Funny, the one I lost before securing the used wheel covers was the rear one on the passenger side. When I looked at the "bite" marks on that painted wheel I could see that some of the wheel covers tabs were not putting heavy pressure/bite on the wheel.
I think that most of the issue is the condition of the wheel cover tabs that "bite" into the wheel to secure the cover. When I installed a set of NOS Mark II wheel covers, they were very hard to put on and they were very hard to remove, tremendous metal screech as I slowly pried them off moving the pry bar around the cover at least 8-10 times to remove a given cover. The fit was a night versus day difference from my used covers which were in excellent cosmetic condition.
To be on the safe side, I added two stainless steel lanyards and extended valve stem retainers as well on each wheel cover. After driving the car quite a bit over very bumpy roads, I checked the two lanyards on each wheel cover and they all were slightly slack indicating that the wheel covers had never loosened.
I removed the wheel covers about 2 years later when shipping the car to Australia and the lanyards were still slightly slack.
Larry
Larry Durocher
1956 Mark II C5601429
1962 RR Silver Cloud II drophead
2006 Ford F150
2010 RR Phantom drophead
2013 Bentley GTC
2015 Lincoln MKT