The lady salesperson that sold me my 09FLHRC told me the best way to clean the whitewalls was to rinse then spread 'miracle whip' over the whitewalls. Let sit for a few minutes then give them a bit of a scrub.
Holy sheep dip batman, it truly works. Little effort with great results. Just make sure you rinse down the driveway or the next day ants come.

 

Mr. Clean Magic Eraser works better with less time and no mess..and no ants