Proper gearing for your bike is an important part of maximizing both your performance and enjoyment of every ride. Selecting the proper gearing will focus on two parts: the chainrings and the cassette.
The chainrings play the most important role in proper gearing. Chainrings come in different sizes as measured by the number of teeth on the large and small ring. The most common sizes are listed here:
- Standard chainring
- 53 tooth large ring
- 39 tooth small ring
- Mid-compact chainring
- 52 tooth large ring
- 36 tooth small ring
- Compact chainring
- 50 tooth large ring
- 34 tooth small ring
Choosing a Chainring
Chainring selection should be based on how strong of a cyclist you are. Cyclists that use a powermeter have an advantage since they can use power data to determine how strong of a cyclist they are. You can use the measure watts/kilogram at threshold (w/kg) to help with your selection.
Compact chainrings are the most forgiving on steeper climbs. Generally speaking, a cyclist with a w/kg of 2 – 3 is most likely best served with a compact chainring. This range is typical of road riders in the 13-17mph range and triathlon riders in the 16-20 mph range. Beginners, smaller riders, recreational riders and Cat 5 cyclists fall into this range as well.
The mid-compact serves as a great bridge between compact and standard chainrings. The 52 tooth outer is very close to the 53 on the standard which means you will not be giving up any top end speed. But the smaller 36 tooth small ring has 3 less teeth than the standard size making steep climbs easier.
With a w/kg between 3 and 4.5 the cyclist now moves up to a mid-compact chainring. These numbers are typical of road riders in the 18-23 mph range and triathlon riders in the 20-26 mph range. Mid to front of pack triathlete riders, Cat 3-4 cyclists, and generally those considered to be strong cyclists fall into this range.
If your w/kg is over 4.5 you are probably best served by standard chainring. These numbers are typical of road riders in the 21+ mph range and triathlon riders averaging 26 mph or more. This is a triathlete with the best overall bike split, Cat 1-2 cyclists, “freaks on two wheels” category.
While w/kg is a good metric to begin proper chainring selection, absolute power numbers (independent of weight) can be used to modify that choice. In this scenario a strong rider pushing a lot of watts may opt for a standard chainring regardless of their w/kg metric.
Crank Arm Length
Another aspect to chainring selection is picking a correct crank arm length. There is no steadfast rule to determine what length of crank arm is right for you. This will depend on your flexibility and your position on your bike. The trend in triathlon is to move to a shorter crank arm length. This allows you move into a more aggressive and aero position and not pinch your hip flexors. Too much pinching of your hip flexors can cause tightness during the run. Crank arm selection is one of the finer points we cover during our comprehensive bike fitting process.
Cassettes are the gears located on your rear wheel. These gears allow you to change gearing ratios to make pedaling easier or harder. The larger the gear in the cassette the easier it is to pedal. Conversely, the smaller the rear gear the harder it is to pedal. Keep this in mind as we go through the different sizing options for cassettes. The smaller the gear the harder it is to pedal, but the faster you will go. The opposite applies to the larger ring, it is easier to pedal but as a result you will go slower.
You should choose your cassette based on the terrain you will encounter. Cassettes generally come with either 11, 12, or 14 as the smaller gear. You will find a large variation in larger gears. Common sizes include 23, 25, 28, and 32.
Flat to Rolling Terrain
With the appropriate front chainring selected, a typical rear cassette for flat to rolling terrain would be a 11-23 or 11-25 cassette. This gearing will allow faster speeds on the flat sections and still have the larger gears for climbing up the rolling hills.
Hilly to Mountainous Terrain
When tackling mountain terrain you will be spending extended amounts of time climbing in a large rear gear and mostly coasting down the steep downhills. This means a larger gear is more important. A 12-28, 12-32, or even a 14-32 might be most appropriate.
Another factor to consider when choosing your gearing is your preferred cadence range. If you like to spin a high cadence you may want to choose a smaller chainrings and/or cassettes with larger cogs. The opposite is true for riders who prefer a lower cadence, where larger chainrings and smaller tooth count cogs are preferable.
Don’t worry so much about “spinning out” or not having enough gear to pedal the fastest parts of your ride, as much as making sure you don’t run out of gear when you are attempting the longest and steepest climbs that you typically attempt. Even a compact 50—34 with a climbing cassette of 12-32 will provide a speed of nearly 30mph when spinning 90rpms in that largest 50-12 gear combination.
On a typical multi hour ride, you should use every gear on your bike, with the smallest combo being sufficient for the steepest climbs and the largest gears enough for the fastest descents. Also, take note where you “run out of gear” to help guide your future gearing decisions.
More Gearing Information
For more detailed information on gearing selection, crank length, and bike fit, please come by the store or email one of our resident experts. Triathlon gear is an investment and our mission is to make sure you make the correct investments. Do not hesitate to give us a call or email for more information.