[AlanHo]

Our return journey today from Holiday in Cornwall included the M5 motorway to the junction with the M42 - a distance of 140.1 miles. The motorway has distance boards at half kilometer intervals so I used this to measure the accuracy of the trip distance recorder in the car. The result was that the car trip recorder showed 140.1 (225.5 Km) miles over the measured distance whereas the actual distance covered as indicated by the motorway boards was 232.5 Km - a difference of 3.1%.

This means that my fuel consumption figures are 3.1% better than I previously thought, hence the car has averaged 49.1 mpg (5.7 l/100Km) in the 6165 miles (9921 Km) driven since new rather than my previous calculation of 47.82 mpg (5.9 l/100Km).

It's not every day that statistics come out in my favour.

(OK, OK - I know I'm an anorak for going into such detail)

Another interesting comparison is that on the trip down (282 miles - 454 Km) cruising on motorways/dual carriageways virtually all the way at 60 mph (97 km/H) the computer showed a fuel consumption of 53.6 mpg (5.3 l/100KM)
On the journey back (my wife was asleep  ) I cruised at 70 to 80 mph (112-129 Km/H) and the computer showed a consumption of 51.6 mpg (5.5 l/100Km)

Despite this, I remain disappointed with the economy of my car after reading some of the results achieved by other members as reported here.

[eye30]

Re distance travelled.

When you changed from 1 motorway to another could this account for the discrepency between the car record and the marker post record.

Also, don't forget that when you change lanes, 1 to 2 to 3 to 1 to 3 to 2 etc you are actually travelling slightly further than if you stay in the same lane and don't move from that  lane.

Also, if the tyre pressure is not as quoted when cold as the tyre warms up the distance the tyre has to travel to complete a full circle will again be slightly further.

Does this make good reading or is it gibberish...................

ps Did you enjoy your hols?

[AlanHo]

The distance recorded was confined to the M5 motorway - I finished recording on the last marker post before I took the M42 slip road.

You will note that the mileage recorded on the trip was less than the actual distance - so your theory about lane changing is irrelevant because I travelled further than the trip recorded.  As it happens - I spent 95% of the journey in the fast lane and rarely changed lanes anyway.

I always keep my tyre pressures at 36 psi. After reading your post I just checked them again and they are all still at 36 psi.

We enjoyed a lovely holiday thank you - staying in a thatched cottage near the Helford river. The weather was more than kind to us and we had a most relaxing break.

[eye30]

OK so it was gibberish...................

Another thought ----- when they were putting in the marker posts the ruler the broken so they had to measure the distance by strides.
Now there were 2 people.
 one stride was longer than the other     

[Gibber]

As it happens - I spent 95% of the journey in the fast lane and rarely changed lanes anyway.

Alan, what happened to the other two lanes!?

Sent from my HTC Desire

[AlanHo]

As it happens - I spent 95% of the journey in the fast lane and rarely changed lanes anyway.

Alan, what happened to the other two lanes!?

Sent from my HTC Desire

They were occupied by other traffic on their way to or from holiday. The motorway was awful busy and littered with people pulling caravans or boats. I did move over a few times to let madmen doing the ton get past - I have 3 points on my license for doing 93 mph on a motorway (mobile speed camera on a bridge 2 years ago) and wish to avoid collecting any more.

[2i30s]

i have read a post about a members  odometer not being correct,I'm sure it was kittykat. she had followed another car and compared the distance travelled,their distance was more than hers.  if that makes any sense.

[Gibber]

It may have been discussed before but the odo could be pre set for example 15 inch tyres and if you have 16 inch then it would account for 5% difference.

See this calculator http://www.miata.net/garage/tirecalc.html

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