Cruise Control & Adverse Weather Conditions

[c240yaz]

I use CC all the time, on the flat, uphills, and motorways. I definately get more MPG using it.

Only downside is when I'm cruising along and proceed to go downhill, the car speeds up and I have to brake to maintain desired speed, at say 30.

 

[MBManInKen]

I use CC all the time, on the flat, uphills, and motorways. I definately get more MPG using it.

Same here. Using the CC prevents the minor accelerate/decelerate sequences that you get otherwise trying to maintain a set speed, which is why I think it returns a better mpg performance.

Only downside is when I'm cruising along and proceed to go downhill, the car speeds up and I have to brake to maintain desired speed, at say 30.

My car will keep to the set speed including by reducing throttle and/or shifting down if necessary on downward slopes.

 

[DrNick]

So do you get best economy by driving at a constant load (speed) or by accelerating as fast as possible and then coasting down to a low speed?

 

[glojo]

Cruise control has no intelligence whatsoever, it will accelerate to increase speed to the required setting and then slow the vehicle down if it exceeds that setting. A good driver with forward observation will make intelligent allowances for these minor adjustments that might need no braking, or acceleration.

Top Gear is NOT a Motoring Journal of any authority, but who remembers the Clarkson marathon when he drove the Audi diesel to from London to Scotland and return on one tank of fuel. The first thing that was switched off was............

I fully accept that some drivers will get better economy when using cruise control, we all have different driving styles and we all think we are correct. I say live and let live and my wife loves using cruise control on both our vehicles.

John

 

[portzy]

So do you get best economy by driving at a constant load (speed) or by accelerating as fast as possible and then coasting down to a low speed?

I would say that the best econony is acheived at a set speed and, if you have to deviate from this say at roundabouts etc, then a gradual acceleration back to the target speed is better than a rushed acceleration.

On the coast, (over-run), the fuel is cut if I am not mistaken providing you leave it in gear or D.

Just as a matter of interest there at least two things that I've noticed my 7G auto does:-

In cruise, the braking system does indeed intervene to keep the speed in check, I can feel this is in the brake pedal and I also get the sensation of braking with or without any auto downshifting.

Depending of my last previous driving style. The acceleration rate differs when I select ''Resume''. Thats to say if I have been pootling around its a steady resume or, if I have been having fun its a rapid resume if you see what I mean .

Portzy.

 

[c240yaz]

So do you get best economy by driving at a constant load (speed) or by accelerating as fast as possible and then coasting down to a low speed?

No vehicle will get good fuel economy if you floor it.

Gradual acceleration = economy,..... in most cases.

 

[television]

All fuel economy runs are done by getting the car into top as soon as possible, but as said that is not by flooring it, just do it quickly and gently it also helps to have some for sight so that you come to a stop almost without using the brakes

 

[Diesel Benz]

All fuel economy runs are done by getting the car into top as soon as possible, but as said that is not by flooring it, just do it quickly and gently it also helps to have some for sight so that you come to a stop almost without using the brakes

I agree with this. The idea is to use the engine at its best efficiency. At low engine load, the efficiency is low. Eventually the best efficiency load needs to be given away as the car would run too fast. A quick acceleration would result to the best average efficiency.

Of course in real traffic it is important to anticipate traffic like John mentioned, avoiding braking would mean less gas consumption. Sometimes this just isn't reasonable for others.

One should not compare gas consumption if first driving with cruise on and then driving with gradually reduced speed at uphills. A fair comparison would ask for the same time spent for the journey. If one slows down for uphill, one would need to speed up elsewhere to maintain the same average speed as with cruise on.

Have not seen any studies but perhaps cruise still loses against a good driver as one should not brake at downhill roads (depends on the car, Distronic/Distronic Plus would literally use brakes if engine braking is not enough). Letting the car either roll free (manual tranny) or use engine braking with auto tranny (assuming no Distronic Plus) to let the cruise speed being exceeded for downhill road portions, and go below cruise speed at uphill portions might be best. But I bet a driver would soon get tired doing it accurately enough to actually perform better than the cruise would work.

Would like to see accurate comparisons for the case where the same travel time would be assumed with and without cruise.

 

[Dryce]

Would like to see accurate comparisons for the case where the same travel time would be assumed with and without cruise.

If you sit on cruise near the limit on a long stretch of road you will get passed and repassed by some vehicles several times over. Upshot is the drivers are doing about the same average as you but varying their speed a lot more. In most cases they are probably being less economical (the higher speed segments have disproportionate drag that is unlikely to be offset by savings from the lower speed segments).

On the other hand you see drivers who are probably on cruise come up against the tail of a queue of slower traffic and the brakes come on last minute as opposed to coasting up to safe distance behind the queue with no braking.

 

[Diesel Benz]

If you sit on cruise near the limit on a long stretch of road you will get passed and repassed by some vehicles several times over. Upshot is the drivers are doing about the same average as you but varying their speed a lot more. In most cases they are probably being less economical (the higher speed segments have disproportionate drag that is unlikely to be offset by savings from the lower speed segments).

On the other hand you see drivers who are probably on cruise come up against the tail of a queue of slower traffic and the brakes come on last minute as opposed to coasting up to safe distance behind the queue with no braking.

I was thinking more about a theoretical case, driving alone, no traffic lights etc. etc., just the road going up and down every now and then.

Again, as John mentioned, the cruise has no intelligence while the driver is supposed to have one. It is obvious that at complex traffic conditions a clever driver would do better than the cruise.

 

[c240yaz]

If you sit on cruise near the limit on a long stretch of road you will get passed and repassed by some vehicles several times over. Upshot is the drivers are doing about the same average as you but varying their speed a lot more. In most cases they are probably being less economical (the higher speed segments have disproportionate drag that is unlikely to be offset by savings from the lower speed segments).

On the other hand you see drivers who are probably on cruise come up against the tail of a queue of slower traffic and the brakes come on last minute as opposed to coasting up to safe distance behind the queue with no braking.

I couldn'd agree more. This happens to me all the time on long drives, mostly on the M74 / M6 north.

It can also be very annoying when they pass you, then they slow down, then you have to pass them, and the same happens over and over again.

 

[television]

The advantage with distronic is that you can set it to keep a 2 sec gap, that is 100m at 70mph and is OK if you are happy to sit in one lane. I find that for the best part that is fine as you can use the throttle with upsetting distronic, so if the lane that I am cruising starts to get messy,I just go by them all and let distronic take over again, it only decouples if I touch the brake the same as on cruise control

 

[Dryce]

It can also be very annoying when they pass you, then they slow down, then you have to pass them, and the same happens over and over again.

There's a pyschological thing with many drivers on dual carriageways/motorways that means they catch up the car in front but don't really want to go faster so once they pass they slow down.

It's not so pronounced on single carriageway roads because they actually have to overtake instead of just pulling out.

 

[crockers]

The advantage with distronic is that you can set it to keep a 2 sec gap, that is 100m at 70mph and is OK if you are happy to sit in one lane. I find that for the best part that is fine as you can use the throttle with upsetting distronic, so if the lane that I am cruising starts to get messy,I just go by them all and let distronic take over again, it only decouples if I touch the brake the same as on cruise control

Don't need any of these fancy gimmicks....I have a wife who screams if I get too close to another car....

 

[hawk20]

If going up a long climb,in cruise the box can kick down to maintain the speed, where as without you can coax it up without

Oh Malcolm that really is as farfetched as one can get. I use cruise a lot and have all my adult life mainly doing 40k per year. It consistently uses less fuel than driving oneself.

Staying in too high a gear going uphill does not save fuel. See any manuals on how to drive economically.

The real saving from cruise is that it has 100% concentration. Humans don't. Choose a cruising speed on the motorway and it sticks to that. Humans often keep slowing down and then accelerate to get back up to speed or they find themselves gradually speeding up and going faster than they meant to do.

 

[television]

Oh Malcolm that really is as farfetched as one can get. I use cruise a lot and have all my adult life mainly doing 40k per year. It consistently uses less fuel than driving oneself.

Staying in too high a gear going uphill does not save fuel. See any manuals on how to drive economically.

Sorry Hawk it is not far fetched, try my turbo charged V70R it will change down at 70 on a long climb to get you up to cruising speed again quickly, where as with out cruise I can keep almost the same speed and the box not changing.

Manuals or books do not apply to driving an automatic in this instance, as its normally always in the right gear at the right time.

If you read all of the preceding post you will also see that if the car was driven in a leisurely manner before you engaged cruise the changes down in cruise are far less the had you been belting the car and then going into cruise.
Though my 2.3 V70R has the same BHP as my SL500 the V70R has to work hard to keep up and in cruise it will change down on motorways and without it it will not.

This is all fact and not fiction, as when it changes down it annoys me.

There has been many post on the same subject and most say that cruise is not always more economical

 

[hawk20]

Sorry Hawk it is not far fetched, try my turbo charged V70R it will change down at 70 on a long climb to get you up to cruising speed again quickly, where as with out cruise I can keep almost the same speed and the box not changing.

Manuals or books do not apply to driving an automatic in this instance, as its normally always in the right gear at the right time.

If you read all of the preceding post you will also see that if the car was driven in a leisurely manner before you engaged cruise the changes down in cruise are far less the had you been belting the car and then going into cruise.
Though my 2.3 V70R has the same BHP as my SL500 the V70R has to work hard to keep up and in cruise it will change down on motorways and without it it will not.

This is all fact and not fiction, as when it changes down it annoys me.

There has been many post on the same subject and most say that cruise is not always more economical

OK let's say with some cars there are some situations where you can do better than cruise. On hills may be one. I am talking mainly Mercedes diesel autos where the torque is so huge that gearchanging is rare in situations where you sensibly have cruise on. Normally cruise is most used on motorways where as several have said it has 100% concentration, keeps a constant speed and saves fuel.
Many also use it nowadays in speed limited areas to save watching the speedo all the time. Once again it keeps a steady speed and saves fuel. In complex situations and variable traffic it is far less useful and then I don't use it.

 

[television]

OK let's say with some cars there are some situations where you can do better than cruise. On hills may be one. I am talking mainly Mercedes diesel autos where the torque is so huge that gearchanging is rare in situations where you sensibly have cruise on. Normally cruise is most used on motorways where as several have said it has 100% concentration, keeps a constant speed and saves fuel.
Many also use it nowadays in speed limited areas to save watching the speedo all the time. Once again it keeps a steady speed and saves fuel. In complex situations and variable traffic it is far less useful and then I don't use it.

I know you well,l and you know me well, this is one of those situations where someone ask a question about their car, and someone else joins in and says, hey my car is doing that even though it is a different model so things go downhill from then on.


When I wrote this up, sure I was not thinking about the torque of a diesel, just my own experiences, so we are both right in what we said

Hawk that was your 1000th post

 

[hawk20]

Good Lord; I hadn't even noticed it was coming. Thanks for saying. What better than to do it with a posting agreeing with you Malcolm. Odd with cars. There are so many variations of situation, and of people's behaviour and of car types that there are far fewer simple answers even to what look like simple questions. You must be close to your millionth post on all forums together?

 

[Dryce]

On hills may be one. I am talking mainly Mercedes diesel autos where the torque is so huge that gearchanging is rare in situations where you sensibly have cruise on.

There are some pretty poor engine/auto combinations out there. I had a Rover 75 2.0 V6 for several weeks that was just wrongly geared for long inclines and refused to change down unless you wellied it or used the selector do do it manually.