Quote:
Originally Posted by Bernard333
I would not expect to see 8 to 10mpg difference , an average S60 D5 would be about 3 to 4% better than a V70 D5 on fuel and slightly faster on acceleration due to its lower weight but differences between the condition of specific cars could easily cancel this out on an older car . The roof rails will make a very small difference to mpg but over 100k miles you would have spent about £11500 on diesel so if its costing 0.5% of the fuel you would pay an extra £100 in diesel for the benefit of them over 200k miles . Thats my guess and I doubt anyone but Volvo would know the real answer , as far as I can find out they do not publish this information .
Auto express sponsored some tests which Thule spout in their sales spiel :
http://www.autoexpress.co.uk/news/au...thbusters.html
I am not happy with the basis of part of the tests , its based on some poor engineering practice , I do not believe that a 72kg load in a roof box makes no difference to the fuel consumption . If this could be proved by doing proper tests then the effect of roof rails alone would not be measurable but this does not make sense to me . |
Yes it's odd that adding passenger weight makes a big difference but adding cargo weight in the form of a roof box dosn't. The roof box also increases the amount of air the car needs to push out of the way so you would expect mpg to increase with speed.
The tyre pressure results are odd as well. The bike club I belong to tested loads of tyres at different pressures and they all used far more energy at lower pressures. Try riding a bicyle with the tyres fully pumped then at low pressure, you can really feel the difference for yourself.
I suspect the bikes on the back affected the aerodynamics. Interesting they never tested the bike rack and bikes on their own.
Engine oil makes a difference as well. Magnatec dosn't give the best mpg.