solve bind_param

<?php
include('connect.php');
?>

<fieldset>
  <legend>Masukan Data</legend>
    <form action="tambah.php" method="post" enctype="multipart/form-data">
      Nama Sepeda :<input type="text" name="nama_sepeda">
      Size Sepeda :<input type="text" name="size_sepeda">
      Harga Sepeda:<input type="text" name="harga_sepeda">
      <input type="file" name="gambar">
      <input type="submit" name="tambah" value="Tambahkan">
    </form>
</fieldset>
<?php
if(isset($_POST['tambah'])){

  $tempatgambar = $_FILES['gambar']['tmp_name'];
  $namagambar = $_FILES['gambar']['name'];
  move_uploaded_file($tempatgambar,"gambar/".$namagambar);

  $query = $db->prepare("INSERT INTO sepeda (nama_sepeda,size_sepeda,harga_sepeda,gambar) VALUES (?,?,?,?)");
  $query->bind_param('ssis',$nama,$size,$harga,$gambar);

  $nama = $_POST['nama_sepeda'];
  $size = $_POST['size_sepeda'];
  $harga = $_POST['harga_sepeda'];
  $gambar = $_FILES['gambar']['name'];
  $query->execute();

  if($query){
    echo "data tersimpan";
  }else{
    echo "data gagal tersimpan";
  }

  $query->close();
  $db->close();
}
?>