Gearing a bike for touring is a challenge. As I posted earlier in New adventure, new bike, I’m trying to figure out how I’m going to gear the bike. As a part of this I decided to take a test ride to the most challenging uphill climb near my home. This climb is about 1,5 km long and has about 100 m elevation gain. On average its grade is about 6% but the steepest part is over 12% for about 100 m. Without any packing on the bike I could easily climb the hill without using the lowest gears. But, I know from experience that 10 or even 20 kg of stuff attached to the bike makes all the difference in the world. Especially at the end of a long day.
Choosing the right gear
Using 39/11 as the highest gear I spin out at about 35-40 km/h which is fine, there’s no need to pedal when going downhill when touring. The 30/26 lowest gear was a bit too easy without packing. Since I already decided to switch out the 30 chain ring to a smaller one, the question was if I was going to get a 22, 24 or 26 one. I decided that a 26 would be fine. As I did the math to find out if the rear derailleur would handle the range I found out that there are crank-sets with 38-26 available for mountain bikes. Since my bike is equipped with mountain bike parts my chosen chain ring would not pose a problem.I also did the math just to make sure. How to do this?
Can my bike handle the gears?
It’s quite easy to calculate if your bike can handle the gearing you want to use. Just find the specifications for your rear derailleur, it will say how big the largest sprocket on the rear can be. However this can be increased using a longer derailleur hanger and using the adjustment screw to make the derailleur sit closer or further from the cassette. (I actually did this on my road bike to handle a 11-30 cassette). The specifications on the derailleur will also state a total capacity. What you do is take the number of teeth on the biggest ring in front (39 in my case) and remove the number of teeth on the smallest ring (26), this results in my case in 13. Then you do the same thing for the cassette. In my case 36-11, which, last time i checked still is 25. Now add these figures together, 38 in my case. The derailleur I have on the bike can handle a 43 tooth difference, meaning I’m well in range. Just make sure which version of derailleur you have on the bike since there are both long, medium and short versions.
Another way of easily determine how you can change your gearing is to make sure the difference between the big and the small chain ring is about the same as the bike came with. I’m not doing this so I have to do the math.