at one time there was a class action going that the stock rear tires had too light a load rating...
soooooo.... they changed the rear wheel and made tires that do have a high enough load rating, it appears the idea was to prevent folks from using the too light tires as cheaper replacements...
Not really. If a customer installs a tire that doesn't meet the minimum safety requirements like speed and load ratings, Harley would have no liability whatsoever. The same would apply to Chevy if some nimrod installed rims and tires that didn't meet the minimums for that vehicle. The manufacturer cannot be held liable for actions by others that do not comply with their minimum specs.
Harley has just chosen rim and tire sizes that are unique so they could corner the market on replacement parts, plain and simple. There were plenty of rims and tires they could have used, but they chose instead to create new unique sizes that no one else uses, and then arranged to have Dunlop make an exclusive Harley branded tire to fit the oddball rim size. They started with the CVO's, and now that they've gotten away with it for many years it appears they want to try expanding that anticompetitive arrangement to some standard models. Make no mistake, it's all about making big bucks selling replacement parts.
Check the New Model Drivel they put out for 2014 that basically states you must use only the brand and size of tires that comes from the factory. It's pure BS, very similar to all the BS they put out for decades trying to convince people they had to use genuine H-D parts to maintain warranty coverage. Federal law states quite clearly that isn't the case, but that didn't and doesn't keep Harley from trying to BS customers.
Jerry