Sprocket and Chain (or Belt) Diameter Calculations
When changing sprockets you normally do not change the number of theeth
extremely and hence the size of the sprocket will not change a lot either.
However sometimes all margings have (nearly) been used and is it important
to know how big (or small) the new sprockets will be. For instance when you
want to use a larger front sprocket but need to make sure it will fit or the
same if you want to fit a smaller one, to make sure the chain does not rub
the swingarm near the front sprocket. Also in the rear not all sizes will
fit as often space is limited by a chainguard.
As sprockets are rarely listed with their actual diameter I have added a
sprocket size calculator to the Gearing Commander. It is activated by
loading your bike, adjusting the sprocket details and loading of the
'Sprocket Diameter Graph', using the button below the table called "Top
speed in Mph per gear for 49 final drive combinations at M.P.RPM in Custom
setup".
This calculates sprocket diameters for both chain drive bikes and belt drive
bike. However the results are to be interpreted differently.
For both type of sprockets the so called 'pitch diameter'
is calculated and displayed.
For chain sprockets that is the diameter which defined by the centerline of the
chain rollers on the sprocket (red circle):
Pd = Pitch Diameter (smaller as actual
sprocket diameter Sd)
Sd = Sprocket diameter (max. sprocket diameter)
Cd = Chain Diameter (diameter sprocket and chain together)
To check if your sprocket and chain will fit you need to check for
the Chain diameter (Cd) as that is the biggest one.
For belt sprockets also the pitch diameter is
calculated (blue dashed circle). It lies outside the sprocket, in the belt.
Mostly at the height of the tensile cord.
Pd = Pitch Diameter (bigger as actual sprocket diameter Sd)
Sd = Sprocket
diameter (max sprocket diamater)
Bd = Belt Diameter (diameter of sprocket
and belt together)
To check if this sprocket with belt will fit you need to check for
the Belt diameter (Bd) as that is biggest one.
For belt driven motorcycle mostly belts with a 14mm pitch are used. For
those belts the total belt height and the tensile cord part thickness is
known, it is about 4 mm (0.158"). Only for these bikes (14mm pitched belt)
the Gearing Commander can calculate the Belt diameter. For bikes with
another pitch NO Belt diameter (Bd) will be calculated and
it will be shown with the same size as the Pitch diameter (Pd).
In that case the graph Legend will show:
"NOT all Belt Diameters (Bd) calculated as the belt height is unknown
for belts other than 14 mm pitch"
Sprocket Pitch Diameter graph
Back to Gearing Commander
|
