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Things You Never Knew About Bicycle Spokes

by John Neugent

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Things you never knew about bicycle spokes

When people think about a bicycle wheel, seldom do they pay much attention to the spokes.  As Rodney Dangerfield would say, they don’t get no respect. I remember when I was first getting into the wheel business asking DT Swiss, one of the top spoke makers in the world, why they were not selling complete wheels instead of “just” the spokes. They said they didn’t want to compete with their customers but my guess is what they really meant to say was – why should we – the spoke business is more profitable (now they sell lots of complete wheels). Of course I don’t know that to be true, but I often pay more for the spokes in a wheel than for the rims – and often a little less than I do for the pair of hubs. I am not skimping on the rims and hubs. Those little pieces of wire cost a lot of money.

DT Spokes

Bicyle spokes, like these from DT, are surprisingly complex

To give you some idea why, Sapim recently introduced a new super spoke. It was bladed like the CX Ray spokes now preferred by many of the top pros, but was lighter still. They had introduced the spoke a couple of years ago but were having a hard time producing it. There was only one person in the company who knew exactly how to make it and he unfortunately, died.

So even though these pieces of wire look simple, they’re not.

Pillar bladed spoke

Picture on left: Pillar bladed spoke

About 15 years ago, bike companies were doing two new things with spokes (doing one new thing is dangerous; two is like walking a tight rope). They were reducing the spoke count and also asking for black spokes. When you go from 36 spokes to 24 or 28 spokes and also make them black you are asking for the spokes to be a lot stronger and you are treating them with a coloring process (which unfortunately made them brittle). Since spokes fail by fatigue these issues took about a year to surface and affected thousands of wheels. Luckily, or not, this was a problem primarily affecting the Taiwan spoke makers.

While anyone can buy the same wire as the top spoke companies, or something very similar, there are lots of trade secrets on the manufacturing processes and it’s those processes that determine the quality of the spokes – especially the butted and aero spokes.

Spokes can be categorized into three categories: straight gauge, butted, and bladed.  For the purpose of this article I am not going to go into aluminum or carbon spokes – just steel spokes.

Straight gauge spokes are generally either 13 gauge (2.3 mm), 14 gauge (2.0 mm) or 15 gauge (1.8 mm). Virtually all high quality steel spokes are made of stainless steel. The top brands mostly use a Sandvik 18/8 alloy (18% chromium and 8% nickel) that can be hardened by cold working (important for the butted and bladed spokes).

Butted spokes are made by cold working the center to a smaller diameter than the ends. Interestingly, the process involves peening the center with many small anvil type heads. The thinner the spoke, the more it’s been peened and therefore the more it’s been cold hardened and the stronger it is. Spokes are never stretched to reduce their gauge. Also, the spoke threads are always rolled and never cut.

Typically a 14 gauge spoke will be either 1.8, 1.7, or 1.5 mm in the middle. The thinner the middle, the lighter the spoke but more care is needed in building because with the thinner center they have a tendency to wind up. I know what you are thinking, there is very little difference between these in terms of weight and strength. That’s not so. A butted spoke with a 1.8 mm section is about 6 grams. One with a 1.5 mm section is a little over 4 grams.  The difference, times 44 spokes is 88 grams for a set of wheels – that’s a lot of wheel weight considering it’s just the spoke diameter changing. As an added bonus, because fatigue causes spoke failure, the lighter spokes are stronger because they stretch a little better (and have been hardened more).

Bladed spokes became widely popular with the introduction, by Mavic, of the big aero blade. The increasing importance placed on aerodynamics also added to their popularity. For steel bladed spokes there are a wide variety of options, the most popular being the Sapim CX Ray which is both extremely light (a little over 4 grams) and very strong (the strongest spoke Sapim makes (except for their 13 gauge spokes). Both DT Swiss and Pillar have similar spokes.

Pillar, in Taiwan, makes a wide variety of big bladed spokes that I used for many years with great success. They are a 13 gauge spoke (2.3 mm) that is bladed to a wide center (3.5 mm or wider) that necks down to 2.0 mm 14 gauge at the threads so you can use a 14 gauge nipple. These are big spokes (about 9 grams) but are incredibly strong. You can use fewer spokes but you then have more issues with rim cracks (the bane of all lower spoke count wheels).

One of the major developments over the last 10 years or so that receives little or no respect is the increase in spoke strength allowing for fewer spokes. I would imagine that quality improvements were gradual and largely in house production changes but the cumulative effect is significant. One could argue aluminum alloys for rims also have allowed for lighter and stronger rims – which I agree with – but the fact you can now safely use 16-18 front spokes, and 20-24 rear spokes on a wheel (some use even less) is a game changer not only for the weight of the spokes but also for the increased aerodynamic performance.

Think of wheels as little egg beaters with the spokes being the blades. The more blades the more they are going to churn the air. So by using fewer spokes, you are not only reducing the wheel weight but also increasing the aerodynamics.

There is a point of no return however. Some wheel makers, in an effort to make even lighter wheels use 20 spoke rear wheels.  Many strong riders find that that’s not enough and result is that they are not stiff enough and you get brake rub.

I have never seen a direct study on spoke count and aerodynamics and I suspect wheel companies are more interested in claiming overall better wheel aerodynamics rather than pointing out they are just using fewer spokes.

An extremely common belief is that spoke tension determines wheel stiffness. It does not. A spoke that is under any tension (not loose) will be a stiff as a spoke under very high tension. Tour mechanics of the past (and probably still) often de-tension spokes for the cobble classics thinking that it smoothed out the ride. They were wrong. The reason for high spoke tension is that spokes stretch over time and the higher the starting tension, the longer you will go without getting a loose spoke. Another reason is, on the rear wheel, the added number of sprockets cause a more severe dish which lowers the non drive side spoke tension. Since the non-drive-side spokes essentially center the rim, the only way to increase their tension is to increase the drive side spoke tension.

So although a spoke appears to be a relatively simple piece of wire, there’s a lot of material and processing development that go into them. Sometimes the things that appear to be simple are very complicated to develop and produce. So give those spokes a little bit of respect.
