Post by spunkymonkey on Sept 2, 2008 15:58:10 GMT
Just been having a think about car tax and the drive to reduce carbon footprints. Not that we pay tax on Betty (1972), nor that I particularly subscribe to the global warming bit. But I was curious about why tax is now based on a "g/km" rating rather than something that people might actually understand.
You see, it struck me that the amount of CO2 that an engine kicks out must be directly related to the amount of fuel it burns (where else does the CO2 come from?) So, surely, grammes per km are just another way of stating miles per gallon? Sure enough, it seems that if you take an MPG figure and divide it into 6583, you'll get the corresponding g/km. Simple maths.
In fact, an older and less "efficient" engine will be throwing some of its fuel out the tailpipe as unburnt hydrocarbons - which, as far as I'm aware, don't contribute to "global warming". So an old car giving, say, 35mpg will actually have less effect on atmospheric carbon than a new one.
How does this relate to the car tax bands? Something like this:
Band A (<100 g/km £0 tax) = 65mpg
Band B (-> 120 g/km £35 tax) = 55mpg
Band C (-> 150 g/km £120 tax) = 44mpg
Band D (-> 165 g/km £145 tax) = 40mpg
Band E( -> 185 g/km) £170 tax) = 35mpg
Now, my dear departed Montego Countryman estate had official consumption figures of 50.5mpg urban, 68.6mpg at 56mph and 48.4mpg at 75mph. Even with over 140k miles on it, I used to average around 50mpg in real use. Which should qualify it comfortably for band C, maybe even band B.
Yet, it was lumped with everything else over a "certain age" and cost £180 because it was old and, therefore, polluting. I'm sure it's not the only example out there - in fact, I suspect that £35 band C (55mpg) would be within reach of the aircooled Dafs - will have to monitor it carefully when ours is finally on the road!
Finally, given how close some of those bands are, I suspect that driving style would have far more effect than the vehicle. Our current Colt diesel can give mpg figures anything from high 30s to low 60s on the same route, purely depending on what mood I'm in at the time.
All I can imagine is that the "g/km" unit was invented as a way to obscure things in the name of GW. But that would just be too cynical
You see, it struck me that the amount of CO2 that an engine kicks out must be directly related to the amount of fuel it burns (where else does the CO2 come from?) So, surely, grammes per km are just another way of stating miles per gallon? Sure enough, it seems that if you take an MPG figure and divide it into 6583, you'll get the corresponding g/km. Simple maths.
In fact, an older and less "efficient" engine will be throwing some of its fuel out the tailpipe as unburnt hydrocarbons - which, as far as I'm aware, don't contribute to "global warming". So an old car giving, say, 35mpg will actually have less effect on atmospheric carbon than a new one.
How does this relate to the car tax bands? Something like this:
Band A (<100 g/km £0 tax) = 65mpg
Band B (-> 120 g/km £35 tax) = 55mpg
Band C (-> 150 g/km £120 tax) = 44mpg
Band D (-> 165 g/km £145 tax) = 40mpg
Band E( -> 185 g/km) £170 tax) = 35mpg
Now, my dear departed Montego Countryman estate had official consumption figures of 50.5mpg urban, 68.6mpg at 56mph and 48.4mpg at 75mph. Even with over 140k miles on it, I used to average around 50mpg in real use. Which should qualify it comfortably for band C, maybe even band B.
Yet, it was lumped with everything else over a "certain age" and cost £180 because it was old and, therefore, polluting. I'm sure it's not the only example out there - in fact, I suspect that £35 band C (55mpg) would be within reach of the aircooled Dafs - will have to monitor it carefully when ours is finally on the road!
Finally, given how close some of those bands are, I suspect that driving style would have far more effect than the vehicle. Our current Colt diesel can give mpg figures anything from high 30s to low 60s on the same route, purely depending on what mood I'm in at the time.
All I can imagine is that the "g/km" unit was invented as a way to obscure things in the name of GW. But that would just be too cynical
