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supersonicLives Here
Joined: 25 Nov 2005
Posts: 50524
Location: Chapeltown, Sheffield
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 Posted Mon Aug 31, 2009 10:34 pm |
First question most people ask is: why do we have so many? A car usually only has 5 or 6?! A general mountain bike with a triple chainset (3 cogs up front) may have 24 or 27 in total: the reason for this is due to power and efficiency - we simply can't match a car engine for efficiency over a wide range of revs. Typically we are most efficient pedalling at about 60-100 revs of the pedals per minute, so the gears allow us to tune our cadence as we move to different speeds. The more cogs at the back then the closer the ratios are together.
Many gears do overlap though and this can be seen by looking at the gear ratios ie the number of the teeth on the cogs. 32/16 is the same as 22/11 for example, but the latter causes an undesirable chain angle as mentioned later. In all you have about 14 or so unique combinations.
With a triple chainset you will probably be in the middle chainring for the majority of you time, and in this ring you can use all the rear cogs. Once you you have changed down to the highest gear, and require more speed, shift into the largest chainring: here you can use the 3 or 4 smallest rear cogs to tune your pedalling. Similarly if in the middle ring and largest rear cog yet require a shorter gear, shift into the smallest front ring: this time you can use the 3 or 4 largest rear cogs. Going outside these 3 or 4 in the above instances skews the chain across at an angle causing rub, chain slip and premature wear - and are usually these gears that are replicated in the middle ring anyway.
With practice you automatically know what gear you are in and can pre-empt the change so you are always in the right chainring. Ease of the power as you change: with thumb levers you may have to hold it there for a fraction after the click to complete the change.
So to sum up, for a triple chainset:
In the smallest front chainring you can use the 3 or 4 LARGEST rear cogs.
In the middle front chainring you can use ALL the rear cogs.
In the largest front chainring you can use the 3 or 4 SMALLEST rear cogs.
Zaskar LE 1996
Zaskar Carbon Team
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