Most Economical SpeedWith fuel prices constantly on the increase its important to know what the most economical speed of your car is. This way you can get the optimum fuel economy from your car when traffic conditions allow. Unfortunately there is no one speed that returns the best fuel economy for all cars. Fortunately though its very easy to find out your own car's most economical speed.
Your car's most fuel efficient speed depends on its engine size and type, gearing ratios, its aerodynamic profile and a whole host of other factors. However in simple terms, the most economical speed will roughly be the slowest speed you can comfortabley go in top gear without the engine laboring. Now different engines labor at different engine revolutions but you should be looking to run the car roughly somewhere between 1750 - 2000 revs. Below 1500 revs for instance is likely to be laboring the engine and would have a negative effect on both fuel consumption and your engine's well being. Most cars these days have tachometers so you can keep an eye on your revs or you can just listen to the engine and feel how the car is behaving. If there's a rattling or knocking noise or the vehicle is struggling to maintain its speed your revs are too low.
For a vehicle with 5 gears you'll probably find your car's most economical speed is somewhere around 45 mph (or 65kph). But you also need to take into account a road's speed limits. If the speed limits are substantially higher than this you'll need to travel faster in order to keep up with traffic and avoid creating hazardous situations. In the U.K. and many U.S. states the motorway and freeway speed limits are 70mph so the lowest speed you should probably do is 60mph otherwise you'll start to hold up heavy goods vehicles and other traffic. Similarly in Australia where some freeway speed limits are 110kph you should probably do 100kph. At these speeds your car will still return excellent fuel economy.
If the speed limit is substantially lower than your car's most efficient speed you'll burn less fuel if you change down a gear and get back in the optimum rev range.
Its commonly believed that 56mph is the most economical speed. This is not true and the most efficient speed of your car will almost certainly be slower than this. The reason for this misconception is that fuel consumption in some countries used to be measured at this speed (in addition to slower speeds) but there was no reason that 56mph was chosen that related to fuel efficiency.
If you have an automatic gearbox you can still determine your car's most economical speed. Wait for the car to engage its highest gear or overdrive gear by listening to the rise and fall of the engine. Once the engine has shifted through all its gears find the slowest speed you can that does not cause the engine to labor or the gearbox to keep down shifting. The speed should be pretty similar to a non auto car. Make sure you've engaged the overdrive function if you have one and disengaged any Sports settings.
By driving at your car's most economical speed as much as possible you'll notice a significant lift in your fuel economy and save considerably on your weekly fuel bill.
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