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I've recently started commuting with a bicycle (Giant hybrid bicycle). I've been trying to learn a little about bicycling to make my commute easier and my time on the bicycle more enjoyable. Please forgive me for using the wrong terminology.

I've read that I should keep my pedalling speed mostly consistent and use my bicycles gears to adjust my speed. The problem I'm having is understanding the 'how'.

My bicycle has 3 gears on the front of the chain and 8 gears on the back.

Low gear == easy to pedal High gear == harder to pedal

What I've found is that the gears don't follow a very logical (to me anyway) progression and because of that - I don't know how I should be shifting. Currently, I've been keeping my front gear in the middle and using the back shifter to change between gears 3-7 or so. I'm only use about four gears on my '21 speed' bicycle!

I'm also pretty sure the salesman said it was a 21 speed bicycle - but by my count there are 24 combinations. I know (now) that I'm not supposed to have the front gear in the lowest position and the back gear in the highest (and vice-versa) but that seems to leave 22 gears.

How should I be shifting? Should I really use all 21 or 22 gears? I haven't done the math but it really feels like there is a big amount of overlap between the gears. I hope this ascii art will make sense to someone. This is just how it 'feels' to me.

----1----2----3----4----5----6----7----8----
------------1----2----3----4----5----6----7----8----
--------------------1----2----3----4----5----6----7----8----

Does that make sense? Is it right?

It feels like there is overlap between the three front gears and that to shift the most 'smoothly' I'd need to constantly change both gears. But this seems really complicated to me.

I've ridden bicycles with only three gears and I found myself thinking 'More would be nice' - but now I'm overwhelmed. I'm also questioning if anyone really benefits from so many gears?!

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3 Answers 3

up vote 14 down vote accepted

Don't overthink it. Since you've got a triple, you're probably right to be in your middle ring most of the time That's normal.

  • In the middle ring you should have access to the whole cassette/freewheel in the back, though you might get a little extra noise as you approach the extreme gears in either direction.
  • You'll use the big chainring when you're going downhill or your on flat ground and in a hurry. Stay out of the biggest couple of cogs in the back when you're in the big ring up front. This causes extra strain and extra wear on the drivetrain which can result in premature failure.
  • Your little ring up front is your climbing ring. Use this for hills, or as your bail-out ring when you're totally out of energy. Just like big-big is a no-no, so is small-small, so stay out of the smallest cogs in the back when you're in the smallest ring in the front.

Regarding your hunch that you've got a lot of overlap between gears, you're absolutely right. Think of each ring as a gear range (climbing for small, normal use for middle, ass-hauling for big). If there were no overlap between the chainrings you would either A) have far fewer gears in the back or B) have a range of gears in the big and small rings which were far too small or far too big to be usable.Think about how big the jumps between gears would be if there was no overlap at all! Trust me, it's not what you want. Typically, you'll find yourself Shifting the front in one direction and immediately afterwards shifting the back in the opposite direction so that it feels like you've only skipped about a single gear in either direction. In time, you'll come to appreciate the overlap between gears in the different chainrings.

Finally, if you really want to see how much overlap you have, you can divide the front rings by each of the back rings to get a ratio for every gear combination. There are fancier ways of doing this, but for your purposes this is the easiest and most straightforward.
EDIT: Here's a pretty good article on Wikipedia about bicycle gearing if you'd like to get more in depth.

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Nice Answer! I would add that when I talk with people, especially those new to "these fancy bikes", I try to steer them away from "27 speed", "20 speed", etc and rather to 3x9, 2x10, etc. I think this, mixed with a gear picture (nice ASCII one above BTW), gives a better feel for how the gearing can be used. –  Ken Hiatt Aug 3 '12 at 0:16
    
+1 Nice Answer- I would add that crossing the chains is not as big a "No No" as Ghost Busters crossing the beams. It should be avoided where possible, but won't do any damage unless you do it regularly - it means you'll get 4376 miles out of the chain rather then 4845 miles. –  mattnz Aug 5 '12 at 22:03

This chart shows the number of teeth front and back (which is a total estimate but should be representative), the index number of the gear front and back, and the I/O ratio. The I/O ratio is the number of teeth in the front divided by the number of teeth in the rear i.e. the number of rotations of the rear wheel induced by one rotation of the feet.

A high I/O number means the bike will move faster for fewer leg rotations. This speed comes at the sacrifice of greater difficulty imparting force/motion on to the rear wheel at lower speeds because changes happen so slowly. In contrast to how easy it is to impart force onto the wheel from the pedals in a low gear ratio but then you need to start pedaling super quickly too soon and your legs can't keep pushing forcefully at 100+ rpm.

As for the idea of whether or not there are redundant ratios, the chart indicates there are several combinations which are either exactly the same or very similar. This is ok because even if some combinations are the same the respectively adjacent gears will be different ratios. Also, you can see that the smallest front sprocket (1, yellow) is predominantly low ratios (slower speeds at a natural cadence) and the largest front sprocket (3, blue) is predominantly high ratios (high speeds at a natural cadence). All the while the middle front sprocket (2, green) spreads across the whole spectrum but never really fast and never really slow.

gear ratios

So, in conclusion, you should be shifting gears so that you are pedaling at a comfortable (and constant-ish) cadence for whatever speed or incline you are traveling.

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1  
While your table is mathematically correct, I would say that the choice of chainring depends more on what you expect to be doing further down the road. In particular, when you are accelerating or trying to go up a long steep hill, you don't want to shift chainrings unless absolutely necessary-- even if there's gear-combo on another chainring that is more contiguous with your progression. The chain is far more likely to be dropped during a front derailleur shift under power. Also it would never be advisable to go from granny to big (1-3) or vice-versa. –  Angelo Aug 3 '12 at 13:06
1  
@Angelo Yeah, I wasn't really suggesting this is the gear change progression one should use but rather this is the physical progression of ratios. I was trying to illustrate how much overlap there is and the trend of the each of the front rings. You are totally right though, changing front gears should be a conscious and deliberate move that is not spontaneous. and takes into account expected future conditions. Also some of these ratios, while physically existing, should not be used (i.e. big in front-big in rear or small in front- small in rear) –  Brad Aug 3 '12 at 13:22
    
Great description. But why do rear 1st and 3rd gears have the same number of teeth (36) in the chart? Should rear 3rd be 26? –  user6031 Jan 30 '13 at 23:17
    
@Dave Doh! well...the gist is the same. not remaking the graphic at this point –  Brad Jan 31 '13 at 3:24

Generally you'd only use the small ring for hill climbing. And when you're having to shift a lot (rolling terrain, stop-and-go traffic, etc) you'd set the front on the middle ring and just use the rear to pick a range.

But when you're getting "in the groove" on a straight stretch, you might first find the "right" rear gear given the middle ring, then, if that's not quite "perfect" for you, shift up to the large front ring, then down-shift the rear one or two clicks. Depending on exactly how your gears are spaced, this will put you near to the previous gear ratio -- a little above or a little below. It's a bit of an intuition thing that you learn over time.

There are several gear calculators on the web where you can input the tooth counts of your gears and it will show you the ratios. You can the observe the order of the ratios and see how you might shift between gears to hit every gear in order. Not that it's important to do this (vs the intuition thing), but it will give you a sense of what's going on.

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