kopcicle
antidisestablishmentarian
Sprockets with a “prime number” (which cannot be divided by any number except themselves and one) tooth count reduces the frequency with which a specific tooth engages a specific chain roller. Prime number tooth count reduces low-frequency vibration by raising the frequency and reducing the tendency of harmonics of frequencies to interact. Under ideal conditions both the transmission and rear wheel sprockets, and the number of chain links should be prime numbers. If not all three, then two, &c.
If no prime number is possible, use a tooth count with the fewest factors.
E.g., 55 (5 x 11), 57 (3 x19) or 58 (2 x 29) are preferred to 56 (2 x 2 x 2 x 7) or 60 (3 x 5 x 2 x 2).
Last resort: use an odd number rather than even (which is always divisible by 2).
Useful primes:
Transmission sprockets 17, 19, 23, 29
Rear wheel sprockets 41, 43, 47, 53, 59, 61, 67
Chain links 89, 97, 101, 103, 107, 109, 113
A small sprocket's instant load on the teeth, roller axles and bearings/bushings is very high compared to a larger sprocket.
17 teeth is considered the minimum size to control this and should be used when practical.
There is also considerable speed variation as each roller climbs the tooth and falls into the root, where the exact timing will vary slightly between rotations (about 3.4% for 12 teeth, 15 teeth cuts this to 2.2%, 18 to 1.5%, 22 teeth is 1%). This is a function of tooth count, so it's better with a higher tooth count.
With that said (many thanks to "Panic") you all might want to look at this
http://www.gearingcommander.com/
~kop
If no prime number is possible, use a tooth count with the fewest factors.
E.g., 55 (5 x 11), 57 (3 x19) or 58 (2 x 29) are preferred to 56 (2 x 2 x 2 x 7) or 60 (3 x 5 x 2 x 2).
Last resort: use an odd number rather than even (which is always divisible by 2).
Useful primes:
Transmission sprockets 17, 19, 23, 29
Rear wheel sprockets 41, 43, 47, 53, 59, 61, 67
Chain links 89, 97, 101, 103, 107, 109, 113
A small sprocket's instant load on the teeth, roller axles and bearings/bushings is very high compared to a larger sprocket.
17 teeth is considered the minimum size to control this and should be used when practical.
There is also considerable speed variation as each roller climbs the tooth and falls into the root, where the exact timing will vary slightly between rotations (about 3.4% for 12 teeth, 15 teeth cuts this to 2.2%, 18 to 1.5%, 22 teeth is 1%). This is a function of tooth count, so it's better with a higher tooth count.
With that said (many thanks to "Panic") you all might want to look at this
http://www.gearingcommander.com/
~kop
