Hi
I've noticed that the mpg figure for vehicles and their grammes of CO2 per km are not linear. Ie one car that does 30 mpg may say produce 150 g/km whereas another that does 30 mpg may produce 175 g/km. Why? Surely if you burn the same amount of fuel per distance you produce the same amount of CO2 per the same distance - the chemistry of burning the fuel doesn't change. So how can the g/km figures vary so much between cars that use the same fuel type and have the same mpg?
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Probably because both values are measured at or over different engine speeds and conditions.
The different speed vs power/torque characteristics of different engines can contribute to car A being better than car B in the standardised urban consumption test, but car B better than car A in the extra urban test.
If you measured both MPG and CO2/km at the same speed for each vehicle then I'm sure you would get the same answer if MPG was equal.
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Mike Farrow
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If you measured both MPG and CO2/km at the same speed for each vehicle then I'm sure you would get the same answer if MPG was equal.
Clarification: I mean keep the speed equal for both MPG and CO2/km readings, not keep speed the same for each vehicle.
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Mike Farrow
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