Let’s start by listing the different types of gearboxes available:

• 5-speed manual – these are standard on many vehicles now since the 1990′s. In this one the gears are fixed. The gear lever is used to change between the gears 1,2,3,4,5 and R. Of course, you get better economy when you’re in the highest gear and your throttle is lowest. To accelerate, you have to switch gear to prevent the engine from running too loud (too fast en faite). You’ll use more fuel at 60kph under 3rd gear than in 5th gear because you’d be running a petrol engine at 2500 rpm (tours par minutes) rather than 1500 rpm.
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• 4-speed step automatic – this is the awed slow thirsty automatic. It has only 1,2,3,4 and R. If you have to compare these ratios to the 5-MT above, it’ll be like 1.5, 2.5, 4, 6 and R for Toyota. The gear changes can be more abrupt and the last gear, known as an overdrive, is made for economy. The problem with this type of step auto is that there is loss in power due to its design. Some technical reason for that. It is prevalent in vehicles designed before the early/mid-2000 as well as some new cars. Don’t go buy a brand new automatic Corolla in Mauritius cause that’s what you’ll get! It’s also what you get in the Mazda 3 1st gen and most automatic second hand cars from Singapore (Japanese prefer CVT).
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• 6-speed manual – this is becoming the new standard. Germans Luxuries and sports cars (even Japanese) have been having it for years now. You have then in many lower end cars in Europe and USA now e.g. Corolla, Avensis, Civic, Lancer etc. The gear ratios depend on the type of vehicle it’s made for. Sports cars won’t be more economical. Whereas a 6-speed Civic will be more economical than a 5-speed Civic, because you’ll run the engine at a lower rpm for the same road speed.
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• 5-speed automatic – improved over the 4-speed. You used to get this in luxury cars only. Now you have it in the new Honda City sold in our local market. It’s much more economical than the 4-AT.
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• CVT automatic - Continuously Variable Transmission, like the name says, constantly changes the gear ratio such you have a continuous range from Gear 1 to 6. You can compare it to a 20-speed gearbox. So there’s no shock, and changing of gear! E.g. in a Honda Fit (not Jazz), you can accelerate from 0 to 60kph while keeping the engine at a constant 1500 rpm in less time than a 5-speed manual. The gearbox electronics control the engine rpm based on how hard you press the accelerator. So it’s smoooth, more economical than a manual. Video here: CVT Explained from Youtube
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  All new Japanese cars made for Japan – meaning second hand! have CVT e.g. Vitz 2nd gen (we call it Yaris here), Mazda Axela (Mazda3 here), Toyota Corolla Axio, Civic, Mitsubishi Cedia (Lancer), Galant Fortis (Lancer EX). Note that only ABC motors is selling CVT in a Japanese brand in Mauritius. You have CVT gearboxes in the Tiida and Murano (yeah it’s sports SUV).
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  Second hand vehicles from Singapore usually have 4-AT. E.g. the Honda Jazz will have 4-AT or 5-AT while the Fit has CVT automatic.

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• Double-Clutch 6-speed – this is the standard automatic you get in sports cars including Lancer Evolution, Porsche, Ferrari and most automatic supercars. As the name says, this one has 2 gearboxes close to each other. One has gears 1,3,5 and the other 2,4,6. While you’re driving in 2nd gear, the other gearbox can be in 3rd. Once you press the paddle (gear shifter), you can imagine the speed in switching. It’s more expensive but sporty as well.
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• Double-Clutch 7-speed – newer version of the DC-6, seen it only in super cars. Bugatti claims that it’d be impossible to accelerate 0-100kph in less than 3 seconds with a manual gearbox. So they developed a 7-speed double clutch for the record breaker 1001hp Bugatti Veyron.
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• 6-speed step automatic only for rear wheel drives due to their size. You get is in BMW’s.
• 8-speed step automatic only on Toyota Crown and Lexus IS-F.

Well lorries have even more gears, but that’s another subject. Gearbox types in bold are the ones you have to know about.

So the point is that before you buy an automatic car, check if it’s CVT. If it’s the old 4-AT, prepare for lower economy. The problem with CVT now is that they cannot handle the load of a big lorry or bus engine. So these vehicles are stuck with step-auto until further development. Like manuals, they use oil. And another precaution is not to drive in neutral gear (you wouldn’t need to) because of reduced oil pressure…

I’ll write more soon.

Useful websites to learn more are:

http://auto.howstuffworks.com/

http://en.wikipedia.org/wiki/Continuously_variable_transmission

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