Bicycle gear inch calculator.js

/*
Description:
#Gear Inch Calculator On a bicycle there are many ways to measure the size of the gear being used, one of which is gear inches. A gear inch refers to the equivelant diameter of the wheel of a penny farthing wheel in order to give the same gearing. As the safety bicycle (a bicycle where both the wheels are the same size) was developed, the gear inch remained a unit of measurement for gearing. The way gear inches is calculated is demonstated by this image from wikipedia:


Of course, lots of bicycles now have variable gears, rather than just one, on these bicycles with more than one chainring and with multiple sprockets at the back there are quite a few different options for gear inches.

You are going to create a function which gives all of the options for gear inches for the given chainrings and rear sprockets. The gear inches will be calculated based on a 700c wheel with a 23c tyre, which gives a diameter of 26 inches (this is an approximate measurement, but for the sake of this kata we will be using 26 inches as the diameter).

You will return a two dimensional array where there is an array for each chainring, and in the array there is a list of the gear inches given the combination of the chainring and the given sprockets. The gear inches will be rounded to one decimal place. eg. gearInchCalculator([50, 36], [11, 12, 13, 14, 16, 18, 21, 24, 28]) === [ [ 118.2, 108.3, 100, 92.9, 81.3, 72.2, 61.9, 54.2, 46.4 ], [ 85.1, 78, 72, 66.9, 58.5, 52, 44.6, 39, 33.4 ] ]

Everything passed to the function will be a valid input. Have fun!

If you want more information about what gear inches are, check out the wikipedia page
*/
function gearInchCalculator(chainrings, sprockets){
   return chainrings.map( c => sprockets.map( sprocket => Math.round(+(26*c/sprocket)*10)/10));
}