Well the problem is, I have no idea how long the loading can be individually. I found a workaround, by setting the animationDuration to 0, so I have no animation, but the bar goes straight to the new value.
Thanks for your help.
Quick edit :
I also tried this, for testing purpose : $(".myGrid").jqxGrid('sortby','id', false, null, false);
$(".myGrid").jqxGrid('sortby','id', false, null, false);
I thought the last argument was here to prevent reloading data, but an AJAX request is sent anyway.