Gears and understanding shifting


For beginners, gears can be very intimidating.  Modern bikes typically have 20 gear combinations or more. (today’s “10-speeds” are really “20 speed” bikes)  What gears you need and when to use them is sometimes a big mystery.

All bikes have two sets of gears* – the group of 5 to 11 gears on the back wheel and the set of 1, 2 or 3 gears connected to the crank arms and pedals.  The back set of gears is commonly called the “cassette” and is shifted by a mechanism called the rear derailleur.  The front set of gears are called the “chain rings” or “crankset” and are shifted by the front derailleur.  Derailleurs do basically what they sound like they do – they “de-rail” the chain so that it comes off of one gear and goes onto another.  How you actually shift your gears will depend on whether you have a road or mountain bike setup, and whether your parts are made by Shimano, Campagnolo or SRAM.  The rear cassette gears will always be controlled by your right hand, and the front rings will always be controlled by your left, however.

So, why do you need gears at all, then?  Gears offer you a mechanical advantage to make riding easier and more efficient.  The number of teeth on each gears determines that mechanical advantage.  On a standard road bike, for example, there are typically two rings on the front – one with 53 teeth and one with 39 teeth.  (Don’t ask me how that became the standard!)  The rear cassette will typically have gears ranging from 12 teeth, all the way up to 25 teeth.  …So, using this example, if you put the chain on the small ring in the front and the big gear in the back (this is best for climbing hills), your gear ratio will be 39/25, or about 1.6 to 1.  In other words, for every one revolution of your pedals, your back wheel will rotate 1.6 times.  …Looking at the other extreme gear combination, if you were going downhill, for example, you’d put it in the big ring in front and the small gear in the back.  In this case your gear ratio would be 53/12 or about 4.4 to 1.  This time for every pedal revolution your back wheel will go around 4.4 times!

And, as you can imagine, there are lots of ratios in-between, depending on your gear combinations.  Some bikes have three rings in front (considered uncool for serious cyclists, but can be a big mechanical advantage for beginners!).  Some bikes have more or less gears in the back.  (Older “10-speed bikes have 2 in front and 5 in back, new Campagnolo-equipped bikes have 11 in the back!)  …Note that many of these gear ratios overlap, so you really don’t get 20 unique “speeds” if you have 10 in the back and 2 in the front.  Several of the combinations work out mathematically to the same gear ratio.  It’s just more convenient to not have to switch the front AND rear derailleurs all of the time, so they make some redundant!

So, you might be asking by now, “how do I know when to use which gear?!”  The answer is that it depends on how fast you’re riding and how steep the incline or decline is.  Basically you try to keep up a constant cadence (the speed at which your pedals go around).  The correct cadence value is whatever is comfortable for you, typically in the range of 80 to 100 revolutions per minute for most people.  The pros tend to pedal faster than this, and you’ll likely be slower than 80 when you first start out.  Beginners tend to pedal too slowly.  …So, anyway, you select the gear that allows you to pedal at your comfortable cadence – or as close to it as possible.  I tend to like around 90-92 RPM these days.  If I’m going up a slight incline, that typically means the small gear in the front and one of the middle to larger gears in the back.  For big hills you’ll use the small gear in the front and the two or three largest gears in the back.  Don’t worry about going too slowly – it’s better to keep your cadence up than to try to “grind” up the hill!  For declines use the big ring in the front and the most comfortable gear in the back to take advantage of the situation.  (No point in going too slow if it’s downhill!)  On steep downhills I like to put it in the big gear in the front and the smallest cog in the back.  I can typically get going 35-45 mph in this configuration.  The pros will do more like 50-60!


Once you ride for a while, you’ll likely realize that you need to change your cassette and/or crank a bit to suit your capabilities, riding style and home terrain.  Some areas like Florida, for example, are extremely flat.  In those situations you can get away with very big gears in the front and small ones in the back.  (The advantage to this is that you have very small steps in-between each gear ratio, which makes riding very efficient.  You can always find the “right gear”.)  In other areas, such as Arizona, there are more hills, so you’ll likely want smaller gears in the front and bigger ones in the back.

Changing the back gears, or cassette, is pretty easy and common.  Originally I had a standard 12-25 cassette on my bike (meaning the smallest gear had 12 teeth and the largest one 25), but I needed help climbing hills, so I changed to an 11-28 cassette instead.  This gave me a easier to pedal ratio (39/28 = 1.39 vs the old 39/25 = 1.56).  The lower the gear ratio, the easier it is to pedal (but the slower you go).  It also gave me a higher top ratio (53/11 = 4.82 to 1 vs. the old 53/12 or 4.42 to 1 ratio).  I rarely use that 53/11 combination, though, unless I’m going downhill at over 35 mph!

If I wanted even lower gear ratios overall, I could have gone to what they call a “compact crank” on the front.  Basically this refers to smaller, more compact gears on the front crankset.  Many people prefer to go this way, as it generally makes pedaling easier overall.  The only sacrifice is that you give up some overall top speed.  But rarely does one wish they had bigger gears to go faster – more often it’s a desperate cry for smaller gear ratios as you’re struggling to get up that hill.  “Please, oh please, just give me one smaller gear ratio!”  …So, in the previous example, if I would have had a compact crank (typically they have gears with 50 and 34 teeth), my smallest gear ratios would have been 34/25 or 1.36 with the standard cassette or 34/28 or 1.21 with the new, hill-climbing cassette.  With gear ratios that approach 1 to 1, you really move slowly, but you can climb just about anything.  You can actually go even lower than this – many of the new systems offer really small ratios for beginner riders.  (Mountain bikes typically have low ratios that are less than 1 to 1.  Road bikes with triple chain rings in the front can go this low as well.)

*This is techically not true, actually – some single-speed or fixed-gear bikes have one gear in front and one in back.  No shifting required!  (hopefully they chose the correct gear ratio, though!)

More content and images coming soon – if you can’t wait, please create a reply/comment and I’ll get to it sooner than later!

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