nikto93i7, как-то так...
<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8" />
<title></title>
<style>
optgroup {
display: none;
}
</style>
</head>
<body>
<div class="value_two">
<label class="radio1">
<input id="radio1" type="radio" name="two" checked="checked" />
<span class="radio-text1"></span>
</label>
<label class="radio2">
<input id="radio2" type="radio" name="two" />
<span class="radio-text2"></span>
</label>
<label class="radio3">
<input id="radio3" type="radio" name="two" />
<span class="radio-text3"></span>
</label>
<label class="radio4">
<input id="radio4" type="radio" name="two" />
<span class="radio-text4"></span>
</label>
</div>
<select id="char_platform" class="option_menu_style">
<optgroup data-id="1">
<option class="car3_5" value="1">3.5t 32 kWh</option>
<option class="car3_5" value="2">3.5t 42 kWh</option>
<option class="car3_5" value="3">3.5t 52 kWh</option>
</optgroup>
<optgroup data-id="2">
<option class="car5_5" value="4">5.5t 32 kWh</option>
<option class="car5_5" value="5">5.5t 42 kWh</option>
<option class="car5_5" value="6">5.5t 52 kWh</option>
</optgroup>
<optgroup data-id="3">
<option class="car9_5" value="7">9.5t 52 kWh</option>
<option class="car9_5" value="8">9.5t 62 kWh</option>
</optgroup>
<optgroup data-id="4">
<option class="car26" value="9">26t 60 kWh</option>
<option class="car26" value="10">26t 62 kWh</option>
</optgroup>
</select>
<script src="https://code.jquery.com/jquery-1.11.3.js"></script>
<script>
$('#char_platform option:selected').parent().css('display', 'block');
$('input[type="radio"]').change(function( event ) {
var inpValue = event.target.id.match(/\d+/);
$('optgroup').each(function() {
$(this).css('display', 'none');
$(this).attr('data-id') == inpValue && $(this).css('display', 'block');
});
});
</script>
</body>
</html>