From the ground up: How to pick the parts for a custom road bike build
There comes a time in the life of every cyclist when they have enough experience to form strong opinions on the parts they use. At this point, they are ready to consider a custom bike where every part is handpicked to satisfy their needs and desires. It can be a daunting proposition, but all of the extra time and effort will be rewarded with an immensely satisfying bike.
In this post, Australian tech editor Matt Wikstrom takes a look at what you need to know when selecting the parts for a road bike build. It will also serve as a handy crib sheet for any rider looking to replace any part of a road bike, be it a stem, wheels, or an entire groupset.
The most convenient way to buy a new bike is to choose one of the many factory-built bikes on offer from dozens of brands. These off-the-rack packages offer great value and prospective buyers can take the bike for a test-ride before making a decision. However, the buyer doesn’t get any say in the choice of components or the colour of the frameset, though most bike shops are normally prepared to swap the saddle or fit a different-sized stem to ensure the buyer is happy with the fit and feel of the bike.
At the other end of the spectrum, a custom build allows the buyer to tailor the bike to suit their every need. CyclingTips readers who are familiar with our Bikes of the Bunch series will know how varied the final result can be, and while a lot of these bikes feature bespoke framesets and exotic components, neither is a strict pre-requisite for a custom build.
The greatest strength and appeal of custom-building a bike is that the buyer is in charge of every aspect, starting with the goals and priorities for the build. For some, it might be embracing the latest technology and/or aerodynamics; others may choose to concentrate on weight, specific colours, or replicating a team bike; it is even possible to work with a strict budget and/or recycle parts that have been kicking around in the shed for some time.
While a custom bike provides enormous control over the final product, the buyer won’t get a chance to take the bike for a ride before they spend their money, and they won’t have a clear idea on how the bike will look until is has been assembled. Thus, the whole process requires a leap of faith, but there is an enormous thrill in creating a bike in this way. If nothing else, the owner engages with every part of the bike in a way that is not possible for a factory-built bike, and will have a few stories to tell about how it all came together.
In the past, buyers looking for a custom road bike relied heavily on a good bike shop to obtain all the parts they needed, otherwise they spent a lot of time travelling to, or phoning, different shops to track down specific brands. Now, online shopping has simplified that process, and while shoppers may spend long hours visiting a multitude of shops, there is no need to leave their home, and everything can be delivered directly to them if desired – but of course, that’s assuming they already know exactly what they need, and don’t need to consult someone with more knowledge and experience.
Getting started on a custom bike build
The logical starting point for any build is the frameset. As the core of the bike, it provides a template to guide the build. There are no standards for many parts of a bike, just a discrete number of options with very little redundancy, and thus, it is far easier to pick parts to match the specifications of a frameset rather than the other way around. This applies to any kind of bike, though for the purposes of this article, I will concentrate on the details that are most relevant to road bikes (a category which also includes all-road and gravel bikes).
There’s another good reason to start with the frame: it provides the buyer with a maximum amount of freedom when choosing a suitable frame size and preferred geometry. This is perhaps the strongest reason to consider a custom build, because the buyer can hand-pick a frameset that promises to fulfil their needs and desires.
For those riders with a good understanding of their position, fit, and handling preferences, it shouldn’t be difficult to identify suitable candidates by browsing through online geometry charts for stock framesets. Detailed specifications are normally available, too, so that prospective buyers can weigh up all of the options before making a purchase.
For those with needs that fall outside of the norm, a bespoke frame may be a better choice. Not only will a frame builder be able to fashion the frameset that perfectly suits the fit of the buyer, they can also accommodate any preferences the customer might have for the final aesthetic (such as a sloping versus horizontal top tube) and specific components. Indeed, the customer often has the freedom to dictate the specifications for the frameset, including fittings for racks, fenders, and/or additional bidon cages.
Finding a suitable, even compatible, frame builder can be difficult, though. This is where local bike shows can come in handy such as the North American Handmade Bicycle Show, Handmade Bicycle Show Australia, UK’s Bespoked, and Germany’s Berlinerfahrradschau, to name a few. Attendees are able to view the work of a variety of frame builders in one venue, and often have a chat directly with the builders themselves, to help with their decision.
What about the fork?
For many buyers, there won’t be any need to decide on a fork for the frame. This is especially true for contemporary carbon framesets where the fork is often integrated with the design of the frame and there is possibly no alternative to use another brand or model. Bespoke frames offer more freedom, as do frames that make use of a conventional head tube and a common axle-to-crown measurement.
Almost all aftermarket road forks are made from carbon fibre, and while there are differences in styling, there is really only one main feature that buyers need to pay attention to — the amount of rake — which will affect the handling of the bike and the amount of toe overlap with the front wheel.
In this regard, it is worth stressing that even small changes in fork rake can have a noticeable impact on the steering of a bike. Framebuilders always design the geometry of the frame around a specific fork rake to yield a suitable amount of steering trail, so buyers should have an understanding of both before they tackle this job for themselves.
Spare a thought for the components before deciding on a frameset
Road bikes have become more diverse in recent years, giving rise to specialised designs that have been honed for aerodynamics, comfort, mixed surfaces, and dedicated off-road riding. At the same time, the introduction of electronic shifting, disc brakes, and 1x transmissions has resulted in a variety of dedicated fittings with very little redundancy or interchangeability. For example, a frameset that has been designed for rim brakes cannot be converted for disc brakes (or vice versa); likewise, the ports required to internally route the wires for an electronic groupset cannot normally be added to a frame with fittings for mechanical derailleurs.
There are other considerations, too, such as wheel size and the amount of tyre clearance that will be required. The number and size of the chainrings and sprockets is also important. All will have an impact on the design and specifications of the frame, so there really is no way to select, or order, a frameset without giving some thought to the components that will be needed to complete the build.
Key frame and fork specifications
The key specifications for a frame and fork concern the head tube, fork steerer, bottom bracket, and seat tube. For current factory-built framesets, this information is normally freely available, but there are times when this information may be incomplete, or lacking, such as classic road framesets from last century. In this situation, the owner will have to resort to inspecting the frame and taking measurements to determine the specifications before they start selecting suitable components.
As mentioned above, there are no universal specifications for frames and forks, and while things like bottom bracket shells always seem to be evolving, the number of options at least remains reasonably small and always discrete. As a result, some specifications can be determined by an experienced eye (such as a mechanic); otherwise, a vernier calliper will be required to make accurate measurements of the internal and/or external diameters of the head tube, fork steerer, bottom bracket shell, and seat tube.
Mating the fork with the frame
Many road framesets are supplied with a headset, but in those instances where one is not, the head tube and fork will need to be inspected and measured. There are two general types of headset, threaded and threadless, and a quick inspection of the fork steerer is all that is required to decide the matter.
The overall size of the headset is defined in terms of the external diameter of the fork steerer, and there are three common sizes: 1in/25.4mm, 1.125in/28.6mm, and 1.25inch/31.8mm. In some cases, this diameter will be uniform for the length of the steerer, but tapered designs are more common. In this instance, the diameter of the fork steerer increases as it approaches the fork crown, and the headset will comprise of a mixture of bearing sizes.
Another important distinction for a headset concerns the way the bearings are retained in the head tube using press-fit cups or integrated bearing seats. For the former, the internal diameter of either end of the head tube will determine what kind of cups can be fitted; the internal diameter of the head tube is also important for the latter, but the angle of the seats and the overall depth must also be determined.
Every headset requires a crown race at the base of the fork steerer, and in many instances, one must be fitted, however integrated races are becoming more common. For those forks that require a crown race, the internal diameter of the race must match the base of the steerer, which can be easily measured. While the options for crown races has not been standardised, the number of variations is relatively small and largely dictated by the lower headset bearing.
With all of this in mind, it’s fair to say that identifying a suitable headset for a frameset can be a little tricky. Fortunately, Park Tools, Cane Creek, and Chris King have developed online tools to help with this process, but when in doubt, consult an experienced mechanic.
Before leaving the topic of headsets, it is important to note that, with almost no exceptions, threadless forks need to be fitted with a threaded anchor for the compression bolt of the headset. These usually take the form of an expanding plug for carbon steerers, or a star nut for steel or alloy steerers. In both instances, buyers need only match the plug or nut to one of three sizes: 1in, 1.125in, or 1.25in.
The bottom bracket and crank compatibility
There are almost a dozen different bottom bracket types for road bikes, and that number only grows when off-road bikes and fat bikes are added. That range can be divided into two broad types, threaded and threadless (or press-fit), which are then further differentiated on the basis of the internal diameter and width of the shell.
Fitting bearings to the bottom bracket shell is only one half of the equation when building the bike because they must suit the cranks as well. More specifically, the internal diameter of the bearings must match the diameter and design of the crank axle, and there are no standards. Rather, most are proprietary designs limited to specific brands, and while those brands may sell matching bearing sets, none are able to cater to all of the bottom bracket shells in use today.
Fortunately, there are a few companies — C-Bear, Kogel, Enduro, and Wheels Manufacturing, amongst others — that not only specialise in creating bearing sets that allow various crank designs to be installed in different bottom bracket shells, but also provide detailed charts for identifying a suitable product. With that said, this is one area of a bike where incompatibilities frequently arise and it may not be possible to fit some brands of cranks to a given frame (e.g. any crank with a 30mm axle cannot be fitted to a Trek road frame with a BB90 bottom bracket). See our article Bottom brackets, crank axles and bearings: Your guide to a compatible fit for a more detailed discussion of this.
The seat tube
The specifications for the seat tube are important for the saddle and the front derailleur. Regarding the former, the majority of frames have a seat tube into which a seatpost is inserted for attaching the saddle. In this instance, the internal diameter (and shape) of the seat tube dictates the size (and shape) of the seatpost. While there are some common seatpost sizes, such as 27.2mm and 31.6mm, there is a large number of possibilities, and all must be matched precisely (e.g. a 27.0mm seatpost cannot substitute for a 27.2mm post).
Some frames employ a proprietary (non-round) seatpost designs or have integrated designs where the seatpost is basically just an extension of the seat tube. In both instances, a suitable post or fittings are normally supplied with the frame, however the amount of offset for the saddle and the range of colours are normally limited to whatever the frame manufacturer is prepared to offer.
For those frames that must be fitted with a conventional seatpost, a clamp will be required for the frame unless one is supplied or integrated with the seat tube. If a clamp is required, then it must match the external diameter at the top of the seat tube, which can be easily measured with a vernier calliper.
The external diameter of the seat tube is also important for fitting a front derailleur (if required). Some road frames are fitted with a slotted tab, to which the front derailleur is attached. In the absence of this tab, a clamp will be required, and there are three common sizes: 28.6mm, 31.8mm, and 34.9mm.
Choosing a groupset
A groupset comprises all of the shifting, braking, and transmission components for a bike, and for many buyers, is the most convenient and cost-effective way to obtain the majority of the parts required to complete a custom build. There are three major brands to choose from — Shimano, SRAM, and Campagnolo — and all have a range of options to suit different builds and budgets. Other brands such as Rotor, FSA, Miche, SunRace and MicroShift offer a smaller range of groupsets or transmission/braking components.
We’ve already covered all of the important details in our post on what to know when buying a groupset, but in brief, there are two sets of criteria that a groupset must satisfy: first, it must match the specifications for the frameset so that all of the components can be fitted; and second, it must satisfy the needs of the rider, which can be based on weight, performance, and/or price.
It is the latter that provides the clearest distinction between the different levels of groupsets on offer from each manufacturer, and for many buyers, the decision in favour of one level over another will be driven by budget. Since the number of features and overall weight are closely associated with price, it’s a sound strategy. As for the choice of brand, this is a matter that can be decided on the basis of personal preference and aesthetics because there is little that separates the overall performance of each.
There is no need to buy a complete groupset when choosing the parts for a custom build, and indeed, it is possible to mix components from different brands. This is something that we have covered in detail in our post on mixing road groupsets; in short, there are a variety of incompatibilities by which buyers must abide.
At the very least, the derailleurs must be matched to the shifter/brake levers as well as the number of sprockets (and to a lesser extent, chainrings) present in the transmission. By contrast, there is much more freedom when it comes to choosing a crankset, and to a lesser extent, rim brake callipers. Disc brake callipers, on the other hand, usually must be matched to the levers.
Regardless of how the groupset is assembled, every buyer will have to face two important decisions before heading to the checkout: crank length and gearing. These are both topics that we have covered in detail in our posts on the importance of crank length and understanding gear ratios, so I will only mention them briefly. In the case of the former, a professional bike-fitter will be able to provide advice on the ideal crank length for an individual, while the latter will depend upon the rider’s local terrain, preferred cadence, and his or her capabilities.
Understanding gear ratios is not only important for choosing the chainrings and sprockets for a groupset, it will also have a bearing on the choice of derailleurs. This is particularly important for the rear derailleur, where a longer cage will be required to use sprockets larger than 28T. For those building an all-road or gravel bike, larger sprockets and sub-compact cranks will be a necessity, not only for tackling unpaved roads, but for contending with the effect of larger tyres on every gear ratio.
Deciding on a handlebar, stem, saddle, and pedals for a new build is largely a personal matter, but there are a few points to keep in mind when choosing each:
Stem: In the first instance, the stem must match the fork of the bike, so a threadless fork demands a threadless stem, while a threaded fork requires a quill stem. In both cases, the diameter of the fork steerer is important, though it is the outer diameter (1in/25.4mm, 1.125in/28.6mm, 1.25in/31.8mm) that is important for a threadless stem, and the inner diameter (22.2/25.4/28.6mm) that is important for quill stems.
The stem clamp diameter is also important and must match the handlebars. The majority of quill stems have a 26.0mm clamp but some Cinelli stems can have a 26.4mm clamp. That 26.0mm diameter was once the most common handlebar clamp diameter for threadless stems, too, but it has been replaced by 31.8mm (strictly speaking, it is 31.75mm; most brands round up but Deda rounds down, hence its 31.7mm clamp diameter). Easton and Deda also offer a 35.0mm clamp diameter for some threadless stems, but the range of products is very small.
The only other measurements that are important to a stem are the length (measured centre-to-centre) and angle. Both are important to the final position of the handlebars, and thus, need to be selected according to the needs of the individual. Stem lengths generally increase in 10mm increments while there are normally just a few stem angles available (typically ±6°, ±8°, ±17°).
Finally, for those working with a threadless fork and stem, a set of spacers may be required to adjust the height of the handlebars. Spacers are available in at least a few heights (3, 5, 10, and 25mm are the most common) and must match the diameter of the fork steerer.
Handlebars: As mentioned above, the handlebars must match the clamp diameter of the stem. The other important measurements relate to the overall width of the bars along with the amount of reach and drop. The choice of each largely depends upon the rider’s fit, although personal preference (and perhaps flexibility) can play a role in deciding the amount of width and drop for the bars.
It is worth noting that there is variation on how the width of drop bars are measured. Traditionally, it was measured at the end of the bars, typically centre-to-centre, but some brands chose to use total width (outside-to-outside) instead, which would add an extra 20mm. The introduction of flared drops has confused this further, since the bars will be narrower where the levers are mounted, so some brands have taken to sizing their bars according to the width at the lever mounts (measured centre-to-centre).
Saddle: Deciding on a saddle is a highly personal matter. The overall width of the saddle has an impact on its fit, as do its contours, however there is no ready way to identify a good match without trial and error.
It is important to pay attention to the size of the saddle rails. All metal rails have a 7mm diameter, while carbon rails have a rectangular cross-section that measures 7x9mm. For some seatposts (such as Enve and Specialized, and Trek seat mast toppers), a different set of fittings will be required for carbon rails.
Seatpost: As mentioned above, for those frames that make use of an adjustable seatpost, the diameter of the post must match the internal diameter of the seat tube precisely. Posts also vary in their length and the amount of offset for the saddle clamp. Frames with a sloping top tube will require a longer post (up to 400mm) than those with a horizontal top tube, while the amount of offset will dictate how much setback can be provided for the saddle. For those riders that require a lot of saddle setback, a post with 25mm of offset will be a better choice than a zero-offset post, however the final choice will depend upon the angle of the seat tube.
Pedals: Choosing a pedal is largely a matter of personal preference. One thread size fits all road cranksets, however some brands (such Shimano and Speedplay) offer longer axle lengths for those that need a wider stance on the bike.
Compared to other parts of the bike, like the bottom bracket, the wheel fittings for road frames have remained fairly static, but there have been some changes in recent years. Contemporary road frames (with rim brakes) and forks accept 9mm quick-release axles with 100mm spacing for the front hub and 130mm for the rear hub. Looking back at earlier eras (pre-dating the 8-speed era), the only difference concerns spacing for the rear hub, which was once 120mm (5/6-speed) or 126mm (7-speed).
The introduction of disc brakes to road bikes has been accompanied with new wheel fittings employing thru-axles. The design is inherently safer and better suited to contending with the forces of braking than quick-release axles. Hub spacing for the front hub remains 100mm while it has increased to 142mm for the rear hub.
Thru-axles with a 12mm diameter have become a common choice for road disc bikes, however some road disc frames employ quick-release axles with 135mm rear hub spacing; others have opted for a 12mm thru-axle for the front wheel and a 135mm quick-release axle for the rear; and in some instances, a 15mm diameter thru-axle, borrowed from mountain bikes, may be used for the front wheel in combination with a 12 x 142mm thru-axle for the rear.
The choice of any wheelset (or hubs) must abide by the frameset specifications for the axle fittings, however it is possible to convert many disc-brake hubs with a quick-release axle to accept a 12mm (or even 15mm) thru-axle (and vice versa). There is no way to convert a rim brake hub to accept a disc rotor, though. Thus, it is equally important that the wheelset also suits the braking system (i.e. rim brakes versus disc) that will be fitted to the bike.
The other part of the hub to pay attention to is the freehub body, which must match the choice of groupset (or transmission components). Buyers choosing to use a Shimano or SRAM groupset require a Shimano/SRAM-compatible freehub that suits the number of sprockets to be installed; Campagnolo groups require a different freehub body design, as does SRAM’s wide-range XD cassettes designed for 1x transmissions.
Almost all road bikes must be fitted with a 700C wheel, but some newer gravel frames (such as the 3T Exploro, Ibis Hakka MX, and others) can accommodate 650B (aka 27.5in) wheels. Randonneur framesets can also make use of this smaller wheel size, while a bespoke frame can be designed around 650C wheels to suit small riders.
For most shoppers, a factory-built wheelset will be the most accessible and convenient option for any build, but a custom-built product shouldn’t be overlooked. There are strengths and weaknesses associated with each approach, but the latter shines when it comes to meeting the specific needs of the rider and finding a colour palette that suits the final build.
One of the major choices for a wheelset concerns the rims. Aluminium alloy remains the most common choice of material, but carbon fibre has become increasingly popular over the last decade or so with racers and enthusiasts alike. We have discussed all of the strengths and weaknesses of these rims in our post on the value of carbon wheelsets, and in short, carbon fibre rims have a lot to offer in terms of performance (especially in terms of weight and aerodynamics), but they come at a significant cost.
The major performance downside is that the material is not well suited to rim brakes, but this issue disappears altogether for disc brake-equipped bikes. By contrast, alloy rims are very well suited to rim brakes and they are still hard to beat on the basis of value.
Whatever the rim material, buyers will need to match the wheels to the tyre system (clinchers, tubulars, or tubeless tyres) that they want to use. This is normally a straightforward choice that can be decided on the basis of personal preference.
Finally, there is the width of the rims to consider, which has been growing in recent years. We’ve covered this topic in a previous post on the thinking behind wider road rims, which can generally be considered an improvement over narrow rims. The extra width may not be compatible with some older framesets and rim brake callipers, though.
As mentioned above, road riders have a choice of three tyre systems — clinchers, tubulars, or tubeless tyres — and while there is an amount of interchangeability between clinchers and tubeless tyres, the choice of tyre system ultimately rests with the wheels.
There are plenty of brands and models of tyres to choose from, and aside from taking care to match the size of the wheel, buyers will need to pay attention to the width of the tyre. In the past, tyre clearance for some road framesets may have been as little as 23mm, however the majority of contemporary road framesets will accommodate tyres up to 28mm wide. This can be greater for disc-brake-equipped bikes, especially for all-road, cyclocross, and gravel bikes.
Importantly, there is only a weak correlation between the printed size of a tyre (e.g. 25c) and the actual width of the tyre once inflated on a wheel. That’s because it is largely dependent upon the width of the rim bed, and to a lesser extent, final tyre pressure. Wider rims and higher pressures produce wider measured tyre widths, but there is no way to easily predict the result for any given rim-tyre combination without having the specific combination of parts on hand, so some trial-and-error may be required by those working with limited tyre clearance.
Finally, every tyre system has accessories. Clinchers need inner tubes, tubulars require glue (or tape), and valves and sealant are necessary for tubeless tyres. In each case, there are a variety of products to choose from and buyers will need to ensure that the valve stems match the depth of the rims that they intend to use.
There are a variety of ways to add a personal touch to a custom build (or your current ride) and it’s worth taking the time to dwell upon these minor details.
Custom paintwork for the frameset will always produce a striking result, and some components, such as the stem, bars, seatpost, and hubs can also painted to match. Artisans like Busyman Bicycles can re-cover the saddle with a custom leather finish and furnish the bike with matching bar tape, pump strap, and even a saddle bag, but all of these touches will add to the cost of the build.
There is no need to refinish the frame and parts, though, when some discerning choices can work just as well. In some cases, it might be enough to make use of a suite of parts from the same brand; in others, removing labels and logos can be just as effective. Collecting together a group of parts with the same kind of finish (e.g. matte black) also works, too. Making these kind of choices will require some visualisation and a bit of faith, though a dry build with some parts can be helpful.
Perhaps the easiest way to personalise any build is to pay attention to the bar tape and bottle cages. There’s an enormous range of options for both products, including different colours, materials, and designs that can be used to complement the rest of the build.
Another simple touch is to replace standard black brake and gear housing with coloured housing. Alternatively, segmented aluminium housing from brands like Nokon, Alligator, and Jagwire can sometimes be had in different colors. It is also possible to swap a variety of bolts for different colours such as black titanium and anodised alloy for a little extra bling. Similarly, there are some exotic chains on the market from KMC and YBN that will have the same effect.
One final touch that is worth considering is custom stickers for the frame. For some, this might mean simply putting their name on the top tube of the frame, but others might find more appeal with a quote or message to help their motivation. The same thing can be done with custom bar ends and a top cap for threadless headsets.
Bringing it all together
Once all of the parts have been collected (or delivered), the obvious strategy for assembling the bike is to find a good mechanic. Some bike shops won’t welcome a new customer with a box full of parts acquired from online sources, so it might be worth calling around and getting a few quotes first. Otherwise, hunt down a service-only business where you can talk directly with the mechanic that will do the work for you; it may even be possible to watch the bike being built.
For those that have some mechanical aptitude, it’s worth having a crack at it because there is enormous satisfaction in building your own bike. An experienced mechanic can be enlisted to take care of any jobs that need specialised tools (e.g. installing headset cups) and they can check over the build and/or take care of any fine-tuning to make sure the bike is road-worthy.
In broad terms, building a bike from the ground up is not a difficult thing to do. After all, the number of parts is reasonably small and there is a healthy industry that provides a wide range of products to suit a variety of needs. The rise of online shopping and easy access to international sellers has made it incredibly convenient to source parts for a custom build, so the only real barrier is one of familiarity with the variety of specifications for each part of a road bike.
One way to gain that familiarity is to get some hands-on experience replacing a groupset or resurrecting a classic road frameset. Alternatively, a lot can be learned by going through the process of composing a dream build and doing a bit of virtual shopping to complete the project (I’ve known some people to maintain spreadsheets with a diligent accounting of both the cost and weight of such builds). There are even a few online bike configurators (Trek’s Project One is outstanding) that can be used to visualise different builds and/or experiment with different finishes.