Read marketing and reviews for steel bikes and you’ll inevitably encounter words like lively, soul, heart, personality, spirited and feel. Anyone would think that a steel bike is a living and breathing animal. The big question is, is steel still a relevant frame material today?

Unquestionably, steel is where bikes began and despite those almost forgotten beginnings, steel bikes have maintained a cult following. Just as 1980’s Casio watches are now trading at 20x their original value, steel bikes are a hot property with the current craft beer generation. While basing a buying decision on nostalgia is somewhat understandable for a bespoke N+1* steel hardtail, to do so on a € 5,000 full-suspension bike is lunacy. At this price point, steel has to deliver serious performance to fight it’s corner against the formidable aluminium and carbon competition. Throwing all the overused steel hyperbole out of the window, we wanted to take an open-minded look at the latest steel bikes on the market.

*Where N is the number of bikes you currently own and N+1 the number of bikes you should own

Can steel trail and enduro bikes really hold their own against the competition from super-brands like Canyon, Santa Cruz, Specialized, Trek,Yeti and YT?

Skinny tubes to match skinny arms – putting steel bikes to the test

It seems that mother nature has a cruel sense of humour. While the UK was driven into lockdown by the global pandemic, the normally hostile Scottish climate delivered eight weeks of uninterrupted sunshine. Dusty trails sat unridden, drier than they had ever been. And then we were out! Restrictions eased, allowing us to rush back to the trails with weedy, pipe cleaner arms. It was time for some ‘sun’s out, skinny guns out’ action. Coincidentally, to match our skinny arms, we had a brace of skinny-tubed steel bikes to put through their paces.

Bike Price Weight Travel f/r Wheelsize
Cotic RocketMAX Gen3
(Click for review)
€ 5,575 15.40 kg 160/160 mm 29″
Pipedream The Full Moxie
(Click for review)
€ 4,070 16.10 kg 150/146 mm 29″
Starling Twist
(Click for review)
€ 5,226 15.90 kg 160/160 mm 29/27.5″
Where is the mud, where is the rain? Scotland delivering some trail gold.

What is steel?

Steel is one of the world’s most important engineering and construction materials, used in almost every industry and application. There are over 3,500 different types of steel, but all are ultimately an alloy of iron and carbon, augmented with a number of different elements. The most common steel alloy used in bike frames is 4130 Chromoly which adds small amounts of chromium and molybdenum, resulting in a high strength-to-weight ratio. Steel is completely and easily recyclable without any degradation in the properties of recycled material. It also requires relatively low amounts of energy to produce (almost three times less than aluminium) and possesses great durability if properly looked after.

Why are steel frames skinny?

Fabled for its compliant and comfortable ride, especially when used in hardtail frames, why are steel frames so much skinnier than aluminium bikes? Accepting some generalisations, steel is around three times denser than aluminium, but also three times stiffer. Steel is also significantly stronger than aluminium. However, stiffness and strength are very different parameters. The stiffness of a material is described by its Young’s Modulus, defining the relationship between stress (force applied on the material) and strain (the deformation of the material). The strength of a material is described by its Yield Strength, the point at which the material passes beyond its elastic limit, and deforms permanently (bends). When it comes to bike frame manufacture, the frame should be designed in such a way that the normal forces encountered are far below the yield strength of the material used. As such, strength plays a subordinate role, and it’s a combination of tube dimension and material stiffness that will influence how a frame rides.

Understanding the differences between stiffness and strength and knowing the density differences between steel and aluminium allows us to understand why steel frames are skinnier. Given the same wall thickness, a larger outer diameter tube is stiffer than a tube with smaller outer diameter – doubling the diameter of a tube roughly increases the tube stiffness four times. Of course, increasing the diameter of a tube whilst using the same amount of material requires a reduction in the tube’s wall thickness. Steel is a dense metal, so frame designers are limited in how much overall material they can use before the frame becomes too heavy. When increasing the diameter of the tubes, there will be a point where the tube walls become too thin to offer enough impact resistance and strength. In contrast, aluminium is less dense, so can be shaped into much larger diameter frame tubes with thicker wall thicknesses (as a larger volume of material can be used) resulting in a stiffer frame.

If steel frames are less stiff, are they less durable? Compared to aluminum, steel has a much higher fatigue life, resisting the weakening effects of being repeatedly loaded. In contrast, aluminium degrades if it is allowed to flex or experiences high peak stresses repeatedly. The stiff design of an aluminium frame with thicker and larger diameter tubes reduces the peak stresses and bending, preserving the material. In contrast, with its higher level (we’re still talking very small amounts) of elasticity, steel can resist repeated flexing forces below its fatigue limit, and these forces will never cause failure.

In conclusion, the density of steel limits how stiff you can make a frame if you want it to weigh a reasonable amount, because the wall-thicknesses can only be so thin and larger diameter tubes require more (heavy) material. However, the higher fatigue limit of steel means that steel bikes can be designed with skinner tubes that offer some degree of flex for comfort and compliance, but are strong enough that all ‘normal use’ forces fall below the fatigue limit, so in effect, will last indefinitely.

Made properly, a steel bike is more durable than an aluminium or carbon bike, with a higher fatigue limit and taking hits for longer.

Buying on a label

Purists will wax lyrical about the unique properties of different grades of steel, is 853 better than 4130? Can you ‘feel’ a higher quality steel? All steels have the same Young’s Modulus (a measure of the tube stiffness) regardless of their composition. In truth, given the same dimensions, even the most boutique steel is no ‘stiffer’ than the steel you will find in scaffolding poles or the cheapest supermarket bikes. A bike manufactured from cheap tubing will be no less stiff than an identical one made from the most expensive steel. However, it will not be as ‘strong’.

Cheap steels like the mild steel used on nasty budget bikes have a lower yield strength, so need thicker-walled tubing to maintain the necessary impact and buckling resistance – that also means more weight. Higher quality steels like 4130 CrMo or Reynolds 631 and 853 have a much higher yield strength, 3–4 times stronger, allowing much thinner-walled (hence lighter) tubes to be used. However, there’s a limit to how thin you can go, limiting how light a steel frame can ultimately be. Some metals like 4130 can be weakened during the welding process and need further heat treatment to restore the strength of the frame, while other metals like the expensive Reynolds 853 increase in strength after cooling in air after welding. Frame builders also have to consider the ‘butting’ of the tubes, where the outside tube diameter is constant but internally the wall thickness varies. Designing a steel frame is a balancing act. Understanding this, we understand why it’s not always best to buy a steel bike based solely on the fancy sticker on the downtube. Instead, it’s better to focus on whether the designer has taken into account tube shapes, wall thicknesses and diameters to give the frame the desired compliance and performance.

Does steel make sense for an ENDURO bike?

The elastic properties of steel might make perfect sense for a hardtail frame but do they make sense for a hard-hitting enduro bike? While the words may have similar definitions, there’s a world of difference between compliance and stiffness. A full suspension enduro bike needs to be capable and confident on the roughest of trails, stiff enough to charge direct lines through rock gardens, and compliant enough not to rattle your eyeballs out on big hits or metre long braking bumps. When it comes to stiffness, aluminium and carbon fibre are considered king if used correctly, making use of large diameter tubes to create stiff and strong frames and relying on the suspension for comfort and control. Could the properties of steel make it a suitable material for a full suspension bike?

Three bikes, three very different companies

To find out if steel is still a contender, we put three steel bikes to the test on the trails of Scotland. Starting with the big-hitter, the Cotic RocketMAX is a fusion of an overbuilt Reynolds 853 front triangle with a 6066-T6 aluminum rear triangle, aiming to combine the best of both worlds. When it comes to performance, the RocketMAX throws down a mixed metal gauntlet at the feet of the best aluminium and carbon enduro bikes. We also tested the Pipedream Full Moxie, who’s slender frame silhouette and skinny stays champion the aesthetic of steel and who’s short travel and aggressive geometry suggest a bike to do-it-all. Completing the test field is a Starling Twist, the very definition of less is more. In contrast to its simple suspension design and classic lines, the on-trend 29/27.5” mullet wheels and coil suspension point at a very modern shredder. We had many questions to answer. Does steel offer benefits as a frame material? Does steel feel different? Is flex good? One answer we already knew – after months of lockdown we were going to have a total riot finding out.

Why the hell would I buy a steel bike?

Nostalgia aside, is a steel full-suspension bike really worth it? With the prices of our test bikes ranging from € 4,000 to € 5,000, the truth is that you could get a LOT of bike for the money if you bought aluminium or carbon. Look at the likes of the Nukeproof Mega 290, YT JEFFSY or Canyon Strive, all dripping with the blingest components and undercutting the steel bikes by a considerable margin. Do you get more performance if you buy a steel bike? No, not at all. At the same price point, you will get a lighter bike with better components if you choose aluminium (and sometimes even carbon). However, what you do get is something special that is tougher, will last longer, not date so quickly, and mark you out as someone who thinks differently. In many cases, the frames are manufactured to order, even offering custom geometry.

At this point, it would be easy to romanticise about modern versus classic cars, about tearing down country lanes in a Focus ST or a Triumph Spitfire, but that would be doing a disservice to the bikes in this feature. Far from traditional classics, the bikes tested feature up to date geometry and a thoroughly modern ideology. Each bike demands to be considered on its performance and not be defined by the material it’s constructed from. For most riders, the skinny tubes and simple designs will hold little appeal when compared to the sexy hydroformed competition, but to some, the ‘two fingers up to model years’ ethos and rugged durability of steel will be irresistible.

The competitors

Cotic RocketMAX Gen3 (Click for review) | 160/160 mm (f/r)
15.40 kg in size L | € 5,575
Pipedream The Full Moxie (Click for review) | 150/146 mm (f/r)
16.10 kg in size Long | € 4,070
Starling Twist (Click for review) | 160/160 mm (f/r)
15.90 kg in size L | € 5,226

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Words: Photos: Trev Worsey, Finlay Anderson