Is Cruise Control Economical?

[Nath.]

Just to add.

If you have a lower powered car doing 70 on the cruise, you come to a hill and the car attempts to stay at 70 with the cruise flooring it and using loads of fuel. The same car driven without cruise, the driver would use a little more throttle but accept that he/she will slow down a bit up the hill.

A higher powered car on cruise at 70, comes to a hill, the cruise tickles the throttle a bit more and keeps it at 70 by using just a tiny bit more fuel.

Higher powered and torquey cars (diesel ones) get better MPG on the cruise at 70. 1.2 petrol cars get better MPG round town.

Horses for courses.

 

[bigbadjay]

Would that be 3d? Like contour lines?

 

[shnazzle]

Just to add.

If you have a lower powered car doing 70 on the cruise, you come to a hill and the car attempts to stay at 70 with the cruise flooring it and using loads of fuel. The same car driven without cruise, the driver would use a little more throttle but accept that he/she will slow down a bit up the hill.

A higher powered car on cruise at 70, comes to a hill, the cruise tickles the throttle a bit more and keeps it at 70 by using just a tiny bit more fuel.

Higher powered and torquey cars (diesel ones) get better MPG on the cruise at 70. 1.2 petrol cars get better MPG round town.

Horses for courses.

I've experienced this a lot. 1.0L Ford was as fuel (un)economic as my old 2.0L FR TFSI I traded it in for on the same journey

 

[sgb27]

Just to add.

If you have a lower powered car doing 70 on the cruise, you come to a hill and the car attempts to stay at 70 with the cruise flooring it and using loads of fuel. The same car driven without cruise, the driver would use a little more throttle but accept that he/she will slow down a bit up the hill.

A higher powered car on cruise at 70, comes to a hill, the cruise tickles the throttle a bit more and keeps it at 70 by using just a tiny bit more fuel.

The question really boils down to; how should you control your speed to get from A to B in X minutes using the least amount of fuel. I think there are too many variables involved to say that in poweful cars it's better to stay at a constant speed (using CC), and in low powered cars it's better to slow down a bit on uphill parts and go a bit faster on downhill parts. It would depend on the exact characteristics of the engines, the slope of the hill, the gear ratios, the base-line efficiency of the car (more powerful cars are almost always less fuel efficient than their equivalent lower powered versions) etc.

Also in a powerful car just tickling the throttle could easily use more fuel than the lower powered car can use at full throttle

 

[EndlessNameless]

The question really boils down to; how should you control your speed to get from A to B in X minutes using the least amount of fuel. I think there are too many variables involved to say that in poweful cars it's better to stay at a constant speed (using CC), and in low powered cars it's better to slow down a bit on uphill parts and go a bit faster on downhill parts. It would depend on the exact characteristics of the engines, the slope of the hill, the gear ratios, the base-line efficiency of the car (more powerful cars are almost always less fuel efficient than their equivalent lower powered versions) etc.

Also in a powerful car just tickling the throttle could easily use more fuel than the lower powered car can use at full throttle

You should always use gravity to your advantage if you're driving for economy, even in a powerful car. It just makes more difference if you have a relatively small engine in a heavy car.

In my car, CC is much better than my right foot.

 

[andycupra]

dont confuse the most efficient revs on an engine as being the most efficient revs to meet a specified demand.

anyway the answer to the thread title is:
for most people yes.

 

[sgb27]

You should always use gravity to your advantage if you're driving for economy, even in a powerful car. It just makes more difference if you have a relatively small engine in a heavy car.

If you assume your engine is equally efficient at all speeds then it's best to stick to a constant speed, the increased air drag on the faster downhill bit will more than outweigh any advantage gained by going slower up the hill (because air drag is proportional to speed squared).

So the only way it would make economical sense to slow down on the way up is if your engine is operating in more efficient manner at eg 60 mph compared to 70 mph when under higher loads, and also more efficient at 80+mph compared to 70 mph when under lower loads. Those efficiency gains need to outweigh the extra work needed to be done against the air drag for it to make sense to slow down going up hill.

Unless you're slowing down on the way up and forgetting to speed up enough to make up the lost time on the way down, then you might as well have just stuck to a lower constant speed in the first place.

 

[Dilligaf]

Well, my mapped Leon FR PD150 just gave me 58mpg over 10 miles of the M5 @ indicated 70mph using my right foot. Not bad me thinks Now I'm bored and back at 85.....

Sent from my HTC One S using Tapatalk 2

 

[Nath.]

Well, my mapped Leon FR PD150 just gave me 58mpg over 10 miles of the M5 @ indicated 70mph using my right foot.

Sent from my HTC One S using Tapatalk 2

You must have been going down more hills than you were going up hills on your 10 mile trip to get 58.

IMO 10 miles isn't enough for the computer to calculate an accurate mean average.

 

[S3 AKR]

My old PD150 did 62mpg at a steady 70mph when I used to commute between London and Colchester in it. Only did that for 2 weeks as an experiment, then went back to 46mpg at 90! That was with all the mods on it too.

 

[garycupratdi]

Guys would you hate me if told you that my E90 330d does 52mpg at about 75mph and in my car
it is definitely more economical using cruise as the car can react quicker then you be it going up
or downhill.
I really worries me reading how uneconomical these vag tdi engines are as you would expect mid
50's at least out of a 2.0L derv, it wouldn't surprise me if a 2.0 tsi was only a couple of mpg less
and that then defeats the whole point of a tdi.

 

[Dilligaf]

S3 AKR's experience is the same as mine and many other old PD owners. These newer 2.0 tdi are nearly 10 mpg worse off. A mate had an Altea FR 170 and we often travel together on the same journey but alternate cars. The Altea was always far worse mpg. My average over 30,000 miles is 46mpg but that is generally not sparing any of the tuned horses! The Altea after 10,000 was only 38!

Remember above that my 10 mile average was with with a warm engine, and when I reset the trip I was already doing 70mph so didn't have to accelerate up to speed. The trip mpg is most definitely accurate enough over 10 miles! Otherwise the tank average of 500 miles over 50 trips would be miles out. The car calculates to within 0.2 mpg of my manual calculations every time.

Check out an Android app, Fuelio, it records the data you give it and it graphs it and gives stats.....

Sent from my HTC One S using Tapatalk 2

 

[sgb27]

Guys would you hate me if told you that my E90 330d does 52mpg at about 75mph and in my car
it is definitely more economical using cruise as the car can react quicker then you be it going up
or downhill.
I really worries me reading how uneconomical these vag tdi engines are as you would expect mid
50's at least out of a 2.0L derv, it wouldn't surprise me if a 2.0 tsi was only a couple of mpg less
and that then defeats the whole point of a tdi.

BMW diesels are well known for their high efficiency, before my Leon I had a 120d (in Germany with my fuel paid for, so I didn't hang about much ) and would regularly get close to 1000km (600 miles) per tank if I wasn't driving stupid speeds.

The trip mpg is most definitely accurate enough over 10 miles! Otherwise the tank average of 500 miles over 50 trips would be miles out. The car calculates to within 0.2 mpg of my manual calculations every time.

I don't think he meant the actual trip mpg calculation was inaccurate, just that a single value from a 10 mile stretch is not likely to be accurate for the car in general. Over 10 miles just a single extra small uphill or downhill bit can radically change the average mpg, or if you have a slight tail-wind or head-wind etc.

 

[betty_swollox]

Thanks for info folks.

But, surely i should be seeing more than 44.5 mpg at 70mph? I have to say i am disappointed in the lack of economy from my FR generally.

Would like to know what mpg other PD170 drivers are getting?

Also, do you all run on V-Power Diesel? As i am currenly using Shell Fuel Save Diesel.

Thanks again.

My PD170 was f**king pathetic for mpg. I get an extra 5-10 mpg driving the same way in my CR170.

 

[betty_swollox]

Like someone else said, it will also depend on how you accelerate upto that speed before setting the cruise control


I can get an extra 5mpg on the same journey by not accelerating upto 65mph as quickly.


I never used to be arsed by MPG, but I am saving a fortune in this car. Yes, I miss my cupra so badly, but with the amount of miles I was doing, i could rarely afford to hoof it.


at what RPM are you changing gear?

 

[DavidS]

Well today i faced another Oxford to Scotland jaunt...

This time i set Cruise Control at 67mph, (It did add an extra half hour onto my journey but was in no real hurry) returned 51.4mpg over 420 miles. I know its not the best, especially compared to the CR170, but i was over joyed to see the better side of 50mpg!

Also realised that i cannot live without Cruise Control! Haha.

 

[bigbadjay]

I agree 50 is the magic number!

 

[Drizzle]

Well today i faced another Oxford to Scotland jaunt...

This time i set Cruise Control at 67mph, (It did add an extra half hour onto my journey but was in no real hurry) returned 51.4mpg over 420 miles. I know its not the best, especially compared to the CR170, but i was over joyed to see the better side of 50mpg!

Also realised that i cannot live without Cruise Control! Haha.

What gear was you in?
Also I find it easier to brake and reset rather then slow down with the stalk, how about you?

 

[DavidS]

What gear was you in?
Also I find it easier to brake and reset rather then slow down with the stalk, how about you?

I was in 6th gear at 67mph - The rev counter sat bang on 2k revs so didn't think it was labouring overly at those revs.

Yeah mate i agree, i almost never use the stalk to slow down/speed up - Find it easier to break and reset.

Any further tips on better mpg would be appreciate, however i have a feeling 51.4mpg is about as good as its going to get for me! Haha.

 

[AndyG_TSi]

I was in 6th gear at 67mph - The rev counter sat bang on 2k revs so didn't think it was labouring overly at those revs.

Yeah mate i agree, i almost never use the stalk to slow down/speed up - Find it easier to break and reset.

Any further tips on better mpg would be appreciate, however i have a feeling 51.4mpg is about as good as its going to get for me! Haha.

I know this is going to sound pretty obvious but:

Check your tyre pressures are correct (think it should be 29psi for fronts & 32 psi on rears)

and

Check your wheel alignment is correct

if either are out, this makes hell of a difference to your MPG as your tyres are not rolling as efficiently as they should....

check tyre pressures weekly & have your wheel alignment checked every 6 months.

David, when was the last time you checked either?

I had my wheel alignment done 6 months ago it was way out and my car had eaten a set of front tyres to the point they were bald on inside edge & had 5mm left on outside edge. It was stepped wear, so had it done & got 2 new tyres.
Had wheel alignment checked again this week in addition to my MOT & it was out, again, both front & rear. So had to be adjusted again on the 4 wheel hunter machine.
Anything can cause your wheel alignment to be put out, hitting speed humps, pot holes, kerbs etc, ect........

Car feels a whole lot better now & retuns slightly better MPG than it did before the MOT