General Trip computer and high speed fuel economy.

[Shadeyman]

I had a few things to sort out in Scotland yesterday, unfortunately I was running late so had to put my foot down, my house in Wolverhampton(J10 - M6) to Smiths Hotel Gretna Green(J45 - M6), a little under 200 miles took me 2 hours and 14 minutes. Needless to say the cruise control was set well up in license loosing territory.

Fuel gauge was on the full mark when I left and was on half way by the time I'd got there, that's half a tank used(6 gallon).

Trip computer reports 42mpg which considering how fast I was traveling seems too good to be true.

The car used 6 gallon, so 200 miles divided by 6 gallon is about 33mpg, which I think is more realistic and still quite good considering the speed I was doing.

So my trip computer is WAY off the mark.

Edit.
Actually I'm still in Scotland, I'll be heading home later today, can't believe how empty the motorways are up here.

 

[richydraper]

Gretna Green... That fast... What were you doin puttin a stop to your underage daughters wedding?

Lovin the AVERAGE of 80!

Was the mpg zeroed when you filled up?

 

[Davren]

So my trip computer is WAY off the mark.

I think they're all way off the mark once the injectors start to wear.

Off Topic:
Never noticed the spelling mistake on the CN+ for "Travelled" before.

I bought a new washing machine a few weeks ago, one of the programs on the electronic display says "Synthetics Resistent". Perhaps Magneti Marelli and Hotpoint use the same proof reader.

 

[cledan]

When I first got my Stilo it was running on ling long tyres, and the trip to work was further than it has been in any car I've yet done it in.
New tyres and the trip is now correct.
As to the consumption on the computer- I only take it as a comparator, but I dont think i have ever compared computer to actually working it out

 

[Shadeyman]

I'm home earlier than expected, I leave the West Midlands for 1 night and the sh*t hits the fan at home, typical.

Needless to say travelling home I was once again in license loosing territory for most of the journey although not a quick as before.

So a 400 mile round trip cost me £80 for fuel, BP's normal Diesel(£1:43/litre).

That's about 56 litre's or 12.3 gallons.

400 miles divided by 12.3 gallons is 32.5mpg, that's not bad considering the speed I was traveling.

CN+ says 43mpg, that's no where near the real figure.

Gretna Green... That fast... What were you doin puttin a stop to your underage daughters wedding?

Lovin the AVERAGE of 80!

Was the mpg zeroed when you filled up?

Speeding is not something I normally do but needs must this time unfortunately.

I zero'ed the trip computer before I pulled off my drive Saturday morning. What you see includes driving to fill up, driving around in Gretna etc., the whole journey start to finish. I averaged 70mph over 400 miles.

 

[cledan]

Astounding really ive known J10 to M54 taking an hour, I was gonna say lol, but its not funny.

 

[nikkiy9]

Shady, hope you enjoyed Scotland, i'm a geordie now living 55 miles north of Gretna and if you had to go to Glasgow you sure as hell would of loved the M74, read online somewhere it's the fastest bit of motorway in the UK

 

[Caravadossi]

... Fuel gauge was on the full mark when I left and was on half way by the time I'd got there, that's half a tank used(6 gallon).

Trip computer reports 42mpg which considering how fast I was traveling seems too good to be true ...

I wouldn’t disagree with the car.

I’d argue that travelling at 70mph in a diesel will return about the best av.mpg you’re likely to see. For evidence - the car submits it has the capacity to do …

406.6 miles (192.6+214) at 80mph & return 42.6mpg & …
460.2 miles (403.2+57) at 69mph & return 43mpg.

In contrast 32.5 av.mpg would only be valid if you’d pushed a bone-dry car to the pumps at the start, re-fueled to the max of 58litres, & covered 414 miles before spluttering to a halt.

120115

 

[Shadeyman]

I'm not saying my calculations are perfect but they are good enough to show that the trip computer is no where near accurate so it should be taken with a pinch of salt.

 

[Caravadossi]

Have another think about it.

If anyone can’t get 40+ av.mpg in a Stilo 1.9 with cruise set at 70mph for 2 hours – then there’s clearly some fault with the car.

120116

 

[Shadeyman]

Have another think about it.

If anyone can’t get 40+ av.mpg in a Stilo 1.9 with cruise set at 70mph for 2 hours – then there’s clearly some fault with the car.

120116

Remember this?

in license loosing territory

I don't recommend cruising at treble figure speeds for almost 400 miles as I did for 2 reasons.

1. You'll loose your license faster than you can blink.

2. It cost me £80 of BP's normal diesel at £1:43 a litre.
(That's about 56 litre's or 12.3 gallons to travel 400 miles).

My car normally returns 55mpg or more when cruising at 70mph, so there is nothing wrong with my car.

It only achieved 32.5mpg on this trip, but that's what happens when you push a car hard, it uses more fuel. I'll not say exactly how fast I was traveling but I was in 5th gear and the rev counter sat steady at 3,500rpm for 90% of the journey.

 

[Caravadossi]

It’s all getting rather confusing.

We have, 193 miles at 80mph in a time of 2:24 - & an alternative claim of 193 miles in 2:14 (giving 86.5 mph).

Then a claim of 90% of 400 miles at >99mph – that effectively leaves the remaining 10% to be at <1.7mph, to result in a 70 av.mph for the whole round trip.

What are the chances of avoiding any consequences from a SPEC (or other) camera?

But whatever it’s a sobering thought, when you look at it from the point of view that the outbound trip should take 2:45 at 70mph & 55mpg(?) - & the 80 (or 86.5) mph trip `saved’ 21 (or 31) mins, at the cost of almost 70% (or £16) more fuel.

120116T22:30

 

[Shadeyman]

Then a claim of 90% of 400 miles at >99mph – that effectively leaves the remaining 10% to be at <1.7mph, to result in a 70 av.mph for the whole round trip.

I'm not quite sure what your trying to say.

I'm lying?
The CN+ is accurate?
My maths is crap(it is I know)?
What?

The CN+ readings should be taken with a pinch of salt.

Total journey(my house to hotel) according to google maps was 194 miles and should have taken 3 hours 11 minutes.

I did the journey in about 2 hours 14 minutes. That works out to an average speed of about 90mph.
However, I didn't suddenly fly off my drive at 90mph on my way the the local petrol station to fill up before the journey, neither was I traveling at 90mph when I left the motorway in Scotland. I drove somewhere between 0 - 40 mph those parts of my journey, my average speed on those parts was probably below 20mph.
So for me to complete my journey in 2 hours and 14 minutes I must have been going a lot faster than 90mph on the motorway to make up for the time I spent going slow, which was about 30 minutes of the total time(about 15 minutes before the motorway and 15 minutes after leaving the motorway).

 

[gerhardj]

1. Doing a declaration like this on a public forum in South Africa will get you in serious trouble. Should you not be more careful with this info?
2. All the motor programs we get to see here, from the UK (Top Gear, Fifth Gear etc), all moan and bitch the whole time about the speed cameras all over the place. You not scared of them? Or do you do the same as here, remove your number plates if you know that you would be cruising at high speeds.
3. My first observation on the above was, but that is not that fast, 144kph, then the penny dropped, as you said in your last reply, the journey did not start at 90mph from the starting blocks.........................

 

[Shadeyman]

Yes I was worried about my license.

Yes I was worried about speed cameras.

No I didn't remove my number plate.

No I'm not worried about the info I place here on the forum.

Yes my speed was deffinately in treble figures(mph).

I was lucky but needs must this time, speeding is not something I do normally.

But the point of the thread was to show how inaccurate the CN+ is, not how fast I drove.

 

[mzhussein]

FWIW

When i was doing regular trips to leeds (400 mile, round trip). Petrol was paid for by company (at almost double what it actually used btw) so i wasn't worried about the consumption, i just wanted the journies over ASAP as my passenger was not great company, i wasn't going quite as fast as shadey, but for 80% of the journey i was cruising ~90 with the odd trip into treble figures...

The trip computer told me i was doing 30mpg, and i worked it out using exact miles and exact litres of fuel used, and i got 29.4mpg...so at least the petrols (or specifically MY petrol) arent that far out...

Shadey, if your calculations are accurate, that is a shocking difference! i wouldnt expect nearly 10mpg out! Even for a diesel, 40+mpg at 100+ mph, is optimistic at best, so good call on actually working it out.

 

[Davren]

But the point of the thread was to show how inaccurate the CN+ is, not how fast I drove.

The CN+ only duplicates the cluster display for trip information, so it's not a fault of the CN+.

 

[Shadeyman]

The CN+ only duplicates the cluster display for trip information, so it's not a fault of the CN+.

Probably best I rephrase what I said.

But the point of the thread was to show how inaccurate the information the CN+ displays is at higher speeds

 

[Shadeyman]

FWIW

When i was doing regular trips to leeds (400 mile, round trip). Petrol was paid for by company (at almost double what it actually used btw) so i wasn't worried about the consumption, i just wanted the journies over ASAP as my passenger was not great company, i wasn't going quite as fast as shadey, but for 80% of the journey i was cruising ~90 with the odd trip into treble figures...

The trip computer told me i was doing 30mpg, and i worked it out using exact miles and exact litres of fuel used, and i got 29.4mpg...so at least the petrols (or specifically MY petrol) arent that far out...

Shadey, if your calculations are accurate, that is a shocking difference! i wouldnt expect nearly 10mpg out! Even for a diesel, 40+mpg at 100+ mph, is optimistic at best, so good call on actually working it out.

Even though my car is diesel and well maintained I still wouldn't expect it to achieve 40+mpg while doing over 100mph. Over the hole journey it managed 32.5mpg, that includes the slower parts of my journey where I know the car would have been doing at least 40mpg so the actual figure for consumption while traveling at 100+mph would be less than the 32.5mpg average, my guess would be below 30mpg.

It would seem the faster one goes the more inaccurate the info the CN+ displays is. I know the same applies to the speedo, the faster a car goes the less accurate its speedo is. Perhaps this is what causes the error?

 

[Davren]

It would seem the faster one goes the more inaccurate the info the CN+ displays is. I know the same applies to the speedo, the faster a car goes the less accurate its speedo is. Perhaps this is what causes the error?

Isn't the speed inaccuracy at higher speed just a percentage issue?

i.e. 10% inaccurate at 1mph = 176 yards.
10% inaccurate at 100mph = 10 miles.