I was riding my Nel Lusso today and finally figured out why people have gotten frame cracking on the welded on racks.
The issue is the rack insert that extends for you to put stuff on.
Unless this is shimmed for a tight fit or you wrap the U extension with some sort of tape, it is going to be loose enough to cause the hole welded rack assembly to vibrate violently.
This is what causes the frame cracking on the bike of the huffy models that have welded on racks.
After driving up and down hearing a serious buzz when I got up to 25 I made sure everything was tightened down and drove it a bit holding various parts of the bike to find out where the buzz was coming from. Sure enough as soon as I removed the rack extension- Buzz GONE.
And this was on the 66cc china girl.
I'd recommend either removing the extension or perhaps cutting off the legs of the U and welding the rear part to the rack if you like the look.