just4fun said:
Depending on your level of fitness you might find a big change in how your cycling stamina is from when you last rode a bike so i'd advise just to take it easy at first, think of the tortoise and hare story. Is your commute 20 miles total or 20 each way? When the option is available, many people might get a trainlift one way of the journey so as not to do too much to soon in regards to cycling, but this option isnt always available.
To start with you could alternate cycling and driving days, or cycle one day a week or one in three days or whatever. Is there somewhere safe at work to leave the bike if, say, you cycle in and feel shattered by the end of the day and want to get a taxi home or something? (although I find, on my albeit short, commute, that even when I feel whacked after a hard physical day, I can cycle ok - slowly, but ok.
As others have said, you'll find out what gears suit you when. Depending on how hilly it is, you may find that you have one gear you're in most of the time, and you change up one or two for downhill and down one or two for uphill and that's it most of the time. Find a comfortable cadence (rate of spinning your feet round) and use your gears to let you maintain it as best you can - so uphill you'll do down gear, and go slower, but still spin round, and downhill you'll change up and go faster for the same spin.
Another thing to think about is what extra stuff you need apart from the bike. Have you got a good lock (a D-lock is best, spend what you can), lights, the 'right'* clothes, luggage**?
*You can cycle in anything. But over a distance like that, it'll be more comfortable if you have some padded shorts or padded undies. A teeshort will do, but a cycling jersey will carry sweat away from the body better. A waterproof jacket will keep you dry, and a breathable one will stop you overheating and sweating too much. Shoes - depends on your choice of pedal type. If you're coming back to cycling, you may want to start with ordinary flat pedals, and ordinary shoes - maybe with toeclips. The stiffer the sole of your shoe, the more efficient you'll be. Many poeple swear by the 'clipless' type, where you are (confusingly) clipped to the pedal by a cleat on your shoe - that's when you need to think about the right pedals and shoes. Personally, I've stuck to pedals with toeclips and it does me fine....
**depends on the type of bike - if yours has a rack, then it's worth having some panniers, especially if you need to carry stuff to work. If no rack, you might be able to use a saddle bag. A rucksack is ok for a short distance, but not ideal, as it puts the weight up high and backs your back sweaty.
Finally, it might well be worth getting a copy of
Cyclecraft - the bible of how to cycle on modern roads. If you haven't cycled in a long time, concepts like primary and secondary will be new to you, and slightly counterintuitive to start with, but good positioning technique can make all the difference to how other road users treat you.
