Winter is not the best time to get fuel economy from a car, but I’m pleased that my 2 tonne limo has averaged over 40mpg so far this winter. That includes all the traffic nonsense and Christmas shopping! I know I could do better with a smaller car and that the fuel costs are only a small percentage of the overall running costs, but I doubt my miles could have been more relaxed or comfortable.
Anyone with a light grasp of basic physics will know that heavy acceleration and braking are no friends of economy, but even in steady state running, winter is bad news.
The cold prevents engines getting up to working temperature as quickly, but less well know is that the gearbox and the diff suffer the same fate, reducing efficiency.
Winds are rarely helpful, only a tail wind bringing any benefit and cross winds normally spoil the carefully honed aerodynamics of our cars and increasing the cd. Headwinds are just a disaster!
But it is the wet that really kills the economy in three different ways.
1. The additional physical drag due to increased rolling resistance on wet surfaces. This is especially true in the flooded ‘truck ruts’ familiar to most of our main roads.
2. The kinetic energy loss in moving vast amounts of water mostly against gravity.
3. A phenomenon known as spray drag. This is the result of research by the Aerodynamist responsible for both the outright and diesel land speed records, Ron Ayres. (And father of the Bloodhound missile!) Ron was interested as to why so many record attempts were failing on the salt or desert surfaces where a lot of spray was produced. His conclusion holds true for wet roads and states that because the area behind the car is now filled with particles it has increased in density and therefore the vehicle is moving through a more viscous ‘fluid’ than pure air and so the drag is increased. Increases massively above 300mph but still a factor at motorway speeds…
I’ll get my anorak….
Anyone with a light grasp of basic physics will know that heavy acceleration and braking are no friends of economy, but even in steady state running, winter is bad news.
The cold prevents engines getting up to working temperature as quickly, but less well know is that the gearbox and the diff suffer the same fate, reducing efficiency.
Winds are rarely helpful, only a tail wind bringing any benefit and cross winds normally spoil the carefully honed aerodynamics of our cars and increasing the cd. Headwinds are just a disaster!
But it is the wet that really kills the economy in three different ways.
1. The additional physical drag due to increased rolling resistance on wet surfaces. This is especially true in the flooded ‘truck ruts’ familiar to most of our main roads.
2. The kinetic energy loss in moving vast amounts of water mostly against gravity.
3. A phenomenon known as spray drag. This is the result of research by the Aerodynamist responsible for both the outright and diesel land speed records, Ron Ayres. (And father of the Bloodhound missile!) Ron was interested as to why so many record attempts were failing on the salt or desert surfaces where a lot of spray was produced. His conclusion holds true for wet roads and states that because the area behind the car is now filled with particles it has increased in density and therefore the vehicle is moving through a more viscous ‘fluid’ than pure air and so the drag is increased. Increases massively above 300mph but still a factor at motorway speeds…
I’ll get my anorak….
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with the consequential low mpg espscially with 3.2 petrol
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