post_max_size is 8M, the server still receives maximum of 24339 characters with $_POST

$save = $_POST['save'];

print_r(strlen(json_encode($save)));
print_r(ini_get('post_max_size'));

This is on the end of the AJAX request and it prints:

24339
8M

But on the client side I’m sending 28364 characters:

console.log(JSON.stringify(save).length);

var data = {
    action : 'my_store_save_function',
    save: save
};

$.post(ajaxurl, data).done(function(res) {
    console.log(res);
});

There must be another limiting factor besides the post_max_size variable that is affecting the size of the POST request. Any ideas?