John, I would have agreed with "I have yet to see a 'factory authorized' conversion kit from cushion to pneumatic" about a year ago, but I recently had a traded in Toyota (my memory has it a 6 series) with a pneumatic frame, and solid tires that was what I would have called cushion, (not a press on replaceable tire, but a hard poly tire molded to a wheel, replacement was the whole wheel and tire =1 piece), and was from and recognized by the local Toyota dealer as a "special option". In this case it was a factory option to make a pneumatic a cushion, and the "conversion was to get the pneumatic wheels and mount regular tire back on them