Cruise control and mpg

[donutwheels]

Hi all,

I noticed that my mpg improved on average when not on the cruise control and when it's on my mpg is worse on average.

At the risk of sounding stupid, maybe it's my imagination but shouldn't it be the otherway around?

could any of you clarify this for me

thanks for your help

[HDi fun]

It's not especially easy to quantify this, let alone qualify it.

I have heard similar comments elsewhere. The differences are likely to be pretty small, and further, how easy is it to re-create EXACTLY the same journey for scientific analysis.

[pgarner]

no cruise control tries to keep the engine at a steady speed. this generally means its using a little more throttle than manually.

its more economical if your like loads of drivers, like myself, that start off sitting around 75 then slowly speed up and up and up the CC keeps you at a steady speed.

how much a difference are you seeing ? normally motorway driving i seem to be around 1mpg lower on cc over long distance

[RobBentley]

Interesting one this one....

R36 is slightly more economical if you drive it frugally as opposed to on cruise control.

W8 is notably more economical on cruise control - no matter how hard I try manually.

No idea why this might be.....

[pgarner]

Originally Posted by HDi fun

It's not especially easy to quantify this, let alone qualify it.

I have heard similar comments elsewhere. The differences are likely to be pretty small, and further, how easy is it to re-create EXACTLY the same journey for scientific analysis.

not very scientfic but i can be cruising along at 80 and boost is showing 15" of mercury where as with the CC on theres slightly less vaccum at normally around 10-12"

[donutwheels]

My mpg indicator is jumps about more driving manually which is expected. HOwever I find it averaged only slightly higher (3-5mpg more) than when on cc (which jumps about less).

I'm sure it's more psychological than anything else.

[waynne]

Cruise control will accelerate on a hill to maintain the speed. A human will tend to drop speed a little going up a hill and this is where the saving usually is.

I've always understood CC to be less economical than a good human driver.

[HDi fun]

CC cannot anticipate the hill, that's why it might be less economical. It has to react to something, and that something is a slight drop in vehicle speed. It's the only thing it senses.