SpheresBearings are at the heart of every rotating part on

your bike, but will swapping steel for ceramic make a significant difference to your ride? Or is it all just balls?

Words Stu Bowers Photography Danny Bird

ver since the ancient Egyptians used a platform of tree trunks to move giant stone blocks into place while building the Pyramids, bearings have helped the human race to keep rolling along.

Interestingly, the first official patent for a ball bearing was for a bicycle. French

mechanic Jules Suriray fitted them to a bike that went on to win the world’s first city-to-city bicycle road race, Paris-Rouen, in November 1869. These days, bearings are better known to all cyclists as those things that fall apart during disassembly and require hours on hands and knees searching under workbenches or fridges to retrieve.

History lesson aside, bearings play a huge part in how bikes can move so freely. Pedals, cranks, wheels, headsets, jockey wheels… if it rotates, bearings are at the centre of it, and without them we’d be struggling to ride anywhere fast. There are many different types of bearing, so it’s worth making a few definitions clear at this stage to remove confusion.

When we refer to a ‘bearing’, we mean a component that consists of five basic parts: balls, seals, ball cages,

E

of influenceraces and grease. The concept is simple – several balls are sandwiched between two concave surfaces (races), allowing them to rotate against each other (one is usually fixed) with minimal friction. The cages and seals hold everything in place and keep out dirt, while the grease lubricates and protects the moving system.

Most modern bike applications now favour ‘cartridge bearings’. These sealed units have several benefits over the ‘loose bearing’ systems of old, which are largely confined to low-end, cheaper components (although a select few top-level parts still choose to stick with the loose ball, cup and cone system due to its finer adjustability). Cartridge bearings generally require much less maintenance, and when they do eventually wear out, it usually won’t cause terminal damage to the parts around it. Plus they can be replaced easily.

‘Ball bearings’ refers to the balls themselves. Ball bearings can be made from different materials, including chrome steel, stainless steel and – the more recent arrival into the bicycle world (of which more later) – ceramic, usually silicon nitride (Si3N4). A ‘hybrid’ bearing is one with ceramic balls and metal races.

Magnifying a 1/4 inch steel ball to 20 times its

normal size shows off the tiny imperfections

on its surfaceP

Focus b Bearings

72 cyclist

All bearings are not created equal, regardless of what they’re made of. I once saw a top bike mechanic take out a jeweller’s magnifying glass, scutinise an apparently clean, shiny ball bearing and state, ‘I’m not putting those in my hubs. They’re like cake decorations.’ As with most things, a hierarchy exists in bearings and you get what you pay for.

What goes around… isn’t necessarily roundThe cheapest ball bearings may not even be perfectly round. Bearings are generally graded according to a scale of roundness, measured to millionths of an inch. A grade 200 steel ball means it is round to a tolerance of 200 millionths of an inch. Hence a lower number – grade 25 for example – is a much more precisely manufactured ball. For the sizes used in bikes, grades vary from 2,000 to 3, with anything under 100 generally being considered a ‘precision ball’. This grading system is used for both steel and ceramic balls, as well as a further gradation for surface roughness, where ceramic usually achieves a much smoother outcome – just one of it’s inherent benefits.

Do these tiny differences in roundness and surface make any real difference to the average cyclist? Alan Weatherill of UK-based component manufacturer Hope Technology says, ‘Ultimately, if the balls are poor quality and aren’t perfectly round or smooth, they will cause increased friction and premature wear and tear of all components of the bearing. It will inevitably fail. The quality of the ball, regardless of the material, is the most important factor.’

The importance of ball bearings is far greater than their size might suggest, which is why the cycling industry is making such a fuss over ceramic balls. Here’s the deal: ceramic balls are generally rounder, smoother, harder and lighter than steel balls, so should theoretically provide less friction and greater longevity. They are also significantly more expensive, so it’s worth taking a proper look at the potential benefits of ceramic balls before parting with your cash…

Modern marvel or marketing hype?Jacob Csizmadia, founder of CeramicSpeed, was the first person to introduce ceramic hybrid bearings to professional cycling back in 2000.

‘Bearings are graded according to a scale of roundness, which is measured down to millionths of an inch’

P

P

Focus b Bearings

74 cyclist

Ceramic balls are generally rounder,

harder, smoother and lighter than their steel equivalents… but also

much more costly

CeramicSpeed’s test data claims, somewhat boldly, a six-to-nine watt power saving over steel bearings. If true, that’s a decent chunk of energy and potentially time saved by simply swapping out your bearings, but not everyone thinks that ceramic bearing are quite the miracle that some would have us believe.

Weatherill explains why Hope felt the need to offer a ceramic bearing option for its hubs and bottom brackets: ‘We did it because it was asked of us [by the market]. We didn’t do it from an engineering point of view. A lot of it is hype. Ceramic bearings are used in industrial machines because they spin at 25,000rpm and there are significant advantages, but a bike wheel only spins at, say, 300rpm, so the differences compared to the very high-quality steel balls we were already using is very slight.’

CeramicSpeed director Martin Banke is keen to dispute Weatherill’s view, and defends his test data by saying, ‘Ceramic bearings are not a marketing hype. Ceramic balls are superior to

steel balls under any load experienced on a bike – assuming suitably high-end ceramic quality.’

It’s this issue of quality, Banke suggests, that might be why some people are still unconvinced by ceramic bearings: ‘The quality of [other manufacturers’] ceramic bearings varies. This means some very poor, usually cheap bearings with higher friction, higher brittleness and short longevity are in the market and that’s why some, for good reason, still question ceramic bearings.’

When asked to comment on Weatherill’s statement about the necessity of ceramic balls at the lower rotating speeds of the bicycle, Banke says, ‘If you look on the first page in the big book about hybrid bearings, you’d say the answer is no [to needing them on a bicycle]. Actually this is far from true. It is correct that ceramic bearings were originally invented for high-speed applications where the lower weight and high stiffness of the balls and low friction of the bearings enabled the machines to spin faster without destroying the bearing. But, like with lots of other technologies, ceramic bearings proved to have extremely good properties for bikes as well. A material like carbon fibre was

not originally invented for bicycles either, but is now used by everybody.’

As if to back Banke’s point, one recent entry to the ceramic market after an initial period of uncertainty is Chris King, the US brand with perhaps the most prestigious name in bearings for bicycles. In the early days of the ceramic ‘boom’, Chris King was not keen to leap in, and continued to fight steel’s corner for some time. Yet it too now offers ceramic upgrades for all its components, with the exclusion of headsets.

‘There has been a large amount of hype surrounding ceramics since their introduction, and a number of products introduced into the market haven’t had the overall design to bring this material to its best performance, thus in some cases giving it a bad name,’ says King, owner of the eponymously named company. ‘The decision to offer a ceramic option was a conscious choice, not a marketing-driven one,’ he stresses, and he justifies the company’s tardy entry to the ceramic fray by saying, ‘Quality steel balls and lubricants perform very well and we have years of experience that prove this. To learn about the attributes of ceramic balls we put them through extensive testing. The decision to offer a ceramic option came about only after we proved to ourselves that there were genuine benefits.’

One of those benefits, King claims, is that ‘ceramic balls have an exceptional ability to retain their “true” spherical shape under load. This creates the conditions for our ceramic-equipped components to have an exceptionally long and smooth running life.’

Yet King admits that the performance benefits are not huge: ‘Our research has shown that our hybrid ceramic bearings offer subtle benefits to the discerning consumer.’ The benefits lie mostly in the ability to use lighter lubricants. King says, ‘In a King hybrid ceramic bearing the use of a ceramic ball reduces the lubrication requirement so lighter grease and less of it may be used than on a comparable steel bearing. Less lubricant means less drag on the bearings.’

This feels like ‘marginal gains’ territory. Perhaps more performance could be squeezed from bearings if all the parts were ceramic instead of just the balls? Chris King, Hope and CeramicSpeed all provide ‘hybrid’ ceramic bearings (ceramic balls in steel races), so would ceramic on ceramic be even better?

King says he has ‘not yet been able to prove that there is a need for fully ceramic bearings’ and also cites cost as the biggest reason for not going fully ceramic. Banke suggests ceramic races can be more brittle with greater potential for failure, so he too is sticking with hybrid.

When asked what they think the future holds, both Banke and King agree that ceramic bearings

‘Ceramic balls have an ability to retain their “true” spherical shape under load for a long running life’

P

Fact and frictionCeramic bearings – true or false?

* High-quality ceramic balls are ultra-smooth, resulting in a bearing with very low coefficient of friction. TRUE

* Less friction leads to a longer lifespan. TRUE

* Ceramic bearings don’t need lubrication. FALSE ‘A high-quality ceramic bearing will work better than steel in the absence of lubrication and have a longer lifetime than a low-end ceramic, but if you want the most out of your ceramic bearing you must lubricate them,’ says Martin Banke of CeramicSpeed.

* High-quality ceramic balls are very stiff so don’t deform as much under load as steel, which improves resistance to wear and increases stiffness in the entire system (eg, bottom bracket lateral stiffness). TRUE

* Ceramic balls are lighter than steel equivalents. TRUE While the overall weight difference it makes to your bike is negligible, lighter ball bearings spin faster, reducing friction and improving rolling resistance.

P

Focus b Bearings

cyclist 7776 cyclist

Rolling stockHow are bearings made?

are here to stay. Banke even predicts ‘a huge increase in the number of aftermarket upgrades – many people who buy an expensive wheelset one year will probably be buying a bearing upgrade kit the next’.

How not to spot a good bearingHands up if you’ve done this… put a bike in a workstand or turn it upside down, get the wheels or bottom bracket rotating fast and then see how long they spin for. The longer they spin, the better the bearings, right?

It’s a trick used by manufacturers at bike shops and trade shows, where punters are invited to spin a wheel or BB and marvel as it turns effortlessly for an age. An easy way to achieve this is to take the grease out of bearings and use a light oil to reduce friction and make it spin easier. It’s something that road racers, especially time-triallists, used to try to gain an advantage.

Of course, what this fails to take into consideration are the sizeable forces on a bearing that the pedalling action and the rider’s weight imparts. As soon as you sit on the bike, let alone sprint it up the road, the balls will be forced hard into the races, and unless the lubricant can cope with that force it will simply be squeezed out of the contact patch, resulting in the ball running straight against the surface of the race unlubricated.

Banke explains, ‘A steel bearing with no seals, completely clean and dry, could spin very well in the stand. But as soon as you add weight the steel balls touch the steel races and friction increases dramatically.’ The same effect can also be achieved ‘by adding too much clearance in the bearing. Out on the road you will experience play and increased wear rate, and the bearing will probably fail quickly.’

The moral is: don’t believe the spin – literally. The only way to ensure longevity and genuine, if marginal, performance gains is to be certain of the quality of your balls. Stu Bowers is deputy editor of Cyclist and is bearing up well

Creating a ball bearing is a lengthy process. Steel balls begin life as a rod, which is chopped into sections approximately the length of the diameter required for the finished ball. It is then compressed between two dies into a basic spherical shape, but this process leaves excess material around the ball which, at this point, is still far from perfectly round.

Creating perfect roundness and removal of the surface roughness is achieved in stages. Firstly, rolling the balls in grooves between steel plates under pressure knocks off the larger pieces of excess steel (called ‘flash’) and creates a perfect sphere. Next the balls are tumbled and rolled between plates with less pressure, but with an added abrasive paste to remove surface imperfections. Ball bearings must be both perfectly round and perfectly sized so this is achieved by varying the amount of time and pressure applied during these milling and rolling processes.

The final process is tumbling and rolling the balls once again, under further reduced pressure and in a lapping solution that cleans and polishes the surface.

‘Many people who buy an expensive wheelset will probably buy a bearing upgrade’

]

P

78 cyclist

Focus b Bearings