pensuke said:

So Argonought, i wouldnt suppose you have that information, in regards to the peak values in 5th, as i was never blessed with a car manual when i purchased my stilo. Also, do these values fluctuate as the car gets lighter due to consumption, weather etc.

Also, i've had a new exhaust put in with a big bore. My dad recons it's running rich due the residue inside the exhaust. If, my car is running rich, i assume that would have a detrimental effect to my MPG even IF im driving economically, is that correct to assume?

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It's 4000rpm on the 1.6 which I'd imagine is pretty fast but remember this is optimal and you always get better mpg if you drive slower. Theory and practice break down a bit when you're not using all the power (as when climbing a hill) and you have to take account of frictional losses within the engine at those sorts of revs when driving on the flat. For instance, it wouldn't make any sense to drop a gear just to maintain 4000rpm since the frictional losses within the engine would be higher than the extra efficiency the engine is able to deliver at those higher revs (but which isn't needed as you're driving on the flat).

A simpler answer might be to say a car is being driven economically when it doesn't take much effort (in the sense of pushing the accelerator) to keep it going.

Keeping revs at 4000rpm when climbing a fairly steep hill is important to remember though as it will definitely save you fuel

And this would happen because if the revs are down, so is the power, and you may be forced into thinking that you are making an economy when in fact you have the accelerator half way to the floor to maintain speed.

In my 1.4 i can get between 42-50mpg in 6th gear at 60mph (depending on wether im going up or down hill) It mght be worth noting that i use shell V power petrol though and i see a 4-5mpg increase when using this fuel over any other. On the backroads however i havnt really taken account of best speeds etc but just yesterday i managed to get from Bangor, N. Wales to Cardiff on a quarter tank...taking the windy roads through the mountains mainly 2nd, 3rd and 4th gears

MiniMonster said:

If i drive at 90mph it depends if im driving north or driving south to whether I save fuel or not. I have experienced driving 85mph burns less fuel than 80mph going up north... coming down south is 80mph all the way as it burns the same if not less than 85mph.

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Driving from north to south should be better for your MPG as you're driving downhill

I've heard 55mph (probably more like 60 on the speedo) in 5th gives you the ultimate MPG. Thing is it'd take you AGES to get anywhere & it'd be no fun!

Bob Fleming said:

Driving from north to south should be better for your MPG as you're driving downhill

I've heard 55mph (probably more like 60 on the speedo) in 5th gives you the ultimate MPG. Thing is it'd take you AGES to get anywhere & it'd be no fun!

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I have noticed its really good MPG going that slow... but yea it would take an additional hour and a half theoretically!
My car pulls best from 3,500rpm to 4,500rpm... as for a fuel consumption "Sweet Spot", you cant argue with having the engine off!

I have tried many times to get the best MPG in my car and the 580 Miles to a tank is my best. That was pure motorway sitting at about 2300RPM which was about 65MPH(Speedo).

That works for me whenever I want to get the most MPG.

Well, i just went on a trip to Doncaster over the weekend, and from the looks of things my speedo is drastically optimistic. At 80mph on the speedo, Tom Tom tells me I'm only doing 70 or so. So when im sitting at 65-ish I'm only only doing 56-58. Is this normal, or do i need to get it re-calibrated?

From the discussion so far, 80 on my speedo (which equates to about 70-ish) is roughly 35/37,00 rpm. I tried to do the mix of Optimax and Regular, and the round trip cost me about £35. According to the trip computer i averaged 39.2mpg and from Birmingham to Doncaster took me 1hr 39mins.

GPS systems are almost always inaccurate. I've tried my Mio S500 on several cars, and it's always off by 4 km/h exactly. Since I haven't found any fluctuation in this gap, I presume it's the GPS's fault.

It's more than likely the other way around, GPS is deadly accurate if you're on fairly flat ground. Almost all cars tend to be optimistic on their speedometer to avoid manufacturer litigation if people get caught in speed cameras etc

I've tested mine on VW Golf 5, both my stilos, an audi A4 2008 model and a Skoda Octavia 2 from 2007. All were showing 4 km exactly more than the GPS. I guess you could be right, and most manufacturers have an average hidden agreement to set them off by 4 km/h just to be safe.

vladof said:

I guess you could be right, and most manufacturers have an average hidden agreement to set them off by 4 km/h just to be safe.

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What's that in % terms out of interest ?

If your talking about miles, It's 2.5 miles off. The percentage of which it is off changes with the speed. For example, for 100 km/h its 4%, 200km/h its 2%, etc.

I find my speedo to be around 7% off at all speeds, comparing the GPS to the "analogue" dash.

Regarding the fuel sweet spot, the 1.6 is balanced at 100 km/h (equals 60 mph) in 5th gear. It has to be in superflat Denmark though, as Norway is too much up and down, and the 1.6 gets kind of underpowered pretty fast, making 4th gear very common.

Regular speed limits here are 80 km/h, some 90 km/h on highways and rarely 100 km/h on some "high quality" highways. Don't get caught speeding, 110 km/h in 80 km/h will give a penalty of £725GBP. I know for sure...

i don't know how, but I'm currently getting 32mpg on my 12 mile journey to work into london at 8am in my 1.8...and that's just driving sensibly using forward planning....

Morty Mort said:

Regarding the fuel sweet spot, the 1.6 is balanced at 100 km/h (equals 60 mph) in 5th gear. It has to be in superflat Denmark though, as Norway is too much up and down, and the 1.6 gets kind of underpowered pretty fast, making 4th gear very common.

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What do you mean balanced Morten ? - you referring to the fly-wheel

Do you mean that if you're driving at 150 km/h the gps is telling you that you are actually going at 139.5? And if you're going at 70 GPS actually tells that the actual speed is 65.1?

I find that kind of odd, my GPS is always telling me I'm going slower with 4 km/h.

Argonought said:

What do you mean balanced Morten ? - you referring to the fly-wheel

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Hehe, no. Bad Norwegian / English. Balanced as "highest possible speed within area of lowest stable fuel consumption".

vladof said:

Do you mean that if you're driving at 150 km/h the gps is telling you that you are actually going at 139.5? And if you're going at 70 GPS actually tells that the actual speed is 65.1?

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That's right.

I will check in parallel more than one GPS while driving to see if they give the same results.