Brown Staining on Whitewalls

[petew]

Lay the tire down and Let a 50/50 mix of bleach and water sit on the spot for 5 minutes or so then scrub and rinse .
If that doesn't work try sanding that area with some 320 wet sandpaper . The sanding will not damage the tire.
That will remove the stained area and expose the clean surface underneath provided the stain hasn't gone too deep.

[8EL]

Thank you both, I will give it a go. I am concerned that this could be bleeding from behind. How deep do you suppose does the white compound go?