Precious Metal

Stainless steel bikes are highly prized and highly priced. What are you getting for your cash?

Stainless steel is the latest material to grace the upper echelons of handmade bicycles, but what exactly are you getting for your money?

While it may have been commonplace around the home for decades – check your sink, cutlery, nail scissors – stainless steel has only recently been used to make bicycles. And although your spoons may be seen as cheap and utilitarian, bikes made from stainless steel tend to be exotic, hand-crafted and at the expensive end of the scale.

An obvious benefit is its resistance to corrosion, but this alone cannot justify the hefty pricetags, which often dwarf carbon fibre alternatives, so Cyclist looked to the industry experts to find the real reasons for choosing stainless steel, and whether it’s worth the money.

Any old iron

Before we delve into the intricacies of bicycle-specific stainless tubing, it’s worth explaining what stainless steel actually is. It might surprise you to know it’s essentially just an alloy of plain old iron, and not entirely unlike other forms of steel in terms of composition, apart from one key constituent – chromium.

In its simplest form, the term stainless steel just means an iron alloy that has a minimum content of 10.5% chromium by mass. It’s the chromium content that prevents the oxidisation that occurs on carbon steel (the standard type of steel, which has a carbon content of up to 2% to add strength) when in contact with air and moisture – in other words, rust. This orange cancer, or more precisely iron oxide, is an active process, which means that rusting rapidly facilitates more rust. That’s why it is a hard process to stop once the rot has set in, and also why eventually the base metal will be eaten away to nothing.

This is a potentially big issue for standard steel bike frames, as moisture trapped inside the frame, hidden from view, can be doing its damndest to rust tubing away from the inside out. In the worst cases, this will eventually lead to frame failure.

Stainless steels contain enough chromium to form a passive film of chromium oxide, stopping the surface corrosion in its tracks. This alone makes the material worth considering in many people’s eyes, but the less discussed benefit is its potential performance characteristics, which we’ll go into shortly.

As with most manufacturing materials there are many different grades of stainless steel, and not all would be suitable for building bike frames. Richard Hallett of Hallett Handbuilt Cycles tells us, ‘Standard stainless steel – something like 312 – is actually quite soft. The materials we use are a long way from that.’

This is the first clue towards why bike frame prices are higher compared to items made from other grades of steel. Albert Steward, product manager for Genesis, also hints at the complexities of highgrade stainless steel production, saying, ‘Reynolds 953 is only made in really small batches. The smelting, undertaken in the US [953 stainless steel is manufactured for Reynolds by US Carpenter Technology Corp, with whom it co-developed the steel alloy used], uses a double-vacuum process before a whole heap of other stuff they don’t really like to talk about. It’s really multi-faceted and time-consuming.’

Even though it’s a fairly new frame material for bicycles, there are three manufacturers producing tubesets that are readily available to the custom or small batch frame builder. UKbased Reynolds, US company KVA and Italian company Columbus all have at least one product in the marketplace. Reynolds offers the most, with three different options: 953 tops its list, followed by 931 (which is ‘precipitation hardened’ using heat treatment) and 921 tubes (which are ‘cold worked’, increasing strength by deforming the material). KVA’S MS3 is precipitation hardened like 931 and has similar tensile strength (a standard measure of strength) at around 1,300-1,400MPA. Columbus XCR is a martensitic (very hard) steel, like 953, but the tensile strength falls somewhat below Reynolds’ best at just 1,350MPA versus a maximum of 2,200MPA for 953.

As a material choice, stainless steel is often spoken of as having properties similar to titanium, but Keith Noronha, managing director of Reynolds Technology, explains a bit more about Reynolds’ stainless steel offering, and how the various grades might compare to other materials.

‘Titanium has lower stiffness [modulus of elasticity score] as a raw material – 115GPA against 207GPA for all Reynolds steels, and with its tensile strength of 900MPA it’s not as strong as our 921 tubing [1,000MPA], and our strength scores go up significantly higher for 931 and 953. Aluminium is often thought of as lighter than steel, but in 953 you

can build lighter [thinner-walled] tubes for a greater tensile strength too.’

Because stainless steel is harder than carbon steel, it’s highly dent resistant, so the thin walls of the lightest tubes can present significantly less risk than with aluminium or carbon fibre, where impacts can be potentially catastrophic. Considering the additional tensile strength, and the potential for the creation of light, stiff, corrosion-resistant frames, why isn’t the industry flooded with stainless steel bikes?

Posh plumbing

There’s an old adage: creating a bike frame is not that difficult to do, just very difficult to do well. This is perhaps the Achilles’ heel of stainless steel – it’s notoriously tricky to work with. Much of the difficulties arise from the material’s inherent hardness, especially when it comes to 953. Genesis’s Steward tells us, ‘When developing the Volare frame in conjunction with Reynolds, some of the more complex tubes would need to go through more than 40 processes to get formed into the profiles we were seeking. When the material arrives at Reynolds in Birmingham it’s then subject to an astonishing 47 separate operations to produce just one length of butted 28.6mm 953 tubing, and that’s before any further tube working such as swaging or ovalising.’

For a frame builder, once a chosen set of steel tubes is in their possession, the first stage is to cut the tubes down to size. Hallett explains some of the issues facing the stainless builder before a welding torch or brazing rod is even in the picture: ‘Stainless tube sets are very difficult to machine. The steel is very hard. This means that you must feed the tube onto the cutter very slowly and tools will blunt quickly. This is an added expense of working in stainless – having to replace tools frequently. It all needs to be factored into the frame costs.’

Steward adds, ‘Labour-intensive is an understatement. It takes four times as long to cut a 953 tube as 4130 steel and the result is it takes a long time to physically build a frame – and time is money. That’s simple economics.’

Once the tubes are finished, they’re ready for the joining process. ‘Welding or brazing stainless steels does require a significantly higher degree of skill and additional equipment,’ Noronha says. ‘This dramatically reduces the number of people able to offer steel frames.’

‘There are two ways you can join stainless steel tubes: TIG welding and silver brazing/soldering,’ Hallett says. ‘Whichever you choose, the problems stem from the fact that stainless steel is a very poor conductor of heat, so it gets very hot locally. If you are silver brazing, it’s very easy for the tube to get too hot from the brazing torch. It can overheat easily and burn the flux. Do that and it simply stops working. Flux prevents oxides forming on the surface of the metal during brazing, so if it stops working the base metals will not have actually joined together.’

Steward says, ‘When the wall thickness of the tube is so thin – down to 0.4mm in places – it’s prone to burn-through if the welding torch isn’t in the hands of a very accomplished welder. If you’re TIG welding 953 you have the added expense of purging. This is when Argon gas is pumped into the frame to prevent any impurities contaminating the back of the welds. Not many frame manufacturers in Asia are set up for this. When you find them, they cost more, but it’s a skills base you need to get a consistent, quality product.’

Future avenues

Stainless, then, might possess many ideal credentials for a bike frame but perhaps too many complexities to ever reach the mass market. One solution offered up by Noronha is the possibility of mixed media.

Frame builders capable of silver soldering have been able to marry different materials within their frames since the first stainless tube sets were developed, but it wasn’t an option open to the TIG welding fraternity – until now. At the recent 2015 North American Hand Built Bike Show (NAHBS), Reynolds presented the 829 tubeset. Working with the metallurgy department at Birmingham University, Reynolds assessed the weld capabilities of certain weld wires until they tested a configuration capable of passing the EN standard for frames.

One potential example of the mix-and-match approach would be to build a frame with a 953 lower half (where the stiffness, corrosion resistance and stone chip damage elements are ideal) welded to an 853 top half. This could keep costs down but still offer many of the benefits.

Asked if this mixed approach and new products becoming available would ever catapult stainless into the limelight as the new ‘must have’ material in the mass market, Noronha tells us, ‘We’re seeing some more OEM [original equipment manufacturers] setting up for stainless but we expect it will still remain “high-end, low volume”, and mainly a niche for custom frame builders.’

Hallett does not fully agree, though, saying, ‘There’s no real reason why stainless theoretically couldn’t become more mass market. Get enough people capable of welding with it and you could build a lot of frames. The potential is certainly there. But it will always remain expensive.’

Steward has the final word, saying, ‘Look at the fact that Reynolds is still developing its product range despite having a big offering already. It’s fair to say that the stainless wagon has only just got rolling, and more people are likely to get on board.’

Neil Webb is a writer and frame builder who works with words and aluminium