First long run.

[Sidot]

2000 miles on the clock and my first motorway run last week from West Midlands  to South Wales via M5  and M4.
Car performed very well at speed in sixth gear ( when I could find it !).
A bit of wind noise but a very smooth ride.
I have forgiven the auto lights because the main beam and auto dipped when oncoming traffic was a revelation in country roads .
BUT......The car let itself down on the way back by displaying the information sign of tyre pressure being low on the motorway.
Pulled into nearest service station and spent £1 on checking tyre pressure only to find all tyres ok and up to pressure.
Did the calibration when got home but it's disconcerting to get that kind of message if not correct.
Overall 8/10 with 47 mpg. Was hoping for more.

[Ozzie]

If you are doing a steady 70mph the mpg will be lower than if you are doing 60mph. If you ease off a bit the mpg will rise 

[John Ratsey]

Overall 8/10 with 47 mpg. Was hoping for more.

Driving into a moderate south-westerly wind (if that is what it was - there's been a lot recently) would have cost several mpg and made the wind noise worse.

Add a 15mph head wind onto 70mph and the wind resistance (which is proportional to speed squared) would be the equivalent of 85mph in still air.

[ColinB]

Overall 8/10 with 47 mpg. Was hoping for more.

That sounds a bit disappointing. I've done several long motorway runs now, including a couple around 120 miles each way on the same day over the same route (which ought to even out the effects of hills & headwinds as much as possible). In both cases the computer was suggesting an average of around 61 mpg for the first leg (so pleased with that I took a picture !), dropping back to 58-59 on return home. Was aiming for 70 mph in 6th most of the time using the cruise control as much as possible, but traffic conditions occasionally forced more economical speeds. Also, Trip B hasn't been reset since buying the car, so the overall average for the first ~2500 miles is around 52 mpg. I'm pleased with the overall economy. Of course it's entirely possible that the computer isn't 100% accurate ...

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[VicW]

Of course it's entirely possible that the computer isn't 100% accurate ...

On board fuel readouts are notoriously inaccurate, some owners will say that they indicate as much as 10% better consumption than actual.
Mine must be one of the better ones as it gives consumption readings, on average, about 2mpg better than actual which is close enough for me

Vic..

[culzean]

Of course it's entirely possible that the computer isn't 100% accurate ...

Mine must be one of the better ones as it gives consumption readings, on average, about 2mpg better than actual which is close enough for me
Vic..

I find it best to use the onboard mpg display as a guide to how different driving styles affect mpg,  but it is important to zero the trip before experimenting with different methods as the average MPG  responds quickly when not many miles on the trip computer but gets more and more sluggish in its response as the miles build up and it 'averages' the mpg over a larger mileage and any gains in mpg are hidden,  as it approaches 100 miles it is very slow to change even when going down a long hill mpg hardly moves.

also the smoother your driving the better the accuracy of the mpg display,  so congratulations Vic you must be one smooth driver.

[Sidot]

I don't trust the on board computer reading on mpg. Didn't with my Mk2 either.
The only true way is to fill up tank on departure note the milage,  fill up again at the end of journey deduct miles at completion from miles at start then divide by gallons into tank.
Very windy day and much rain which I think took about 5mpg off performance.

[edam]

Your speedometer is inaccurate and hence the milometer is also inaccurate.
Your speedo could be saying you are doing 50mph  but in reality you are doing 40mph but the speedo should never show less than your real speed

[John Ratsey]

Your speedometer is inaccurate and hence the milometer is also inaccurate.
Your speedo could be saying you are doing 50mph  but in reality you are doing 40mph but the speedo should never show less than your real speed

My Mk 3 Jazz is no more than 2mph high at 60mph according to my sat-nav. I have also wondered in the past about the odometer reading high but a check of the car's distance against the distance on a route as given by Google Maps or similar route planning facility shows close agreement. I think the speedo reads high by design (but less high than in vehicles of yesteryear) but the odometer attempts to be accurate. There's also the matter of why the computer's mpg always reads high (in my case somewhere between 5% and 10%).

[VicW]

I think you will find that the Construction & Use Regulations say that speedometers are not allowed to under read at all nor over read by more than 10%.

Vic.

[guest5251]

I think you will find that the Construction & Use Regulations say that speedometers are not allowed to under read at all nor over read by more than 10%.

Vic.

your speedo will always be inaccurate, only when the car doesn't rely on the road wheels will your speedo become accurate.your speedo depends on your wheels rotating when a tyre is new it has a larger diameter so therefore it travels further on 1 revolution and your speedo runs slow,when your tyres are nearing the end of life the diameter is smaller so therefore travels less on 1 revolution and your speedo will run faster.