Shifting gears while biking

So You Think You Can Bike – Shifting

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I always find it a bit hard to talk to my clients about proper shifting without going into a little bit of a cycling history lesson.  The lesson that I focus on is the idea that cyclists used to ride the Tour De France (Td’F) on single speeds; yeah that race, with no gears.

When cyclists where forced to ride on a single gear they had no choice but to push as hard as needed to overcome whatever terrain they were on.  Prior to 1937, racers would have to dismount in order to change their wheel from downhill gearing to uphill gearing. Then Simplex introduced a cable-shifted rear derailleur which allowed the rider to change the gear ratio to better handle the current road situation while staying on the bike.  Through the years the derailleur has gone through a lot of improvements which has given the rider more gear ratio options to use during their ride, all the way up to the the 11-speed rear derailleur released this year (2013) by Sram.  You now even have the option of wireless shifting from Shimano and Campagnolo.

The reason for all these gears is so the rider can maximize efficiency.  There is a particular combination of cadence and resistance that will produce the most power with the least amount of stress on the body; of course that ideal combination of cadence and resistance is individual to the given rider. The whole idea of shifting gears is to select the gear ratio in which this combination of cadence and resistance is met.  Whether you are riding on a flat road or uphill, on a smooth or bumpy surface, going fast or slow, theoretically your legs should always be pushing the pedals with the same amount of power.

To repeat —  this combination is highly dependent on the the individual rider and there is not a right or wrong combination for everyone to follow.  Some people are “mashers” — they prefer a lower cadence with heavier resistance.   Others are “spinners” — they like a high cadence with lighter resistance.  If you watched cycling back when ‘he who should not be named’ (Lance Armstrong) was racing the Td’F, battling against Jan Ulrich you would have seen a spinner vs a masher side by side, as they climbed some of the tallest peaks in Europe. Lance liked to climb with a high cadence above 90 rpm while Jan was a classic masher and had a much slower cadence.  But both of them climbed the mountain at the same speed.

Which one is better, spinner vs masher, will be addressed in a future post.  The key for now is that they each chose their style of climbing based on THEIR preferred combination of cadence & resistance.  They maximized their efficiency while producing a similar power output (watts/kilogram). If Jan tried to match Lance’s pedaling style he would not feel “comfortable” and probably would not be able to sustain the power output needed to climb at the same speed. Jan was more comfortable with a slower cadence and heaver resistance; so he picked a gear ratio that worked for his style.

Now let’s understand gear ratio.

Gear Ratio is the ratio of angular velocity of the input gear (chainring) to the angular velocity of the output gear (cog).  At this point it is not important to understand how it is calculated but rather how it is expressed.  Let’s focus on one of the ways it can be expressed — the gain ratio expression. The gain ratio is a combination of the chainring, cog, crank arm length and tire size. Below is a example of a gain ratio chart for a common bike set up with a:  Compact Crank (50 tooth and 34 tooth chainrings), 12-25 cassette (collection of cogs on the back wheel), 172.5 crank arms and 700×23 tires.

50- Chainring 34- Chainring
12 – cog 8.1 5.5
13 – cog 7.4 5.1
14 – cog 6.9 4.7
15 – cog 6.5 4.4
16 – cog 6.0 4.1
17 – cog 5.7 3.9
19 – cog 5.1 3.5
21 – cog 4.6 3.1
23 – cog 4.2 2.9
25 – cog 3.9 2.6


As you can see the 50/12 combination yields the highest gain ratio of 8.1 and the 34/25 combination yields the lowest gain ratio of 2.6.  This is where you get the “higher gear” and “lower gear” from.  If someone says “shift up” they are referring to shifting to a higher ratio; “shift down” to a lower ratio.  The higher the ratio the heavier the resistance is, the lower the ratio the lighter the resistance.

How does this help you know why to shift rather than how to shift?  The key is in the highlighted ratios in the chart.  As you can see, there are a few duplicate gears and this is important especially when approaching a climb.  We can achieve the same ratio with a combination in our ‘big chainring’ or our ‘little chainring’, so if I was pedaling in my 50/19 combination I would have the same exact resistance if I shifted to my 34/13 combination. If I have the same gear ratio (resistance) and the same cadence I would would be traveling at the same speed, and this is a crucial point.  Here is a classic illustration — if I am riding on a flat road in my big chainring (50) and I see a big climb looming in the distance, I would already be sizing up the climb and thinking to myself “Am I going to need to get down into my easiest gears to get up that climb comfortably?” If the answer is yes then as I approach the climb I am going to pay attention to which gear ratio I am in. If I am in my 50/17 combination as I approach the climb and feel the need to ‘shift down’ to an easier gear ratio and I know that the next gear ratio is one of my duplicates I would know that this is the time I want to shift down to my small chainring (34), while also shifting into a smaller cog (13) because it will yield the same ratio as if I stayed in my big chainring (50) and shifted into a larger cog (19).  This can be hard to follow so let’s look at it again.

Riding along in 50/17 (ratio of 5.7); when I see a big hill approaching I can: A) Shift to 50/19 (ratio of 5.1) or B) Shift to 34/13 (ratio of 5.1).  Which is the best option? Does it really matter?  Yes — B is the better option.

The reason: shifting down to the 34/13 combination gives you 8 more gear combinations as you shift down on the climb.  If you had shifted to the 50/19 you would theoretically only have 7 gears to use.  One gear difference may not sound like a lot, but “theoretically” is the key here.  If you ride uphill and get into the 50/25, your only shifting option at that point is to drop to your 34 tooth chainring, because the chain is under to much strain at that point to do a double shift (down in front, up in back). So if you chose option A, you would actually have only 4 gears to get you through the climb, not 7 and that is not good.

A cyclist is thinking about this well before the climb; the triathlete isn’t thinking about this until they are already on the climb.  The triathlete who gets stuck on the climb in the big chainring because they where not thinking ahead is going to be stuck with either A) dropping from 50/25 (3.9) all the way to 34/25 (2.6) and losing all of their momentum, or B) staying in the 50/25 and grinding out the rest of the climb burning a match (legs burning) along the way. At this point the triathlete is stuck between two bad options (we will expand on why these are both bad options in a future post discussing climbing).  This is how understanding gearing can keep you out of bad situations.

Shifting is probably the most important aspect to cycling for a triathlete because one of the keys to a successful run is a consistent effort on the bike; limiting the peaks and valleys of power (burning matches).  By understanding how to use your gears to meet your goal power (balancing cadence and resistance) you maximize your efficiency while posting a great bike split, while increasing the likelihood of posting a great run split as well.

This is crucial for triathletes because we don’t have the luxury of drafting, so we feel every slight change in the wind and grade of the road which affects the resistive force we have to overcome. These slight changes in resistive forces require us to make subtle changes in our power (cadence & resistance) by shifting our gear ratios so we can maintain our desired cadence while remaining comfortable — or should I say comfortably uncomfortable.


Ride and shift like crazy. While shifting like crazy pay attention to your cadence and how the resistance feels against the pedals, along with your speed. Try to find the duplicate gear(s) as well by shifting from the large chainring to the small chainring on a flat road.

Ride and get into your comfortably uncomfortable place and notice what 10 rpm window your cadence stays in (80-90 rpm, 85-95 rpm, etc).  Also pay attention to how you feel if you go above that window and below that window. If you dip below your comfortable cadence window you will probably feel the discomfort in your legs from a “pushing” kind of feeling; if you go above the window you will probably feel the discomfort more from a respiratory feel of a “rushing” feeling.

Ride on a rolling route (without major climbs) you are familiar with and try to maintain the same power (cadence & resistance) throughout the entire ride; the same going uphill, downhill and on the flats.  Whenever you feel a slight change in resistance on your legs, you need to shift to return to the desired resistance (resistance gets easy “shift up”, resistance gets harder “shift down”).

Work, Live, Tri

Coach Hammond


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