RealCyclist - Cranksets
To squeeze the most performance from your ride, break away from your bike’s stock gearing.by Dan Hall
Cranking it up
Let’s face it–stock is never good enough. Because cyclists of all abilities pedal at all corners of the world, manufacturers tend to spec their bikes with components that will work for the greatest number of riders. Customizing your gearing for your riding style and locale will squeeze the most performance from your ride. This guide will help you dial your ride in.
Finding the right gear ratio starts with considering your location: rolling-farmland hills, cloud-scraping mountains, or iron-board plains. It ends with a reflection on your abilities: are your legs stronger than your brain? Are you returning to the bike after a long hiatus? Are you a dedicated cyclist with tell-tale heart-shaped calf muscles? All of these riders could use a different combination of chainrings and cassettes to get the most out of their rides. Let’s look at the crank options.
SECTIONS IN THIS GUIDE
Standard vs. triple vs. compact:
Cranks typically come stock with standard 53\39 chainrings—the same that pros push without a problem in most race situations. However, mortals do not have the horsepower to spin gears that high, so manufacturers offer triple cranksets to give average riders a wide range of gear ratios; they are very popular with the touring crowd for this reason. But, just like the standard 53\39, triples can also be excessive for recreational riders, lugging around extra gears that they never need …
Then along came the compact crankset. Putting performance back into recreational riding, compact cranksets—lighter because of less material—offer a lower final gear ratio like triples do. However, there has to be some compromise on the high end; a compact crankset’s final high ratio is lower than a standard.
Compacts allow you to run a tighter cassette. For example, instead of a 53-39 and 12-27 combo, they can use a 50-34 and 11-23. The 11-23 has a much tighter gear range that allows for fast shifts—the chain does not have to jump as much. Think of a close-ratio gearbox in sports cars. Also, consider the lighter weight of a compact crankset as compared to a standard. They spin up faster thanks to less rotational weight, like lightweight flywheels on the aforementioned sports car. Close ratios, quick shifts, and a fast spin—sounds like you can’t lose right? Well nothing comes without a cost. Expect cassettes, chains, and chainrings to wear out faster.
The three types of road cranks:
Triple: Great for recreational cyclists, touring, mountainous terrain
- Lowest gearing for really hard pitches
- Widest range of gears for the right cadence at any speed
- Slow shifts
Standard: Great for stronger riders/racers, time trials, flatlands
- High gear ratios
- If you want lower gears, you have to use a cassette with a wide gear range; as a result it shifts slower, and it’s harder to find the ideal cadence
- Light weight
- Faster shifts than a triple
- Higher speeds
Compact: Great for recreational cyclists, mountainous terrain
- Lighter weight due to fewer materials
- You can run a tighter cassette—fast shifts, cadence stays dialed
- Wears out faster
- Can run out gears due to the lower final ratio
Can I just change the chainrings from my standard crankset to compact?
- Yes and no. This depends on the Bolt Circle Diameter. Most standard cranks have a 130mm BCD. This diameter is typical too large for compact chainrings. Compact cranks have a 110mm BCD—smaller diameter for the smaller chainrings. So, unless your BCD is already 110mm, you do have to change the crank arms to go compact.
Do I have to change the front derailleur?
- In most cases no. The original FD will have to be re-adjusted to work properly. FSA does offer a compact-specific FD that follows the curve of a compact chainring’s smaller diameter. If you find your original FD is not mating up well with a compact crank, then consider the FSA compact FD.
The bottom Line:
Consider a compact if you’re not using the higher end of your standard crankset or live in the mountains. The performance gains from a lighter drivetrain will be rewarding. Don’t consider a compact if you are strong and use the high end of your standard crankset, or if you reside in the flatlands. Consider a triple if you want the lowest possible gear ratios yet still want a high end.
Crank arm length:
Take the number of years you’ve been riding and divide that by the length of your top tube in centimeters. Multiply that number by 486. Well, actually, we just pulled that equation out of our asses. Bike-fitting opinions are abundant, as are the many disciplines of cycling, and humans are not all proportionate; so there is no easy (or complex) formula to give you your ideal crank arm length. But with some deductive reasoning, you can determine if a longer or shorter crank arm would suit you the best. Here’s a breakdown:
Shorter cranks: Good for crits, cyclists with short legs
- Faster spin/higher cadence
- Less stress on joints
- More clearance for cornering
- Lighter than longer cranks
- Less leverage/torque for climbing
Longer cranks: Good for time trials, climbing, and cyclists with long legs
- More leverage for turning higher gears
- More stress on joints
- Heavier than shorter cranks
- Less clearance when cornering
If you like to spin with hummingbird-vigor, you’ll like a slightly shorter crank arm. If you like to turn big gears with a diesel’s RMPs—then round up a bit. Just remember nothing is set in stone.
Use the chart below as a rough guide to make an educated choice. Data here is generalized; manufacturers’ fames sizes are not all the same, just as cyclists’ muscles, bone structure, and riding styles are not all equal. If you enter “crank arm length calculator” into any popular search engine you will receive plenty of hits to help bewilder you even more.
Think of your drivetrain as the ones in big rigs with multiple gearboxes/transmissions. The crankset is your main “gearbox;” the cassette is your secondary “gearbox.” After you decide on your crankset, you then dial in your ideal gear ratios with the cassette.
Wide Gear Ratio (i.e. 11-27)
- Lower gear for hill climbing
- Haul extra weight, touring, spare tire
- Large jump in between gear ratios makes ideal cadence harder to achieve
- Slower shifts
Tight Gear Ratio (i.e. 12-21)
- Faster shifts
- Manage cadence—close ratios
- Lighter weight
- Hard low gear
- Lower life expectancy
If you want your crankset to have a gear ratio for mountainous terrain, run the cassette with the lowest possible gear (i.e. an 11-27). If you want snappy shifts for crit racing or time trials, run a cassette with tighter gearing (i.e. an 11-21). There are many variations in between. Keep in mind cassettes are rotational weight, so you will not only benefit from dialing in the ideal gear ratio, you could also potentially drop some unneeded weight.
Other crankset options to consider:
External vs. Integrated Bottom Brackets:
Unlike external bottom brackets, which have cups that thread into the frame (more parts to deal with), integrated bottom brackets have bearing cups built into the frame. However, despite having to deal with more parts, the benefit to having external BBs is that they can be changed (depending on the manufacturer), and they fit a frame standard that has been around for many moons. Integrated BBs are manufacturers’ latest attempt, along with oversized axles and stiffer frames, to achieve ever higher levels of simplicity and efficiency.
Square-taper Bottom Brackets:
- Large ball bearings handle high loads
- Inexpensive, good for commuter bikes
- Flexy axle—square tapers can break
- Crank arm-to-axle interface can come loose if improperly installed
- Solid crank arm-to-axle interface
- Stiff Axle
- Tiny bearings (tiny because of the larger axle) can wear out faster
- Doesn’t handle high loads
- Large bearings handle high loads
- Stiff oversized axle
- Solid crank arm-to-axle interface
- Bearings are not serviceable; like Octalink, they need to be replaced when worn out
Integrated Bottom Brackets:
- Less parts
- Lighter weight
- Stiffest interface/axle
- Large bearings handle high loads
- Frame could be damaged when replacing bearings—press fit
- Bearings are not serviceable
When changing cranks make sure that they are compatible with the bottom bracket you currently have. Or change the BB with the cranks. Typically, all new bikes have either outboard bearings (Truvativ GXP- or Shimano-compatible) or an oversized integrated standard—depending on manufacturer—such as BB30.
Aluminum vs. Carbon crank arms
Aluminum crank arms have been the industry standard because of their inherent stiffness; before then, we were forced to run heavy, flexible steel cranks (amazingly, some elite big-box brands still spec steel crankarms …). Now carbon has taken over as the most popular high-performance material used to produce crank arms. Of course, there are exceptions; most notable is the new Dura-Ace 7900. Manufacturers aim to balancing performance, weight, and price. Here’s the breakdown:
- Less expensive to manufacture (Dura-Ace FC-7900 aside)
- Heavier (Dura-Ace FC-7900 aside)
- Construction and weave can be tweaked for performance gainsLightweight
- More flex than aluminum
- Expensive construction