Tomorrow's World: Exotic Bike Materials
By Alan Dowds
In 2020 we’ve got supercharged engines, electric suspension, wheelie control, carbon wheels, aerodynamic wings and 220bhp litre-class road bikes!
But if you’d showed me that list 20 years ago, I’d have been a teeny bit disappointed. Because there’s a load of high-tech materials which, a bit like nuclear fusion, have been on the cusp of reality for decades now. When I was a lad, the future was supposed to be about ceramic engines running without oil or coolant, titanium-piped turbochargers boosting power to massive levels, and advanced composites like carbon fibre used all over the chassis. Titanium, magnesium, beryllium, lithium would all be alloyed into super-metals which would be stronger than steel, lighter than aluminium, never rust and be sprinkled about bikes with abandon.
So where are they all? Well, there are two main factors at work as far as we can tell: economics and race regulations (which generally boil down to cost, so probably economics as well…) Firms are there to make money, not fantasy machines for materials geeks, so if they can make a bike work well with cheaper, more prosaic materials, then why wouldn’t they? At the end of the day, the majority of bikes are built to a fairly sensible price, and once you take off all the costs of dealership margin, tax, delivery and the like, there’s not a lot of cash left over to make the thing at the factory.
Race regulations might not seem like a big deal, and indeed, they haven’t stopped the development of things like ABS and electronic suspension, which don’t really have direct applications on the track. But there are several areas where materials are actually banned, outright, in the technical regulations of WSBK and MotoGP, as well as lower level production based racing. Some of this is down to safety on track, some of it is down to cost reductions, but you can’t have titanium frames, aluminium-lithium brake calipers or carbon fibre wheels. Engine internals have to be made mostly of steel and aluminium, with the odd exception like titanium valves and carbon or Kevlar outer casing protectors.
So, here’s a list of some of the ‘banned’ materials which we don’t see used on bikes in an unlimited fashion – and a look at how they could make bikes even better…
This is one of those ‘what could have been’ materials. Beryllium is low down in the periodic table of elements, down next to lithium with the atomic number 4, so it’s a very light, strong metal. It’s also very stiff, has enormous heat conductivity, a high melting point, alloys very well with aluminium and other metals, and has been used in Formula One engine pistons, military jet fighter brakes and spy satellite parts.
On a bike, beryllium motorcycle brake calipers would be extremely light, and save a chunk of unsprung mass. The extreme stiffness of the metal would also provide super efficiency, and give enormous amounts of feel and feedback: almost all the effort you put into the lever will be transferred to squeezing the pads onto the disc face, instead of distorting a comparatively flexible aluminium caliper body and pushing it apart away from the disc faces.
Adding beryllium to aluminium produces a ‘super-alloy’, with the beryllium improving the physical characteristics of the aluminium – making it stiffer and lighter, while being much cheaper than pure beryllium. Such an alloy could make an excellent main frame and swingarm on a superbike, with extreme stiffness and lighter, smaller components. It could also make a great material for pistons inside the engine: they’d be much lighter than aluminium, allowing higher revs, lighter con-rods and boosting power production all round.
So why the hell don’t you have beryllium bits all over your Panigale? Well, unfortunately, beryllium is poisonous, with its dust creating a lung disease just like asbestos. So while it’s sort-of okay when used as an alloy with other metals, it’s quite difficult to work with in terms of machining and other production techniques. It’s also quite a rare material, and so very expensive to use, compared with alternatives like aluminium. It’s also banned by race regs, so you’ll not be seeing it on even the most exotic bike any time soon…
This is one of the few ‘materials of the future’ which has become fairly common on bikes. It’s a composite material, made up of carbon fibre threads, which are extremely strong in tension, suspended in a resin base/matrix, which is strong in compression. Each material thus complements the other, making the overall component extremely stiff and strong for its weight. In addition, parts can be intelligently designed to add more carbon fibres in different areas, and arrange them in a precise way so they can deal with the exact stresses on a part. So you’d position more fibres around a mounting point, say, and arrange the fibres along the lines of most stress, reducing material where it’s not needed.
Basic carbon fibre is ideal for stuff like mudguards and bodywork panels, where its light weight and super stiffness make up for the extra cost of production. It’s made just like fibre glass, with carbon matting laid up in a mould and resin applied and cured, sometimes with heat and pressure. It’s simple enough, and not super expensive.
Building larger structures with the material is much trickier. And with parts like wheels and frame components, there’s no margin for error. So producing carbon fibre wheels, swingarms and frames is much more involved, with higher tech materials and procedures. The fibres might be arranged by robot or 3D printer (see below 3D printed S1000 frame) to ensure accuracy, and the resins will be from the cutting edge, with extreme measures during curing and laboratory conditions of cleanliness and accuracy.
Carbon is allowed on race bikes in non-critical areas, like bodywork, but is banned in wheels. It’s also banned in cylinder heads, pistons and blocks, but is positively encouraged in engine casing crash protectors and the like. MotoGP also uses carbon-carbon brakes in the dry, which aren’t strictly speaking carbon-fibre composites (they’re almost pure carbon rather than threads or cloth suspended in resin.)
On road bikes, carbon fibre appears extensively in its simplest ‘cosmetic’ role – carbon mudguards, footpeg plates, small bodywork trims and the like. Silencers using carbon outer sleeves are common enough as aftermarket options, though they’re not as fashionable as they used to be. It’s there to look smart, and the minor weight gains will be cancelled out by your next large Big Mac meal.
‘Proper’ carbon is limited to high-end machinery. The first bike to use carbon frame components was the Bimota SB8 in 1999, which used two carbon fibre plates at the swingarm pivot, bolted and glued to an aluminium twin-spar upper frame. And since then…there’s not been much in the way of mainstream carbon fibre frames. Bimota produced a handful of other bikes with exotic carbon frame and swingarm components through the 2000s and 2010s, but they were little more than super-niche hand-built one-offs.
There have been a couple of *slightly* more mainstream options in recent years. The BMW HP4 Race is an S1000RR-based track bike, and features a proper full carbon fibre frame, as well as carbon bodywork and wheels. The Ducati 1299 Superleggera has a carbon frame too – but it also boasts a carbon swingarm, and it’s even road legal, which is nice. Both bikes are the wrong side of £70k, and ultra-limited editions though – so it’s fair to say that carbon fibre as a serious chassis material for ‘normal’ bikes is some way off.
Light, hard, immune to heat and wear, on the face of it, ceramic materials should be ideal for use inside an internal combustion engine. Make your pistons out of this stuff, and they’ll not need any coolant or even oil lubrication, since they’ve got super-low friction, and don’t expand when they get hot.
Back in the 1980s, this seemed like a likely spot for engine researchers, and ‘Tomorrow’s World’ types were predicting all sorts of advances. When car firms Toyota started to use ceramic turbines in their Japanese market turbocharged engines, it looked like things might be about to happen.
Sadly (or not), firms have been able to get more than good enough performance from dull old aluminium, especially in parts like pistons. Ceramic materials have found their home right next to pistons though – most modern bikes use ceramic-type coatings on the cylinder walls, applied directly to the base aluminium cylinder block. Those characteristics – hard wearing, low-friction, resistance to thermal shock – have made ceramic bores an ideal choice, giving longer life and better performance all round. It makes repairing damaged or worn bores much harder than with simple iron bores, but the advantages outweigh that downside, especially since engines are generally so reliable nowadays.
If you scan the periodic table, you’ll see that lithium is the first element that isn’t a gas, coming in at atomic number 3, right after hydrogen and helium. That low atomic number makes it light – it’s the lightest metal in existence, so you can see why we’d be interested in using it in a bike. Sadly, it’s no use on its own: lithium is a so-called alkali metal, and reacts violently with water, exploding in flames in in the same way as sodium and potassium metals (which is why lithium batteries are such a worry on planes and the like).
So it’s a fire hazard when pure – but lithium is really useful when used as an alloying agent in special aluminium alloys. Lithium-aluminium alloys, with up to four per cent lithium, are used in planes like the Airbus A380 and the F16 where their light weight (three per cent less than aluminium) and super stiffness (five per cent more than aluminium) are essential.
In the automotive world, Al-Li alloys have appeared on Formula One brake calipers – but the material is specifically outlawed by the FIM’s MotoGP technical regulations for use in brakes. For road use, the big problem is corrosion: lithium is such a reactive element, that even when alloyed in small amounts, it wants to corrode away. This is manageable in a high-end part like an Airbus airliner or Boeing fighter jet, where there’s regular servicing and safety checks. On a road bike, mixing with water salt and dirt, with only an annual MoT check (maybe), the risk is too great for the benefit.
So – like beryllium, lithium brake calipers would be lighter and stiffer, and if we could use lithium alloys in place of aluminium in other areas like frames and swingarms, we’d get the same benefits. But the cost and safety concerns rules it out.
Where we do benefit today from lithium’s light weight is with bike batteries. The latest generations of lithium-ion batteries give a great weight saving over lead-acid units, and plenty of performance machines now come with them as standard, or as an option.
If you’ve got a periodic table to hand, you can see what we’re getting at here. Magnesium is close to lithium and beryllium and isn’t far from aluminium, up the top left hand side. These are all light metals, with various levels of reactivity, and magnesium has a good level of both. It’s lighter than aluminium, and while it’s more reactive, it’s not as sensitive as lithium or sodium.
Magnesium hit the big time in World War II where the US, German and British aircraft industries all used it for large castings and forgings in their plane designs. Alloyed with aluminium and other metals, it was used for engine casings, landing gear mounts, wing spars and much more. It’s lighter and stiffer than aluminium, but has a greater risk of catastrophic fire in a warplane.
In bikes, magnesium is actually quite widely used. It appears in engine cases on high-end machines, and is also widely used in super-high-performance forged wheels. Indeed, magnesium is one of the recommended materials for MotoGP race rims.
Like lithium, the downside of magnesium alloys is corrosion over time. Race rims are fine because they’re regularly checked, but for road use, magnesium wheels need to be carefully examined, and paint or some other outer sealing coating needs to be well-applied and maintained. The smallest chip in the finish will let in water, air and salt, kicking off really nasty corrosion which can affect the strength badly.
Metal Matrix Composite (MMC)
A rather obscure type of material, but metal matrix composites (MMC) are a bit like carbon fibre – just with metal replacing the resin. The principles are the same, with super-strong fibres embedded into molten metal to give reinforcement, improving strength and stiffness without excessive weight. These fibres obviously need to be able to cope with the heat of the molten metal, so ceramic ingredients like boron, nitrides and carbides are used. These are super-tough, hard and strong materials, and embedded in aluminium, magnesium or titanium base matrices, can produce extremely exotic material characteristics.
MMC components are specifically banned by the FIM’s technical regulations for MotoGP, but they have appeared in some high-end road cars. Honda’s NSX supercar used MMC cylinders inside its V6 engine, and many military and aerospace designs use MMC in armour and other super-strong components.
On our fantasy money-no-object ultrabike, we’d like MMC pistons and brake discs, probably, where the super-strong, super-light materials would ratchet up performance massively.
If there was a metal Olympics, titanium would take home a load of medals for sure (hence our top policy is called Titanium Cover). Its alloys are as light as aluminium, but stronger than steel, resist corrosion, are reasonably easy to machine, weld and work, and have a high melting point. It’s the perfect material for many requirements on a high performance bike – yet it’s not as common as it could be.
Titanium is expensive, but not horrendously so, and is often seen in high-end exhaust systems, chassis bolts and fasteners, and engine inlet and exhaust valves. It’s unusual to see in frames, swingarms, wheels or other parts though, and this is partly down to cost, and partly down to race regs. The FIM rules outlaw titanium frames, swingarms, handlebars, wheel and swingarm spindles, handlebars, shock and fork structural parts on safety grounds. That’s partly down to historical problems with some early designs failing in the 1970s, but is also a sensible cost saving measure.
You see the odd titanium-framed special these days, made in similar fashion to steel tube frames, but with smaller lighter thinner tubes. But for standard road bikes, titanium is generally restricted to exhausts and engine valves these days. If you’ve got a load of money to burn, then gradually replacing all the fasteners on your bike with titanium replacements is a fun hobby – though by the end of it, you’ll have to have spent hundreds of pounds sterling to save just a pound of weight…