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Friday, October 03, 2008

WONDERFUL CLOCK!

HerHimnBryn emailed this link to me. I enjoy clocks and watches (the mechanical kind) and this really floated my boat. I just had to share it with you all.

It is derived from John Harrison's wonderful clock of the 1700's (this is a long link, but the fascinating story it tells is well worth perseverence).

Thursday, October 02, 2008

BICYCLE GEARS - HISTORY LESSON

(apparently this "Penny-Farthing Band - German - is available for hire)

Barrett Bonden asked me about my cycle gearing in my previous posting and I said that my lowest gear was "23 inches". A non-cyclist would be justified in saying "pardon?" So I thought you might like to know the history behind this calculation.

In English speaking countries cycle gearing is usually measured in inches. You don't really need to know what these inches stand for, just that a large number makes you push harder to go faster whereas a small gear allows you to winch yourself slowly uphill.

Gear inches come from the days when geared bicycles superseded the ‘ordinary’ – now known as a penny-farthing. This had its pedals fixed directly to the front wheel and if you wanted to go faster you needed a larger one. So bicycles were rated by the diameter of this wheel. A 52inch ordinary bicycle was big and potentially fast for its time, but only a tall man could ride it.

Then the safety bicycle was invented, on which all modern bicycles are based and in which the pedals are connected to the rear wheel by a chain and gears. These make the wheel turn faster (or slower) according to the ratio of front chainwheel divided by rear sprocket. A gear ratio of 48 by 16 for example, makes the wheel turn three times for one turn of the pedals. The effect is the same as if the pedals were fixed directly to a wheel three times as big, making a 26 inch wheel equivalent to one of 78 inch diameter. Such a bicycle was said to be geared to 78 inches – that would be one heck of a tall penny-farthing!

This system may be antiquated, but referring all gearing arrangements (including hub gears) back to a simple size of directly driven wheel gives us an easy way to compare all sorts of pedal cycles.

To calculate gear size you enter the diameter (in inches - or metric people could enter it in cms) of the actual wheel, and the numbers of teeth on the front chainwheel and rear sprocket, into the following formula:
Gear = Wheel × Chainwheel ÷ Sprocket

Not a lot of people knew that! But now you do. My lowest gear (23 inches or 58 cm)would have me riding an old penny-farthing with a front wheel that size - it would be like a small child's bike!