Many bikes that you buy for commuting or general riding may not have the correct ratio of gears you need for touring.
On touring bikes the primary purpose is not to 'go faster' but to be able to endure for long periods of time. While flat roads are your friends, hills can be your worst nightmares. Therefore you need to purchase your touring bike with the consideration of hill climbing, with heavy loads for long periods.
Few standard bikes have the gear set that best suits touring by default. What you need is a very small from chain ring on the front and a very big rear chain ring on the rear. Don't under estimate the importance of this set up, you will spend enough time riding or pushing up big hills to repent at leisure if your gearing is not low enough for you.
You can count the teeth on a chain ring to see what size you have, some rings have the number of teeth stamped on them as well.
The front cluster
On the front of your bike you will have 3 chain rings. The smallest will be for hill climbing, the middle for relatively flat cycling and the biggest is for speed and downhill.
When cycle touring you will hardly ever use this biggest chain ring, your life will consist of changing back and forth between the smallest and the middle ring.
Sheldon Brown notes that Mountain bikes typically have chain rings of 26-36-46 teeth, or perhaps 28-38-48. If you want the lowest gear possible for climbing hills, the inner chain ring should be 26 or even 24, if that will work with the front derailleur on the bike. I use a 24 for my smallest with a very low 38 tooth ring for my big ring. This gives me 3 close ratios of gears to use, I still only use the big ring rarely, but when I do its a usable ratio, unlike the bigger toothed gears.
A ratio like this might not be common on a mass produced bike, you may need to talk to your bike shop about creating a custom set up. I have found that the smaller the chain rings on the front the better it will be for touring. Standard setups are not the most efficient for touring cyclists and you will pay for it on the hills.
Here is an example of a new CANNONDALE Touring Ultra 2008 Touring Bike with a ratio of 22/32/44. A great range for touring.
The rear cluster
The rear cluster creates more controversy than the front.
With the
front you have a choice of chain rings, 2 or 3. only an idiot would take
2. However on the rear you have a great range of 7, 8, 9, or 10! and 10
is not necessarily better than 7.
Again as with the front gears the standard gearing on a bike might be totally out of step with what you need on a touring bike.
On a touring bike you need LESS teeth on a cog to make it more lower geared and easier on the hills. On the rear you need MORE teeth on a gear to make it easer on the hills.
So on your rear cogs get as big a toothed cog as you can get.
What choice 7, 8, 9, or 10 cogs?
The chain factor
Between the front chain rings and the rear chain rings is the chain itself. as the number of cogs increase the more the chain has to flex sideways between the top cog and the lowest. also the chains get finer in quality and smaller, becoming more precise to shift between closely spaced cogs.
The upshot of this is that the chains for the 9 and 10 speed cogs are thinner, and finer than 7 and 8 speed ones. This means there is more potential for chain problems with misalignment and wear being more of an issue.
So the sturdiness of the chain becomes a factor of the number of cogs you choose.
This site has some good background reading on the changing dimensions of increasing the cog numbers.
More cogs do not mean more speed
No matter what the number of cogs are on the rear the top and the bottom cog are the same numbers. So the benefit of more cogs is better matching your cycling cadence with your speed, it doesn't make the bike faster or better climbing just because of the extra cogs.
So, no more speed is gained from having more cogs for a touring cyclist, no higher or lower gears are added with new cogs, and the more cogs you have the weaker and potentially unreliable the chain.
My recommendation
Choose 7 or 8 speed gears to get a more reliable chain and sturdier equipment. These cogs will also be more able to be serviced in 'out of the way' places as well, being older and more common. They are also cheaper to purchase as well.
Get as big a back cog range as you can, remember you are not building for speed, but for climbing under heavy load for long periods.
Bike Gears Summary
- Standard gears both front and rear are not optimised for touring
- Get the smallest cog on the front and the biggest cogs on the rear that you can
- Chain sturdiness decreases as you add more cogs, 7 and 8 speed chains are more reliable than 9 or 10.
- More cogs do not mean more speed, for the touring cyclist.