Your
primary drive, transmission and rear drive sprockets all combine to
determine your cruising rpm as well as your final top speed. This
calculator will show you your speed in each gear from everything from a
stock bike to an all out drag bike with a separate jackshaft as well as
the one we love the most, the Bonneville racer. The big end is where
it's at!
Engine RPM
-- You can enter your final redline figure or any other rpm, say the
rpm you want to cruise at for a given speed, and the calculator will
help you figure out the transmission and sprockets you will need.
Primary Drive -- This can be the oem
compensator sprocket which is connected by a double row chain to your
clutch...or a belt primary which comes in a variety of pitches and
widths. In any case, it's a front and rear sprocket of some sort. One
end at the crankshaft and the other end going into the
clutch/transmission.
Transmission -- Four speed early items,
five speed later transmissions, aftermarket six speed gear sets, two
speed and three speed planetaries, high gear only Pro Dragsters...there
are lots of options out there. Enter your given ratios and see what
your speeds are.
Jackshaft -- Some drag race bikes and
some Bonneville designs will use a intermediary jackshaft either to
gain an offset to clear a wide tire or to prevent a final drive chain
from being "too long".
Diameter of the Rear Tire -- You need to know the height (diameter) of your rear tire when properly inflated.
Tire Growth
-- At speed the tire will grow. For regular road tires the effect is
neglible but for the larger drag racing slicks it is considerable. As
the tire expands your final drive ratio changes. In effect the tire
becomes a variable gear and part of your "transmission".
Wheelspin -- In drag racing and at
Bonneville you are going to have a percentage of wheelspin you are
going to have to plan for. This will depend on a lot of factors which
have to be determined, mostly through experience. You will have to gear
"taller" to achieve your desired trap speed. For drag racing with ultra
high horsepower apps like our 113 ORCA Turbos this should be about 5%.
For Bonneville where traction is a variable depending on salt
conditions you may have to figure in 10-20%...i.e. rear wheel going 220-240,
front wheel going 200.
