You should also notice that if you put wider tires to your car the tires arent anymore behind the bumber/wings. If they are narrower they might be too much inside...
I think that migh be the biggest reason for my bad fueleconomy with these Nokian Hakkapeliitta R. Should get also different ET rims. There are so many things that affect everything that its difficult say which fault the change is... For Nokian winter tires the outer edge of the tire is sharp and I have thought of grinding it round
.
Soon I will have about 7 sets of similar aluminium wheels and will start doing my own winter tire tests which combo works best on my lupo.