Hello to you, and welcome, Dear Reader! Anybody’ll tell you, wheels are wheels, right? And there isn’t really anything much to know, true? Well, I reckon you suspect there’s more to it than that; than a wheel being just a wheel. Well, we’re in the same boat. For me, it’s only recently since taking the plunge and building a bunch of my own wheels (for some vintage roadster re-builds) that I’ve really learned my way around the complexities of how wheels work. I’m hoping to pass on what I’ve learned in as simple a way as I can. So it turns out this is a large article. I’ve split it into two parts. The first part being a simple explanation of the parts of a bicycle wheel and how they work together – the essentials, I guess you could say. The second part I’ll treat like a FAQ, looking at some bicycle wheel topics in more detail but in a way I hope is still understandable for any new cyclist. While it’ll probably make more sense reading at your own pace through the whole article, nevertheless, I also wanted to give you the option to jump to a few of the key questions as below…
- What are the parts of a bicycle wheel?
- How are bicycle wheels built?
- What size of tire fits my bicycle wheel?
- What tire width do I need for my bike?
- What’s the difference between a clincher, a tubular and a UST tubeless tire?
- Is a freewheel or a cassette better?
- Disc brakes vs rim brakes?
- Hub widths and O.L.D. measurements?
Part 1: Bicycle Wheels, Essential Knowledge
Q: What are the parts of a bicycle wheel?
A: If we were doing a bicycle-wheels-simplified, we’d say that a bicycle wheel consists of three parts. The first is a rim around the outer edge, on which a tire is mounted. The diameter measurement of the rim determines how we label the wheel’s size (700c, 650B, 26inch, 29er for example). The second is a hub at the center. The hub rotates on bearings around a non-moving axle which itself gets bolted, screwed or clamped to the bicycle frame or forks. And the third is a means of joining the center hub to the outer rim. For most current bicycle wheels, that means of joining will usually be a set of spokes in varying numbers and type.
Diagram of a front bicycle wheel
A simple side-on view of the front wheel with the tire fitted and the quick release skewer in place, looks like this…
Diagram of a rear bicycle wheel
Once the inner tube is deflated (as it would be if punctured!) and removed, the tire can be removed as can the rim tape. Here, I’ve also removed the gear cassette which, as you can see usually comes with several gear sprockets attached together and one or two smaller sprockets loose. These are slotted onto the freehub body and secured with a screw-fitted lockring…
Q: Bicycle wheels aren’t complex, they’re simple, aren’t they?
A: Yes, I’d agree that bicycle wheels are one of the simple technical beauties of cycling. Good bicycle wheels, they just function. But then even a bicycle wheel can be gloriously complex, as I found out while writing this! But yet they don’t impose any requirement that we as new cyclists know a lot about how they work. So that’s how I’d like to proceed. I want to explain what the component parts of a bicycle wheel are and how they all fit together and work together. Why? Because when you know what the parts are, it’s easier to follow any maintenance-related information you might need to read later on. If that’s all good, then let’s spin them wheels!
Q: How do we get from wheel parts to a functioning bicycle wheel?
A: When building a wheel, from the rim, hub and spokes, the spokes, which have a shoulder at one end and helical screw threads at the other, are laced through the holes in the flanges of the hub body and pulled towards the rim. Threaded nipples are passed through the rim eyelets towards the centre, and are held in place inside the rim because each nipple has a head. The nipple is then threaded onto the spoke as shown below.
The spokes will have a certain lacing pattern. Sometimes they’ll go straight from the hub to the rim without crossing any other spoke, this is called straight lacing. Other times the spokes will cross variously in front of some spokes and behind others to give the distinctive spoking pattern, see the image below. Here on my rear wheel, the drive side (where the gears are) has a 2-cross lacing pattern. That means each spoke once it heads out of the hub flange, must cross two other spokes before it reaches the nipple. Whereas on the non-drive side, which doesn’t have to contend with such torque forces, the lacing is radial. This means the spokes do not cross any other spokes between when they leave the hub flange and when they enter the rim.
Often, the spokes on the gears side – usually the right, are shorter than those on the left. This gives a “dish” effect when viewed from the rear. The need to create some space on a hub to fit a gearing cassette has given rise to this, see below.
The front wheel pictured below is a wheel designed for use with a normal rim caliper brake. It has no need to create any lateral space on the hub for gearing (because it’s the front) or for a disc brake rotor. Therefore, it’s symmetrical. It has no dishing.
Disc brake rotors do demand space on the hubs, front and rear and give a similar but lesser dish effect on the left side as on the drive side. The most noticeable place to see the dish effect is, as shown above, on the drive side of the rear wheel.
So once the spokes are all laced, each nipple is tightened in turn until the rim is in perfect tension and alignment both radially (through the center) and laterally from side to side. At this point the wheel itself is built! Tahdah!
If you have your local bicycle shop, or someone knowledgeable you k now fix your punctures, take your wheel off for cleaning, change your tires or adjust your brakes maybe, then that’s really all you’ll need to know. If you’ve made it to here and you’ve understood, then well done!
That’s the bicycle wheels 101 course passed! Yay!
Part 2: FAQs for wheels…
If though, you have any lingering questions, or you’re simply interested in what else there is to know, read on and complete the Bicycle Wheels 201 course. Not really! Just more cycling questions (.com)
Q: Is our newly built bicycle wheel ready to fit on the bicycle?
A: Almost, but there are a few other steps we need to take first. There’s the rim tape for covering the nipple holes in the rim, how to know the right size and type of tire needed and understanding the difference between the gear cassette or sprocket. We also need to know what braking system we’re fitting the wheel to because different brake systems require different wheel builds. And finally, we should think about what way the wheel attaches, bolts or clamps to the frame (rear wheel) and fork (front wheel). So, taking these one at a time…
Q: Rim Tape? On a wheel? What’s that for sticking the tire on?
A: Actually, it can be! The rims used to build bicycle wheels that take standard inner tubes (see ‘clincher’ below) use a strip of stickable tape or fitted loop of non-sticky vinyl or rubber that covers the inner rim surface. The purpose of this rim tape is to protect the inner tube from any threaded ends of spokes that have been incorrectly sized and protrude through the nipples, from puncturing the inner tube.
Some rims however, are designed to take tubular tires (see section below) and use rim tape, or sometimes glue, as an adhesive to stick the tire to the rim.
Q: How do I know what size of tire fits on my wheel?
A: Rims come in a variety of diameters which determine the wheel height – which is why, a mountain bike wheel might be taller than a BMX wheel. Rims, and the wheels built with a certain rim will often take the label based on the rim diameter, for example what we’d refer to as a “26inch wheel” is made using a rim measuring approximately 26 inches in diameter. If you don’t already know the rim diameter, you can simply measure.
What you’re measuring is the distance from a point on the rim where the tire bead beds into the rim, straight through the centre of the hub axle, to a point on the rim diametrically opposite. What that measurement is, is the Bead Seat Diameter or BSD. For further information see What is the difference between a wire bead bicycle tire and a folding bicycle tire? This diameter, or approximate diameter, will correspond to one of the standard wheel sizes and will inform you of the tire size. Some of the information here is duplicated in my bicycle tire size and type article, but you may find some supplementary information in that article too if you’re interested in reading further.
I’ve listed the most common rim diameters and wheel-naming conventions in the ISO standard wheel diameter table below
|Wheel Name||Diameter in mm||Typical Bicycle Types Using this Sizing|
|27 inch||630 / 635||Vintage / Indian 3-speed roadsters|
|700c||622||Most modern road / pavement bicycle wheels|
|29er||622 (same as 700c just using fatter tires on wider rim)||29er Mountain Bike|
|26 x 1 3/8 inch||590||Vintage English 3-speed roadsters / older dept store road bikes|
|650B||584||Either older style road bicycles, or some newer road bicycles which take 700c wheels use these smaller diameter wheels because they allow the use of fatter tires|
|27.5 inch||584 (same diameter as 650B)||Medium sized MTB wheels, a standard halfway between 26 inch and 29er|
|26 inch||559||Standard MTB size|
|20 inch||406||Standard BMX size, also found on folding bicycles and shopper-style bicycles|
Q: What’s the difference between a clincher, a tubular and a UST tubeless tire? And how do I know which I need?
A: Some rims are specifically made for some tires. What you might know as a standard rim – one which takes an inner tube inside the tire – is called a clincher. It’s so called because the bead around the inner edge of the tire is clinched against a lip on the rim. This gives us the term “crotchet rim” because cut through in cross-section, the rim with the lip makes a musical crotchet shape on both sides. Note as well that rim widths often have the “C” suffixed after the width in millimeters. For example a rim or tire might be labelled “622 x 23C” where the “C” is telling us that this rim is a crotchet type rim or is the tire that fits to it – it’s a clincher tire. So once the tire is fitted and the inner tube is inflated, the pressure within the inner tube pushing outwards against the tire and rim, holds the tire in place on the rim.
… Just kidding 🙂
As mentioned, standard rims generally require rim tape to prevent the inner tube from puncturing on either the spoke holes on the inside of the rim or on any spoke threads poking through the head of the nipple inside of the rim. But some rims do not have spoke holes which penetrate the whole way through to the inside of the rim. These can be of two varieties:
- Firstly, rims designed for tubular tires. Tubular tires are exactly as they sound. They do not require inner tubes because they themselves are tubular with the inner-tube sewn to the inside of the tire carcass. These are then simply stuck onto the rim. A tubular rim has quite a shallow concave profile onto which rim tape or glue are applied to ensure the tubular tire adheres.
- Secondly, rims designed for Universal Standard Tubeless tyres, or UST for short. These rims, like rims for tubular tires are also airtight but have a deeper concave cross section because the tire is pushed outwards laterally when inflated and does not require any adhesive.
Q: What tire width do I need?
A: Well as with many things here, that really depends on your riding style and would be beyond this article about bicycle wheels. Except, that is, to mention that certain rim widths take certain tire sizes. For example, trying to fit a tire that’s narrow onto a wider rim means the tire will have a misshapen profile (too flat) when it’s fitted, or the bead might be dangerously loose, or not seat properly at all. Fitting a tire that’s too wide for a narrow rim can cause the tire to deform dangerously, particularly on corners. It will likewise also result in a misshapen (too tall) profile meaning the rubber won’t contact the ground the way it was designed resulting in lacking traction.
A clincher rim can be converted into a UST or tubeless rim by adding special sealing tape across the spoke holes and around both inner sides of the rim where the tire will make contact. This will seal the air in the tire.
Q: Is a freewheel or a cassette better? And will my wheel take either one?
A: Regardless of whether our gearing system is fixed (no gear changing and the pedals rotate when the wheel rotates ie no ‘freewheeling) or single speed (again no gear changing but ‘freewheeling’ down hill for example is possible) or internally geared (multiple gears hidden within the hub, the bicycle does not necessarily need gear derailleurs) or multiple geared, derailleur shifting, we will need on the rear hub one or more sprocket (toothed cog) to connect the wheel to the pedals/crankset/toothed chainring via the chain. If you’re interested, Park Tool has a good illustrated article entitled “Determining Cassette / Freewheel Type” which outlines how to tell the difference. But in essence…
Modern rear bicycle hubs made for multiple gear applications, tend to have a freehub body. This is a splined body that rotates freely one way around a pawl ratcheted hub. This hub itself has a male thread. That male thread is mated to a female thread on our wheel hub body. Once installed – it often comes installed with the hub when purchased new – a cassette, or cluster of joined gear cogs, is simply slotted over the freehub splines and locked on with a threaded lock-ring.
Below you can see the splines on the freehub body match those on all the sprockets of the cassette. This allows the cassette to rotate the wheel.
Modern bicycle hubs made for single speed applications can have a helical threaded end to take a single freewheel which consists of one cog that rotates freely one way round a pawl-ratcheted hub. This will have a matching screw thread and the whole unit is screwed onto the hub.
It’s generally only older bicycles that take a freewheel cassette. A freewheel cassette is a cluster of cogs (similar in appearance to a cassette) but with a free-spin mechanism built in. This is screwed directly onto the hub via the hubs helical threaded end if the hub is constructed that way.
So that’s how the wheel interacts with the drive system on the bicycle. At this point, we also need to know now what kind of braking system is on the bicycle we’ll be installing our wheels on, whether it uses, for example, rim brakes or disc brakes.
Q: I heard disc brakes were better than rim brakes. Is that true? And can I fit those?
A: Purely in my own experience of both, in most situations where the brakes are of a comparable quality/price bracket, disc brakes do outperform rim brakes. In some situations particularly the wet, that was always particularly apparent to me. In order to match the disc stopping power of low-end Avid BB5 disc brakes on my old flatbar road bike with the equivalent rim brakes on my dropbar road bike, I had to upgrade first the brake pads twice on the stock calipers and then to Shimano BR-R7000 rim calipers, and I’m still thinking of changing out the stock Shimano pads for Swiss Stop BXPs. Again, that’s purely a subjective experience with rim brakes from running out of road at the end of a descent, being unable to slow properly braking single-handed while hand signalling at a junction, and being caught by surprise by a sharp bend on a descent and not having that extra 20% that the discs seemed to previously offer over the rim brakes.
Discs have been almost unilaterally adopted on offroad or MTBs lately and many road bike brands are quickly following suit. However, that being said, rim brakes rarely have let me down, the few examples above could’ve been cut out with a bit better planning, better parts, or greater caution on my part. I think it’s the pace of changing cycling fashions that can sometimes upset us. And so to the second part of this question, can I fit disc brakes to my bike? In all likelihood, if your bike doesn’t have disc brakes then not without a lot of work. Frame and forks both require disc caliper mounting tabs. You can of course replace both your frame and forks for disc-specific variants. After that, your hubs must be capable of taking disc rotors. You can still run non-disc rims if it’s any consolation.
I think this is often the knub of disc vs rim brake arguments
… It’s that most people know discs are kinda better. But there can be an expense in changing, and nobody likes feeling as if they’re being left behind or any kit they own becoming obsolete. Obsolescence being unavoidable of course, being a keystone of our commercial system #fiscalcommentary lol 😀 Personally I don’t much like feeling as if I’m under the dictates of cycling fashion and technology. But then again, on balance, that’s probably not a wholly negative thing. I mean can you really have something that works too well? Specially brakes which are a definite safety concern? I doubt it.
Bicycle Braking Systems: Technically speaking then…
The braking system on bicycles operate generally by slowing the spin of the wheels.
Some bicycles use rim brakes. Here, pulling a brake lever on the handlebars causes a brake caliper to squeeze brake pads against the rim causing friction and slowing the rotation of the wheel and thereby slowing the bicycle. Rims made for a rim brake system have a braking surface on either side that the brake pads can grab onto.
These braking surfaces are machined flat. Braking surfaces should be well maintained and kept clean to facilitate good braking. Wet rims can often be compensated for by reasonably good brake pads, however, dirty braking surfaces or those contaminated by lubricants can severely diminish braking effectiveness and can naturally cause a hazard when cycling, so keep ‘em clean!
Some bicycles do not use a rim braking system but use a disc braking system. Here, brake pads will squeeze against a rotor attached to the hub. Bicycles that do not use a rim braking system will have wheels built using rims that do not have a braking surface on the sides because the braking happens at the hub. Disc rotors, in my experience are far more sensitive to contamination from say, chain lubricants, so spray or apply carefully, and/or clean the disc rotors with a specific disc rotor cleaner, or simply with isopropyl alcohol and a dry, very clean cloth.
Oh if your disc pads do become contaminated, first of all, you’ll notice a catastrophic drop in brake power, I mean, they’ll just not work at all. If that’s the case, pop them out, there’s a little retainer spring between the two pads the pulls out then the pads themselves should wiggle out by their two little handles. Then bake in the oven! Disc brake pads are meant to dissipate heat by their nature. Baking for like 10 minutes, medium heat, won’t damage them, but will burn off any oil or contaminants.
Just for your information, you might find other brake systems on either vintage bicycles, or on super mass-market bicycles often found in regions of India and China which have rod brakes, which are a wonderfully Heath Robinson, but yet fantastically functional, utilitarian kind of mechanical non-cable rod system.
Then there are drum brakes which act similarly to older automotive drum brakes pressing pads against the inside of a drum hub. These are also found on both vintage bicycles and, owing to their weather-sealed properties, often on urban commuter-type, or municipal sponsored bicycles.
Lastly there’s the coaster or back pedal brake which doesn’t rely on a lever at the handlebar, but rather operates a similar kind of pad pressing against the inside of a drum on the hub, but does so via pressing backwards on the pedal. These brake systems require to be anchored to the frame and are most often found on cruiser bicycles, though again, they were a staple of our old school BMXs waaaaaaaay back through the mists of time…
So that only leaves how we attach the wheels to the frame (rear wheel) and forks (front wheel).
Q: How do I attach a bicycle wheel to the bicycle? I just screw it on don’t I?
A: Yes, it’s almost as simple as that. But, as you can probably guess by now, there are differing ways that different hubs attach to the bicycle they’re meant for. The hub axle runs through the centre of the hub from one side to the other and protrudes at each side. It is the axle which is attached to the bicycle frame (rear wheel) or forks (front wheel). Some axles are solid and attached to the frame and forks with hex nuts which have to be installed and removed with a spanner or wrench, or in some older bicycles by wingnuts which can be hand tightened.
Other axles are hollow all the way through, like a thin tube. Through the hollow axle, a thin skewer with helical screw threading on one or both sides can pass. This can then be clamped to the frame and forks via a cam-operated lever, called a quick-release or QR skewer, or with thumb nuts, usually hex-key tightened, which are sometimes installed to prevent wheel theft. Solid or QR axles tend to be 9mm to 10mm in outside thickness.
Some hub axles have to be completely removable from the hub in order to get the wheel off the bicycle. These axles screw directly onto the frame or forks. These are called through-axles or sometimes thru axles. They are generally of a thicker diameter, 12mm, 15mm or 20mm+ depending on how heavily the bicycle will be ridden – downhill mountain bikes or dirt-jump bicycles, for example. Again these are becoming more common on road bikes due to their ability to add an extra dimension of mechanical rigidity and strength through the fork and frame as well as addressing the “lawyer-tab” concerns, of a powerful disc brake overcoming the clamping force of the hub against the frame/fork and popping the wheel out altogether. Whether those concerns are real or theorized, the through-axle eliminates the concern.
One other thing to mention is that the width of the hub and the frame spacing / fork spacing must match. What does that mean? The hub spacing is the distance between the exposed part of the axle on the left and the exposed part on the right (called the Over Locknut Dimension or O.L.D). The frame or fork spacing is the distance between the wheel tabs or dropouts where the wheel will mount the frame – that’s for the the rear wheel – similarly, the O.L.D. must match the fork spacing, or the distance between the front fork wheel mounting tabs, and that’s for the front wheel.
- Front hub O.L.D. / Fork spacing: some older vintage bikes used a 90mm spacing. Most QR skewer front hubs tend to be 100mm spacing. As standards evolve, Boost-type hubs with through-axles are going from 110mm up to 120mm and, beyond that, fatbikes – though who knows if that trend will continue? are going all the way to 150mm to stabilise the huge wheel and tyre sizes.
- Rear hub O.L.D. / Frame spacing: again, the older vintage bicycles I’ve worked on started around 110mm before needing widening (see Little fyi below). Most current road bikes use 130mm spacing while most (I think I’m still right in saying most) mountain bikes use a 135mm spacing. This seems to be changing too with the use of through-axles with the Boost-type hubs going to 142mm. Again the fatbike hubs with their greater need for accommodating frame width run up to 197mm for Hope and other manufacturers.
Steel frames and forks can be what’s called “cold set”. This means mechanically widening a frame or fork to accept hubs wider than those for which is was designed. I have performed this operation on many vintage steel frames in order that they can accept more modern hubs. I’ve widened by up to 20mm without issue. The wheel tabs / dropouts need to then be realigned so they’re parallel again. This is done with realignment tools. Again, steel! Aluminium or other materials can crack with that kind of manipulation.
And so we’ve arrived at the end! If there were a Knowing Bicycle Wheel Terminology 201, you’ve just passed that too! Thank you for reading! I fear that any more and it would turn into some kind of a book! Speaking of which, if you’re interested in an authoratative technical, but nonethess wonderful wheel-building site and book, I would highly recommend Roger Musson’s “Professional Guide to Wheel Building” from the website Wheelpro.co.uk
Q: What other variants exist beyond this introductory explanation?
A: Believe it or not, yes, that was just the introduction to bicycle wheel information. I’d worry about overloading you with information, so all I’d like to finish with is to mention in passing some of the other variants. We’ve more or less discussed the standard bicycle wheels. Wheels however, can be what’s known as composite wheels.
Composite wheels are built as one part, perhaps with three or four “spokes” usually from a carbon or glass-fiber compound, though the hub and rim generally work exactly the same. In the early days of composite wheels, these were sometimes catastrophically dangerous. Prior to that in the 1970s and 80s, we used to call these “mag wheels” back in the oldschool BMX days, the most noteable of which being Skyway Wheels (www.skywaywheels.com).
Some wheels are what’s known as disc wheels – wheels that are a solid, lightweight disc as opposed to disc-brake compatible wheels. These are usually constructed from a lightweight carbon or polymer compound. Both of these types are designed for better aerodynamics than traditional spoking.
Further, rims and their corresponding hubs can have varying numbers of holes, the common numbers at the minute 20/24/28 on road wheels and 28/32 on off-road wheels. Variants do exist either side of those hole counts of course depending on application ie. what the rim’s riding purpose is.
Some rims themselves are similarly built for aerodynamics, called deep-section because of the depth of the rim when viewed side on.
Spokes themselves can be straight gauge / plain gauge which are the same thickness across their entire length. They can be butted where they’re imperceptibly thinner in the centre and thicker at the edges for strength and weight saving. They can also be constructed of carbon compounds and can be bladed rather than rounded, again for aerodynamic concerns.
Hubs themselves can also be constructed from carbon composites, they can be asymmetric to negate or mitigate against the dishing we mentioned above.
And you know what, I’m going to stop right there. This has gotta be my sudden, unannounced, “And they all lived happily ever after. With their wheels spinning,” juncture. Because I’ve written more than I set out to, and risk losing you altogether Dear Reader! But thank you again for checking out this bicycle wheels article. I’d appreciate your comments regarding anything helpful here, how it could be more helpful to others like yourself, or what else you think might do with being added.
Meantime, have fun, ride safe, keep them wheels spinning, David.