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Discussion Starter · #1 ·
May sound like a
dull question, but what is the best speed for cruising on dual
carriageways or motorways for the best fuel consumption.

I have a 1.9TDi MK V SE.

I generally set the cruise control for 80mph, but find the average mpg is low (about 47-49).

Any info would be very handy!
 

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You will get better mpg at any speed by switching off the cruise control. If you are high 40's at 80mph, manual driving should push it over 50mpg. If you drop the speed to 75mph, you will do this easily.
 

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You will get better mpg at any speed by switching off the cruise control.
Why?
Not really qualified to give a technical answer Al but its something to do with the fact that cruise will always try to maintain a steady speed and as a consequence is less efficient than the right foot when any change in gradiant is encountered. Its been discussed here before and I have tried it and you do gain several mpg if you turn off cruise and continue 'manually' at the same speed.
 

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I do 2 x 50 mile motorway commutes every weekday and at a cruise controlled 70mph I used to get 52/53mpg. Since I reduced to 56mph or thereabouts, the mpg shot up to nearer 61 mpg.
And it takes you 15mins longer each way.

Do you really waste half an hour of your life every day in the name of mpg?
 

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I do 2 x 50 mile motorway commutes every weekday and at a cruise controlled 70mph I used to get 52/53mpg. Since I reduced to 56mph or thereabouts, the mpg shot up to nearer 61 mpg.
And it takes you 15mins longer each way.

Do you really waste half an hour of your life every day in the name of mpg?
Yeah, knackers to it, put your foot down[:p]!
 

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I agree that using cruise control on roads with quite a lot of gradient changes might actually result in higher fuel consumption than if driven manually. This is because cruise control systems cannot anticipate differing gradients ahead like we do. Consequently a cruise control system might accelerate hard up a short steep hill to try to maintain the set speed irrespective of the fact there might be a steep descent just a hundred yards ahead. When we drive, even though we might intend to keep a constant speed, we usually vary it slightly according to conditions. Consequently, we'd not try quite so hard to maintain the exact same speed up a short hill and consequently use less fuel.

Personally I believe the TDI Mk Vs are more suited to cruise control than the 1.6 FSI models. I got the distinct impression when driving a 6 speed 1.6 FSI Mk V that its lower torque and the higher 6th gear meant it had to work harder to maintain 70mph. I didn't have the car long enough to see what an effect this had on fuel consumption.

Stuart
http://www.stuartdalby.co.uk/vwgolfmk5
 

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I agree that using cruise control on roads with quite a lot of gradient changes might actually result in higher fuel consumption than if driven manually. This is because cruise control systems cannot anticipate differing gradients ahead like we do. Consequently a cruise control system might accelerate hard up a short steep hill to try to maintain the set speed irrespective of the fact there might be a steep descent just a hundred yards ahead. When we drive, even though we might intend to keep a constant speed, we usually vary it slightly according to conditions. Consequently, we'd not try quite so hard to maintain the exact same speed up a short hill and consequently use less fuel.

Personally I believe the TDI Mk Vs are more suited to cruise control than the 1.6 FSI models. I got the distinct impression when driving a 6 speed 1.6 FSI Mk V that its lower torque and the higher 6th gear meant it had to work harder to maintain 70mph. I didn't have the car long enough to see what an effect this had on fuel consumption.

Stuart

http://www.radox.freeserve.co.uk/vwgolfmk5.htm
Yes, I would think that you are largely correct in those assumptions especially related to the 1.6 FSI based car (the one which I own). I have done a round trip today to Rye (on the SE Coast) on give and take roads ie. indifferent 'A' roads and 'B' roads and found that if I engaged CC I got noticeably lower mpg figures compared with maintaining the same speeds using my right foot!

Whilst it may be 'cool' to drive with CC engaged I think that there is a price to pay for this, in terms of petrol consumption, especially if the roads are hilly and you have a high-geared car (6th gear) with low torque. On the other hand on very long drives it is nice to give your right foot a rest sometimes.

For the day's mileage of approx. 116 miles, I averaged 47mpg, according to the computer's readout.
 

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Hahaha! I'd love anything over 40mpg on the motorway. My golf is just too fun to drive... Prefer to stick cruise control at 110mph and cruise to my destination faster, and have the pleasure of overtaking everyone, probably wishing they had a sexy new golf!
 

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What a load of bo11ox, I've never known any of my cars, diesel or
petrol, to be more economical without cruise than with and don't know
anyone who has found that. As it can make tiny micro adjustments
it is more precise than just using your foot.
 

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What a load of bo11ox, I've never known any of my cars, diesel or petrol, to be more economical without cruise than with and don't know anyone who has found that. As it can make tiny micro adjustments it is more precise than just using your foot.
Nope,

The cruise will always accelerate more aggresively (I'd say 1/2 throttle) than than a human (human has to be in granny mode though) where said human can apply a very light throttle. However as you've said, if your not in granny mode cruise will be better.

Acceleration is the real enemy of MPG and the gentler it can be done, the better.

I had an aftermarket cruise system which I fitted t my last car and you were able to adjust the rate of acceleration, I wonder if this can be done somehow with vag-com ?

... Also, doing 56mph makes suprisingly little difference to journey time if the journey is reasonably short, like most of our daily commutes. Different matter if your doing 100's of miles though in a journey.
 

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You will get better mpg at any speed by switching off the cruise control. If you are high 40's at 80mph, manual driving should push it over 50mpg. If you drop the speed to 75mph, you will do this easily.
100% agree engine braking uses fuel and does not anticipate the road head - END OF
 

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You will get better mpg at any speed by
switching off the cruise control. If you are high 40's at 80mph, manual
driving should push it over 50mpg. If you drop the speed to 75mph, you
will do this easily.
Not in my experience or that of friends who know what they're talking
about and that's what I'd rather go by. Opinions are like
ar*eholes - everyone's got one and everyone elses's stinks.
 
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