Friday, 14 August 2009

GM Chevy Volt Spurious Claim Number 1: achieving 230mpg

How can a car that has a 12 gallon tank and a range of 640 miles get any number of miles per gallon up to infinity? Easy, just get a GM Marketing mathematician to do the maths. Because the Chevy Volt does the first 40 mile on battery and doesn't use any petrol, if you only drive 40 miles a day your tank will never need refilling and it will get infinite mpg. How good is that? However, the marketing gurus of GM are making some assumptions here. Firstly, that the electricity doesn't have a petrol equivalent, in effect it doesn't count. If this method of calculating mpg was viable we'd all be driving milk floats and getting infinite mpg from those too. Secondly, that the general public can't do simple maths.

Unfortunately, all they mean is that the petrol is only hit after 40miles. This is a bit like having a current account and a savings account and saying that so long as you only take money from the current account, you are not spending anything. In reality, the pure petrol consumption (after 40 miles) is easily calculated at 50mpg. The bit before that is slightly more complicated, but it certainly doesn't save fuel or energy, not until the whole electricity generating system is renewable that is. Fuel is still used to generate the electrical energy needed to drive the first 40 miles. It's just that the fuel use is hidden in the generation of the electricity. How far will it really travel on a gallon of petrol? Easy, put in a gallon and set off. If it's fully charged, you'll actually get to 40 miles and not use any. After that, the petrol engine will kick in and you'll get another 50 miles. Total, 90miles, only 140 miles short of the 230 miles range. To get the next 140 miles you'd need nearly 3 more gallons. So, to actually drive 230 miles would take 4 gallons of petrol in total or about 60mpg. Maybe that small efficient diesel engine isn't looking so bad after all - and you can drive it without having to plug it in every night.

Why are GM being allowed to make these spurious statements and are the American public really so dumbed down and innumerate that they will believe them?

Spurious claim number 2 follows!