MOT exempt

Those grapes must be very sour.

50Twuncle wrote: »

[...] why should an old banger that puts out unlimited amounts of CO and pollutants, get a waiver from tax - whereas a new (virtually non polluting (105g/km) - suddenly go from £20 to £140 ?
[...]

You really don't understand vehicle emissions very well, do you? That's obvious from the way you conflate CO, "other pollutants", and CO2 all together.

Firstly, the vast majority of vehicles this will affect can't emit "limitless" quantities. Anything first used after, iirc, Aug 1975 has limits of 4.5% CO and 1200ppm unburnt hydrocarbons.

In practice any car in good mechanical conditon will be well below those limits - typical from my own experience over the years would be around 1.5% - 2% CO and under 200ppm hydrocarbons. And that's at idle, which is the most inefficient and highly polluting condition for an engine. As soon as load and speed increase, those figures drop significantly.

The CO2 they emit (which car tax is based on) has absolutely nothing to do with how "clean" the engines are. It is only a measure of how many MPG you're getting. So your modern car that claims 105g/km of CO2 will only achieve that if you're getting a real world 62.4mpg overall.

If - in the real world - you find you're getting a more believable 40mpg overall because of conditions, driving style, and all the other factors that come into effect, then your real world emissions will be 164g/km. That is exactly the same amount of CO2 that an "old, polluting" car will emit if it's also giving 40mpg.

A large number of the cars this will affect comfortably average 40 or more MPG now because of the type of use they're put to and the way they're driven.

In fact, technically, the new car will emit very slightly more CO2 than the "old, polluting" one for the same MPG because the catalytic converter on the new one is taking that CO and hydrocarbons that the old car throws out of its tailpipe (see first paragraph) and converts them to CO2 as well.


eta: A for lifetime CO2 emissions, old cars have long ago "paid for" the emissions of producing several now ones and continue to save overall emissions by recycling the majority of parts - it's much better environmentally to repair and re-use a part than melt it down and recycle.

They also mostly use much smaller tyres - there's a huge energy input in tyre manufacture and it's a hell of a lot less for, say, a 155/13 typical of the '70s than it is for a modern 225/16 or bigger! It's also much less dead rubber to enter the waste chain when they're worn out.