Beyond the Diamond. Composite monocoques.

The shape of cycle frames, constrained by the characteristics of available materials, has hardly changed in over 100 years. In this extract from his book MIKE BURROWS considers how developments in materials technology will shape the future.

If designers and engineers are ever to produce better bicycles, they have to forget about tubing of any sort. Instead they need to think about forming the frame directly, using some form of composite or even plastic material. This is getting very close to home, of course, as I started the ball rolling in 1982 with my first carbon fibre monocoque design. The reason was, as always on my racing bikes, to reduce the aerodynamic drag by producing the frame in one smooth form. Nonetheless, it was obvious there was tremendous potential for stronger and lighter frames than would ever be achieved with simple tubing.

[Pictured; Mike comparing his carbon monocoque with a rusty old steel tube]

One person who understood this even better than me was Chris Hornzee-Jones, a fellow recumbent builder. He went on to design an elegant monocoque mountain bike, briefly marketed as a Lotus. It was actually produced by Composite Air in California.

I like to think it was my original design that inspired Chris. But it was his understanding of composites that really made it work. (The other pioneer of composite bikes was Brent Trimble in the USA. He produced some very nice moulded diamond frames that eventually became the Kestrel range.)

There are now many copies around, either full monocoque or moulded modified diamond. Most seem to have been designed by people who lack Chris's understanding of composites, and who would probably be a lot happier working with steel tube.

To be fair, getting a monocoque right is, as I well know, not an easy thing. This is especially so with one intended for volume production. The first obstacle is the components. These have evolved over the last 100 years to suit the diamond frame and there is nothing in the Shimano (or any other) catalogue that was designed for anything other then the tubular frame.

Then there is the manufacturing process. You have a choice at present of ‘slow and expensive' or ‘slow and even more expensive'. Fine for the aerospace industry, but for the real world we need something a little more ‘push-button'.

And finally, and even more important if the monocoque really is to become the superbike of the future, is the design itself. For whilst the simple aerodynamic forms I have been producing over the years are OK, to be able to reduce weight without sacrificing stiffness, a more scientific approach is needed. That means computers, of course, and Finite Element Analysis (FEA). Only using this approach can the variables of the frame shape, type of material, its thickness at any point and fibre direction be checked fully.

This is now standard procedure for many industries. Although not common in the cycling world, Trek did some pioneering work back in 1985 to help them optimise the tube sizes for their aluminium frame.

All this dictates that the monocoque needs a lot of money spent on it. This requires a large and profitable company - not a common thing in our industry. The ones that do exist tend to leave the real innovation to the smaller companies. Needless to say, I am working hard to try to change this.

HPVs - recumbent alternatives

All of the foregoing refers to the rigid safety bike - still by far the most popular form of the bicycle, but far from the only one. Any designers who feel constrained by the diamond only need to move sideways a little to find the world of recumbents or Human Powered Vehicles (HPVs)*. As yet, no one is absolutely certain how many wheels HPVs should have, let alone what size they should be - or even where they should go! So there is still plenty of opportunity for using the tube in new and exciting ways, plus lots of scope for moulding.

This is an area that I have been working in for some time, and which I still find very exciting. I have tended to favour the monolithic or ‘big fat tube' approach, but would not claim it to be necessarily the best. It just suits my way of working.

Anyone with a special interest in HPVs should think about joining the British Human Power Club. Or if you think you might be interested, write for a copy of their ‘how to do it' booklet. This covers the subject rather more fully than this largely ‘upright' book can.

Dual-suspension MTBs

Also offering plenty of scope for new design approaches (and even the chance to make some money!) are dual-suspension mountain bikes. Not exactly brand new - Alex Moulton did it in 1988 - but they have suddenly come of age with the recent increase in downhill racing. Here many of the traditional drawbacks of suspension - like added weight and unwanted rider-induced bounce - are hardly a problem. This is because the riders are not so much pedalling as falling in a semi-controlled way down the rough side of a mountain. So the need is for 150 mm of travel at both ends, some good brakes and sufficient durability to last at least a couple of races before bits start breaking off!

Conclusion

Many of the current designs are still based on the diamond frame, but the trend is towards more specialised designs. Many of them are driven more by marketing than functional concerns. But then we know more about marketing than dual-suspension, so why not?

Moulded designs would seem a very logical way to go, except that things are changing rapidly, and the tooling can be very expensive and inflexible.

*HPVs are not necessarily recumbents (or even wheeled vehicles) but most are.