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Hello AndroidGB......Interesting - your experience is the complete oposite of mine.
I use the cruise control all the time, it is so nicely located and easy to operate. Also, it has nice characteristics; for example, when operating resume the transition form current speed to the resume speed is very smooth.
I have had cruise control on all of my vehicles for many years and this is my first with manual transmission.
Having lived in the US for many years we did lots of long distance journeys, always with cruise activated - in fact, in the US it is promoted as a way of 'saving gas'.
I wonder if your experience is due to the fact that, in truth, these vehicles are a bit underpowered for their weight?......therefore the automatic may change down earlier? Just a thought?
As for final drive ratios I think that all the 616CDi chassis rated at 5990kg, regardless of manual or automatic have the same ratio - at a steady 50mph our tacho shows about 2600, at a steady 56mph the tacho is 3000. It would be interesting to know if the auto is different?
Obviously, myself like most others are keen to get the best fuel economy!
I think you may have hit the nail on the head re power/weight ratios.
If you are driving a car with reasonable power and torque, along mainly flat roads, with low traffic density, and low cruising speeds, you are probably going to achieve good MPG, because there's very little adjustment that the cruise has to make.
My car has a power to weight ratio of 153bhp per tonne, compare that to the vans 26 , and you can see how much extra power the cruise is going to have to feed in to maintain the same speed.
Regarding the rear axle ratio I think they did a 5.125 and a 5.75 and I thought they put the lower in the auto. I may be wrong on that, but I do believe the auto has a slightly lower 5th gear. According to the specs the 5.125 requires 2471 rpm for 80kph, and the 5.75 requires 2773 rpm.
I'll try and see if I can work out which mine is when I next take it out.
We have a Mercedes 316 based La Strada it's now eight years old and have yet to find an alternative van good enough to make us want to change.
This being our third Van the fact that it is a Merc is a major factor I may find it difficult to consider an alternative base vehicle having sampled some of the alternatives.
I find the autocruise fine when abroad but rarely use it in the UK.
When we bought the van the salesman advised us " you have a 100mph van here".
Didn't really take him serious but being a Biker decided to give it its head on the Autobahn, sure enough over the ton, I decided to chicken out having seen 104 on the speedo how accurate this is ?
I assume about 10% fast.
I think you will always be able to achieve better MPG if you drive manually at the same sort of speed that you set the cruise at.
Basically because you can anticipate road conditions and drive accordingly, for instance when you encounter a hill the cruise will keep feeding in power in an effort to try to maintain speed.
Unfortunately the cruise control fitted to these vehicle are only operating on one parameter, but I believe systems are being designed which take into account a number of factors, and could ultimately make them more efficient than driving manually.
I find cruise in the UK of limited use because with our crowded roads and with it set at 50 -55mph you're in with the truck and are constantly coming on and off of it.
I usually average about 19MPG (carry a fair bit of kit) but on the occasion I mentioned I achieved over 22MPG, bear in mind mine is an auto with a lower rear axle ratio (Therefore more revs for any given speed than a manual)
Andrew
Hi all.......this is an interesting topic, particuarly the above excellent posting. AndroidGB brings together both negetive points in the use of cruise on UK roads. First I fully agree with his comment associated with crowded roads and the use cruise, just not comfortable for safe stress free driving IMO. Second locking the speed is always going to demand more fuel to maintain that speed over varying terrain.
Not sure about our current vehicle but on the previous American RV's all had Cruise Control (CC) using an extremely accurate form of feeding back the road speed to the engine control unit (ECU) which then operated the throttle or fuel control. They used an alternator made up of a permanent magnet on the drive shaft (rotor) spinning within stationery coils (stator). This delivered a current at a frequency depending on the speed of the drive shaft to the ECU. Deployment of CC at a selected speed delivered a reference frequency to the ECU. Any mis-match is countered by adjusting or feathering the throttle hence the speed to keep both frequencies in line. Such fine adjustments went unnoticed most of the time, just like being chauffeured by an expert driver. However as Android GB states only one parameter is being controlled albeit expertly it still remains against a fixed locked speed, and the necessary fuel to keep it there........Crindle.
Maybe it's a personal thing?........I find that without cruise control my speed alters up and down, usually more up! I'll see an obsticle (another vehicle!) so I'll speed up to get by but then don't slow down again. I am a fully paid up member of the push on brigade.
To me, the cruise is just an easy way of sticking to a speed - which I find far less stressfull.......on top of that I find that the position of the throttle in relation to the seat is akward (regardless of how I adjust the seat) and it really troubles my knee and foot. Or am I just getting old?
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Germany
but leaps to the dizzying heights of nearly 34 BHP/tonne when empty.
