As long as you do not let the dirt grease and gunk build up on the sidewalls too long, Pledge Lemon always work pretty good at getting them cleaned up. I use it on all my gum lever hoods too. Even my white Diacompe hoods and white cork bar tapes come up looking brand new after scrubbing them with Pledge. I think it also helps preserve them.
Good thing with Pledge is it is not too harsh on most things. Gum tire sidewalls tend to be sensitive to harsh solvents that can dry them out as are brake lever hoods.

Chombi