Just be wary if the sidewalls are all cracked to begin with - better the condition to begin with the better the results you'll get. Make sure you rinse well to get all the jif residue off, or it just dries like white dust. I use a soft scrubbing brush - cheap crappy one from amazon for 99p usually.
Definitely don't scub at the logos - they will come off (I found out the hard way as usual........)
I also find that gumwalls can go milky looking when wet - don't panic though, they go back to normal colour when they dry