The Bicycle Book. Bella Bathurst

Чтение книги онлайн.

СКАЧАТЬ that a heavily used downhiller takes means that it’s no use stinting on materials: anything cheap or badly made will get destroyed by the first tree stump it meets. It isn’t that uncommon to hear downhillers complaining of getting through two or three front forks within the space of a single competition, and since the hydraulics in a good-quality fork can cost hundreds if not thousands of pounds, it’s not a sport for the parsimonious or faint-hearted.

      The bikes Graeme and I want to make are less demanding, and the parts are a lot easier to come by. So our first job is to come up with a series of measurements. To get a proper, comfortable ride on a bike, you need to know how heavy you are, how long your torso is, how long your arms are and what your inside leg measurement is. As a very rough rule of thumb, most men have proportionately longer torsos and shorter legs, while with women it’s the reverse. The length of your torso dictates the length of the top tube, the length of your leg dictates the length of the seat tube and the length of your arms will eventually dictate where and how you arrange your handlebars. Your weight will determine what type of materials you use. Clearly if you’re 6ft 3in., 13 stone and use your bike for doing the school run, it’s no good welding a couple of metal twigs together and hoping for the best. And so the next job is to pick out the parts we’ll need for our frames. There are four main tubes in a classic diamond-frame road bike: the head tube (the short, thick post running down from the centre of the handlebars to the top of the front wheel forks), the top tube (or crossbar), the down tube (which runs from the head tube to the bottom bracket) and the seat tube (which runs from the bottom bracket to the saddle). The forks flare out from the head tube to enclose the front wheel. At the back there are the two chain stays on either side of the rear wheel, and the seat stays, which run from the top of the seat tube to the centre of the rear wheel.

      Within those basics, there are a lot of possible variables. The angles will vary substantially from person to person and from bike to bike, and each type of bike has a different geometry. Mountain bikes, for instance, will have long head tubes with slacker head angles to help absorb shock. Road bikes will have a short head tube with a steep angle – usually between 73° and 74° – and an equally upright seat tube. The more upright both head tube and seat tube are, the more responsive but less comfortable the ride. The sharp angles mean that the rider has to reach forward over the top tube, reducing his resistance to the wind. The more curved the angle of the forks, the more comfortable but less efficient things will be. Road and track bikes are usually designed to be ridden with the saddle higher than the handlebars – in other words, when you’re riding it, your bum will be higher than your hands. Which is aerodynamic, but uncomfortable.

      According to Dave, the first and most important thing in framemaking is to find out what the bike will be used for. ‘The primary requisite is that the frame fits the rider and is suitable for the purpose. So if you want a touring bike, there’s no earthly use in making an audax bike. You can do anything on anything – you can tour on a racing bike, you can race on a touring bike, but you’ll do neither very well. So you have to get the frame to fit the customer and the purpose. If you’re going to build a track frame to ride in Manchester, the position of the track frame is completely different to a touring frame you’d make for riding around the world. With a track bike, the priorities are speed and efficiency. A track bike is not much good for anything other than riding on a track or short trips on the road. A touring bike, other extreme, you want something that’s comfortable to sit on all day, that will carry a load. A good racing bike, you steer with your backside and you think it round corners. You don’t have to physically steer it, it just goes. It’s an extension of the body and everything flows. When you’re racing at a high level, the bike is absolutely critical – the rider has to have complete confidence in it. And if there’s anything not quite right, it will affect his performance. That’s the trick in building a good frame – in getting inside a rider’s head, seeing what his or her vision is and translating that into something that’s going to do the job.’

      Will a well-made bike make you a better rider? ‘No. But it will stop you being a worse rider. There are some people who will never be good racing cyclists. I’ve seen many riders with the right physical attributes, but nothing up there. They haven’t got the confidence, they haven’t got the drive to succeed. I’ve seen riders that wanted like nothing else on earth to succeed and flogged themselves almost to death. But they would never do it because they haven’t got the physical attributes – the lung capacity, the heart capacity, whatever. You’ve got to have those physical attributes, and if you haven’t got them, you’ll get to a level and that’s the size you’ll stay. And the best frame in the world won’t make a blind bit of difference. A good bike will stop you being any worse. If you put a good rider on a bad bike, he won’t ride to his full potential. If you put a rubbish rider on a good bike, he’ll still be a rubbish rider.’

      He gets quite a few gear freaks, the cycling equivalent of the planespotters outside Coningsby, who love the names and numbers more than they love the ride. ‘A classic example is a customer who came to me in the early eighties wanting a frame built. He had a drawing – “Can you make that?” I looked at it. “Yeah, I can make that, who’s it for?” “It’s for me.” “It’s not going to fit you, it’s far too big for you.” ‘But that’s what I want.” “Why do you want this?” And he said, “That’s Eddy Merckx’s bike. That’s the dimensions of Eddy Merckx’s bike.” I said, ‘Yeah, but Eddy Merckx is 6ft 1in. and you’re 5ft 4in.”’ He laughs. ‘Not quite, but there was a disparity. So I made it and I sprayed it and he built it up, and I saw him for years riding round on it looking completely ridiculous – it was far too big for him. It was too long and too big. But that’s what he wanted.’

      Anyway. Since the four main tubes are those which dictate the basic geometry of a road bike, they come in a variety of different shapes and sizes. The simplest and strongest will be a straightforward plain-gauge steel tube, same idea as a metal curtain pole. Next up will be single-butted tubes, which have one end thicker than the middle, thereby making the frame stronger at the point of connection. And finally there will be double- or triple-butted tubing, stronger at the ends and lighter in the middle. The strength in plain-gauge tubes will be the same throughout their length, whereas the strength in single- or double-butted tubing will be concentrated at the joints. To join these tubes together, there are two alternatives: welding or brazing. Welding raises the temperature to the point where the steel melts and joins to its neighbour. It produces practical but ugly joints – the cheap hybrids and mountain bikes you see with big gobby lumps of steel at the seams will probably have been TiG (or tungsten inert gas) welded. Brazing, on the other hand, uses another metal inserted between the two steel tubes to make a connection. It’s less heat and energy intensive and therefore less likely to damage the alloys. With brazing, you can use two methods. Either there are lugs, separate, ready-made joints which are then connected to the tubes with brass filler; or there is fillet brazing, where the joints are filed to a perfect fit, filled completely with brass and then sanded down to form a seamless connection. Fillet brazing looks beautiful but requires both time and skill, so Graeme and I are both sticking to lugs. Because over the years Dave has built up a good set of contacts among bicycle-makers, he’s already got a ready-made supply of new- and old-style lugs and tubes in stock. Having picked out the components we want, Graeme and I stand there for a moment or two, daunted.

      To begin with, everything is divided into a series of sub-assemblies which will then be joined together on the jig at the end of the week. First job is to file a careful mitre to the bottom of the seat tube and then to connect it to the bottom bracket (the big joint through which four tubes meet and the crank axle for the pedals passes). Having given us the necessary briefing on the uses and abuses of oxyacetylene gas, Dave gives both of us a pair of welding glasses, fits the tube and the bracket into the jig, gives it a daub of flux (to prevent the steel from oxidising), sparks up the torch and passes it over. The brass is a long, thin rod which is held very exactly over the joint until it reaches melting point. The aim is to get the brass to melt neatly and without lumps or gaps into the space between bracket and tube. This is not easy. If you don’t hold the flame over the lug and the brass for long enough then nothing will happen, and if you hold it for too long you’ll burn away the steel of СКАЧАТЬ