Because it's Monday, and I wish I was riding instead of sitting here at work on my lunch hour, I though I'd weigh in on the old sprocket size debate. The standard 1995+ KDX sprocket ratio is 13/47. A common mod is to replace the 12T countershaft sprocket (CS) than with a 13T CS . As Jaybird has pointed out in many posts, the loading on your chain and CS sprocket is greater with the smaller 12T CS than with a 13T CS and I have no argument with that. But there are a couple of offsetting factors to consider. Real world observations have lead me to the following conclusions:
1) While CS size may be a factor in chain life, it is not a dominant factor for most of us. The fact is today's chains are pretty well made. Riding environment (Mud, grit, etc) , and maintenance practice all seem to play a much larger part in chain/sprocket longevity than a small reduction in CS size. When I lived in a dry western climate, my chains and sprockets easily lasted twice as long as they do here in the east for the same (or more) miles ridden. Now that I subject them to weekly immersion in Northeastern mud paste, let them saw on logs and rocks when I get stuck, and otherwise subject them to eastern woods trail abuse - well no surprise that they don't last as long. My setup is 13/50, but I ride alongside other KDX's that use 12/47 and as a general rule, their chains are lasting about the same as mine. I definitely chew through a lot more chain guide wear blocks though.
2) Sometimes we focus to much on the downside (extra wear). There can be a significant benefit to 12/47. Around here I've been riding with some relatively new riders. A woman rider, new to dirtbikes, was having a lot of trouble in the more difficult technical terrain. She recently changed her CS from 13T to 12T and it has been amazing to see her improved ability to negotiate technical trails. The lower gearing has really added to her confidence. Unlike going to a larger rear sprocket Changing from a 13T to 12T is cheap and easy. Her bike is pretty new and the existing chain & sprockets still have a lot of life in them. The expense of a new chain, rear sprocket (and probably a new chain guide because a 50T rear is kind of tight with the stocker) would have definitely deterred her from making a change that has transformed her confidence and ability.
My point here that while extra wear is something to consider, it should not automatically rule the day. Sometimes the tradeoff is worth it.
1) While CS size may be a factor in chain life, it is not a dominant factor for most of us. The fact is today's chains are pretty well made. Riding environment (Mud, grit, etc) , and maintenance practice all seem to play a much larger part in chain/sprocket longevity than a small reduction in CS size. When I lived in a dry western climate, my chains and sprockets easily lasted twice as long as they do here in the east for the same (or more) miles ridden. Now that I subject them to weekly immersion in Northeastern mud paste, let them saw on logs and rocks when I get stuck, and otherwise subject them to eastern woods trail abuse - well no surprise that they don't last as long. My setup is 13/50, but I ride alongside other KDX's that use 12/47 and as a general rule, their chains are lasting about the same as mine. I definitely chew through a lot more chain guide wear blocks though.
2) Sometimes we focus to much on the downside (extra wear). There can be a significant benefit to 12/47. Around here I've been riding with some relatively new riders. A woman rider, new to dirtbikes, was having a lot of trouble in the more difficult technical terrain. She recently changed her CS from 13T to 12T and it has been amazing to see her improved ability to negotiate technical trails. The lower gearing has really added to her confidence. Unlike going to a larger rear sprocket Changing from a 13T to 12T is cheap and easy. Her bike is pretty new and the existing chain & sprockets still have a lot of life in them. The expense of a new chain, rear sprocket (and probably a new chain guide because a 50T rear is kind of tight with the stocker) would have definitely deterred her from making a change that has transformed her confidence and ability.
My point here that while extra wear is something to consider, it should not automatically rule the day. Sometimes the tradeoff is worth it.
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