what gets better gas mileage a car useing criuse control or a car without

If they are going the same speed, then neither. Cruise control just maintains the speed.

If a car goes the same speed as it is on cruise control then it really wouldn't make a difference.

In real world situations using cruise control is better. Human reactions will have a tendency to overcompensate for slight hills and valleys using more gas. Cruise control is more precise in its control.

It depends on the driver. While a driver using a manual transmission can waste gas, so can a driver using cruise control.

If there is a slow vehicle ahead, a lot of people hope that the one ahead speeds up, wait for the last moment and then brake hard when the one ahead doesn't. Without cruise control you compensate instead of hoping.

When the speed limit changes to a lower speed, cruise control drivers tend to wait and then use the brake to slow down. Without, you simple release the accelerator and let the car slow down without brake. But even without cruise control, a lot of drivers us the brake to slow down.

The terrain also plays into the question.

On a flat, open, road, the curse control does a better job at maintaining a constant speed than most humans. There for it will usually get better mileage.

However, on hilly terrain, it's a whole different situation with many variables coming into play. I don't have time at the moment, to get into this. I'll be back later with an explanation.

thanks a lot my father and i have been debating about this for some time now all though i would like to hear more from vw engineer about he terrain again thanks alot

Hopefully, I'll have time to cover this...

The hills question is a complicated one. There are so many factors, like the size of the hills, slope, model of the car, etc.

This is further complicated by the fact that many modern cars will save fuel by limiting or even shutting of fuel to the engine when it is coasting.

In an ideal condition, when you are driving through rolling hills, when you are going down hill, you can use a little bit of throttle to speed up as you go down with gravity doing a lot of the work, this extra momentum can get you partly up the next hill without you needing to upon up the throttle for the climb. Cruse does not know the situation of the hills and will simply just reduce the throttle to correct for the added speed as you go down.

However, doing this now days may or may be a benefit. A lot of cars these days will actually cut off the fuel to the engine when you are coasting. The momentum of the car through the tranie keeps the engine turning and ready to go when you step on the gas again.

So now, you can go down a hill using no gas at all, and then climb as you would with cruse. I don't know this balance out for fuel usage.

Another thing to note is this can vary ca to car in exactly how this is implemented. I had one car that would shut off fuel to the engine if the car was coasting under 50 MPH. Over 50, it kept the fuel on. I know of some cars that will practically put themselves in neutral in this situation.

In the end, fuel economy when suffer. There are a lot of different schools of thought on how to make the best of this.

Also note that I'm talking about rolling hills, like in the Appalachian "mountains." I'm not talking about long up or down hill runs going up or down major mountains.

Coming down out of the Rocky mountains can give you some very good fuel mileage. I know someone who got something like 200 mile per gallon coming down the rockies. However, he paid for that when he averaged 12 on the way back up.

It is highly variable.

Personally, in my my manual Maz RX8 I only use cruise control when I'm on terrain that is only on gradual inclines/declines. I've noticed a tendancy for my car to overcompensate at the crest of steeper hills, and to undercompensate at the base of said hills, resulting in speed fluctuations of +-7mph. I've also noticed that it wants to stay at this certain speed, so if it slows a few mph, it will use extra gas to get back to the set speed.

With my foot, I am very lenient on the speed, allowing the speed to go maybe 2mph over, and up to 8 under. The difference is that I don't get back to the exact speed if it's not necessary. And then if needed, i can gradually accelerate back to the certan speed.

But it varies widely.

Agreed

quote:

Originally posted by C128:
It depends on the driver. While a driver using a manual transmission can waste gas, so can a driver using cruise control.

If there is a slow vehicle ahead, a lot of people hope that the one ahead speeds up, wait for the last moment and then brake hard when the one ahead doesn't. Without cruise control you compensate instead of hoping.

When the speed limit changes to a lower speed, cruise control drivers tend to wait and then use the brake to slow down. Without, you simple release the accelerator and let the car slow down without brake. But even without cruise control, a lot of drivers us the brake to slow down.

when I'm on cruise control, I use the coast & resume/accel buttons to adjust for speed limits... and if it's raining, I can make my truck take off like an airplane (which is impressive since it normally has the glide path of a brick)

quote:

Originally posted by wv_engineer:
Coming down out of the Rocky mountains can give you some very good fuel mileage. I know someone who got something like 200 mile per gallon coming down the rockies. However, he paid for that when he averaged 12 on the way back up.

I typically get very close to the same fuel economy when driving through the mountains as when on the flat despite (or because of) heavy throttle usage but I've never averaged 106 mpg!

thanks for clearing that up wv and to all