Expose an additional property in RadGauge that controls the margin for the gaugeArea.

Add border and border appearance options like color, width and type for the RadGauge. Currently the background color of the RadGauge is set to the wrapper of the control. Improve that color so that it fits in with the border and the shape of the control.

For the time being you can use the following workaround:

        <script>
            var pointerSize = 35;

            function pageLoad() {
                var gauge = $find("<%=rgEpmScorecard.ClientID%>");
                gauge._gaugeObject.options.scale.rangeSize = 25;
                gauge.repaint();
            }

        </script>
        <telerik:RadRadialGauge ID="rgEpmScorecard" runat="server" Skin="Metro" Height="99px" Width="100px">
            <Pointer Value="50" Color="Black">
                <Cap Size="0.5" Color="Black" />
            </Pointer>
            <Scale MajorUnit="10" Max="100" Labels-Visible="false" StartAngle="-45" EndAngle="225">
                <MajorTicks Visible="false" />
                <MinorTicks Visible="false" />
                <Ranges>
                    <telerik:GaugeRange Color="#ac1d23" From="0" To="16.67" />
                    <telerik:GaugeRange Color="#c26522" From="16.7" To="33.33" />
                    <telerik:GaugeRange Color="#d2b408" From="33.5" To="50" />
                    <telerik:GaugeRange Color="#b5be25" From="50.04" To="66.66" />
                    <telerik:GaugeRange Color="#0c833f" From="66.8" To="83.33" />
                    <telerik:GaugeRange Color="#0b6cb3" From="83.38" To="100" />
                </Ranges>
            </Scale>
        </telerik:RadRadialGauge>
        <script>

            var dataviz = kendo.dataviz,
                draw = dataviz.drawing,
                Path = draw.Path,
                DEFAULT_LINE_WIDTH = 0.5;

            kendo.dataviz.RadialPointer.fn._renderNeedle = function () {
                var that = this;
                var options = that.options;
                var minorTickSize = that.scale.options.minorTicks.size;
                var center = that.center;
                var needleColor = options.color;

                var needlePath = new Path({
                    fill: { color: needleColor },
                    stroke: { color: needleColor, width: DEFAULT_LINE_WIDTH }
                });

                needlePath.moveTo(center.x + that.radius - minorTickSize + pointerSize, center.y)
                          .lineTo(center.x, center.y - (that.capSize / 2))
                          .lineTo(center.x, center.y + (that.capSize / 2))
                          .close();

                return needlePath;
            }
        </script>

There are some issues with the appearance of the gauges in RTL mode. They vary across browsers.

An easy fix is to add a CSS class to each of them and force direction: ltr:

<telerik:RadRadialGauge CssClass="rtlFix" ID="radialGauge1" runat="server" Width="272px" Height="272px">
    . . . . .
</telerik:RadRadialGauge>

.rtlFix
{
    direction: ltr;
}

If you need to swap the places of the min and max value the Reverse property of the Scale inner tag must be set to true.

Workaround:

  1) Use   RenderAs="SVG".
  2)  Set 100% width to the gauge's wrapper prior the resizing
 
Use the solution below to make the control responsive:
     <table style="width: 100%;">
            <tr>
                <td>
                    <div style="width: 100%;" id="gauge"></div>
                    <telerik:RadLinearGauge runat="server" ID="RadLinearGauge1" RenderAs="SVG" Width="100%">
                        <Pointer Color="Gray" Size="10" />
                        <Scale Vertical="false" Min="0" Max="40">
                            <MinorTicks Size="20" />
                            <Ranges>
                                <telerik:GaugeRange Color="#D7E5D1" From="0" To="10" />
                                <telerik:GaugeRange Color="#EBE6D2" From="10" To="20" />
                                <telerik:GaugeRange Color="#F5D2D1" From="20" To="30" />
                            </Ranges>
                        </Scale>
                    </telerik:RadLinearGauge>
                </td>
            </tr>
        </table>
            <script type="text/javascript">
                var $ = $telerik.$;
                $(window).resize(function () {
                    $("#<%= RadLinearGauge1.ClientID %> > div")[0].style.width = "100%";
                    $find('<%= RadLinearGauge1.ClientID %>').get_kendoWidget().resize();

                });
            </script>

As a workaround the width of the range placeholder can be set through the gaugeObject:
JavaScript:
		function pageLoad() {
			var gauge = $find("<%=RadRadialGauge1.ClientID%>");
			gauge._gaugeObject.options.scale.rangeSize = 30;
			gauge.repaint();
		}
		<telerik:RadRadialGauge runat="server" ID="RadRadialGauge1" Height="350px" Width="350px">
			<Pointer Value="220" Color="Black">
				<Cap Color="Gray" Size="0.1" />
			</Pointer>
			<Scale Min="120" Max="300" MajorUnit="30" MinorUnit="5">
				<Labels Format="{0} °C" Position="Outside" />
				<Ranges>
					<telerik:GaugeRange Color="Orange" From="150" To="190" />
					<telerik:GaugeRange Color="Green" From="190" To="230" />
					<telerik:GaugeRange Color="Red" From="230" To="300" />
				</Ranges>
			</Scale>
		</telerik:RadRadialGauge>

If the gauge must display a huge range of values (e.g. Min=0, Max=500 000) having visible MinorTicks blocks the browser and ultimately throws an "out of stack space error".

The workaround is to set 
MinorTicks.Visible = false 
or Scale.MinorUnit to a sufficiently large value. If the minor unit is not set properly the minor ticks will clutter together and will be unreadable.

This should also allow accessing them in the code-behind through their names and not only by their index, e.g.:

GuageName.Scale.Ranges[GaugeRangeName].From = value;

Add a new property to HtmlChart as well as Gauges to AutoResize on parent control size change. A precondition to this is Height and Width of the control must be set in percentages of the parent control.

To implement this we can either use window.onresize or ResizeObserver.

Reference

Reference 2

The underlying Kendo Linear Kendo stopped rendering the track in 2014.3.1314 and, respectively, so does RadLinearGauge as of 2015.1.225

For example, the following snippet should render a wide, green, semi-transparent track, but it does not

			<telerik:RadLinearGauge ID="gauge" runat="server" Height="280">
				<Pointer Value="20">
					<Track Color="#5ca038" Opacity="0.5" Size="30" />
				</Pointer>
			</telerik:RadLinearGauge>

For the time being you can position a style element with absolute position below the gauge cap that will store the current value of the gauge. See an example in the http://www.telerik.com/forums/some-questions-c37b45192cef forum post.

You can vote for this feature so that it must be implemented in the Kendo Gauge first http://kendoui-feedback.telerik.com/forums/127393-kendo-ui-feedback/suggestions/3692105-hi-need-a-label-for-the-pointer-shown-in-the-line
Once it gets implemented, it can be ported to the UI for ASP.NET AJAX Gauge server wrapper.

You can do this with the Template property of the Label object

			<telerik:RadLinearGauge runat="server" ID="rlg1">
				<Scale Min="1" Max="4" MajorUnit="1">
					<Labels Template="#= getLabelText(value)#" />
				</Scale>
			</telerik:RadLinearGauge>
			<telerik:RadRadialGauge runat="server" ID="rrg1">
				<Scale Min="1" Max="4" MajorUnit="1">
					<Labels Template="#= getLabelText(value)#" />
				</Scale>
			</telerik:RadRadialGauge>
			<script>
				function getLabelText(e) {
					return "label for " + e;
				}
			</script>

For old versions the template can be set through the kendoWidget:

ASPX:

        <script>
            function setGaugeLabels(value) {
                switch (value) {
                    case -10:
                        return "Min: " + -10;
                        break;
                    case 35:
                        return "Max: " + 35;
                        break;
                    default:
                        return "Name: " + value;
                        break;
                }
            }
            function pageLoad() {
                var gaugeObj = $find("<%=RadLinearGauge1.ClientID%>")._gaugeObject;
                gaugeObj.options.scale.labels.template = "#=setGaugeLabels(value)#";
                gaugeObj.redraw();
            }
        </script>
        <telerik:RadLinearGauge runat="server" ID="RadLinearGauge1" Height="300px" Width="100px">
            <Pointer Value="11" Color="Green">
            </Pointer>
            <Scale Min="-25" Max="50" MajorUnit="15" MinorUnit="1">
                <Labels Format="{0} °C" />
                <Ranges>
                    <telerik:GaugeRange From="-25" To="-5" Color="Blue" />
                    <telerik:GaugeRange From="-5" To="15" Color="LightBlue" />
                    <telerik:GaugeRange From="15" To="30" Color="GreenYellow" />
                    <telerik:GaugeRange From="30" To="50" Color="Red" />
                </Ranges>
            </Scale>
        </telerik:RadLinearGauge>

It would be nice if RadGauges, the radial ones especially, could include a title element

I would like to consider the ability to customise the labels for the GaugeRange items that may not be part of a numerical index. For example, you may have a 3 range gauge that is low (green) / medium (orange) / high (red). Currently there is no way of customising these values.

I believe this would be similar to what is currently done in the Slider control ( http://demos.telerik.com/aspnet-ajax/slider/examples/slideritems/defaultvb.aspx)

Currently RadGauge has an option to turn on/off the animation when the chart is rendered through its transition property. If that property is set to true the requested feature will allow setting the speed/duration of the animation.