Most road bike wheelsets feature spokes. But what do you really know about these “wires” that play such an integral part of your bicycle riding experience?
Why spoked wheels?
Something must connect a bike hub to the rim. Every spoke serves the fundamental purpose of linking the hub to the rim. The tensioned wire-spoke wheel was designed by G. F. Bauer in 1800 CE, around 50 years before the invention of the bicycle. This is an often-overlooked facet of the history of the bicycle. The tension-spoked wheel would eventually become a method of reducing the overall weight of the vehicle’s wheels. A number of improvements would be required before this discovery could be transformed into the predecessor of the present bicycle wheel design.
Modern spokes come in a range of lengths, forms, materials, finishes, and attaching methods. When we consider dynamic loading patterns, this ostensibly simple static function becomes significantly more complex. Bicycle wheels are subjected to repeated complex loading conditions referred to as “fatigue cycles.” Spokes must carry a combined load from the principal sources listed below.
What do spokes do?
Carry: spokes carry the weight of the bicycle as well as the rider and any other load (water bottles, saddle bags, etc).
Absorb: spokes absorb the irregularities of the road and ensure the comfort of the rider. Transmit: spokes transmit acceleration power and braking effort (for rim brake wheels) of the rider.
What is spoke tension?
The amount of pulling force exerted along a spoke is referred to as spoke tension. Component companies usually measure and describe spoke tension in kilograms of force (kgf) or Newtons (N).
Key Factors to Spoke Tension Load
Wheel tension: The force exerted on the spokes as they are tightened during construction. Tension between spokes can reach up to 30-130 Kgf.
Weight of the rider: A heavier rider adds stress to the wheel when it is subjected to cyclic fatigue loads.
Torque loading: Both rear-wheel power and disc braking forces provide torque to the spoke system as a whole.
Increased tire pressure results in decreased spoke tension, hence increasing fatigue sensitivity.
Potholes and pavement characteristics result in significant stress changes in a spoke system.
Spoke length and rim depth. A deep wheel rim offers aerodynamic advantages and allows for shorter spokes since the rim is occupying the space where a spoke would be in a shallower rim. A carbon wheel can have significant depth often as high as 90mm.
Lateral loading: The force exerted on a wheel to its side.
Rear vs. Front Wheel – the rear wheel spokes have more stress placed upon them because this is where drivetrain power is applied via the cassette and more rider weight is distributed to the rear wheel than the front.
Spokes respond to complex dynamic loads by stretching under tension and utilizing the stored energy in the material. Spoke tension cannot be determined visually. A tensiometer can be used to determine the maximum tension and uniformity, which is crucial for the wheel system’s long-term fatigue life.
Why does spoke tension matter?
If the spokes don’t have similar tension, the rim of the wheel will start rotating in a wobbly manner. This is called being out of true. This can cause issues for a cyclist including causing the entire bike to wobble or worse, wheel failure, both leading to crashes and injuries. If out of true, the wheel will need to be trued by adjusting spoke tension.
When a wheel builder trues a wheel, he or she is adjusting spoke tension. Individual spoke tension isn’t the only factor to consider. Proper tension needs to be maintained across all spokes over the entire wheel system.
The wheel of a bicycle flattens slightly where it hits the ground when it is ridden. As a result, the spoke tension at the bottom of the rim decreases. This cycle of increasing and decreasing tension occurs during each ride. When the tension on a wheel is too low, the spokes might relax too much during a ride, causing a snapping effect and putting too much stress on both the spokes and the rim. De-tensioning, or the loss of spoke tension over a short period of time, can occur as a result of this. This can result in damaged spokes, rim fatigue, and a wheel that is more likely to run out of true. Too much tension, on the other hand, can result in wheel failures such as cracked rims, broken spokes, or even damaged hubs.
Which road bike wheel spokes do I need?
The correct spokes for your wheel will be determined largely by two factors: your intended riding style and the load the spokes will bear.
Spokes are available in a variety of lengths to accommodate the wide variety of wheel sizes available on the market, ranging from 20″ BMX wheels to 7000c road bike wheels. However, there is no standard range of sizes because the dimensions of the hub and rim also factor in – the length of spoke required is determined by the distance between the hub’s flange holes and the spoke holes on the rim, not the radius of the wheel. When you factor in deep-section rims and wide-flange hubs, it’s easy to see why this is complicated.
To determine the required spoke length, consult your wheel manufacturer’s manual or use an online spoke calculator. This will allow you to enter the dimensions of your hub and rim in order to determine the length of spoke you require.
Intended riding type: High-quality general-purpose spokes can be used to construct wheels for virtually any discipline, as it is the number and pattern of spokes that determine the strength of the wheel, more than the type of spokes (see below for more about spoke lacing). However, certain types of thin, lightweight, and aerodynamic spokes designed for fast, lightweight wheelsets can make you faster. However, aerodynamic spokes are not recommended for heavy-duty wheel construction for events like downhill mountain biking, and straight-pull spokes and hubs are incompatible with standard j-bend spokes.
What is the best road spoke shape? Round, bladed or oval?
There are three shapes of spokes typically used on bikes, round, bladed, and oval (elliptical). Which spoke shape is best for you is determined by rider goals including simplicity of use, speed, durability and other factors.
Round Spokes
Round spokes have been used for years. They are durable. The angle at which round spokes sit in relation to the YAW angle of the wind has no effect on their performance since the shape is consistent around the spoke. The downside to round spokes is that the aerodynamic properties, while consistent, are not optimal for aerodynamic performance. They are consistently slower than the other pre-dominant shapes.
Bladed Spokes
Bladed spokes are flat rather than round. For high-performance applications, road riders use bladed spokes to reduce weight and control high tension wind-up.
Because there is less cross-sectional area in the lateral plane, bladed spokes contribute to slightly lower lateral stiffness. This can cause some lateral flex issues for heavy riders or during hard accelerations, braking, or cornering.
Are bladed spokes stronger than round spokes?
Not in the truest sense. They are often as “strong” as a comparable round spoke. This is because the cold forging which a bladed spoke undergoes in the process from becoming a round spoke to a flattened spoke increases strength. Bladed spokes all start as round spokes and are compressed or squeezed into flat spokes by a die.
Oval Spokes
Oval spokes seek to merge the best facets of rounded and bladed spokes. They are more laterally stiff than a bladed spoke while providing more aerodynamic benefits than a rounded spoke.
Oval Spokes. Vs. Bladed Spokes
One difference between bladed and ovalized spokes is that bladed spokes have a larger cross-section area in the bladed section. Bladed spokes are very wide. Ovalized spokes are not much wider than standard spokes and are able to fit through standard round spoke holes.
FLO’s Approach to Spoke Shape
FLO Cycling has chosen to use the oval Sapim CX-Ray spokes. Our wind tunnel testing has shown these spokes to be 9 seconds faster in a 40km Time Trial scenario and 42 seconds faster in an Ironman distance biking section.(See the study here: https://blog.flocycling.com/aero-wheels/aerodynamic-difference-between-sapim-cx-ray-and-round-spokes/). Oval spokes create a stiffer wheel than do bladed spokes.
What is a butted spoke and a double butted spoke?
Not all spokes are consistently thick throughout their length. Wheel manufacturers discovered that they could maintain spoke strength while reducing weight by varying the thickness of a spoke. These are called butted spokes.
Straight gauge spokes have the same thickness throughout their length.
Single-butted spokes taper their thickness at one point usually near the hub flange to be thinner the rest of the way to the rim.
Double-butted spokes taper at two places, being thicker at the hub and at the rim while thinning in the middle.
A butted spoke of any type saves weight.
Not every section of the spoke works as hard as the others. The middle section of any spoke holds less tension. The stress applied at the end of each spoke ends is much greater. Depending on how the head and the J-bend are supported, the elbow is susceptible to bending strains. The sharp groove of the threads on the rim end of the spoke, on the other hand, causes stress concentrations at the nipple. Because of these factors, the majority of spoke breaks occur near the elbow or nipple.
What are spoke lacing patterns?
Radial vs. Tangential
Spoke patterns on bicycle wheels vary. Tangential spokes connect from the hub to the rim at an angle rather than in a straight line. They cross over each other. Radial spokes connect the rim to the hub in a straight line. Tangential patterns are stronger than radial patterns, but radial patterns are more lightweight.
What is the best spoke count?
The number of spokes on a road wheel affects wheel strength, stiffness, and weight. Fewer spokes are obviously lighter and cause less aerodynamic drag, however, too few spokes begin to compromise other aspects of the road wheel’s performance including safety, durability, braking performance, and loss of power transfer from the cassette to the road due to the flexing of the rim.
FLO’s Approach to Spoke Lacing Pattern and Count for Road Wheels
For rim brake wheels, FLO’s front wheels have a 20-spoke radial lacing pattern, while our rear wheels have a 24-spoke two-crossed, tangential lacing pattern. This reduces weight, improves aerodynamics, creates a dynamically responsive wheel while enhancing strength where it’s needed the most.
For disc brake wheels, FLO’s front and rear wheels have a 24-spoke two-crossed, tangential lacing pattern. This reduces weight, improves aerodynamics, creates a dynamically responsive wheel while enhancing strength where it’s needed the most.
Road Wheel Braking and Spokes
How do rim brakes versus disc brakes affect the spokes on road wheels?
Disk brakes place more stress on spokes than rim brakes. Rim brakes place minimal stress on the spokes because of where the stopping force of the brake pad is applied, on the outer edge of the wheel. The rim and tire carry more momentum than the hub, so slowing the wheel at the rim reduces the momentum that is transferred to the center of the wheel that has less momentum- aka the hub. In contrast, a disc brake wheelset applies the stopping force closer to the center of the wheel. This stopping power must be transferred out to the rim and tire which carries greater momentum. This force must be leveraged from the center of the wheel to the rim via the spokes. This places more stress on the spokes. However, a quality spoke with a quality build should easily be able to handle this increased tension. Most bike manufacturers are moving away from a rim brake in favor of a disc brake.
Spoke Nipples
What are spoke nipples?
The little nut that secures the end of each spoke to the rim of your wheel is known as a nipple. Each nipple is a small brass or aluminum cylinder with an internal thread, a conical or spherical head that lies inside the rim, and flattened portions on the outer end of the cylinder (facing inwards towards the hub) that may be grabbed and tightened with a special tool (spoke wrench or’key’). Spokes also come with a hex head design that allows the spokes to be turned between the brake tracks. Hex head nipples are required for wheels that do not provide access to the bottom of the nipple like the FLO Aluminum + Carbon line and the FLO DISC wheels.
Nipples operate by applying tension to the spokes, with the nipple’s threaded interior matching the screw thread on the spoke’s end. The tension on the spoke is increased or decreased by tightening or loosening the nipple, and one of the essential abilities of wheel building and adjustment is establishing the correct tensions so that the wheel spins ‘true.’
How to Select the Proper Nipple
• Diameter: It’s critical that the spoke thread’s external diameter matches the nipple thread’s internal diameter (normally 2mm, even in butted spokes). As a result, most spokes are equipped with nipples at purchase.
• Materials: Brass or aluminum for most nipples. Brass is more expensive, but it is also more durable. Aluminum nipples may save some weight (considering the importance of rotational weight and the cutting-edge carbon construction of many high-end wheels), but they are more prone to damage, so be careful not to strip the threads (pay attention to the manufacturer’s maximum load rating) or round the flats.
• Size: Spoke nipples are typically 12, 14, or 16mm long. When employing aluminum nipples, the spokes should be long enough to engage the entire length of the spoke nipple threads, transferring the load from the spoke to the nipple’s top.
FLO’s Approach To Nipple Type
At FLO we use Sapim Hex Head Nipples with their SILS system. SILS helps hold the nipple in place once spoke tension is set. This helps reduce the need to true the wheels over their lifetime.
What size spoke nipples are there?
3.23mm, 3.30mm, and 3.45mm. are the most common sizes. While rare, some wheels come with spoke nipples in two different sizes; one size is used on the rim, while a different size is used on the other end of the spoke at the hub.
Spokes Matter on Your Road Bike. So They Matter to FLO.
Even though they aren’t always top of mind, your road bike’s spokes play a significant role in your ride experience. FLO Cycling considered all our spoke options when we designed our wheels. We ultimately selected the Sapim CX Ray spokes as the best option for FLO road bike wheels, providing aero advantages, comfort, durability, and the needed stiffness and light weight you need for road cycling success.
SAPIM on their CX-Ray
The CX-Ray still receives one of the best results in fatigue testing of any spoke. Its unique strength and flexibility make the CX-Ray suitable for most bicycle disciplines. The middle section of the spoke is drawn then pressed in a special mold to form its specific profile. CX-Ray spokes are used by top bike racers around the world Special alloy treatment and sophisticated production make this all possible. The CX-Ray fits in all standard hub holes.
- No extra hub hole design; hub manufacturer guarantee is unaffected.
- Almost as light as Titanium.
- More long lasting than any other spokes on the market.
- Extremely high fatigue test results.
- Special alloy treatment and sophisticated production.
- The best aerodynamic eliptic spoke available.
- Produced from high-tensile, fatigue-resistant 18/8 stainless steel conforming to the Sapim quality standard specifications.
- Diameter: 2.0 – (2.2 x 0.9) – 2.0 Length: 145-310 mm Weight: 279 g (64 x 260 mm) Strength on middle section: 1600 N/mm2
When laced to our hubs and rims, you’ll have one of the fastest, safest, and most comfortable road riding experiences available.
Co-founder at FLO Cycling. Jon manages the day to day operations and acts as the lead engineer for all FLO products.