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13 thoughts on “Contact

  1. Nick, I’m wondering how the head tube area is holding up on your bike? My build is at the point where i need to determine if any exterior strengthening is needed around the area. I was thinking of a layer of 3 oz epoxy glass (transpearent) to help hold it all together. I don’t see you or renovo doing it and your wood is pretty thin around the metal tube. I’m just looking for some advice from someone who has already built a bike.

    Thanks, Brent

    • The head tube is fine. I’ve had well over 1000 miles on it now with plenty of pot holes (some intentional to test it!) and emergency stops. I haven’t gone as far as to do a proper load test to the European requirements but id wager money on the forks failing before the head tube. Having said that, I reinforced the joint internally with several layers of fiberglass tape wrapped around the alu tube and bonded into the frame.

      The only area I’ve had any issues is the seat tube insert which came loose after a particularly large pot hole. I’m sure that was a result of not prepping the tube properly before bonding it in. I haven’t had any issues since I filed the surface and bonded it back in.

      Let me know how it goes.

  2. Hi there,

    I read your engineering section and wanted to point out that you are probably under playing the axial stiffness of wood. Bike frames are traditionally trusses with the members in tension or compression.

    If you considered the members as tension compression members, you’d come to the conclusion that wood is not comparable to the more conventional materials available.

    However, wood is pretty. Don’t get me wrong, have you considered a bike constructed of small diameter steel in a tight fitting wood sleeve which would give it sufficient bending resistance?

    It might facilitate inserts, etc.

    • Hi Norbert, thanks for the message. I’m going to disagree on this one. You’re right that the bike frame acts as an axial truss. It is, however, a very stiff truss so the vertical deflection that you get in the frame is very small (not much more than a mm under seated load). There is also some additional vertical deflection from the other components. So even if you use a material that is axially more flexible the difference in vertical frame stiffness would hardly be noticeable.

      Now, you should have picked me up on torsional stiffness as I ignored it on the engineering page. Get on your bike, rest against a wall stand on one pedal and bounce up and down while holding the brakes. You’ll see a significant lateral deflection of the bottom bracket (20-30mm on flexible frames). This is a direct measure of the torsional stiffness of the down tube as you’re applying a torque at the BB and resisting it with your hands at the handlebars. This has a much bigger impact on how the bike feels and affects the efficiency of power transfer, steering response and overall feel of direct contact with the road.

      In fact, the panacea of road bike design is to achieve vertical flexibility to give you a comfortable ride at the same time as overall stiffness for efficiency. These are obviously in direct competition with each other but explain many of the features you see built in carbon frames like curved seat stays, elastomeric dampers, skinny seat posts etc.


      • Ah. That makes sense.

        My thought was that if the axial stiffness is too soft, it starts acting like a stiff, full frame mountain bike suspension; you start losing efficiency based on deflection and damping of the material. I can definitely see the advantage of a wide top tube, seat tube and down tube to give the frame lateral rigidity. The top tube gets put into lateral bending and torsion, the seat tube gets put into tension and bending, and the down tube gets put into tension and bending.

        Would you say that’s reasonable to say that the energy lost to the frame proportional to 1/2*stiffness*deflection^2? Work = force x distance, with force varying from 0 to k*distance (distance in our case is the deflection of the frame, which is not useful to propulsion)

        So twice the deflection (lateral or axial) means four times the energy lost into the frame. I can see the lateral component being much larger than the axial component as you say.

        Certainly having a stamped High strength steel sheet metal frame (3mm x 0.5 mm at 25 mm off of the axis of the tube) inlayed into your outer wood layer would add axial stiffness as well as increase your section modulus dramatically for that lateral stiffness you’re talking about. The wood would provide buckling resistance to the thin sheet metal. I figure this will only add ~24 g/m of tube length so you’d get up to 0.70 kg/m with the composite construction. Looking at it, the axial stiffness IS only increased by ~4% (14353 kN) but that does get you an extra ~0.38 kN/m^2 of bending stiffness (based on the steel being 25 mm off the axis of the tube), which gets you an extra 7.3% of lateral stiffness.

        I mean, you’re actually riding this thing. So if it seems rigid enough, I guess why mess with a good thing.

  3. Hi Norbert
    I like your analytical way of thinking but unfortunately you’re starting from wrong assumptions and deducing false conclusions. Here’s a bit of a long but hopefully interesting reply.

    Wrong Assumption 1 – Wood is a poor engineering material and needs to be reinforced with a material like steel to perform properly

    I get this a lot. ‘Why not coat it in fibre glass?’ ‘ Why not bond in metal tubes for the full length?’ ‘ Why not lay up carbon fibre strips on the inside?’ If I thought that wood was a poor material then I wouldn’t use wood, I’d use a more conventional material that was better suited to the job. A dense hardwood has similar strength to weight and stiffness to weight ratios to steel and aluminium (and I’m using Reynolds 953 and X-100 as the benchmarks not 531 and 6061). A dense hardwood would easily outperform a 531 steel frame in terms stiffness, strength and weight. In fact, using a material with a similar strength to weight ratio but lower strength has advantages as you can build with a larger diameter and thicker tubes which will produce a more robust frame (hence why aluminium can be made in larger diameters and stiffer than steel)

    Wrong Assumption 2 – Axial flexibility is bad

    This is wrong. Manufacturers try to reduce the axial stiffness of their frames to make them more comfortable to counteract the huge increases in stiffness gained by large diameter tubes and oversized BB’s (Trek Domane, curved stays on Pinarello Dogma, ultra thin seat stays on Cervelo Project California). A frame that is super stiff in the vertical direction gives an uncomfortable ride so a degree of vertical compliance is beneficial. This should not come at a cost to the stiffness of the bottom bracket to head tube connection though. Look at beam bikes. Huge axial flexibility, very comfortable, but high performance. In fact the difference in axial flexibility that you will see between a flexible and stiff frame would be small compared with the additional vertical flexibility you’d get by taking 20PSi out of the tyres.

    Wrong Assumption 3 – Axial flexibility equals lost energy

    A 100% efficient elastic system will return the energy imparted into it without losses. Frames are not 100% efficient and any energy that is lost occurs through damping in the system. A steel or aluminium frame has very little damping so even a flexible frame will not ‘lose’ energy. It may however lose the instant reaction to rider input because the frame causes a power lag due to the frame deformation. Carbon fibre and wood both have considerably higher damping coefficients due to the non homogenous material structure. This is actually seen as beneficial from a comfort point of view as it allows the high frequency road vibration to be reduced by damping. When you hear people talk of steel forks and carbon forks being ‘comfortable’, the steel s comfortable because it’s flexible and bends but the carbon is comfortable because it damps vibration. Wood has much higher damping than carbon so absorbs more vibration. In theory this is absorbing energy but it is so small that it is insignificant.

    Wrong Assumption 4 – Wood provides local tube buckling resistance

    It obviously does, because people make hollow frames from wood (me!). However, local tube buckling is one of the weakest areas (as it is for steel, carbon and aluminium frames) and should not be assumed. My Woody 2 frame has tubes that are only 2.5mm thick in places and I have tested 2mm thick tubes with various forms of stiffening. Assuming that the wood can provide local buckling resistance, then if you needed to increase the section modulus then it is much easier to just make the tube larger, not add steel.

    Wrong Assumption 5 – Lateral stiffness comes from bending stiffness

    As I said in my first reply, lateral stiffness comes from torsional stiffness. Remember there are no direct lateral forces applied to a frame, only vertical (your weight) and torsional (the offset of your weight from the centreline of the frame). To achieve torsional stiffness you need large diameter tubes which indirectly develop a high lateral bending stiffness. This is where wood becomes really tricky. Unlike a metal, which has a simple set of material properties, wood has 3 E values, 3 G values and 9 Poissons ratios. The natural inclination of the wood is with the grain along the length of the tube which leaves the critical G value relating to torsion at approximately 1/8 to 1/10 of the longitudinal E value. This is compared with about 1/3 for steel and aluminium. So achieving a high torsional stiffness is much harder than I made out in my very simplified post comparing material properties. In fact, a student did an entire engineering masters thesis on the topic for me! With hugely oversized tubes it can be achieved though.


    • Hi Nick,

      Let me know if you’d like to continue this by email.

      Regarding 1: My point was, much like metal inserts, there may be room for further optimization in the tubes. Certainly your point regarding stiffer hardwoods- and putting them on the outside.

      Regarding 2: accepted your stipulation that axial deflection is not a problem

      Regarding 3: disagree with your conclusion. you’re putting the energy in, once you apply the force, that energy is wasted and can’t be put back into your foot. The damping in the wood just means the frame vibrates less as a result of the deflections put into it. Does not mean its less efficient. I think this is the BIGGEST selling point of the wood as a building material for the bike (other than its gorgeous and nice to work with)

      Regarding 4: Section modulus is affected most by the stiffness of the outer fibers. Therefore to meaningfully make your section stiffer, you have to use stiffer wood or make the section wider. inlaying a stiff alternate material in your section seemed efficient as buckling is the reason that steel tubes are not made thinner. With the low density wood, its possible to use it (would need to be verified) to stabilize a very thin steel (or carbon or whatever you like). Thereby being more efficient than a steel tube could. also the steel would help your torsional resistance which you mention in 5.

      Regarding 5: I’m actually going to go through a little calculation myself. Imagine the seat tube is a beam attached rigidly to your top tube. then look at this:

      while you pedal, your offset foot tries to torque the end of the beam. The amount of deflection is related to the section modulus of the beam. The chainstays have some angle to them so they’ll act pretty purely in tension and compression. The downtube I can concede will probably have some twist put into it – but it will have to act in bending to resist the lateral deflection that you’re trying to induce by pedaling.

  4. Hi Nick,

    you don´t know me, but I have to tell you, you was my BIG inspiration, that I can build a wooden bike at home without special tools. And your website give me enough courage to complete this “mission impossible”. 🙂

    Thanks a lot!!!


    • Glad it helped. That’s a beautiful frame. Nice work. I’ll add your website to the links page as inspiration for others.

      Is your signature on the chain stay done with a soldering iron? I’ve thought of something similar myself but never tried it. And are the logos metal recessed into the frame or are they stuck on?


      • Yes, I used for my signature onthe chain stay soldering iron. It’s not so easy to do it like with a permanent pen, but much more easier like to build a bike. 🙂
        I glued the logo with epoxi on the frame.

  5. Wow, I didn’t know there were so many of us (re)inventing our own wood bikes! How did you insert your bottom bracket? Did you do it during the layup, or afterward from the side? Mine failed after about 300 miles of riding, and it looks like the aluminum debonded from the epoxy, which then failed the wood as well. Looking to rebuild it stronger, and I like what you did with fiberglass. I will probably do something similar with carbon cloth.

    • Hi Randy
      That’s a shame. Mine were inserted from the side after the frame was complete. I made sure that the surface of the bb was heavily grooved using a file with grooves in a cross hatch pattern. I also roughened the inside of the bb hole in the frame. When inserted from the side the hole was a fairly loose fit so that there was initially a small gap. I sealed one side, put the frame on its side and poured in epoxy to fill the gap all round. I’ve probably done over 10,000 miles in all weather on my single speed frame without any problems now.
      I’d also recommend that the layup of the wood at the bb has grain in 2 directions to avoid cracking across the grain. Good luck with the repair.
      I’d love to see a photo of the frame and include it on ‘Readers Rides’

      • Fantastic idea to over size the hole, then fill with Epoxy. Was trying to figure out how to keep the tolerances tight and not squeegee off all the glue, but this will work a treat.

        There is a short diary on imgur of the build of my bike. Click the hyperlink on my name to see it. You are welcome to include it in your readers rides. I will probably be building one similar to your woody 2 next, so you can definitely count me as a reader!

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