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The calculator is designed to return pulley, belt and chain information for a given set of circumstances.
The measurements may be in millimetres or inches, as long as they are the same throughout.

• Supermoto Street Gearing
• Supermoto Tires

There are five main sections in the calculator, dealing with pulleys andbelts (or chains and sprockets - see below), togetherwith speed. In each section, only one variable is calculated, dependingon which radio button is selected. In the first, a selection is madewhether the system is belt or chain driven. Assume Belt drive for now(see later for Chain, for which all references to'Pulley' in the following text would read 'Sprocket', and 'Belt' would read'Chain').

Chain Length Calculator For our FLT/H Chain drive conversions we supply a 120 link O-Ring EK Chain. We also have a Sprocket Diameter Calculator that determines a sprockets diameter based on the pitch of the chain and the number of teeth.

In the second section, the first listed pulley is the driver. Thedriven pulley is the output, which may be for a drill, saw, polisher or otherdevice. Most pulleys have a 'V' grove to accept aV-belt. If this is the case, the diametershould be measured to the root of the 'V'. If the drive pulley islarger than the driven pulley, the driven pulley speed will be higher thandrive pulley speed by the ratio of the sizes, and vice versa. Byselecting the appropriate radio button, the program determines the unknownfrom the other two values.

In the third section, the centre-to-centre measurement is the distancefrom the centre of the drive shaft to the centre of the driven shaft. The length of the belt is the circumference of the belt at the point itcontacts and grips the pulleys. One value is calculated from the otherparameter by selecting the appropriate radio button. If the chosen beltlength is too short, or the centres are too close together, no calculation isdone and a warning is given. If the gap between the pulleys iscalculated to be less than 5% of the average of the pulley diameters, awarning is given since, although a belt might fit OK, the pulley flanges couldclash.

The thickness of the belt is used to calculate its external length- see fifth section.

In the fourth section, the input RPM is the speed of the drive pulley(usually known from the motor speed) whilst the output RPM is the speed of thedriven pulley. By selecting a radio button, its value is calculated fromthe other parameter.

The fifth section shows the minimum belt wrap anglefor the driven pulley and the gap between pulleys. These are alwayscalculated from the other factors - they are not input fields. The internal diameter of the belt (as if it were a circle) and the externalbelt length (allowing for its thickness) are also given since one or other ofthese is often quoted by suppliers.

Enter all known variables in sections above and click Calculate -the other factors are returned. If 'Calculate Automatically' is checked,clicking on any radio button will also initiate a calculation. Click onClear Values to reset to defaults and clear any previous answers.

For Chains, the same principles apply, except it ismore convenient to use chain links as the unit of measurement. Thismeans the values entered for Sprockets (Pulleys) in the second section wouldbe its number of teeth, and the value entered for the 'Belt length' would bethe number of links in the chain. So that the distance between sprocketcentres is meaningful, a Chain Pitch must be entered in the samemeasurement units (eg. mm) as the centre-to-centredistance. Although the chain length can be calculated from thesprocket centres, the number of chain links must obviously be aninteger! (And preferably an even number.) So the answer given mustbe rounded up accordingly and the centre-to-centredistance recalculated. Please note this calculator can only assume achain without a tensioner (as on a motorcycle). A bike withDerailleur gears has a tensioner, which requires extra links, the number ofwhich depends on the tensioner. However, this calculator can give arough guide to minimum chain length in this situation - forDerailleurs, enter the largest sprocket on each end, ie. for the lowest gear.

The Drive Ratio and Speed sections may also be used for gears,though obviously the other sections will be meaningless since gears must be ondefined centres to mesh properly.

Supermoto Street Gearing

Supermoto Tires

Belt, pulley and chain covers are useful to prevent inadvertent contactwith fingers and clothing!
Caution - ensure belts are rated for the pulley speeds and minimum bend radii.