This is one of those topics of discussion that most people get wrong. In older petrol cars that used carbs, coasting or freewheeling downhill would save you fuel, and this method worked quite well for those older cars. Modern petrol cars with Electronic Fuel Injection, do not work the same way. Modern cars with EFI have a Fuel Return Pipe which sends unused fuel back to the tank, so if you just simply leave the car in gear, and keep your foot off the go pedal while on a downhill stretch of road, the engine will not be using any fuel. If you were to use the old technique of coasting in neutral on a downhill stretch in a modern EFI car, when the revs drop below approx 1000rpm, the tickover valve kicks in, and you are burning fuel to keep the engine running. So the best way to save fuel in modern petrol cars is to effectively coast in gear, and when slowing down, use engine braking as much as possible, by simply going down through the gears, to keep the revs above tickover, with the fuel supply cut off, then when you have almost stopped, you simply have to let the engine reach idle speed. Most diesel cars have a Fuel Cut Off Valve, that works in a similar manner by simply cutting off the fuel supply when you take your foot off the pedal, so the same method of coasting works for both EFI & diesel cars.

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Yes it will, I would recommend increasing tire pressures to improve fuel economy, and you should inflate them to the maximum allowed for your tires.although I would normally go 2-3 psi over the rated pressure for that extra few mpg, please note that I’m talking about PSI not BAR when inflating your tires, get this wrong and you will hear a loud bang that you won’t forget! Also please note that tire pressures will naturally increase in warmer weather, and decrease when it gets colder.

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If i fit bigger wheels will I get better mpg?

Again the answer is yes, this approach can make a significant difference to economy, but it comes at a price, and care must be taken. If you go too big with your wheel/tire combination, you may experience the tires rubbing against the wheel arch! You should consider the following points before trying this method.

1) Changing the wheel/tire size will affect the gearing of your car, this can be a problem in an already underpowered car as acceleration will be even slower.

2) Fitting bigger wheels will affect the turning circle of your car, you will require more road space for U-turns & 3 point turns etc.

3) The accuracy of your speedometer & trip meter will be affected. A typical example of this is your speedo showing 40mph, when you’re actually doing 50mph! On a more positive note, the car would be more relaxing to drive, with a softer ride & less engine noise at cruising speeds.

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In a nutshell, Yes, but only if you are changing from standard steel wheels to alloy wheels. Lighter alloys and tyres of the same specification as the originals, will reduce rolling resistance and improve fuel economy.

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Yes it normally does, but if you let the revs drop so low, that your engine starts chugging, or struggling in any gear, then that will hurt fuel economy. If it’s chugging, then you need to drop a gear, ie chugging in 3^rd, you drop to 2^nd. What you must understand is that, the engine is just a power source, with a fixed rev range, the gearbox is a means to tap that power, so in theory, the lowest revs, in the highest gear, would yield the best economy. In practice though, if you are driving along a flat road in your highest gear, (5^th or 6^th) depending on how many gears you have to play with, your car will struggle below 35mph in it’s highest gear, to get the best economy, you need to keep the revs as low as possible, in the highest gear, without stressing the engine, in most cars, this is normally achieved on a flat road, in 5^th gear (highest) at around 30-40 mph, depending on the car in question, it is always much easier to apply this driving style in a Diesel car.

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If your car is a standard petrol engine, or a naturally aspirated (no turbo) diesel, then you should not warm it up on cold mornings, it is far more fuel efficient to just drive off immediately and let it warm up naturally. If your petrol or diesel car is fitted with a turbo, then you should wait at least 1-2 minutes before driving off, this is purely to allow the engine oil to reach the bearings of the turbocharger, and prevent excessive wear, and when you get to your destination in a turbocharged car, you should let your engine idle for 30 seconds to give the turbo a chance to spin down. If you switch off the engine as soon as you stop, your engine is no longer pumping oil to your turbo, and if it’s still spinning, and there’s no oil in there, then it’s going to cause wear on the bearings of the turbocharger. Most often, people who ignore this tip on turbocharged engines, end up with costly repair bills. The aim of this site is to save you money, even if it’s at the expense of fuel economy!

For more Fuel Economy Tips, please read the other posts.