Update Panel Refreshing Whole Page?

Question

hi Friends,In my project Update panel refreshes the whole page.Here is my code...Can any one solve my problem...
<asp:ScriptManager id="scriptmanager1" runat="server"></asp:ScriptManager>
<asp:UpdatePanel id="updatepanel1" runat="server" UpdateMode="conditional" ChildrenAsTriggers="true">
<ContentTemplate>
                    <div id="search">
                          <div class="row-fluid">
                            <div class="container">
                              <div class="main-body clearfix">
                                  <h3>Tyre Segment</h3>
                                        <div class="form-wrap">
                                        <div class="span3">
                                            <asp:DropDownList id="ddltyretype" runat="server" AutoPostBack="True"
                                            OnSelectedIndexChanged="ddltyretype_SelectedIndexChanged">
                                            <asp:ListItem>--Select Type--</asp:ListItem>
                                            <asp:ListItem>Sedan</asp:ListItem>
                                            <asp:ListItem>Hatch back</asp:ListItem>
                                            <asp:ListItem>SUV</asp:ListItem>
                                            <asp:ListItem>LCV</asp:ListItem>
                                            </asp:DropDownList>
                                         </div>
                                            <div class="span3">
                                            <asp:DropDownList id="ddltyrebrand" runat="server" AutoPostBack="True"
                                            OnSelectedIndexChanged="ddltyrebrand_SelectedIndexChanged">
                                            <asp:ListItem>--Select Brand--</asp:ListItem>
                                            <asp:ListItem>Michelin</asp:ListItem>
                                            <asp:ListItem>Bridgestone</asp:ListItem>
                                            <asp:ListItem>Apollo</asp:ListItem>
                                            <asp:ListItem>JK tyre</asp:ListItem>
                                            <asp:ListItem>Yokohama</asp:ListItem>
                                            <asp:ListItem>Pirelli</asp:ListItem>
                                            <asp:ListItem>Continental tire</asp:ListItem>
                                            <asp:ListItem>faulkan</asp:ListItem>
                                            <asp:ListItem>MRF</asp:ListItem>
                                        </asp:DropDownList>
                                      </div>
                                    </div>
                                  </div>
                                </div>
                              </div>
                            </div>
    <!-----datalist1------>
                        <div id="showcase">
                          <div class="row-fluid">
                            <div class="container">
                              <div class="main-body clearfix">
                                <h3><asp:Label ID="lbltype" runat="server"></asp:Label><asp:Label ID="lblbrand" runat="server"></asp:Label></h3>
                                <asp:DataList id="DataList1" runat="server" RepeatColumns="5" CellPadding="5">
                                <ItemTemplate>
                                <a id="imageLink" style="height:500px;width:500px" href='<%# Eval("Name","~/images/Tyre/{0}") %>' rel="lightbox[Brussels]" runat="server" >
                                 <asp:Image ID="lblimg" CssClass="lightimg" runat="server" Height="140px" Width="180px" ImageUrl='<%# Bind("Name","~/images/Tyre/{0}") %>' />
                                </a>
                                </ItemTemplate>
                                <ItemStyle BorderColor="#660000" BorderWidth="1px" HorizontalAlign="Center" VerticalAlign="Bottom" />
                                </asp:DataList>
                              </div>
                            </div>
                          </div>
                       </div>
    </ContentTemplate>
</asp:UpdatePanel>