Anatomy of a bicycle, #2

Good afternoon.

Returning to the cycling theme, the bike-building will be starting soon, as I've just ordered my frame! After reading Robert Penn's "It's All About The Bike", I opted to go for a steel frame. A custom-fitted, hand-built Rourke frame is (ahem) slightly outside my budget, so instead I'm going for a Genesis Equilibrium 56cm frame. It's within my budget, I've read some rave reviews of it, and it's the bike of choice for the mechanics at a couple of local bike shops, so I think it'll be a good starting point.

[Aside: This will be the first time in about 20 years that I've had a steel-frame bike. The last one was a wonderful chromoly Peugeot BMX that I had up until I was about 13. After that, I went without a bike at all for the best part of 10 years. I often wonder what I could have done in that 10 years I was lost to cycling.]

So, that's the frame - a series of tubes welded together, in a roughly diamond shape. The best diagram I've found to explain the geometry of a frame is this one, which just happens to be annotated in Japanese:

• Top tube (トップチューブ): The topmost, horizontal tube, which runs from where the saddle would be to where the handlebars go.
• Seat tube (シートチューブ): The tube which goes down from where the saddle would be to where the pedals are.
• Head tube (ヘッドチューブ): The small tube at the front.
• Down tube (ダウンチューブ): The tube which runs diagonally from the bottom of the head tube to where the pedals are.
• Seat stays (シートステイ): The two tubes which run diagonally from where the saddle would be to where the back wheel is attached.
• Chain stays (チェーンステイ): The two tubes which run (almost) horizontally from where the pedals are to where the back wheel is attached.

Also annotated on this diagram is the fork, the steerable bit at the front which runs through the head tube and to which the front wheel is attached.

My first assembly job is coming up soon ... fitting the fork and the frame together, which requires me to read up on and familiarise myself with headsets. Expect to read something about them in the near future!

Off-topic: Mental health and debt

Although the subject matter of this blog is primarily bikes and cycling, tonight I discovered something which ties together a few disparate but related threads so beautifully, that I couldn't help but remark on it.

When I first thought about taking on this challenge, I was conscious that the money-raising aspect of it would be as difficult, if not more difficult, than the cycling part or the building-my-own-bike part. With the onset of crunchy credit and recessions and increasing unemployment and the like, I was well aware that a lot of people have a lot less money going spare for contributions to charities. I'm delighted to say that, in spite of this, my friends and colleagues have proved fantastically generous so far, as the totaliser at uk.virginmoneygiving.com/AlanGibson attests. You'll also hopefully be aware that all of the money I raise will be going to Mind, charity which provides help to the 1 in 4 people who experience mental distress each year.

However, I think we're probably all looking for ways to save money to a certain extent. One source I regularly use, whether it's finding the best insurance prices, cheap flights, voucher codes, you name it, is moneysavingexpert.com, and if you aren't already a subscriber to their weekly newsletter, I recommend that you sign up for it here.

Surveys have indicated that, of those who do suffer mental distress, almost half also have severe or crisis-level debts. For this reason, Money Saving Expert has teamed up with a number of organisations (including Mind) to produce a guide to mental health and debt, which can be found at:

http://www.moneysavingexpert.com/cards/mental-health-guide

Revelation!

Of course, it's not necessary to understand how something works in order to enjoy it. I myself was a frequent and satisfied user of such popular products as gravity, photosynthesis and electromagnetic radiation for many years without the slightest idea how they worked. But if there is one thing I learned from my good old granddad, it's that knowledge opens the gateway to even more exciting discoveries ahead.

And so it is with the derailleur gears on my bike. I've used them every day for years and years, and although I always knew there were cables and cogs and clicky sounds, and that the cables had to be tight and the cogs free of gunk and the clicky sound just a "click" and not a "click-ick-ick-ick-ick-ick", I didn't really know how they did what they did.

All that changed when I watched this video:

  

There's little more explanation required, but I'm going to anyway. To my mind, it is actually much like gravity. The lowest gears, both front and back, are the ones where the chain is closest to the frame (the "ground"). A spring in the mechanism ("gravity") exerts a force to keep the chain at this level.

Then, when you change up a gear, the cable pulls on the mechanism, slightly overcoming its force,  guiding the chain out to the next highest gear, with the tension in the cable keeping it there. When you change down a gear, you're letting some of the tension out of the cable, and the mechanism's tendency to drag the chain inwards will take effect.

The key, therefore, to getting nice, smooth changes up and down is to ensure the tension in the cable increases and decreases enough to allow the mechanism to move just enough to go up or down a single gear. The people who make these gear mechanisms are (thankfully) very clever, and build them so that if you adjust the cable tension to get a smooth shift from the lowest gear to the second-lowest, it'll all just magically work for all of the other gears too.

Anatomy of a bicycle, #1

Good evening.

One of the things I've always found most confusing when learning about bikes are the terms used for the various different bits and pieces. Even when I've read fairly detailed descriptions or watched tutorials that go into some depth, there's usually some fundamental unexplained term that throws me.

And I figure that if I've been thrown, then maybe so have you. Hence this series of articles, starting with something fairly simple but very fundamental indeed - the wheel.

Picture courtesy of Herr Kriss

The wheel is made up of the following parts, starting with (hopefully) the most obvious first:

• Tyre: That hard black rubbery thing that goes all the way around the outside.
• Rim: The round metal bit that the tyre is tucked into.
• Inner tube: The inflatable bit of the tyre, which sits between the tyre and the rim. The only bit of it you can see is the valve, more on which later.
• Hub: The bit in the middle, which attaches to the rest of the bike, and hopefully stays there.
• Spokes: The long metal rods which attach the rim and the hub.
• Rim tape: This sits between the rim and the inner tube, to protect the tube from any spiky or sharp bits on the rim.

One of the things I'm planning not to do in my project to build a bike is to build the wheels up from all the individual bits - I think they're just a bit too important for an amateur to have a go at. In all likelihood, you'll generally always buy or replace a wheel in its entirety, which will reduce your relationship with the wheel to the following:

• Inner tube valves: There are two different types of valves in common use: Presta and Schrader. Presta valves are longer, thinner and pointier (the valve in the picture above is a Presta); Schrader valves are more squat and wider. The only reason I mention this is that one time I bought an inner tube with a Schrader valve, and tried to use it as a replacement for a Presta one. It should have been obvious to me at the time, but the Schrader wouldn't go through the narrower hole in the rim. (Thankfully the other wheel of this particular bike did have a hole big enough for a Schrader valve, so the inner tube wasn't so much a waste of money as it was a prudent investment.)
• Broken spokes: This is pretty terminal. If one spoke breaks, it puts more stress on the others and you're likely to end up with the wheel collapsing. If you break a spoke, get off and push it home. Even if it is tipping it down and you're late for tea.
• Loose hub: The whole wheel should be held in place so that it doesn't "jiggle" to either side of the centre when you're cycling. I have on occasion had it happen that the hub's come a bit loose - you can feel and hear it, especially when you go round corners - the bike doesn't feel quite "with" you any more. You may need a new hub, or it may be possible to get your existing one tightened up, it all depends on how severe the problem is.

That's all for tonight!