Today, lets learn about the crankset: one of the more important component systems on your bicycle. Cranksets are made up of one or more gears, called chainrings, and the cranks or crankarms -- the arm-like parts that the pedals attach to.
Your crankset is attached to the bike frame via the bottom bracket, and connected by the chain to the rear cassette to provide the driving force that moves your bike forward.
Like most other bicycle components, there is a wide variety of cranksets on the market that cater to different riding styles and different needs. This article will go over some of the basic crankset choices that a rider has to make, whether they are upgrading or purchasing a whole new bike.
How many chainrings?
When considering a new crankset, the first question that most riders will need to answer is how many chainrings they would like. Fixed-gear, single-speed, or track cyclists generally have a very easy time here: all of these cycling styles use a single front gear. The rest of us will have a bit more thinking to do.
Experienced riders will be familiar with the concept of a base gear: the gearing that you ride on flat terrain at your normal speed. Some riders spend 80 percent of their riding time in their base gear. The base gear is bracketed by the high gear that you use when powering down a hill at top speed, and the low gear that you use on the steepest hills you ride.
When choosing a new crankset, choose the number of chainrings that will allow you to switch seamlessly between your most commonly used gears. If your high gear is relatively close to your base gear, a double chainring should suit you. If instead, your base gear is right in-between your high and low gears, a triple chainring will provide many more useful shifting options.
Mountain bikes mostly use triple chainrings, which allows for easier ascents up slopes that will soon become steep descents. On road bikes, the situation is a bit more complex. Probably about half of all road bikes use double chainrings, and about half use triples. And in the end, neither choice is necessarily superior.
In general, riders who tackle lots of hills and mountains or who carry heavy loads should go for triple chainrings. The wider array of gearing choices and the smaller changes between each gear make a triple more versatile for this type of riding, and it can save you considerable energy over the course of a long ride.
Determining crank length
The next step in choosing the right crankset is the length of the cranks, or crank arms. For adults, crank length varies between 165mm and 180mm, with the 170mm length being almost ubiquitous. While in general, most riders can’t go wrong with a standard, 170mm crank length, it can’t hurt to try a few different sizes and go with the size that simply feels best.
There are a variety of methods of attaching a crankset to the bottom bracket spindle of your bicycle, so it is important to make sure that your interfaces match up correctly. In all cases, the crankset slides onto the spindle and is tightened in place with a bolt or nut.
The most common types of bottom brackets have a square-shaped, tapering spindle. However, there are several varieties of the square-taper spindle, so it is always best to test before you buy, or get advice from an expert. Other bottom bracket spindle designs include hexagonal spindles and various "splined" designs with numerous interlocking teeth. The open-standard ISIS design is the most common of these, with Shimano’s Octalink a close second.
In general, splined designs deliver a bit more stiffness and efficiency for the rider and are therefore prized by racers. Whichever design you choose, make sure to match your crankset to your bottom bracket spindle. It just won't work otherwise!
Pricing and quality
The crank arm part of cranksets is generally made with aluminum or steel alloys, carbon fiber, or titanium, and are made for maximum strength and stiffness with minimum weight.
Chainrings are generally made of steel, aluminum or titanium. Some TT/Tri chainrings are even covered with a layer of carbon fiber. Cheaper, simpler chainrings are forged or welded together as a single piece, which saves money but does not allow replacing worn chainrings.
High-end cranksets use carbon fiber and titanium components, newer mounting designs, and interface with high-performance bottom brackets to save weight and increase the efficiency of power transfer from the pedals to the road. Prices for top-of-the-line cranksets can reach $1000.
Less expensive cranksets tend to use steel and aluminum. Look for reputable brand names, as even budget parts from these manufacturers will deliver solid performance and durability for years to come. A good, basic cranksets can cost around $100.
Luckily, maintaining a crankset is easy. Like every bike part, the crankset will benefit from being kept clean and dry. Lubrication of the working surfaces of the chainrings will help to extend their life and keep shifting smooth and quiet. Over time, the action of the chain across the surface of the chainrings will wear the metal surfaces, and your chainrings will have to replaced. This process is relatively straightforward and will be documented in a future tutorial.