise control systems with the separate "amplifier" (the box with the cruise control chip) and vacuum servo (like what is installed in my 1988 Mustang GT). From what I remember, you could set how quickly it reacted to drops in speed and how much it would open the throttle by changing a resistor in the circuit.

Ford did have different amplifier boxes for different engines. The ones for 4-cylinder engines were set to pull the throttle and react quicker than ones for V8 engines.

So what Caterpillar did is really just modifying the cruise control to allow more change in speed before correcting.

 

[brianl703]

Originally Posted By: Spazdog
I did get a ticket for 57 in a 55 zone one time.


Any cop who wrote a ticket like that around here would get yelled at by the judge.

 

[Shannow]

One of our states have a zero tolerance policy...1km over is a ticket (just over 1/2 MPH).

 

[ChuckBerry]

Just installed cruise control in my '99 Crown Vic PI and took a road trip to Austin from Lafayette, La. Whereas we would normally get just under 20 MPG driving about 70 mph without cruise, with cruise we picked up 1-1.5 mpg, a definite improvement.

 

[shrooms]

Originally Posted By: Carbon
Cruise control saves some of us from speeding tickets.


+ BILLION

I'd rather waste some fuel than going to court, pay the fee and wasting my time. I smile every time a 'smart' guy passes me, only to be caught later.

 

[steve20]

I never ever use crusie control except when drivin from NJ to FL. We always go non-stop except for food an gas. Has taken anywhere from 16 to 24 hours to make the 1250 mile trip.
If the speed limit is 70, I set the cruise at 75, but use my foot to run about 82-85 mph. So, for me it's only use is to take the extra pressure off my foot. I only need enough pressure to bring it from 75 to 82, instead of the pressure neededto maintain 82mph. Otherwise, cruise control is the least used feature in my vehicle


Steve

 

[grampi]

A cruise control can only save gas if you use it. Most of the drivers I encounter don't seem to use their's as they're constantly varying their speed even when it's not necessary...

 

[Hokiefyd]

Originally Posted By: rshunter
Caterpillar had a cruise system for their on-highway engines that would mimic fuel saving techniques. It would allow a truck to lose a few MPH on climbs, and gain a few on hill descents. It achieved clearly measurable improvements in fuel efficiency.


Most CC systems on large vehicles like this set ENGINE speed rather than ROAD speed. In a tall gear, you can get some road speed variation with very little change in engine speed. Notionally, there would still be an RPM change with a MPH change, but at speed, MPH changes faster than RPM does.

The end result is that, in practice, you get some variation in road speed allowed as the system aims to maintain a given engine speed. As you noted, it can help.

 

[Eddie]

Saves me about 5% on flat or rolling terrain when the hills are not large enough to cause the AT to downshift. I can speak to large hills or mountainous terrain. I can always tell when on a long highway streach when a person is NOT using CC, because their speed is varying +/- 5 mph.

 

[brianl703]

Originally Posted By: Hokiefyd
In a tall gear, you can get some road speed variation with very little change in engine speed. Notionally, there would still be an RPM change with a MPH change, but at speed, MPH changes faster than RPM does.


If the vehicle has an automatic or a slipping clutch, I could see this. Otherwise, any road speed variation it allows has more to do with the circuitry of the cruise control than it does with where it's getting the speed signal from.

 

[Falcon_LS]

I find cruise control helps improve my fuel economy, although much of the terrain here is flat (which helps). I reckon it's easier on the engine, because there isn't much acceleration and deceleration going on.

Now, does the of cruise control help reduce wear and tear on the engine (and oil)? That's a different question!

 

[JDD]

Originally Posted By: Volvo_ST1
Cruise control is useful when I have to look for something on the back seat, or if I want to take a nap.


Ahhh-I see you have the Simpsons' Navitron Autodrive system

 

[morris]

one time i had a truck, that i added a cruse to. i saw that it gained 3-5 mph going up hill, in central-eastern kansas we dont have large hills, not even long ones. i changed the sensitive adjustment, so it lost 3-5 mph going up hill. and i gained 3-5 mpg

 

[mechtech2]

Originally Posted By: morris
one time i had a truck, that i added a cruse to. i saw that it gained 3-5 mph going up hill, in central-eastern kansas we dont have large hills, not even long ones. i changed the sensitive adjustment, so it lost 3-5 mph going up hill. and i gained 3-5 mpg


This simulates a 'dead foot' driver without cruise control.
And you are right - this is how you get the best Gas Mileage from a cruise control eqpt vehicle.

 

[IndyIan]

Neither of my cars have cruise, but depending on how the cruise is set up I think it could use more gas.
Worst case is that it cuts the throttle too much when the car gets to speed and then quickly slows down and then gradually speeds up to the target speed again.
Best case for mileage, is for the cruise to aggressively get up to speed and then gradually bleed speed. This allows the engine to work most efficiently(50-75% throttle at 2000-2500 rpm)for a short time to get up to speed, and then lean out the fuel and crank the advance on the gradual slow down.

Good link explaining brake specific fuel consumption

 

[Craig in Canada]

Originally Posted By: IndyIan
Neither of my cars have cruise, but depending on how the cruise is set up I think it could use more gas.
Worst case is that it cuts the throttle too much when the car gets to speed and then quickly slows down and then gradually speeds up to the target speed again.
Best case for mileage, is for the cruise to aggressively get up to speed and then gradually bleed speed. This allows the engine to work most efficiently(50-75% throttle at 2000-2500 rpm)for a short time to get up to speed, and then lean out the fuel and crank the advance on the gradual slow down.



When I'm on anything remotely resembling level ground there is no oscillation around target speed like you describe. I set it, it stays. "Agressively gets up to speed and then gradually bleeds off speed"? Huh? Maybe they worked like this when first introduced, but my far-from-new 1998 seems a lot more refined than these behaviours that you're describing - it starts to level off throttle as vehicle speed approaches set speed, not suddenly closes the throttle as soon as you've exceeded set speed.

Of course on hills it works to maintain speed exactly which is not the most fuel efficient way to your destination but it's no worse than maintaining constant speed manually. I drive stick so there's no notion of cruise causing downshifts either. Since it's stick and engine RPM relates exactly to road speed, it would be easy to detect variation in speed on cruise and I do not detect any surging, oscillation, hunting, over/undershoot etc...

In general, unless I'm in extremely hilly terrain, I'm going to maintain a constant speed regardless of whether I'm going up or down a hill. Following people driving G-class vehicles who wander all over in speed drives me nuts.