Slotting right in there behind fire, the wheel ranks as one of the most important inventions in the entire history of mankind. So yeah, they’ve kind of been important over the years. So, it stands as no surprise that they serve at the heart of another one of mankind’s great inventions—the bicycle.
What makes a wheel a wheel?
Well, it may seem simple, but it’s an honest question, and one that many self-professed ‘experienced cyclists’ might even have trouble answering. The short answer is that wheels are made up of three key elements: the rim, the spoke and the hub. The long answer, however, is that there’s much more than meets the eye in a standard bicycle wheel. Comprised of many different parts, all working in concert, a bike wheel is not simply the sum of these parts, but also quite dependent on how these parts are brought together. Before you start to get intimidated though, let’s dive in for a closer look, shall we?
While it’s impossible to declare any given part the most important when it comes to wheels, the rim certainly has a big job to do. Tasked with keeping the wheel’s round shape, the rim, aided by a wheel’s spokes, provide the wheel with it’s overall structure. While the earliest rims were made of wood, today, most rims feauture either an aluminum or carbon construction (or in some cases, a combination of the two).
Drilled to accept a given number of spokes, the rim is mated to these spokes via female-threaded nipples (usually brass or aluminum) that insert into the outer rim, and partially protrude through the spoke holes in the inner rim to accept the male-threaded spoke ends.
The predominate rim type, clincher rims are designed for use with clincher tires, and utilize hooked rim walls to secure the tire.
Designed around tubular tires, the tubular rim does not feature extened rim walls and bead hooks, and instead has a concave profile in to which a tubular tyre is then glued with tubular cement.
A subtype of the clincher rim variety, the tubeless rim is designed to use specially designed tires without the need for an inner tube. This necessitates a fully sealed inner rim, but allows riders to run lower tire pressures without the risk of pinch flatting.
The great connecting force between the rim and the hub, spokes are responsible for handling the lion’s share of abuse in any wheel, and as such are a very important part of the wheel system. Essentially, spokes are simply drawn lengths of thick-guage aluminum or steel wire, held in tension between the rim and the hub, but how they are attached, and how much tension they are under is where the real magic is at work, and can seem like a complex science that many claim borders on black magic to the uninitiated. It’s really neither though.
Usually comprised of a hooked end that inserts into the hub end with a head to hold it in place, the other end of the spoke is threaded so that it may screw into the nipple at the rim. How far the spoke is threaded into the nipple determines the amount of tension placed on the spoke.
The last pieces of the puzzle responsible for getting the power from your drivetrain to the ground and keeping you moving forward, hubs are an integral part of the wheel. Comprised of an axle that rests between the dropouts within the bike frame, bearings are mated to the axle, and sit within the hubshell, allowing it to spin freely on the axle. On the outer ends of the hubs, are the so-called hub flanges, to which the spokes are connected, and are drilled with a number of holes that corresponds directly to the number of spoke holes on the rim.
On the rear hub, the so-called freehub body is situated next to the driveside hub flange and contains a freewheel mechanism that allows the freehub to remain stationary independent of the axle, allowing the bike to coast. The cassette then fits on the outside of the freehub body, linking the wheel with the rest of the drivetrain.
Now days, wheels are primarily purchased as pre-built wheelsets, designed as a system and mass manufactured. In the past, however, most wheels began their lives as individual components before being hand-assembled into finished wheels. While this allowed for great control over the desired qualities in any given wheel, it also made for a lot of work!
(We’ll discuss the benefits of custom wheelsets in our next lesson, Wheels 202 : Intro to Wheel Theory, but until then, intrepid students can check out this video from our ‘Ask a Mechanic’ series for a great synopsis.)
For now though, as we’re sticking to the basics, let’s take a look at the most important things to look for in a new off-the-shelf wheelset.
What To Look For In a Wheelset…
Like it or not, unless your net worth is better compared to the GDP of a small country, price will always be an important factor influencing your wheelset buying decision. As the saying goes, you get what you pay for, and with wheels, that saying holds true more often than not. But, that’s not to say that wheelset price isn’t also tied to the law of diminishing returns. Finding the sweet spot between keeping your bank statement in the positive and buying a wheelset that won’t hold you back can seem like a difficult proposition, but in reality its actually quite feasible—especially when you evaluate all of your options by the right criteria.
For starters, let’s begin by setting a baseline for what an ‘average’ wheel weighs. For context, most entry-level wheelsets tip the scales at roughly 2000 grams, or a touch under 4.5 pounds. This number is contrasted by top-of-the-line carbon tubular wheelsets that can often approach a figure of just half that.
Performance is one of those words that often gets thrown around too much by overzealous marketing managers. ‘Unamatched performance,’ ‘unparalleled performance’—you’ve seen the claims before, but what exactly does ‘performance’—of any sort—even constitute? For wheels, performance is judged by a factor of several characteristics, but namely: how well does it accelerate, how smoothly does it spin?, and how light it is on the scale? Ideally, you’d like all three of these characteristics to be at the respective tops of their classes, but, in order to achieve that in one single wheelset, expect to shell out some pretty serious coin.
While never even part of the equation for most of the bike wheel’s history, aerodynamics has emerged as one of the most important features by which a modern wheel is judged. “Free speed” as the performance gains afforded by an aerodynamic wheelset has been called, ironically are usually anything but, with aero wheelsets commanding a much higher premium than their shallow-section counterparts due to the primarily carbon construction used in order to keep weight down for deep profile rims that require a lot of material to achieve such a shape. As a rule of thumb, the deeper the rim’s cross section, the more aerodynamic it will be, although there are many other factors influencing the equation, with manufacturers always being quick to claim a superior aerodynamic design.