The correct tension for a Harley-Davidson drive belt is – tight enough so that the belt doesn’t slip during startup. Check the tightness of your Harley without the tool by following the below steps. * Grab the drive belt about an inch and a half.  * Try to twist the belt if you can. If you feel any severe resistance before twisting it about 45 degrees and can’t twist it, be sure that the drive belt is perfectly tightened. * On the other hand, if you can twist it up to 75 to 90 degrees, then tightening the belt is mandatory.