The significance of spokes

A bicycle wheel can only be as good as its parts. A wheel is made of three main parts; hubs, rims and spokes. If any of these is poor then it will lead to a poor wheel. Even a stout rim will go out of true rapidly the wheel is built badly; and a good build requires good spokes. Spokes literally hold the whole item together. Sapim define a spoke as, ‘being the link between the hub and the rim’ (http://sapim.mia.be/spokes). Spokes enable wheels to have remarkable strength with surprisingly little weight.

I use (almost exclusively) Sapim spokes. Sapim offer a range of high end products, at least as good as DT at more competitive prices. I do have some old DT stock purchased prior to their recent price increases. I have no concerns about the quality of DT Swiss spokes; only that they are roughly equitable quality yet more expensive than Sapim. Sapim have a permanent research centre so despite being established in 1908, they are still continuing to innovate and keep up with market developments. All Sapim spokes are made in either Belgium or France.


Different spoke types

There are three spoke types. The plain gauge spoke, the butted spoke and the aero spoke. The plain gauge spoke is the basic spoke used in approximately 90% of wheels. There are two versions that Sapim makes; the Zinc spoke and the Leader spoke. The Zinc spoke is the most basic version and is quite simply a cheap spoke. It is not imported into the country as standard and is not for our purposes worth further mention. A far higher quality version is Sapim’s Leader. There is a big variety in leader race strong plain gauge spokes, although you may be unable to tell this by eye. Sapim’s leader spokes receive the same strengthening treatments as their butted spokes, which means they have a lot more strength than most competing versions. They are also still made from stainless steel. The main disadvantages of the Leader spoke over other Sapim spokes are weight, flexibility and fatigue life. The Leader is still only really a basic spoke, best suited to economical wheelsets. They are available in a wide range of profiles so they can be applicable for builds which require unusually large spokes. They also offer a huge range of lengths which can be modified if necessary. It is generally in these applications that I use Leader spokes.

A spoke is subject to three key kinds of force. One is constant, because of the tension it is held under and the weight of the bicycle. Sapim refer to this as carry. The others are inconstant (impact and transmission); when an impact is made upon the wheel so the spoke needs to help absorb these irregularities. The spoke will only do part of this, some will be absorbed by other components; rim, frame, handlebars etc. Some is passed onto the rider. It is when a wheel receives these sudden forces that butted and aero (which are also butted) spokes become important. The dimensions of a butted spoke differ from plain gauge because they are not a continuous thickness throughout. Sapim’s butted spokes use the SCFT-system (Sapim Cold Forging Technology). This allows the spoke to be stretched without causing any damage to its molecular structure and Sapim claim this increases the strength in the central portion by at least 48%. Butted spokes can flex and absorb impacts better than plain gauge because their central butting allows them to stretch. The extra material around the elbow and nipple allow strength to be retained in the areas that commonly fail. Finally the thinner central portion allows the butted spoke to be lighter than the plain gauge.

Butted spokes
Sapim’s most common double butted spokes are called Race spokes. This is equivalent to DT Swiss’ Competition spokes. They are 2.0mm thick both ends and 1.8mm thick in the central section. This would be the standard choice for most wheels. They are good for MTB, standard touring, standard road use. However, if you are looking for a more exotic double butted spoke. Sapim offer three other types.

Firstly there is the Laser spoke. This has been made out of a different type of stainless steel. It was developed in response to a growing need for high tension spokes. Higher tensions make a wheel stronger, stiffer and more stable. The Laser also has a thinner central portion as it is butted in a 2.0mm-1.5mm-2.0mm profile. The 2.0mm elbow and nipple end make the spoke compatible with the same hubs as the Race and the same nipples too. They both come with nickel coated brass nipples as standard. The Laser spoke is only slightly more expensive than the Race so it can be an easy upgrade on light weight road wheels. They are not designed for heavy duty applications. They are not recommended for particularly high transmission applications.

Secondly there is the D-Light spoke which has only recently become available in the UK. It is also one of the most recent additions to the Sapim range. The Laser spoke has been rated as not suitable for use with disc brakes. However, the Race spoke is relatively heavy for a double butted spoke. The D-Light compromises between the weight saving of the Laser spoke and the strength advantages of the Race spoke. The D-Light is butted in a 2.0-1.65-2.0mm profile, making it compatible with the same hubs and nipples as the Race and Laser spokes.

This may sound like too niche a spoke to justify producing and importing. However, it is only as niche as the Laser. Essentially if you are running rim brakes you have three key alternatives: The Race as the economical solution, the Laser as the light weight mid-priced option and the CX-ray which is the top quality aero version (which will be discussed in detail later on). If you are running disc brakes, the Laser is ruled out and the D-Light takes its place. However unlike the Race and Laser spokes, only black versions of the D-Light have been imported.

Why only black? Well, Sapim’s black spokes, unlike cheap black spokes, use a special anodising to colour them. This actually helps to protect the steel from corrosion against extreme elements (even stainless steel can corrode slightly). This process is expensive which is why the cost of Sapim’s black spokes is considerably more than the cost of silver versions. Given that the D-Light is a spoke designed for use with disc brakes, it is likely that it will be subjected to the elements along with dirt, grit and so forth in high quantities. Moreover black spokes are a more common preference among disc brake applications. The cost of black D-Light spokes is the same as black Laser spokes.

Finally there is the super spoke which was developed by Sapim in collaboration with Tune. The idea was to create a stainless steel spoke that was strong, yet lighter than any other produced before. The butting profile is extremely light gauge 1.8-1.4-1.8mm. This allows the weigh to be a mere 231g (64 pieces at 260mm). Their profile will cause some compatibility issues with some hubs as well as requiring different nipples. They are made from a different stainless steel which Sapim are being secretive about. This exotic steel accounts for their exceptionally high cost. They are available only as a special order item at the moment and the price is yet to be confirmed. Their strength in the central portion is a whopping 3040n/mm2. They are one of the most expensive spokes in Sapim’s range and designed for use at a Professional level.

Sapim have also produced a triple butted spoke known as the Force, although this is not available in the UK. This is butted in a 2.2mm-1.8mm-2.0mm design. Spokes most commonly break at the elbow, furthermore hub manufacturers have increasingly moved towards 2.5mm hub drilling, which means that a 2.0mm elbow can sit quite loosely. The Force takes advantage of the butted spokes flexibility and reinforces the spoke at its weakest point. Being 2.2mm at the elbow the Force will still fit in 2.3mm hub holes. The Force is one of Sapim’s more expensive spokes because of the difficulties in triple butting a spoke. Triple butting has enable the Force to extend its fatigue life by a margin over the Race spoke without adding much weight.

Another other butted spoke that Sapim produce is called the Strong spoke. This is single butted in a 2.3mm-2.0mm design. Single butted spokes possess less flexibility than double butted. However it is more economical and more available than the Force and it is strong option when flexibility is less important. The Strong is the strongest spoke in Sapim’s range and is recommended for very heavy use applications such as tandems, electric bicycles and is an economical alternative for downhill racing.

laser force cx-ray

Aero spokes
Sapim also produce a range of Aero spokes. Aero spokes are made from butted spokes so they still offer all the butted spoke benefits. In addition to this they offer aerodynamic advantages. The process of making them aero improves their fatigue life and strength. They can also be steadied during building which helps to prevent spoke twist.

The most famous aero spoke produced by Sapim is called the CX-ray. It is 2.0mm at the elbow, the centre section is oval and is 2.3mm deep but only 0.9mm wide. The CX-ray was developed from the Laser spoke. They have hammered it into an aero profile. The profile allows for compatibility with almost all hub types and standard nipples. One disadvantage of previous ‘bladed’ spokes is that they often required hub filing. This was not only tedious but also weakened the hub. Some hubs came pre-filed but this limits choices for builds, now bladed spokes have now fallen out of fashion in favour of aero spokes. The CX-rays are so strong that they are even rated as suitable for downhill racing.

Sapim also produce the CX spoke. The CX spoke is a more traditional bladed spoke. They normally require hub filing as their profile is 2.0 – 1.3×2.8 – 2.0mm. These are heavier than the CX-rays as well although they are a tough spoke. They have been made from a plain gauge spoke which accounts for their economy in comparison to the CX-ray. CX spokes are not imported into the UK as standard.

Finally Sapim have very recently produced the CX Super spoke. No information about this spoke has been released, however we can speculate that this is to the Super spoke as the CX-ray is to the Laser. That means the same weight as the super spoke but stronger, longer lasting and more aero-dynamic.

Below is a chart with a technical comparison of Sapim spokes:

 

Type Weight (x64@260mm) Strength Fatique life (revolutions)
Zinc 424g 950-1050n/mm2 700,000
Leader 421g 1080-1180n/mm2 870,000
Strong 430g 1400n/mm2 1.6 million
Force 368g 1350n/mm2 2 million
Race 360g 1350n/mm2 980,000
D-Light 309g 1300n/mm2
Laser 279g 1500n/mm2 1.25 million
CX 423g 1200n/mm2 To be announced
CX-Ray 272g 1600n/mm2 3.5 million
Super spoke 231g To be announced To be announced
CX Super To be announced To be announced To be announced

It is important to understand that the strength measure is not an overall strength comparison; it is a comparison of the strength of the central portion. The central portions on certain spokes are slimmer which makes them look disproportionately strong. The Strong spoke is considerably stronger than the Laser despite appearing weaker in this comparison.
radial tangential2
Front wheels and lacing patterns

When selecting spokes for a wheelset it is important to understand each wheel differently. The front wheel carries less stress than the rear. Therefore it does not need as strong spokes and fewer spokes are required. Sapim Race spokes are appropriate for most front wheels, although Sapim Lasers could be used if weight saving was important or better still CX-rays. A front wheel can normally be both radially or tangentially laced. This means the spokes can either come directly out of the hub to the rim, or they can come out at tangents to the hub. Tangential spokes normally cross three other spokes before they reach the rim. This has given rise to the term 3X, which is the most common lacing pattern. Many hub manufacturers refuse to warranty products built into radial wheels. There have been instances where the spoke has been pulled straight through the hub flange.

Many wheel builders refuse to build wheels with radial lacing patterns because of the risk of the spoke being pulled through the flange of the hub. However many major wheel manufacturers have moved towards radial front wheels because of aesthetic benefits as well as some weight saving advantages. I have built many wheels with radially laced spokes and none have ever failed at the hub. However, I always point out before building that with the majority of manufacturers, radial lacing invalidates the warranty. I would also discourage the use of radial lacing because it distorts the hubs making for a weaker wheel and it makes for a slightly rougher ride. Another factor in radial lacing is it is a stiffer lacing pattern. This is why most performance wheels now use radial lacing on front wheels. There are two ways you can lace radially. One is heads in, the other is heads out. The spoke can be laced in either orientation. Heads in is stiffer which puts greater strain on the spoke and hub flange. Some manufacturers that allow for radial lacing on the front do so only if laced with heads out. If you are lacing radially for aesthetic reasons, it is best to have heads out. This will offer a more comfortable ride and a stronger build. If you are looking for maximum stiffness and the hub will allow it, lace heads in.


Dishing and rear wheels

324px-Bicycle_wheel_dish_diagram.svgA rear wheel is quite different to a front. It is normally ‘dished’, it also carries a higher proportion of the bike’s load. It cannot be completely radially laced because a rear wheel has turning forces exerted upon it from the hub, these would stress and break the hub flange as the spokes are pulled out. Most commonly rear wheels are 3X, however 40 spoke wheels are done in a 4x lacing pattern. Higher spoke counts still require high cross counts in order to maintain the spoke angle. Other wheels which require particularly short spokes such as Brompton or Rohloff wheels require 1x or 2x. Lower spoke counts necessitate lower cross counts 24 spokes or less requires 2x as 3x would provide compromising angles at the rim as well as the potential for spoke heads to come into contact with other spokes. It is possible to radially lace on the non-drive side of the rear wheel in some instances (not when using disc brakes). This will improve stiffness but again hub manufacturers normally prefer you not to.

Dishing occurs on rear wheels which uneven centre to flange measurements, normally there to incorporate external gears. The right hand flange is moved towards the centre line of the hub in order to fit in the cassette or freewheel. This means that the right hand or ‘drive side’ spokes need to be under greater tension than the left hand or ‘non-drive side’ spokes. The tensions on a drive side are sometimes as much as triple that as on the non-drive side. Wheelbuilders and manufacturers have been creative in their solutions to this problem.

Sometimes people opt for twice as many spokes on the drive side; however quality rims normally have an allocated direction so this can be an inappropriate solution with spokes facing the wrong way in the rim. Moreover this solution requires a stiff rim to remain true; two successive spokes pulling in a given direction separated by only one in the opposing direction makes for a natural waver in the rim. Another solution which I sometimes use is to have different spokes on the drive side to the non-drive side. The non-drive side will commonly use the same spokes as used on the front wheel. The drive side will have heavier duty spokes and importantly spokes with less flex. This means that the spokes flex more evenly on both drive side and non-drive side. A light duty build could use Sapim Laser spokes for the front and non-drive side and Sapim Race for the drive side. Heavier duty could be Sapim Race for front and non-drive side and Sapim Strong for the drive side. You could also use D-Light spokes with Race spokes or Laser spokes to achieve similar slightly varying results. Many wheelbuilders neglect such detail, although it is important for a well balanced wheel. Moreover it does not need to add considerably to the cost of the build. An important factor to consider before doing this is that sometimes a larger spoke elbow (such as the Strong spoke) will sit badly in a hub. Considering the quality of all Sapim spokes, most wheelsets can be laced with the same spokes throughout.

Below is a format modified comparison of the Sapim spoke range made by Sapim:

Usage Light (<70kgs) Medium (<85kgs) Heavy (>85kgs) Very heavy load (tandems, ebikes, …)
Weak rim Low All spokes All spokes All but Laser Strong
Medium All spokes All but Laser All but Laser Strong
Heavy All spokes All but Laser All but Laser Strong
Competition (road, MTB) D-Light, Laser, CX-ray D-Light, CX-ray D-Light, CX-Ray
Professional Laser, CX-ray, Super Spoke, CX Super CX-ray, Super Spoke, CX Super
Stiff rim Low All spokes All spokes All spokes Strong
Medium All spokes All spokes All spokes Strong
Heavy All spokes All spokes All but Laser Strong
Competition (road, MTB) Laser, CX-ray Laser, CX-ray Laser, CX-ray
Professional Laser, CX-ray, Super Spoke, CX Super Laser, CX-ray, Super Spoke, CX Super Laser, CX-ray, Super Spoke, CX Super

Sapim are, I feel, a little harsh on the Laser in this analysis. They have acknowledged to me that it is a high strength spoke. Stronger, they claim than the DT Swiss Revolution spoke which has been rated as capable of withstanding more than the Laser here. However, the problem with the Laser is how prone it is to spoke twist, more so than the Revolution. If the spoke becomes excessively twisting during building or retruing, that will weaken the spoke considerably. This is why the CX-ray, despite being made from the same material and drawing process, is rated as capable of so much more. Holding the spoke steady prevents spoke twist.

 

 

If you are interested in learning more about choosing wheelsets, building wheels and selecting component parts as well as information on repairing wheels please seeBicycle Wheelbuilding: The Manual an ebook which is available exclusively through DCR Wheels.