Quote:
Originally Posted by Tengocity
It's ever so slightly better than what I've got from our new 335dX, so it's certainly cheered me up a little! Not much help to you though I suppose. Sorry!
Highland Pete has been saying for a while though that the real-world xdrive fuel economy penalty of sdrive is much bigger than the official figure would suggest.
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Not surprised at all to be seeing similar mpg results across the xDrive models. We have models with a similar road load, (body, options, etc.), I sense engine differences virtually merge when we drive in similar manner/speed. Obviously when driven lightly the 320d will give better consumption, but that difference erodes quite a lot, when we drive at higher cruising speeds and use similar acceleration rates in day to day driving.
I've been delving into the reasons why the NEDC mpg figures may be giving the impression xDrive is not much different on paper than sDrive. Appears the road load calculations are very optimistic across the tests for EURO 5/6 compliancy. Independent tests are finding figures used are way out, with an average of about 11% lower than what are used in the NEDC tests, some road load figures can be over 30% optimistic. So a lot will depend on what the xDrive road load figures are in the tests, how they have been "adjusted" compared to sDrive. We've no idea if they have the same ratio of error.
Plus we are likely seeing the "small engine vs. big engine" factor. As an example, many F10 users report the 530d returning mpg averages very close to the 520d, when cruising fast motorway speeds. Again it is a case of the road load being very similar at speed. Add in the subtle factors like gearing, boost variation, BSFC for load/rpm, (smaller engines can suffer more) from the two engines for the "absorbed power", we result in similar mpg.
HighlandPete