You'd think this would be simple. Just get into the gear you need to travel comfortably, or even progress with speed, and there you are - in gear and on your way. That's it, isn't it?
Well, mm, there can be a bit more to it. One key thing I don't see people doing is anticipating gear changes. So they are riding along and all is fine, but up ahead is a corner. It's a tight corner and they need to stop pedaling and coast around it . And once around it they will have lost speed, and they'll still be in the gear they entered the corner in. That's when you see people stand up to push the harder gear to get back up to speed. Another way would be to change up just before the corner so they are in the right gear to accelerate back up to speed.
Another classic is not changing up when coming to a stop. It means when they set off they are in the wrong gear - still in the cruising gear they were using for 25kph. Now they are trying to set off in the same gear and that can be tough. It can actually be dangerous if you are at a road junction - you're in the wrong gear, far too hard to set off with, but now you've got to make your way out across a busy road (turning right) and clip in and change gear into something you can work with. You're increasing the chance of grinding to a halt in the middle of the road, or even falling over. Much easier to have changed up just before you come to a stop - then you can pull away in the normal gear you use to set off with.
Even more of a classic is waiting until the steep hill starts before changing gear. This can be a real problem. The hill starts, you are in way too high a gear, your pedaling stops and as soon as that happens all ability to change gear disappears. If you are lucky you can unclip before you keel over. Much better to look ahead, see what's coming up and get into an easier gear - doesn't have to be the exact one for the hill but it does need to allow you to turn your pedals whilst on the hill so you can make further changes as you adjust to the actual incline.
Probably the one that most people are familiar with is not changing into a higher gear as you descend a hill. You've climbed up a steep slope in your lowest gear, then coasted down the other side. Now, at the bottom of the hill, where things level out you want to capitalise on all the speed you've acquired but when you go to turn your pedals they spin uselessly around - still in the low gear you used to climb the hill 10 minutes ago. Should have changed up to a higher gear as you descended.
One thing all this implies is being able to pedal at different speeds, and specifically, the ability to pedal at high cadence. As you approach a climb you get into your "hill gear". OK but this means that for a moment you are on the flat still and in a very easy gear, and additionally you want to keep pedaling as any loss of speed right at the bottom of a hill isn't going to be welcome. It means you're going to have to pedal at high speed, just for a couple of metres. So this means being comfortable with pedaling at different speeds. I've lost count of the number of people I've overtaken at the foot of a hill - them fiddling with their gears whilst I spin by and up.
Does this make sense to you? What are your gear selection experiences?