Why does the BMW 3 2.0 cost less to run than the BMW 3 1.8?

I had a 2005 BMW 3 Series 2.0-litre automatic as my main car in 2010 and I remember it being tax bracket J (190g/km),150PS, and on paper showing 35mpg on the combined cycle. I'm looking to buy a used 2007 automatic BMW 3 Series 1.8-litre to use as a run about. I assumed it would be slower than my old 2.0-litre but I was expecting better fuel economy but it's showing 30mpg Combined, 226g/km (pushing it into tax bracket L) and only 129PS. Do you know if these figures are correct, both cars mentioned are saloons, I am just confused that the lower powered unit actually costs more to run.

Asked on 12 January 2017 by Jay-1001

Answered by Honest John
BMW E90 320 i SE auto 159g/km VED band G. BMW E90 318i SE auto 155g/km, same VED band G. If your previous 320 i was an E46, our detailed data does not go back that far.
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