I know none of us have whitewalls on our cars, but like me, Im sure you have parents whom may have white walls on their car.
My mom for example used to own a Lincoln Towncar. Anyways, they look nice with Whitewall Tires. If you see that whitewalls are becomeing less white... One thing ive found out is that if you just take a little bit of steal wool, some soapy water, and use some good elbow grease, the yellow grim and dirt come right off and the white looks brand new again. Lets hope your whitewalls were as good quality as my moms lol. Try it on a small section at least and see if it works.