Friday, February 20, 2009

GoCycle : World's First Thixomoulded Bicycle

The following article requires a coffee intensity of 9.0/10

Word has it that that GoCycle electric bike, first seen at the Teipei Cycle Show last year, was just officially launched early this week by UK based Karbon Kinetics of London. The wow factor is that it is the first bicycle in history with a frame set and wheels that are injection moulded in magnesium. It won top awards at Teipei, including one for Best Innovation.

The bike is the brainchild of an ex-McLaren engineer named Richard Thorpe, founder of Karbon Kinetics. Thorpe remarks that he was pulled into this idea after his total dissatisfaction with traditional bike design. He doesn't say specifically what he was dissatisfied about (any comments on that, Rich?)

Since GoCycle designed the bike but its core specialization does not include the manufacturing processes required, UK teams have been working on the mechanical parts of the bike while the magnesium frame is being manufactured by a Canadian firm using a unique process called Thixomoulding (see below). Finally, it is assembled by Ideal Bicycle Co of Taiwan. However, there is word that production facilities are now being UK-based to better serve customer demand.


Magnesium is the lightest of common structural metals (Specific Gravity 1.74). It is 34 % lighter than Aluminum and 74% lighter than Steel. In addition, magnesium is one of the earth's most abundant elements, with virtually inexhaustible supply (2,7% of the Earth crust). One of its nicer advantages, compared to plastics, is that it is easily recyclable and readily reused without any loss in mechanical properties (at least that's what is claimed).

Here are a few of the mechanical properties of two magnesium alloys.

A specially formulated nylon filled with long glass fibres is used for crucial mechanical parts like the rear suspension unit. The expertise to injection mould this lightweight yet strong material, which is 60 per cent glass, was provided by UK-based Protomold. I have written about Protomold in a past post, exploring how they helped in the development of the iBike cycling computer body unit. Click here to read that post.

Protomold engineers reported that they encountered a unique situation working with the Gocycle. Said John Tumulty, managing director of Protomold :

“With the GoCycle parts we were really pushing the boundaries of what is possible with plastic, and therefore the materials specified were, in the main, exotic thermoplastics. A very dominant material in the range is 60 per cent long-fibre glass-filled nylon, which is pretty extreme in terms of the glass content, coupled with the fact that it’s long fibre. During the moulding process, those fibres have a tendency to align with flow direction. The way the fibres are aligned affects the mechanical properties of the end part. Our mould technicians here have hundreds and hundreds of years experience between them yet hadn’t worked on anything like this, so it was interesting work. We knew we had incredibly short lead times, which also added to the challenge. On a simple, run-of-the-mill plastic part we can turn that around in 24 hours, but with the GoCycle components we had identified that we were going to have engineering challenges ahead. With that in mind, we pulled out all the stops so that we had more time in the mould shop to experiment and play with the moulding parameters."

"As with most things, the more mechanical property-orientated a material becomes, often the less aesthetically pleasing it becomes,” says Tumelty. “Glass fibres can have a tendency to show up on the surface of a moulded part, which on a black plastic will give a silvering effect. In layman’s terms, you’re looking at the black plastic through a fibrous glass layer. Obviously that’s not very attractive. There’s also quite a lot of effort and experimentation that went into the parameters of moulding the part in order to not only attain the required mechanical properties, but also to get the cosmetics to an acceptable level.”


The development of the bike took some six years from design conception. PRO/ENGINEER Wildfire, a parametric, feature based CAD software was used in the design (similarly, it is now widely known that TREK uses Solidworks).

Interestingly, Richard gives hints that one of the reasons he left Mclaren was due to lack of Pro/E at the company (some companies have their own internal, proprietary CAD systems that could be cumbersome to work with).

Now here are the tech specs of the bike :

The GoCycle can be pedalled like a conventional bicycle until the rider hits a button that revs up a high-powered electric motor in the front hub. It can travel at full legal urban driving speed for about 12 miles before needing a re-charge. The transmission is a Shimano Nexus 3 speed hub. These 3 gears are operated by a twist grip on the handlebar.

But there was an interesting noise issue with the motor. Said a review from Velovision :

"The assist motor is engaged by pressing the red hutton to the left of the handlebars: the motor then kicks in after four turns of the pedals. I must admit I found this strange - it's those first four turns where you need assistance the most when accelerating off traffic lights, for example. I also noticed that the motor doesn't have a lot of torque at low speed - so if on a hill start you're still moving slowly, it will struggle to accelerate you. On the same hill, get up a bit of speed first and it will boost you up powerfully. It's also good to speed you up for longer stretches in traffic. The motor is quite noisy, but not so much as to be an embarrassment. It does have a loudish whine: other cyclists or pedestrians you overtake will definitely know you've engaged the motor and many looked round to see what it was."

The noisy motor issue is in fact called by Gocycle to be a deliberate design feature!

Richard said of the noise :

"We were looking for the fun, spunky, get-me-there vroom-vrooom-vrooom attitude for the city commute."

The need for some vroom-vrooom is hardly surprising considering Richard's roots in McLaren.

The company representatives also said about the battery :

"Considering the total vehicle - weight, range, performance, cost, safety - Gocycle is one of the lightest electric two wheelers available as well as being competitively priced. Considering this is based on NiMh battery chemistry, the inherent safety margin that NiMh offers over Lithium based batteries is a bonus. Lithium batteries will be available as an upgrade option in the future, same battery case same Gocycle frame, but at a higher price than NiMh. The increase in performance will be about 1-2 kgs of total weight savings of the entire vehicle with slightly more range."


Thixomoulding is a net shape forming process that exploits a commonplace, but interesting property of non-Newtonian pseudoplastic fluids. Its called thixotropy. Pseudoplastic fluids exhibit a time-dependent, reversible change in viscosity; the longer the fluid undergoes shear, the lower its viscosity (by the way, a fluid is anything that flows upon shear). When not subjected to shear, it forms a gelled structure. When agitated mechanically, its internal structure temporarily breaks down causing a reduction in viscosity.

Toothpaste is thixotropic. It is much like a solid when left alone. But when you squeeze it, applying a sideways force through the tube, it flows much like a liquid. Thixotropy is why you never construct a building on sand. What happens when its visibly wet and there's a sudden earthquake? Whoops.

Thixomoulding uses this property in injection molding semi-solid magnesium slurry under high velocity into a mold. Magnesium feedstock (in chips or pellets) is added from a hopper into a multi-zone, temperature controlled barrel with a reciprocating screw. The screw is surrounded by heating bands and its rotational action mechanically shears the heated metal creating a semi-solid mixture of Mg alloy. This alloy is then injected into the mould. After metal injection is complete, the end of the screw freezes shut. The plug that forms keeps the semi-solid mixture from leaking out of the screw [Source : High Intensity Die Casting Processes, Vinarcik, E).

Courtesy : ASM International

Here's what a thixomoulding machine would look like :

Picture Courtesy : A B Technology

However, Thixomoulding application involves a set of structured design processes. As with any manufacturing procedure, you have to orient your design in a manner favorable for the manufacturing process (form, structure, material tolerances etc). Some of these design processes to be thought about for thixomoulding are outlined here.

150 production Gocycles have been produced and are currently being evaluated by what the company calls "Pioneer Customers". The availability of the next batch is in March 2009, and anyone interested in ordering can visit to take advantage of special pricing. The retail has so far been placed at around 1000 dollars for a non-motorized version and an extra 500 dollars for the motor system.


Certainly Gocycle is a fresh departure from the norm in what many would consider a stagnant industry. It looks aesthetically sound and other design features quickly bring second looks. Velovision explored most of those features in their review of the bike here. The folding action is not too shabby and the hard case for the bike is impressive.

1) I must admit that it is vital that these first production units from Gocycle do not get a bad image due to technical/product failure. How strong is the frame as far as material thickineses are concerned? Will the long cantilevered seat post support the weight of a rider reliably? In writing "The 8 Second Bicycle", I talked about how Kirk die cast magnesium bikes quickly fell from grace due a poor show in terms of safety in the very initial stages of its launch.

2) There is going to be some stiff competition other folders from Strida, Brompton, Dahon, Friday etc. How is GoCycle going to differentiate itself?

3) Customers are bound to get intimidated or concerned because of potential fire and safety problems involved with magnesium. Few customers would know that today, magnesium alloys are used in such diverse industries as automotive, computers and sporting goods. I think it would do GoCycle some good to educate people on the materials used, the technology used, and how it is safe for human use.

4) How cost effective is the Thixomoulding process? I realize that Thixomat holds the exclusive worldwide patent rights to this process so will final cost passed on the customer absorb the licensing fees for this technology?

5) My last question is that while centralizing production facilities in the UK is good to customers there, would it lead to slow distribution in other geographical locations?

It would be great to have Richard Thorpe talk about some of these issues. So feel free to comment on my blog here.

UPDATE (Feb 26, 2009) : Richard Thorpe has replied to my questions one by one. Please see the comments section for his thoughts.

Anyone else? What comes to your mind when you first think of words like 'magnesium', 'glass fiber' etc?


The 8 Second Bicycle
Design Of The Strida By Mark Sanders
Design Case Study : Innovation Of The Brompton Folding Bicycle
Rational Bicycle Frame Design : Giving Consideration To Functionality
Pioneering Plastics In The GoCycle
PTC Helps Karbon Kinetics To Produce The GoCycle
Thixomolded Component Advantages
Magnesium Alloy Applications

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Enhancement Smoker said...

Is thixotropy the same phenomenon where if you gently squeeze a Stretch Armstrong action figure, it gives, but if you punch it violently it feels like concrete?

phoenix life insurance said...

I didn't see a price for the bike listed anywhere. I love the look and design. If I commuted 3-4 miles to work I'd definitely be interested.

Anonymous said...

The person in the street buys mountain bikes with magnesium suspension fork legs without problem (and cars have gas tanks & batteries), but scare mongering 'experts' doesn't help.

Richard Thorpe, GoCycle said...

Cozy Beehive, here are the answers to your questions :

1. Similarities with the Kirk Precision cycle are: British innovated and engineered. Beyond this, the key difference between the products is the shape of the structures and the choice of processes - Kirk attempted to improve on a diamond framed tube structure, quite a challenge. Even today, high-end carbon fibre frames struggle to beat a well-engineered welded aluminium tube frame. Gocycle?s shape is different - designed to provide benefits to the city cyclist (not the tour de France road racer), such as a easy step-through frame, enclosed chain drive, easy-to-wipe/clean surfaces, and enclosed battery which lends itself to alternative processes such as injection moulded magnesium (very different from traditional die-casting.)

2. Differentiating Gocycle from Dahon, Strida, Brompton etc., is actually very easy and clear - all of these products collapse or fold very easily - Gocycle doesn't. What Gocycle does is get you from A to B very quickly and without breaking a sweat ? if that is what you want.

3. Magnesium usage in mainstream consumer products is widespread.

4. All of our development costs are evidenced in the product's retail price of currently £999 inc. shipping and VAT.

5. Assembly and construction of the highly technical bonding processes is now done in the UK by KKL which services Europe well. Within 6-12 months, products may be available in North America.

Anonymous said...