Even if different size, I would still use vehicle manufacturers specs. Not sure about motorcycles, but almost all, if not all, cars come with optional tire sizes available. There is a yearly book that lists all the optional sizes you can use for every model car on the road. Usually, the low profile tires say to use a higher pressure, but when you do, you lose some handling. Again, there is a "safe" range, as long as you don't go over the max listed.