iconClsTemplate

iconClsTemplate - Specifies the mapping between the icon cls column in the datasource and
the tab icon style and also may define a visualization template. It may be a string value or a function.

<script type="text/javascript">
    $(function () {
        $("#tabs").shieldTabs({
            iconClsTemplate: "{iconCls}",
            dataSource: {
                 data: [
                     { title: "Tab1", iconCls: "iconStyle", iconUrl: "/Content/Tab1Image.png", content: "Tab1 content" },
                     { title: "Tab2", content: "Tab2 content" },
                 ]
            }
        });
    });
</script>

<style>
  .iconStyle {
     width: 35px;
  }
</style>