Many people seem to think that the main reason for having different chainrings on a bike is to provide the rider with two completely different sets of gears. In an earlier article we saw that this is not the case. Most of the gears that are available on one chainring are duplicated or have a very close analog on the next chainring. The main benefit that comes from having different chainrings is that the size of the step up or down from one gear to the next differs on each ring. You get smaller and more refined steps on smaller rings. Understanding how this works can help solve some problems riders may have when shifting between rings.
A common gearing setup for a bike with a double chainring pairs 53 and 39 tooth rings on the front derailleur with a 12 – 25 tooth gear cluster or cassette on the rear derailleur. The table below shows the gears that are available for this setup expressed in meters of development (MoD).
Gears for a 53/39 double chainring and a 12 – 25 cassette in meters of development.
Meters of development is way to describe bicycle gears that is more commonly used in Europe than the US. It defines gears in terms of the number of meters the bike moves forward every time the pedals make one complete revolution. For example, when you are on the 53 tooth big ring and the 17 tooth cog on the cassette, the bikes moves 6.7 meters forward every time you turn the pedals through one full revolution. MoD along with other methods of defining bicycle gears is presented in more detail in Gearing Part 1: The Basics. I’m using MoD here because it makes it very easy to understand what happens when you shift gears.
An important thing to notice about the gears shown in the table is that gear changes are nonlinear. This means that shifting up or down by the same number of teeth on the rear cassette does not usually result in the same change in MoD. For example, if you are in the big 53 tooth ring and you shift from the 17 tooth cog to the 16 tooth cog on the cassette you go from a 6.7 to a 7.1 meter gear. A shift of one tooth on the cog produces an increase in difficulty of 0.4 meters for every pedal revolution. If you take one more step and make another 1 tooth shift from the 16 tooth cog to the 15 tooth cog you get an increase of 0.5 meters per pedal revolution. It’s harder going from the 16 tooth gear to the 15 tooth gear than it is going from the 17 tooth gear to the 16 tooth gear even though both shifts are carried out by shifting down 1 tooth on the cassette.
Being aware that gear changes are nonlinear can help provide solutions for some common shifting problems.
Shifting into an easier gear on the cassette while climbing
Finding the right gear on a climb often involves a series of shifts into easier gears on the cassette until you find one that is comfortable for the gradient. If one of these downshifts is too big, you can spin too freely and lose momentum. A solution is to drop into a smaller ring early in the climb and then drop into progressively easier gears on the cassette as the climb gets harder. The reason this works is that the changes between gears are smaller and more refined on smaller rings. When you drop into an easier gear on the small ring you are not dropping as far as you would from the same position on the big ring. For example, shifting from the 17 to the 19 tooth cog on the cassette when you are in the big 53 tooth ring is a drop of 0.7 meters per pedal revolution. The same shift from the 17 to the 19 tooth cog on the cassette when you are in the small 39 tooth ring is a drop of only 0.5 meters. The more refined steps on the small ring make it less likely you will lose momentum on a climb by downshifting too far.
Shifting between rings while climbing
Wait a minute. If dropping one gear on the cassette is too big a shift when you’re in the big ring, how can shifting to the smaller ring solve the problem? Look at the table. No matter which gear you’re in on the big ring, shifting to the small ring is a larger drop in MoD than staying in the big ring and dropping down one gear on the cassette. Dropping into the small ring looks like it creates a bigger problem.
The solution is to briefly shift into a higher (harder) gear on the cassette right before dropping to the smaller ring.
There are two circumstances where this technique usually comes into play. The first is the situation described above where you drop to the small ring early in the climb because you know you will handle the climb better with smaller drops in MoD with each shift into an easier gear as the climb progresses. To accomplish this without losing momentum you have to quickly shift up through 2 or 3 cogs on the cassette before dropping to the lower ring. Pulling off this triple (2 shifts up on the cassette + 1 shift down to the small ring) or quadruple (3 shifts up + 1 shift down to the small ring) shift is not easy and is going to take some practice.
The second situation where shifting up into a harder gear on the cassette before shifting down to the small ring comes into play happens when the hill is overwhelming you and you need to get into the small ring to keep your momentum going. In this case you usually only need to do a double shift – shift up one gear on the cassette and then drop to the small ring. This is a good deal easier than the triple or quadruple shifts described above.
How do you do these shifts without losing momentum? The trick is to shift quickly with split-second timing so that you spend very little time in the harder gear. Put a surge of extra power into the pedals as you shift up into the harder gear on the cassette. As soon as the chain catches in the teeth of the gear drop down into the smaller ring. When you get the timing right you will be spending a quarter to a half of a single pedal revolution in the harder gear on a double switch.
Getting the timing right will take some practice. If you stay in the higher gear too long you’re in too big a gear for the gradient and you lose momentum. If you drop into the smaller ring before the rear derailleur shift is complete, you run the risk of dropping the chain and turning a small problem into a big one. The goal is to drop into the smaller ring a split second after the rear derailleur shift into the harder gear is complete.
When to shift into the big ring ring from the small ring
Thus far we have looked at shifting to the small ring from the big ring but there are times when doing the reverse and shifting to the big ring from the small ring can pose its own set of problems. I once fielded a query from a rider who was comfortable riding in the small ring but was starting to ride with stronger cyclists and needed the bigger gears on the big ring in order to keep up. He was shifting up into progressively more difficult gears until he reached the limit on the small ring at which point he shifted up into the big ring. When he got onto the big ring the gear was too hard for him and he had to shift into easier gears at which point he fell behind the people he was riding with.
One possible solution is to drop back into an easier gear on the small ring before you shift up to the big ring. This usually doesn’t work because you are likely to lose too much momentum while you are in the easier gear on the small ring.
Gears for a 53/39 double chainring and a 12 – 25 cassette in meters of development
The solution is to shift over to the big ring earlier rather than waiting until you’ve maxed out the small ring. Take a look at the MoD values in the table and remember that the increase in difficulty as gears get harder is nonlinear. If you wait until you’re in the 13 tooth cog on the small ring to switch over to the big ring you’re getting hit with a MoD increase of 2.3 meters. This is a huge jump in difficulty. If you shift into the big ring while you’re in the 23 tooth cog on the cassette you’re looking at a MoD increase of only 1.3 meters. This is still a big jump but it’s not nearly as difficult as the 2.3 MoD increase you get if you shift near the top of the small ring. Moreover, if you work up to the 13 tooth gear from easier gears on the big ring, the final step from the 14 tooth gear is much easier (a MoD increase of 0.6 meters) than jumping to the big ring 13 from the small ring 13 (a MoD increase of 2.3 meters).
The technique for carrying out the shift into the big ring is similar to the one described for doing a double shift to get from the big ring to the small ring. Put a surge of power into the pedals and then shift up into the big ring. The jump in MoD may be too large to maintain and if it is, you can quickly shift down to an easier gear on the big ring. When carried out correctly, this will put you in a bigger gear than you were in on the small ring without losing momentum.
Switching to the big ring sooner rather than later can be useful in any situation where you expect to use the high MoD gears on the big ring. For example, when you have a downhill followed by a flat you can often pick up enough speed on the downhill to keep a large gear turning on the big ring when you get to the flat. If you do the descent in the small ring and then try to switch to the big ring when you get to the flat, the increase in MoD may be too much to handle. If you shift into the big ring early in the descent and keep shifting into harder gears as your speed increases on the downhill, you will be flying by the time you reach the bottom and you’ll be able to maintain a bigger gear for a longer time on the flat.