My Vespa parks in the street, so I like to secure the back wheel with a lock. I used to have a U-shaped lock, but that took up lots of space in the pet carrier.
When I changed from the small HiPer engine to a Leader, there was only ever one angle where I could push the lock through the wheel and then it would either touch the exhaust or rest on the dipstick. I thought about using a chain, but found something better.
This is the Abus Bordo. Almost every bicycle in Berlin has one, it seems.
Folded up, it doesn't take much space.
It's a perfect fit for the LX's glove box.
If you hold it right, you can spear it through the wheel without getting near the exhaust.
It neither rests on the dipstick...
... nor does it touch the hot exhaust. However, it does sit on the ground, so a thief could use maximum force on his bolt cutters. It will probably need an angle grinder, though, to cut through this lock.