public ActionResult Results ( int? PageSize,int? RaceId, int page = 0)
        {
            ///code that uses PageSize and RaceId to get data from DB
        }

public ActionResult _SelectRaces(int id=3)
        {
            var results = db.Races.Where(r => r.Event_Id == id);
            if (results == null)
            {
                return HttpNotFound();
            }
            List<SelectListItem> items = new List<SelectListItem>();
            foreach (var r in results.ToList())
            {
                items.Add(new SelectListItem { Text = r.Name, Value = r.id.ToString() });
            }

            ViewData["Race"] = items;
            return PartialView(results.ToList());
        }

public ActionResult _SelectPageSize()
        {
            List<SelectListItem> items = new List<SelectListItem>();
            items.Add(new SelectListItem { Text = "5", Value = "5" });
            items.Add(new SelectListItem { Text = "10", Value = "10" });
            items.Add(new SelectListItem { Text = "25", Value = "25" });

            ViewData["PageSize"] = items;
            return PartialView(items);
        }

@using (Html.BeginForm())
{
    <fieldset>
        Select Race
        @Html.DropDownList("RaceId", ViewData["Race"] as List<SelectListItem>, new { style = "width: 150px;", onchange = "this.form.submit()" })
    </fieldset>
}

@using (Html.BeginForm())
{
    <fieldset>
        Select Page Size
        @Html.DropDownList("PageSize", ViewData["PageSize"] as List<SelectListItem>, new { style = "width: 50px;", onchange = "this.form.submit()" })
    </fieldset>
    ViewBag.PAge = "Page";
}

@Html.Action("_SelectPageSize")<!--Select Page Size-->
    @Html.Action("_SelectRaces") <!--Select Race-->
    @Html.Action("Results")