Please explain WHY it's never a good idea? I see people do it all the time. AND the reason for my question is to be able to use the new 43 tooth sprocket and maintain as close to my current ratio as possible.
I guess none of us have done a very good job of explaining. I will try a different way. Imagine each roller on the chain as one of your fingers, this applies to the front ( counter shaft) and rear sprocket.
Now say you have the strength to pull a 100 LB load with your arm, imagine that if you used one finger, that would be 100 LB force on it, if you were able to use five fingers, that would be 20 LBS per. So your rear sprocket has alarger diameter so there is a mechanical advantage , plus it has 3 times the number of teeth, so using my finger formula , that 100 lb force on the rear would be over 15 teeth compared to five on the front, so rear would be 6.66 lbs per finger.
So enough about fingers, what happens is similar to what I am trying to convey , if you continued to use one finger, chances are excellent that damage or failure will occur to that finger.
There is a second factor, even though Invader compared the ratios, the smaller the counter shaft sprocket, the higher is the torque, there is a point were you can't go with less teeth because the shaft diameter governs the minimum diameter and thus the minimum number of teeth.
The 520 chain is designed to convey a certain amount of horse power. So to go to extremes, if you had a 30/ 92 which is exactly the same ratio as a 15 / 46, the chain on the 30/92 would be almost impossible to damage as to torque / stretching, compared to the 15 / 46.