Rain and its effect on MPG

[paradigm]

I always see this sort of thing posted but I have never had a car that's.nore than 1mpg out...

This.

No matter how utterly optimistic I think the trip computer has been, if I then calculate it manually, it tends to add up fine.

 

[iaind]

This.

No matter how utterly optimistic I think the trip computer has been, if I then calculate it manually, it tends to add up fine.

Pretty much every car I've owned has been 1-2mpg either way. I just remember those Mazdas were miles off - hence mentioning it here

 

[Uriel]

My MPG calculation differs from the computer by about the same amount as my Speedo differs from GPS measures speed (GPS measures 67mph when the speedo says 70 - so about 4% ish, whereas the computer always reports a few mpg higher than I calculate - 2010 Honda Insight).

If the odometer has the same error as the speedo (which I'm not sure about - not checked) that wold mean the computer mpg is bang-on and the value calculated from fuel receipts and odometer is wrong.

IIRC the allowable error for odometers is 3.75%

 

[telewebby]

Current Jetta diesel is appalling on actual vs dash figures, approx 14mpg worse in real life dash shows 57 actual 44.

my old 3 series was bang on 2mpg out

back on topic, my route to and from work i can get the trip computer to read better coming home than going, it doesnt feel any different but when i did the trip on my road bike it was easier coming back

alex

 

[Dogbreath]

It's probably mostly surface water resistance? Given the big shove you get when you hit a decent sized puddle.

Guess it depends how bad it's raining and winding in your general direction.

Yes, standing water significantly increases rolling resistance.

 

[Jokester]

My diesel Civic is out at least 10% on the trip computer when it comes to mpg.

 

[Rotty]

I get loads worse fuel consumption when its nice and sunny

maybe that's cos I put roof down, turn music up and drive like a nutter though