In
summary
A
sprocket is a toothed wheel upon which a chain rides. There is a
sprocket on a kart's engine shaft or clutch and another one on the
drive axle which turns the wheels. The chain between these sprockets
transmits the power from the engine to the wheels.
Size
Roller
chain and sprockets come in a variety of sizes and have to be
complementary in size to work correctly.
Chain
is sized by the pitch (the distance between roller centers). See the chain shown in the picture. Several different standards are used but
typically you will see ANSI, ISO, or British Standard. In the ANSI
standard, the pitch is given in 1/8" increments as shown in the
left digit or digits of the chain size, so a #80 chain would be 8/8
or 1" pitch. A #35 chain has 3/8" pitch. The right-hand
digit of the standard denotes 0 = normal chain, 1 = lightweight
chain, 5 = rollerless bushing chain. Most 4-cycle carts will use #35 chain.
A size
that is commonly used on 2-cycle karts is #219 chain. The pitch on
#219 chain is .306" while that on the #35 chain is .375".
Since the #219 chain is smaller, it has less strength than the #35
chain, but will also give more possible gear ratios for the same
space available for your sprocket. This gives you a better range of
gear ratios that can be used to optimize your kart.
Speaking
of sprockets
First,
the teeth on the sprockets that you select should be sized to the
chain that you are using. If they are incorrect, then the chain will
not glide smoothly over the sprocket.
After
that, the size of each sprocket is determined by the number of teeth
that you want, and the number of teeth is determined by how fast you
want your kart to go. Sprockets may have no hub or have a hub on
one side and they may be split or not. Split sprockets are typically
easier to install.
How
fast?
Starting
out with the RPM of your motor and the circumference of your rear
tires, you should be able to calculate your speed given the ratio of
the number of teeth on the sprockets on your motor shaft (M motor
sprocket teeth) and your wheel axle (W wheel sprocket teeth).
Max
speed = (RPM*M* Wheel circumference in inches)/W
That
will give your speed in inches per minute. To convert to miles per
hour, divide by 1056.
