Basically everything about road (and gravel!) wheels

Bicycle wheels mainly consist of rims, hubs and spokes with their nipples. You will also need tyres, axles or quick releases, tubeless valves or tubes, a cassette, and possibly rim tape and sealant to fit the wheels to your bike.

I. RIMS

Our efforts on a bicycle go into overcoming three basic forces: rolling resistance (tyres), resistance of air (aerodynamics) and gravity (weight). All three should be considered when choosing a rim.

1. Rolling resistance

tl/dr: Tubeless is the way to go. The rim is better without holes in the rim bed (tubeless without the suffix -ready, aka UST). Hookless rims are helpless on road bikes. Preferred inner (not to be confused with outer) rim width is from 19 up to 25 mm.

Rolling resistance does not depend on the rim parameters at all. But it depends very much on the tyre (which is put on the rim in one way or another). And when choosing a tyre, you must take into account its certain characteristics, which depend on the rim. So we will consider everything at once.

Rolling resistance is easy to measure and depends linearly on speed and load. This makes it possible to compare the results of different tests. I’m basing this on extended data from bicyclerollingresistance.com (available with a paid subscription), as well as consistent research from AeroCoach, In The Know Cycling and other resources.

The rolling resistance of a tyre is directly related to its puncture resistance. The fastest tyres are the weakest and most prone to punctures. In my opinion, it doesn’t really matter how many watts/seconds you’ve saved with the help of fast tyres if you get a puncture and hence lose minutes (as well as your group or at least the patience of its members).

At the same time, the most puncture-resistant tyres — compared to the fastest ones — create up to 50 watts of extra rolling resistance at the speed of 30 km/h (that is at extremities, but 20–30 watts is a real figure). That’s a lot. So it would be good to find a solution where we get as few punctures as possible, but also without overkilling the safety margin (which would reduce speed without real benefits).

A) Tyre fitment

The best method today is to fit tyres tubeless with sealant.

Let’s take a fast tubeless-ready or true tubeless tyre (the latter is different in that it can be fitted without sealant; the true tubeless is often referred to as UST, although that is just one particular implementation of true tubeless — the first one ever, hence the name’s become generic). The tyre itself is not very puncture resistant, but the sealant will fix that. There are three important points here.

Firstly, most sealants don’t work well at road pressures. By many accounts, and my experience as a cycling club leader & camp organiser, one of the best sealants is Orange Seal (Regular, Endurance, Sub-Zero — all work well). Often recommended also are Stan’s Race (specifically Race, not regular) and Silca.

In my experience Stance works not as good as Orange Seal. I have not used Silca — but they say it is so strong that it clogs valves, which is critical for everyday use. Also to consider: how easy a sealant is to clean off, whether it smells funny and if it is compatible with CO₂ cartridges. Again, Orange Seal ticks all the boxes. I always recommend it, and people how follow my advice have always been happy.

Secondly, the sealant works the better the thicker the tyre. For example, the fastest* Vittoria Corsa Speed G+ 2.0 (TLR) is only 1.8 mm thick, while the second** fastest Continental Grand Prix 5000 TL is already 2.8 mm thick. It will seal much better.

* — the ranks have changed since this article was first published. The new king is Veloflex Record TLR. Being 1.1 mm thick, extremely weak to punctures, and far from hard-wearing — this is not the most practical choice, but pretty much the ultimate one for pure speed.

** — I left out the Schwalbe Pro One TT TLE Addix because it doesn’t have much grip — a factor not covered in this article, but no less important. Added later: I keep this outdated comment just to leave a reminder that rolling resistance is not everything, and grip should also be taken into account when choosing tyres.

Thirdly, the sealant manufacturers say it needs to be changed periodically. The official recommendation for Orange Seal Regular, for example, is every 30–45 days, which sounds sad when you imagine “changing” the sealant.

But in reality, it is sufficient to just check the sealant level from time to time (similar to checking oil in a car engine — unscrew the valve core, insert something long and thin, like a ballpen stem, take a look). If it doesn’t come out marked with sealant to a good level, pour some more through the valve. Throughout the lifespan of a tyre, some 20–30 grams of dry sealant will accumulate in it, which is nothing to worry about.

If you are like me and hate the idea of being too disciplined with your bike maintenance — just accept the probability that you will ride out with the sealant completely dry one day and have a puncture. For such an instance, I carry a tiny bottle of fresh sealant in my saddle bag that goes back and forth between my bikes, but a spare tube is fine, too.

The minimal amount of sealant is 20–30 g per 25 mm tyre. I advise to use generously more, as that way the sealant will cover sidewalls better, and if a puncture is not sealed immediately, you will have at least something left after the sealant is partially sprayed out. Extra 30 grams of sealant add about a watt of resistance per wheel (2 watts for both), which is insignificant, as well as the weight, really.

A separate advantage of tubeless tyres is the ability to reduce pressure. As a general rule of thumb, the lower the pressure, the less likely the tyre is to be punctured by an external sharp object, but the higher the likelihood of a “snakebite” — a double puncture of the tube against the rim when hitting a blunt object. Tubeless tyres are way less susceptible to the latter than tubes. This allows you to ride on reduced pressure, which is especially important on bad asphalt or gravel.

Considering how easy maintaining a tubeless setup in fact is, I see only two scenarios where tubes are still relevant: either if you rarely ride a particular bike and sealant is drying out between your rides (which takes weeks of keeping a bike still), or as a spare.

Either way, I keep the below tube ranking only as a legacy feature — these days a light and strong TPU tube costs some 5 bucks/euros/quid apiece (google — or rather baidu — RideNow or Cyclami), so there is hardly any reason to choose anything else. That being said, here is the outdated tube chart:

• resistance of a latex tube (weights 50–80 g) is comparable to that of sealant (a couple of watts per pair of wheels); it has average (for tubes) puncture resistance; but it leaks air so quickly that you have to pump up before every ride;

• lightweight (25 g) thermoplastic (TPU) tube is comparable to latex in its properties and does not leak air, but is not officially suitable for rim brakes (may fail due to overheating); regular (40 g) TPU tube has slightly higher rolling resistance (~4 watts for both wheels), but also higher puncture resistance; it can be used with rim brakes; it is probably the best tube option; the most popular brand is Tubolito (but they now seem way too expensive in comparison with quality Chinese TPUs — same also goes for Schwalbe, Pirelli, Vittoria and other western brands that cannot compete cost-wise);

• lightweight (40–60 g) butyl (i.e. “standard” material) tube is comparable to a regular thermoplastic tube, except it is much easier to puncture. It used to at least be way cheaper — but not anymore. A standard butyl tube weighs 110–150 g (or even more for gravel width) and gives up to 8 w of resistance, which is too much.

B) Hookless/tubeless

There are the following types of rims:
1) tubular,
2) tube-only (non-tubeless),
3) tubeless hooked (crotchet),
4) hookless.

1) Tubular rims: this type of rim is mainly used by athletes in competitions, but even there its popularity is declining. Tubular rubber are something like tyre-thick tubes that are glued onto the rims. The rims themselves have a simplistic shape and only hold the rubber on with the glue.

2) Tube-only (non-tubeless) rims: this type of rim is also a thing of the past and is rarely used. In principle, they are distinguished by the absence of shelves and beadlocks, i.e. the tyre is held in place only by hooks.

In practice, not all rims that look like tubeless rims, i.e. have a shelf and a beadlock on it, are declared as such by manufacturers. The reason may be that tubeless rims are subject to more stringent requirements in terms of accurate adherence to all dimensions, rim wall strength, etc. There have been cases where rims were clearly designed as tubeless rims, but then claimed to be suitable for cameras only — apparently due to failing some testing.

3) Hooked (crotchet) rims — tubeless-ready or tubeless (UST): the difference between the two is that the latter have no holes on the inside of the rim (in the rim bed, inside the tyre) to access the spoke nipples. This makes it harder to assemble the wheel initially, but eliminates the need to replace the rim tape — there is none. Without the rim tape, there’s no risk of it leaking or getting pierced when you stick a plug with a sharp fork into a puncture to fix it.

4) The hookless variety of same tubless-ready or true tubeless. I would not recommend the latter for road bike use for a number or reasons. They offer virtually no advantages (except that it is easier to make a lightweight rim, although a hooked rim can be just as good if the manufacturer tries a little harder), but they have significant disadvantages:

• exclusively tubeless — if you get a puncture that the sealant doesn’t seal, it is not completely safe to insert a tube and ride on;

• limited choice of tyres and there are difficulties with compatibility of specific rubber models with specific rims;

• you can’t pump high pressure; if you exceed the fairly low maximum values (~70 psi/5 bar) even slightly, the tyre may come off the rim, whether at rest or on the move;

• even if you stick to the pressure limitations (for which you need to be quite lean if you want to ride 28-ish mm tyres) and tyre/rim compatibility guidelines, put out air in hot weather or high in the mountains, etc. — there is still a risk that a tyre could come off the rim while moving.

The reason for that is that the hookless technology does not have a good margin of safety in case of a manufacturing defect in either a rim or a tyre, or even just bad compatibility between them where it clearly says “compatible” and nothing is defective in any way. It happens all the time, and personally I would not want to be injured or dead because of just another case.

First they say that hookless will allow for decreasing the prices, but then wheel manufacturers such as Zipp or Enve make even their most expensive models hookless, which looks pretty much like a shameless cash grab to the detriment of their customers, if you ask me.

Yes, hookless has been working perfectly well for many years on cars — and even on mtb — but then the industry decided it was a good idea to bring it to the road cycling: which it’s not, considering the higher pressures and thinner rubber, meaning less tolerances (in the industry where they could not make press-fit bottom brackets fit tightly into freaking round holes so that they wouldn’t creak — and moved back to the threaded because of that — but anyway, one pet peeve at a time :)

Btw, remember the easy way to maintain the tubeless setup that I described above? Well, hookless doesn’t necessarily let you do that — as when you unscrew the valve core, the tyre not just looses pressure, but oftentimes also jumps off the rim beadlocks — and now you have to reseat it with a compressor or a booster instead of just inflating with a regular pump.

Also, that happens if you have a non-sealed puncture and the tyre bottoms out — in which case you could repair it with a plug, but now it is unseated and a spare tube is the only option (not completely safe on hookless, I remind). What a lovely technology: not just safer but also more convenient in so many ways!

Okay, let me make this less of a rant. I should note that rims have different internal shapes, which includes the bead walls of various tallness; hooks, if any, of differing dimensions; narrower or wider (and shallower or deeper cut) beds and, interdependently, shelves of differing widths; beadlocks, if any, in the range of 0.3–0.5 mm, etc.

Depending on all that, the rim can be easier or harder to put a tyre on (which also depends on the tyre itself), and hold it better or worse in place when deflated or burping. I had a personal experience with a rim-tyre combo where the unseated (!) tyre could not be removed from the rim bed by first several experienced cyclists and then professional mechanics in a repair shop — for hours.

That’s where the traditional hooked rim profile adds a margin for error by locking the tyre bead from two opposite directions — holding it in place with the beadlocks on the shelves, as well as with the hooks on the beadwalls. With this construction the tyre-rim coupling is inherently more secure than with hookless — and the risk of disaster is way lower in case of not exactly matching dimensions (outside of the slim tolerances, or within them as happened just recently with Extralight/Continental scandal) or defective tyre beads (whether for a particular sample/batch, or by design of a whole model, as with the recent Pirelli P Zero Race recall).

It’s not just my opinion that the bicycle industry has to either first make sure that the manufacturing processes are up to the standard to meet the (now too tiny for them) tolerances and (yet non-existent) strict standards — or just finally admit that the hookless technology is not suitable for road bikes, provides no real benefits, and puts lives to unnecessary risk (even if it is really more sustainable at manufacturing, and not just more profit-generating).

C) Internal rim width

In the early days of road cycling, 19 mm was the standard tyre width. Then it was 21, 23. Today*** it’s 25 mm — but amateurs, and in some cases professionals, use 28 mm and even 30+ mm: for more comfort and/or better performance on specific surfaces (such as the paving stones at the famous Paris-Roubaix race).

*** — believe it or not, but the racing scene has moved on since the original publication date — in just a couple of years — from 25 to 28–32 mm even for regular asphalt.

There are ETRTO standards for the compatibility of tyres and rims of different widths. As of 2022, they are hopelessly out of date. At the time of their approval, 28–30 mm was not even considered a road width — the bureaucrats had in mind more like city or touring bikes, which experience very different force vectors, etc.

Rim and tyre manufacturers have changed materials, construction, geometry — everything. The standards allow a 32 mm road tyre to be fitted to a rim with an inner width of 15 mm (this section doesn’t touch on the outer width at all, so hereinafter just “width”) — which by today’s standards is not even safe.

Having analysed various manufacturers’ recommendations, studies, tests, I would recommend the following combinations (but always check with your tyre manufacturer’s recommendations):
• 23 mm tyres on a 17–19 mm rim;
• 25 mm tyres on a 19–21 mm rim;
• 28 mm tyres on a 21–23 mm rim****;
• with disc brakes — 30+ mm tyres on a 23–25 mm rim.

**** — such a combination may not fit into rim brakes (especially the standard pivot, not direct-mount, ones) or may fit with minimal clearances, which will cause problems: tyre rubbing against brake calipers when there are minor buckles on the wheel, clogging of the brakes by the dirt, etc.

I do not go beyond that, as 25 mm is as wide as it gets in 2023 for road and gravel rims. That said, I can predict now already that this part will be outdated sooner rather than later, as tyres, and consequently rims, keep getting wider — and for good reason.

Thing is, apart from the rolling resistance measured in laboratory, there are other factors that affect not just comfort, but actually performance. There are studies that clearly show that narrower tyres cause the cyclist’s muscles to do extra work to absorb even the slightest hits and bumps, and road buzz, which immediately increases heart rate — and fatigue over the distance. In the real world, wide tyres are faster than narrow ones.

It should be noted that the nominal tyre size will almost always be smaller than the actual tyre width, which increases as the rim width increases. Even on the relatively small 17.8 mm rim width historically used for testing on brr-dot-com, the vast majority of tyres sit wider than the nominal size (and no tube-only tyre ever sits wider than nominal).

Street tyres are designed with a thicker (and to some extent puncture-protected) centre section and thinner, unprotected sidewalls. The width of the protected part can vary. For example, in the already mentioned Vittoria Speed G+ 2.0, the protected tread accounts for only 35.7 % of the tyre’s total circumference. The rest is the sidewalls, which are only 0.85 mm thick.

This means that if you stretch this 25 mm wide tyre onto a 21 mm wide rim (which is actually the optimal combination), the sidewalls will be in constant contact with the asphalt, significantly increasing the already high probability of punctures on this rubber. The abovementioned Conti GP 5000 TL already has 40.9 per cent, and there is no such problem.

2. Aerodynamics

The aerodynamics of a rim is considered by many to be its most important characteristic. (Obviously, much more important still is the ability to function without falling apart and provide effective braking — more on this below.) This is because the effect of aerodynamics increases progressively with speed, and the top of the wheel is always travelling as much as twice as fast as the bike itself relative to the air mass.

That said, aerodynamics is complicated. Real aerodynamic forces are difficult to model and measure because they are non-linearly velocity-dependent, while constantly changing angles and intensity on different parts of the bicycle: due to wind variability and the influence of other objects. In the context of wheels, those are the moving legs of the cyclist, and — since we are on a motorway — passing cars, other cyclists in a group and so on.

Most aerodynamic studies raise questions about their practical applicability to the riding of an average cyclist in a particular terrain. The findings are not scalable and have little or no comparability with other studies. This is exacerbated by the fact that most tests are conducted or sponsored by manufacturers who can tweak the methodology to make their products appear in the best light.

The seemingly most comprehensive and representative independent (hopefully) study is published by the notorious truth-telling engineer Hambini. It tested a sample of as many as 50 wheel models of different levels and relevance — from popular and relatively inexpensive carbon from Chinese factories to top wheels from Enve, Zipp and Hed. The seemingly appropriate methodology is described, even if subject to some controversy in the past.

Interestingly, the study states that a cyclist is unlikely to feel a difference of 10 watts of resistance between different wheels, but already 15 watts can be felt. That said, at 30 kilometres per hour, the fastest wheel in the study had a 19-watt advantage over the slowest. Wheels were studied in a wide range from shallow 30-millimetre models of 2013 to modern deep 90-millimetre wheels.

That is, at normal amateur speeds, the perceived difference between different wheels is just a placebo, and in reality it is less than between tyres of neighbouring classes, let alone those at the ends of the spectrum... The same study also has data at 50 km/h, where the gap in wheel resistance reaches 74 watts. (Well, now in 2023 I can find a pair of tyres at brr-dot-com that would produce an 80-watt difference at said speed.) The bulk of the other existing research is done at similarly high speeds — and the conclusions are more dramatic. However, such a high-speed scenario is not that relevant for regular cyclists.

As a lyrical aside, the aerodynamics of the frame are even less important. What really matters: the position of the rider on the bike, dictated by the flexibility of the former and the geometry of the latter (the lower and narrower the handlebars, the better the aerodynamics), the cut, fit and materials of the clothing (jersey and bibs — aka cycling shirt and cycling shorts). And yes, a much greater aerodynamic effect in relation to cost — compared to wheels and frame — can be obtained from the right helmet and shoes/socks.

Here are the results of a study with different hand positions on the handlebars, for an experienced cyclist with a well-tuned fit. At 30 km/h, switching from hoods (duals) to bottoms (drops) reduces drag by 5–10 watts; a position with arms bent at 90° from the hoods gives a 10–15 watts advantage. Installing aerobars saves 15–20 watts when used, but adds 5 watts of resistance in the normal position (obviously due to the vortices around the recliner itself). There is more to be gained by tweaking the position than by purchasing even the best wheels.

Anyway, there are three main characteristics of a rim that significantly affect its aerodynamics.

A) Rim depth

A deeper wheel is likely to be more aerodynamic — even if it loses to a shallower wheel in the other two characteristics. Very deep wheels have three and a half disadvantages: weight (we’ll talk about this separately), cost, and riding in cross winds.

The last factor is influenced by the greater sail of wheels with a deeper profile. Sharp gusts of cross wind can turn the front wheel, which makes riding on such wheels — depending on the cyclist’s skills, speed, wind strength — from somewhat nervous to quite dangerous. In any case, owners of deep wheels shouldn’t take their hands off the handlebars at speed.

The rear wheel is much less sensitive to side wind (because it doesn’t turn). But there is little point in making it deeper, as it has much less effect on aerodynamics than the front wheel. Nevertheless, there are some wheelsets with a shallower depth of the front wheel relative to the back one, where the former gives slightly less nervous behaviour in windy weather, and the latter — a small increase in aerodynamics.

The optimum rim depth range for a group road bike is considered to be 40–60 mm. Less deep wheels make sense for riding up fairly steep uphills (7–10 % or more). Deeper ones are aimed at triathletes and time trialists.

Gravel bikes can also have deep-section wheels — but for a slightly different reason than road bikes. As I’ve described below, the deep wheels only work aerodynamically if they are wide enough in comparison to the tyre. However, the gravel tyres are so wide, you just can’t do that.

So, the deep gravel wheels serve two purposes: they bring the spoke nipples closer to the hub, which both makes the wheel stronger and stiffer by changing the spoke-rim interface angle, and a bit more aerodynamic still, due to the reduced radial ratio of spokes to rim, where the former are less aero-efficient than the latter.

The aforementioned remaining half of the disadvantage of deep wheels is related to their appearance. Some people think very deep wheels are good-looking, but their appearance on a group ride bike — as opposed to a triathlon/tt bike — is non-canonical and contradicts many people’s idea of good taste.

B) Rim cross-section

The rim is best if it is toroidal in shape; in cross-section it would resemble an oval — O — with the very top/bottom cut off. That is, getting wider from where the tyre sits to the mid-point and then gently rounding at the point where the spokes are attached. Pointed (V-shaped and egg-shaped) rims and those with the widest part at the tyre border (including rounded, U-shaped) are obsolete from the point of view of aerodynamics.

(a) Modern aerodynamically shaped rims (right — hookless)

(b) A less modern rim with a less aerodynamic pointed egg-shape (with similar dimensions, but find the difference in notion)

(c) Not at all aerodynamic rim (because of the V-shape, even if it were deep)

(d) Asymmetrical rim

The left and right spokes are positioned asymmetrically (except for a front rim-brake wheel). As there is a cassette to the right of the rear hub, there is not enough room to move the right hub flange as far from the wheel centreline as the left one. Same goes for the brake rotor in the front, only now the space is squeezed on the left. As a result — in the case of a fairly shallow rim — the right-hand rear spokes (or the left-hand front) enter the rim at a sub-optimal angle. Asymmetrical rims are designed to solve this problem. This is almost irrelevant for deep rims, as the spoke entry angle is better due to trivial geometry.

C) External rim width

All available studies conclude that the outer width of the rim should be at least as wide as the actual tyre width (remember it is larger than the nominal width). Some researchers conclude that it is preferable for the rim to be 5–10 % wider than the tyre, while others argue that it is better to have a rim and tyre of the same width. Even the latter agree that a slightly wider rim is preferable to a slightly narrower one.

The actual width of a tyre is usually known only after it has been mounted on a particular rim and inflated to the target pressure. (Well, now you can estimate it using my rolling resistance calculator Excel file found in the post linked at the very bottom of this page.) In any case, a tyre on a rim with the optimum internal width will likely sit wider than the nominal size. With this in mind, I state that the outer rim width should be 110 % of the nominal tyre width for the optimal aerodynamic performance.

It is important to note that this refers to the outer width of the rim at the rim-to-tyre interface. However, the maximum width of a modern aerodynamic rim will be greater due to its toroidal shape. In image (a) above is a rim with the external width of 28 mm and a maximum width of 30 mm. This rim is the optimum rim for a nominal 25 mm tyre size (also in terms of inner width).

From an aerodynamic point of view, a narrower tyre wins out over a wider tyre (however, the difference is so marginal, it is hard to even measure it). Therefore, the most aerodynamic option — albeit at the expense of comfort and real-world speed — is a 23 mm tyre on a rim with an inner width of 19 mm and an outer width of 26 mm. However, the choice of 23 mm tubeless tyres is very limited, and a good 25 mm tyre will probably still make up for the slight loss in aerodynamics due to better rolling resistance. That would be an ultimate choice for a perfectly flat road — but as soon as we get a real-world surface, wider tyres trump the narrower for both speed and comfort.

3. Rim weight

When road cycling was already in full swing, but humanity did not yet have the quantity and quality of knowledge about aerodynamics, weight was pretty much the only criterion for evaluating components. (In fact, it still is the only measurable criterion by which two bikes could be compared in daily life — apart from the price, of course.) In recent years, everyone has realised that aerodynamics is more important and has started to compare the benefits of improving aerodynamics with those of reducing weight.

As a result, it is increasingly being argued that weight is almost irrelevant, with reference to test results evaluating the effect of aerodynamics and weight on sustained speed (in this scenario, weight does indeed play a very minor role — even on moderate uphill climbs).

In reality, weight does matter, of course. And of all places on a bike, it is the weight of the rims (and tyres) that matters most. (Although, like with the flexibility/position vs bike/wheels in the case of aerodynamics, it makes sense to pay attention to your own weight first. Dropping a couple of kilos off one’s waist will most likely be healthier for most amateurs than a couple of hundred grams off the wheels. No fat-shaming, just medical facts :)

Firstly, the wheel is a flywheel that we have to spin up every time we accelerate the bike. You don’t see this in tests done at constant speed. But it makes a huge difference to the feel of the bike. A bike that is easy to accelerate feels fast. You get more enjoyment out of riding it — and even a little boost in morale and placebo effect that really makes you ride faster.

Secondly, although most road bikes don’t have shock absorbers, the entire structure of the bike (fork and handlebars, frame rails and seatpost) absorbs bumps by acting as an elastic element between the rider and the wheels. The weight of the wheels is thus the unsprung mass — and therefore affects the smoothness of the ride.

Added later: I must confess that, while the above paragraph is technically true, it misses the point completely. In fact, for non-suspension bikes it’s the opposite — since the main deflection comes from tyres, there is no real unsprung mass to talk of in such a bicycle, but all of it should be considered the sprung mass that we want to be as stable as possible not to shift the function of absorbing bumps further onto the rider’s limbs. Thus, the heavier the bike, the better it feels on the bumps — it holds its line due to inertia, while the tyre deflects around. That’s where the “steel is more comfortable” idea comes from — it wouldn’t be if it wasn’t just heavier ;)

However, when we talk suspension bikes — and now we have not just mtb, but also an assortment of gravels with that feature — the previously said, on the contrary, happens to be true and relevant. The lighter the wheels (as well as fork legs, chainstays/seatstays and other elements moving against the frame when suspension works) in proportion to the rest of the bike, the better.

Are there any disadvantages to lightweight wheels? Since we’re talking about modern deep carbon rims, you don’t usually have to worry about stiffness. Stiffness issues with deep wheels are more likely to occur at the hub-spoke interface (discussed below). As for rims, the downside of weight is cost and/or durability.

Typically, rims use T700 carbon, and lighter rims use the stiffer T800 carbon to compensate for the lower amount of material. This increases the cost of the wheel, and potentially makes it more brittle. Typically, a lower maximum rider/system weight is claimed for these wheels.

The weight of carbon rims changes non-linearly with increasing rim depth. An average 40 mm rim weighs 450 g, while a 60 mm rim weighs 500 g. A difference of 50 grams (just over 10 per cent) is worth the 30 per cent increase in depth (aerodynamics).

Shallow carbon rims are exotic, and they don’t weigh as little as one might hope. (That’s changed now, and there are extremely light gravel carbon wheels with shallow section rims.) On the other hand, finding more or less light wheels with 80 mm profile is already problematic, and wheels deeper than 90 mm are almost never found (unless you count solid discs for track/tt/triathlon).

Some wheel manufacturers build a counterweight into the rim on the opposite side from the valve hole. Being quite a fast descender, I’ve never noticed the practical need to balance bicycle wheels, nor have I seen any research on the subject. However, I do know that even expensive tyres have uneven compound thicknesses that result in weight variations of the same model in the same width, sometimes in the tens of grams. This suggests that wheel balancing is more of a marketing advantage.

Added later: I’ve seen a bikeshow stand of the wheel company that got the idea — as they’ve been demonstrating how they’ve been balancing wheels on a special machine after the tyre’d been installed. What a joke — bring that machine to the roadside when I’ll be changing a punctured tyre next time, lol.

Also, Silca (and likely some others) sell separate counterweights that you can use to balance a wheel yourself after installing the tyre. How precisely you could do that without the machine — and, more importantly, why you’d even bother — remains to be understood.

4. Braking

On disc brakes, the rims have no effect on braking. On rim brakes, apparently the opposite is true.

Carbon rims are said to brake worse than aluminium rims, especially in rain. A typical experience is the complete absence of braking in the wet for a couple of seconds (during which a person has time to have a panic attack), and then a sharp appearance of braking power comparable to braking in the dry.

This is due to the formation of a water film between the pads and the brake track, which the notches on the latter are designed to combat. Notched rims make a rather loud noise when braking, which can be a plus when riding in a group, and can also lead to accelerated pad wear.

In the experience of many, carbon brake tracks are just as good as aluminium ones — at least in the dry — if you use the right brake pads. Btw, you should not use pads intended for carbon rims with aluminium ones, and vice versa — and in any case never touch carbon with the pads that have already been used on aluminium.

Swiss Stop pads are almost universally good — yellow (Yellow King) or black with yellow lettering (Black Prince). The former have better braking intensity in the dry, the latter have better modulation and performance in the wet — so the overall win goes to them.

It should not be overlooked that prejudice against rim brakes in general, and with carbon rims in particular, may be due to the fact that there are many rim brake calipers on the market that lack stiffness and/or leverage. I won’t cite negative examples, but will note that Shimano’s 105, Ultegra and Dura-Ace series brakes show themselves to be the best in tests and will definitely not be a bottleneck in a braking system.

Modern rims with large widths may not fit into rim brakes, at least not with sufficient clearances (small clearances are not recommended, as even a perfectly true wheel can rub the pads in corners and when pedalling out of saddle). For such cases, Swiss Stop produce pads of lesser thickness.

There are a number of stereotypes that carbon wheels overheat and delaminate under heavy braking, etc. This did happen in the past, but nowadays you don’t have to worry about it — the brake tracks of all decent rims have long been made of carbon with a special (high-temperature) resin composition and a suitable weave and fibre lay-up so that nothing like this can happen in normal use.

Added later: while indeed rim brakes can provide enough stopping power if set-up correctly (and with sufficient cyclist’s grip strength), the discs have two significant advantages: they let you fit much wider tyres; and they don’t destroy your $$$$ rims in a single ride if you find yourself in a muddy place that you cannot go around and where you have to brake a lot (based on true story).

That said, I still appreciate the simplicity of a rim brake that never annoys you with repetitive sounds, nor goes out of true in a bike case, or loses performance if an oily drop ever touches it somewhere on the road. So, still an option in 2023 for good-weather and fair-surface riding.

For some reason, not all rims have small holes on the sides, which are called either drainage or pressure relief holes. The drainage function is helpful when you ride on a deep rim into an even deeper puddle, and water can enter through the spoke nipples and without drainage it will probably never evaporate (you’d have to disassemble, take out the tubeless valve and pour it out).

A similar problem, by the way, is also present when tyres are fitted with tubes. Rainwater flows around the valve stem into the internal space and remains there until you take out the tube and pour it out. Not having to disassemble the wheels after each trip through puddles to drain the water is another advantage of tubeless tyres.

And the pressure relief is for an instance where your rim tape leaks and you inadvertently pump up not only the tyre, but also the increase pressure in the internal chamber of the rim — which could destroy it if there is no relief hole. So, better get a rim with the hole.

II. HUBS & SPOKES

There are many standards of hubs. They differ in axle/quick release (qr) diameter and dropout width. It is sufficient for us to distinguish hubs for rim brakes and disc brakes:
• rim brakes — 5 mm quick-releases, 130 mm rear hub, 100 mm front hub;
• disc brakes — 12 mm through-axles, 142 mm rear hub, 100 mm front.

Anything else is either not for road bikes or exotic. (Added later: that’s true, but for gravel bikes there are also boost hubs — 12 × 148/110 mm. Those are used in combination with wider cranks to fit front derailleur together with gravel-width tyres, as explained in the post on rearward geometry linked in the bottom of this page. Also, some 12 mm forks will accept front hubs designed for 15 mm axles, so an mtb wheel could be used in a gravel bike with a conversion axle.) Having decided on the type of hubs, let’s look at their characteristics.

1. Freehub and brake disc interface

Most wheels have an HG freehub for a Shimano or Sram cassette with 11-tooth smallest sprocket. If you want to use a cassette with the 9–10 teeth minimum — Shimano Micro Spline or Sram XD/XDR (note: XDR freehub will accept XD cassette — with a spacer — but not vice versa) or Campagnolo, you need to make sure that there is a corresponding freehub available for the wheel you are interested in.

Brake rotors have two basic standards of mounting on hubs: 6-bolt and centrelock. Both work well, and the differences are marginal.

2. Number and pattern of spokes

Where there is not a lot of torque (the left, non-driving side of the rear wheel and the whole front wheel on rim brakes), you can get by with a radial spoke pattern and/or fewer spokes. Since disc brakes generate additional torsional forces on the wheel, cross spokes and/or more spokes are used.

Classic pattern: 24 spokes at the back, crosses; and at the front — 20, radial, for rim brakes — or 24, crosses, on disc road wheels.

Further variations are possible. On rim brakes, more and more often they are spoked radially on the back-left, sometimes with fewer spokes. On disc brakes — sometimes more.

3. Spoke type

The type of spokes affects the hub-spoke assembly. There are two basic types:
• j-bend, aka classic;
• straightpull or nail-head with its t-head variation.

There are marginal differences between the two types, but both are valid standards. Most modern manufacturers use straightpull, but there are still very expensive hubs (e.g. Chris King or Enve) for classic spokes only.

The t-head standard is a straightpull spoke with a flattened head. It is used by DT Swiss for their own wheelsets. The t-head hubs are called Dicut (while the regular straightpull are called Spline). These hubs are not sold separately. They are even stiffer than conventional straightpull hubs due to the larger flanges, more aerodynamic and prevent unwanted rotation of the bladed spokes in the hub-spoke interface.

(e) Classic hubs with j-bend spokes for 6-bolt brake disc with Shimano/Sram HG freehub

(f) Spline hub with straightpull spokes for centrelock brake disc with Sram XD freehub

(g) Dicut hub with t-head spokes for rim brake (no brake disc interface) with Sram XDR freehub

(i) Shimano Micro Spline freehub with 12 mm axle adapter (for a disk-brake hub)

Let’s take this opportunity to close the question of spokes — it’s simple. Almost all leading manufacturers of road wheels limit themselves to the following choices:
• DT Swiss — mostly Aerolite or, for heavy/powerful riders, Aero Comp;
• Sapim — mostly CX-Ray or, for heavy/powerful riders, CX-Sprint;
• Pillar 1420 — for the frugal;
• proprietary carbon ones from the manufacturer of the wheelset (or its contractor).

Separately, titanium spokes need to be mentioned. They are lighter than steel ones and are positioned higher by their manufacturers (primarily Pillar). But titanium is poorly suited for the stretch loads experienced by spokes, so it is not recommended to use such spokes. The leaders in spoke production — DT Swiss and Sapim — do not use titanium.

I would add that if you need to choose between round spokes, a thinner one is better than the thick, for aerodynamics. At that, a good thin round spoke is not inferior to an aerodynamic bladed one, as tests show — but maybe even better for the crosswind stability and the ease of maintenance (round ones are not sensitive to accidentally rotating them in either the straightpull hub interface, or at the nipple when adjusting). On the other hand, if a spoke twisted all over, you could tell by just looking at a bladed one, but not the round.

Spokes are attached to the rim using aluminium or brass nipples. Most factory wheelsets use aluminium ones — but the brass are more weather resistant if you ride in harsh conditions, and will not corrode as easily.

There are also rims for hidden spoke nipples. Claims are made that this is more aerodynamic and something else. I do not understand how (and why) to live with such wheels — banal tightening of spokes is possible only by disassembling the wheel and redoing the rim tape (true tubeless rim design with hidden nipples is impossible in principle). I thought this inherently flawed design was more or less phased out — but DT Swiss introduced a new line of budget wheels in 2023 with this. I have no idea why on earth they would do that, but they did.

4. Number of engagement points

The rear hub has a freewheel mechanism built into it: when the pedals are turned, they rotate the hub (wheel), but then the wheel can rotate freely without dragging the pedals.

This mechanism almost always involves some free play in the pedals: if you rotate them back a little and then start pedalling, the hub will not follow the pedals immediately until the gear wheel in it engages with the counterpart (of either a ratchet wheel, or pawls — for most of hubs).

The amount of free play is measured in degrees or the number of engagement points. It is essentially the same thing: if we divide 360° by one of these parameters, we get the other.

On the road, the free play doesn’t play a significant role with good pedalling technique (in clipless shoes, of course). But if you do not “turn” the pedals, but “step” on them, you can feel the characteristic clang of the transmission, which will be the more vivid, the less the hub has clutch points and the higher your power. Most manufacturers choose an average number of engagement points for road wheels, ranging from 30 (12°) for Campagnolo/Fulcrum to 40 (9°) for Enve and Mavic.

DT Swiss hubs make it easy to swap gear wheels to change the number of contact points. This manufacturer has ratchet variants with 18, 36 and 54 teeth. However, 18 (20°) are used only in the most inexpensive wheel models, and 54 (6,(6)°) are not used by them at all in road wheelsets. Zipp also uses 36 teeth ratchets (and, in some models, magnets instead of springs!)

There is a reason to believe that 54 contact points are not used by DT Swiss on the road wheels for not just assumed redundancy, but also for the fact that more teeth means smaller teeth, and therefore less strength and/or wear resistance. Not that ratchets with 54 teeth are fragile, but 36 are a priori more robust.

Anyway, there are hubs with even more engagement points. Chris King hubs are not divided into road and mtb/bmx and use either 45 (8°) or 72 (5°) contact points. Industry Nine uses 60 (6°) in the road models — and 120 (3°) in the mtb. This number, one of the highest on the market, is achieved on a gear wheel with the same 60 teeth by alternating two sets of pawls, only one of which is engaged at a time, which keeps the strength of the system at an acceptable level — 120 teeth would apparently be too delicate.

Quite beyond the road applications, there are hubs with infinite contact points (close to instantaneous engagement) thanks to a fundamentally different system. These are produced by Onyx, True Precision Components, and Shimano in their Alfine/Nexus hubs with planetary gears. What they all have in common is their heavy weight and silent freewheeling.

5. Freewheel sound

This is a largely subjective parameter — you either like it or you don’t. Chris King, whose hubs are particularly appreciated for their characteristic sound, describes it as the “angry bee” buzz.

You can draw a parallel with the sound of internal combustion engines — some people like the smooth sound of Zipp wheels V12 (or inline sixes), but the angry roar of a V8 or the hysterical growl of a V10 (or inline fives) is what gets you emotional. As opposed to four cylinders in a row, which seem fundamentally incapable of sounding interesting. Better get Onyx hubs Tesla than.

Going back to the bicycle hubs, there is some similarity. The sound of hubs with not the greatest number of engagement points is generally uninteresting. The tastiest is somewhere between 45 and 72 — as in Chris King hubs. Many people like the sound of DT Swiss hubs with 54 contact points (which may encourage some to upgrade to the respective ratchet wheels, despite what was described in the previous section).

Objectively, what differs between hubs is the volume of the sound. From a practical point of view, the louder the better: the pack head will know that they’re underperpowering, and pedestrians will be aware of where you’re coming from and at what speed you’re approaching. But some people just like it quieter.

6. Hub weight

Good hubs weight approx:
• 100–150 grams front;
• 200–250 grams rear.

There are both inexpensive but light (Bitex, Novatec) and expensive but heavy (Chris King, Onyx). There’s a reason for this. The former are inferior to mid-priced hubs in the other characteristics — and vice versa. Within the same model range, generally the more expensive hubs will be lighter.

The weight of both hubs and complete wheel assemblies is almost always quoted excluding qr/axles. A decent set for both wheels weighs 50–100 grams. As far as qr are concerned, it’s worth noting separately:
• titanium ones, which are lighter, but may annoy you with clicking sounds;
• super light ones, which tend to be inconvenient or may even hold the wheel badly;
• DT Swiss-style, which don’t clamp, but twist like axles — which is handy unless your frame prevents them from making a full revolution;
• qr, which have no lever at all and are tightened with a tool. But lightweight and minimal.

The total weight of a modern road wheelset with rims up to 60 mm (without qr):
• 1300–1400 g — excellent;
• 1400–1500 g — good;
• 1500–1600 g — satisfactory.

(Since the first edition there appeared much lighter shallow-section wheels on the market, sometimes weighting less than 1 kg for a pair. On the other end, a robust pair of gravel wheels may be even more than 1.6 kg which is acceptable if they can hold a punch.)

7. Type and material of bearings

The vast majority of hubs are now manufactured with cartridge bearings. A notable exception is Shimano hubs, which continue to use the cup-and-cone (edit: Shimano shifted to cartridge in 2023, but there are still some cup-and-cone wheels on the market — e.g. by Campagnolo). In theory the latter are slightly more efficient — provided they are well maintained. Given that the ease of maintenance is the weak point of the cup-and-cone bearings in comparison to the cartridge ones, in reality it is difficult to determine a clear preferred option.

There are steel and ceramic bearings. The latter are considerably more expensive, but their real benefit is not obvious. Theoretically, they provide slightly less friction loss (independent tests show results close to the margin for error). From a practical standpoint, ceramics won’t rust if water gets into the hub. But on the road it should not get there. And for the cost of a set of Ceramicspeed bearings, you can replace steel bearings as required for about a lifetime.

8. Quality, reliability and maintainability

DT Swiss are considered by many as robust as the meme-intensive Nokia 3310. Even if you don’t plan to service the hubs yourself, opening a DT Swiss for the first time with one bare hand, you will probably get a pleasant feeling of “wait, you could just do that?”

That said, it’s worth bearing in mind that, firstly, even DT Swiss had problems (there’s been a recall campaign for ratchet EXP systems), and secondly, road wheels aren’t as demanding on hub reliability as they are for dirtier cycling disciplines.

I’ve noticed that the most reliable hubs are the ones with the ratchet-style engagement part (DT Swiss, Chris King, Enve, Zipp), not the pawls. It’s probably just a coincidence — but DT Swiss and Zipp produce their cheaper models with pawls instead of the ratchets. In any case, there should be no particular concern about the reliability of the hubs mentioned in this article.

III. OTHER CONSIDERATIONS

Above, we’ve broken down all the technical aspects of wheels in as much detail as possible. When choosing them, there are also intangible factors, which will be mentioned only in passing:

• warranty conditions, both formal and actual fulfilment;

• availability for separate purchase and delivery time of wheel parts in case of non-warranty breakdowns or in case of desire to rebuild wheels with other components (especially relevant for non-standard spokes — e.g. proprietary carbon spokes — but also important for rims subject to early wear with rim brakes);

• manufacturer’s promises to replace wheels and/or parts damaged as a result of incidents — if a crash replacement programme exists at all, its conditions may vary from free replacement for life (!) to a small discount on new wheels for a limited time (there is also a policy of “contact us if and when that happens, we’ll sort it out”);

• the possibility of a test drive (we buy wheels, ride them for no longer than a certain time, return them without a valid reason in exchange for a refund, sometimes even covering the cost of shipping) and other similar claimed competitive advantages; statistically you will not use them, but what if;

• while the wheels design is mostly functional, the perception of a brand on the decals is an important characteristic of wheels for many. Apart from that, there are truly good-looking wheels (such as Bora, for example) and, of course, some ugly/gaudy ones. Since the main reason for buying deep section carbon wheels is that they are faster you just want a new toy, that’s not the least important point, if you ask me.

Sorry, but I have not found enough internal force to rewrite this article from scratch to make its structure closer to how I see it now. I also intentionally left out some exotic solutions such as ropy spokes, Classified, Rohloff and other internally geared hubs (mentioning only Shimano ones for a different reason), dynamo hubs, powermeter hubs, solid and 3d-structured tyres, molded and printed disc- and bladed wheels, etc. Thanks for reading that much!