C3.js Gauge Min max

Am working with C3.js to produce gauges. I followed one of their basic examples and modified it to this

http://ift.tt/1Ht1EST

What am unable to figure out is how to change the gauge axis. I was hoping something like

chart.gauge.min(20)

would set the star to 20, but it doesn't. I don't want to set the gauge min and max during the generate chart process. I need to be able to do it outside that block of code. Any ideas?

Thanks Kay