JSFiddle - React, Tailwind, and code Playground

HTML

<form method="post" style="padding: 10px 0px 10px 5px;" id="one">
<label>Front/Rear Tire:<br/><select name="tire" class="first">
<option  value="">Select</option>
  <option  value="rear" data-2wd="A.php" data-4wd="A.php" data-mfwd="B.php" >Rear Tire</option>
  <option  value="front" data-2wd="C.php" data-4wd="C.php" data-mfwd="D.php" >Front Tire</option>

</select> </label>
  <label>Tractor Type:<br/><select name="tractor" class="second" >
    <option value="">Select Type</option>
    <option value="2wd" >2WD</option>
    <option value="mfwd">MFWD</option>
    <option value="4wd" >4WD</option>

  </select>  </label>


</form>

<form method="post" action="index.php" id="two" >
</form>

JavaScript

$("#one select").on("change",function(){
  var sel1 = $("select.second").find(":selected").val();
  var sel2 = $("#one select.first").find(":selected").attr("data-"+sel1);
  $("#two").attr("action",sel2);
})