Single Speed Gearing

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Revision as of 16:12, 3 December 2006 by Pvd (talk | contribs) (Personal Selection)
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Often when talking about gearing a singlespeed, the expression "two to one" comes up. Beside the fact that this is a meaningless statement, it implys that the coice of gears is based on easy math rather than real decisions. Let's look at this.

Simple Math

32 devided by 2 is 16. So the ratio of 32 to 16 is 2:1.
34 devided by 2 is 17. So the ratio of 34 to 17 is 2:1.

We call this simple math. Any moron can do this math in his/her head with these numbers. What connection does this have with choosing a gear for a bicycle with at specific rider on a specific terrain? Absolutely none. It is just simple math. To base a gearing choice on the fact that the number of teeth on two chosen gears can be devided into the whole numbers of 1 and 2 is nuts.

Ratios

Here is a table of gear ratios with the more common gearing choices highlighted for off road riding, single gear, 26" wheel. It is a quick and simple way of seeing a facet of gearing choice. It doesn't tell the whole story, but it tells us something.

26-inch-gear-ratios.gif
As can easily be seen, a great variety of gears exist within the 2:1 and 1.7:1 range.

'Real' Gearing

Real gearing is probably not the best term. Typically, this is refered to as Rollout or Developement. What makes this a better system to use is that rather than comparing one gear ratio to another, a gear is described by what it actually does. This is the amount of forward distance moved on the bike by each rotation of the crank arms.

Development-math.gif

Now we can quickly compare 26" MTB wheel gearing to 29" MTB wheel gearing.

26-29-developement.gif

Personal Selection

Personaly, I am running a 34/19 gear (148.4"). We do a lot of climbing where I live, and I'm overweight and not the strongest climber. I would love to go up to 34/18 (156.7") or 32/17 (156.1"). That would help my downhill speeds a little if I could handle the gear on the climbs, but with mud season coming, I may even have to drop to 34/20 (141.0) depending on power losses. We will see.