The Gear: Twmpa wooden gravel bikes
Posted By Gravel Union
On 4 June 2021
We are used to seeing gravel bikes being made from a variety of different materials, titanium, steel, carbon, magnesium and alloy or any combination of them, but what about wood? Emma has been chatting to the minds behind Twmpa Cycles, Andy and Miguel, to get an insider’s view of their new wooden gravel bike frames.
GU - What drew you to making bikes from wood?
Twmpa - Andy is a mechanical engineer by training and has been a woodworker for the last eighteen years. He has been designing and making furniture for much of this time. The first bike frame was a personal project that combined his lifelong love of cycling with his woodworking knowledge and skills.
The idea for this frame came from a chance conversation with local author, woodsman and bike-nut Rob Penn. He commissioned a piece of furniture from Andy as part of a project culminating in his book "The Man Who Made Things Out Of Trees". We discussed, and ultimately rejected, the idea of building an ash bike frame for the project, but for Andy, the seed (ha ha) of the idea had been planted. The first frame became a research project and began to take shape over the next couple of years.
GU –They're beautiful things, but what benefit is there to be had from wooden frames?
Twmpa - We agree that they are beautiful things and that, combined with the "can it be done?" question, was the initial motivation. Our change of mindset came from the incredible experience of the first ride on that first frame. Any frame builder will remember the first time that they rode their first frame. It is a unique feeling of surprise (that it actually works), achievement and pure joy. Andy designed the geometry to give a relaxed and forgiving ride, with all-day comfort prioritised over flat-out speed and steering that would not be phased by a bit of challenging terrain. He felt that he got pretty close to this, but what struck him most was just how comfortable and quiet the bike was to ride over the appallingly surfaced back roads of our native mid-Wales/Herefordshire border region.
Andy then started to look into the unique properties that wood offers as a frame material to determine whether wood can bring benefits over alternative materials. Many people will intuitively feel that a wooden frame might provide a comfortable ride. This turned out to be the case. The use of wood as a raw material also provides environmental benefits that other frame materials don't. We are reluctant to make any firm claims at present. Still, one of our aims is to conduct proper lifetime assessments of the environmental impacts of our bikes.
GU - Does the wood have a natural flex to it to act like a dampening?
Twmpa - Wood is not inherently more flexible than other frame materials (indeed, flexibility is something to be closely controlled in any frame), but it is very forgiving on rough terrain because of how wood responds to external vibration.
Imagine making two identically shaped bells, one out of wood and the other out of steel (or aluminium or titanium etc). When these bells are struck, they respond very differently, with the metal bell ringing a long and sustained note and the wood bell giving a muted "clonk". The reason is that the energy transferred to the material is dissipated in very different ways. The metal has no way of damping the energy, so the bell will vibrate until all of the energy is transferred to the air around it. The wood, however, has a far more complex cellular structure, being made up of multiple compounds, some of which behave elastically and some of which act as a damper. The effect is that the energy from being struck is rapidly dissipated as heat and a little sound.
In a bike frame application, you can then understand why and how a wooden frame provides benefits that other materials cannot match. Energy flows into to the frame from impacts and vibration from the terrain through the wheels. Energy flows out of from the frame as sound, a temperature increase and transmission to the rider, who is effectively a large and active damping mass. Dealing with, and getting rid of, this energy is what we as cyclists do, and it is one of the factors that ultimately causes discomfort and fatigue. Mountain bikes use engineered suspension to dissipate the energy inputs from rocky terrain, which would otherwise make that type of terrain unrideable. Gravel or Allroad bikes, on the other hand, are trying to achieve comfort and rideability both on and off-road, without the weight and performance disadvantages that suspension brings. The fact that the energy from poor tarmac roads and unsurfaced gravel roads can be partially dissipated by a wooden frame is the reason why a wooden frame feels comfortable. Wooden frames are ultimately less fatiguing to ride.
GU - I've only seen a few wooden bikes up close, one made from Glenmorangie whiskey barrels and the others from bamboo. How does your frame differ from a bamboo frame?
Twmpa - We don't have any direct experience of riding bamboo frames, so we can't comment on the differences between them and our frames. What we can say is that they are built in different ways. Bamboo frames use tube-to-tube jointing, as do traditional steel frames. The joints are formed by wrapping with carbon or hemp tape and epoxy resin. Twmpa frames, on the other hand, are milled from a triangular arrangement of jointed, laminated, solid planks. Milling is done by a CNC router that precisely cuts the models we produce on our CAD software. This gives us exceptionally close control of critical aspects of the frame, such as the wall thickness of our hollow tubes and ensures accurate repeatability.
GU - How robust are they and what happens if you take a chunk out of one?
Twmpa - Our frames are tested to BS EN ISO 4210-2:2015, which tests for impact and fatigue, simulating 10 years of use. The kind of impact that would take a chunk out of one of our frames is likely to do considerably more structural damage to, say, a steel frame, where the tubes are more prone to buckling.
GU - If I damage a tube can it be replaced?
Twmpa - If the polyurethane lacquer is damaged, we recommend re-applying protection to the area to ensure that the wood is protected from the elements. If severe damage is done to the wood, it will usually be repairable by splicing in a new piece of wood.
GU - What about frame bags? Will just adding some frame protection be ok?
Twmpa - Always add frame protection when fitting bags. Other than that, treat it like any other bike.
GU - As a UK rider who chews through components with salty dirty winter rides, how will it stand up to this?
Twmpa - Our experience from riding through 3 winters of similar conditions is that Twmpa frames stand up as well as any other. We always clean and re-lube our bikes after a mucky ride, as we would any much-loved bike - they just work better this way. We often get asked about the danger of termites, woodworm and saltwater, and the reality is that we treat the wood in much the same way as a yacht or speedboat hull is treated, and that process gives effective protection against all those hazards.
GU - Who would you see as your ideal type of rider?
Twmpa - We originally designed these frames for the kind of riding that we love to do, so I suppose we are the ideal type of rider! Our bikes will suit the rider who likes to ride both on and off-road and won't feel guilty about their mountain and road bikes languishing, neglected in the garage as they have all the fun on their Twmpa. We also love the ability to strap some bags on and head into the hills of mid-Wales and cover some serious miles.
This is not a club racing bike; it is not a bike for the weight weenie (although a 9.5kg built-up weight is very respectable). It is not a bike for the conservative rider - it is a bike to have an adventure on and to get away from the everyday.
If you would like to find out more about Twmpa Cycles, you can check out their website here
If you would like to read more about the incredible gravel riding that Twmpa have right on their doorstep, check out our Travel Gravel piece here