I\'ve not found an API or previous question that addresses changing the width of the solid gauge data plot.
I can easily change the chart width, plot width, plot pad
You can use innerRadius on yAxis.
plotOptions: { solidgauge: { innerRadius: '75%', dataLabels: { y: -45, borderWidth: 0, useHTML: true } } },
http://jsfiddle.net/jm8E4/6/