How accurate is trip computer for mpg?

[Steveo]

Hi Gents

Still new to my 2.0 HDI (110) Exec.

I haven't yet had the opportunity to do a brim to brim mpg test and so am wondering how accurate is the trip computer for mpg?

I did a long trip up the motorway the other week and sat at 75mph all the way with the cruise control on, and it read an average at the end of the trip of 49.6 mpg... is this likely to be correct?

Does it tend to be more or less accurate at different speeds or driving conditions?

Thanks

Steve

[rwb]

Trip computer accuracy

Probably within 5mpg, but you don't know until you compare to brim-to-brim calculation.

[Steveo]

Thanks RWB

Steve

[grasmere59]

My old 110 Rapier was quite good after a brim to brim check but my 110 Exec under reads by 7-8 mpg according to a brim to brim test.

[lozz]

ithink if you stay around 2500 rpm there acurate, anything above the mpg reading is all overthe place,

[scotty73]

Is it just mine that seems to get stuck on whatever the reading was the day before?... i have to trip mine regularly or it will still read 33/36mpg after half hour cruising but once tripped all seems good... my last visit to top up i had done a 150 mile round trip plus some town driving of about 30 miles and my computer was pretty much what i had used in fuel.

[lozz]

on the renault you can see the mpg go down 1 or 2 mpg if your stuck at lights for 5mins, not moving
never had this with the pugs or citroens,
ireset it before iuse the car,

[rwb]

You can see this on the 406 if the trip has been reset recently -- up to about 10 miles ago, say.

Obviously, as the total distance since the last reset increases the influence of current MPG on the average dimisishes.

You can really see this on the Type C display that has two trips and an instantaneuos readout. I reset the first trip whenever I start a journey, but only reset the second trip when I fill up.

After my last fill I did 120 miles on the motorway, and both trips agreed at about 55mpg.
This morning after my commute to work, the journey trip shows 42 and the other shows 48.

My driving style changed when I got the car and started keeping an eye on the instantaneous readout. (You might think that the values it shows are rubbish, but it still gives you an indication of 'higher' or 'lower'.)