This thread made me go back to my chemistry roots and figure out WHY the white letters are turning brown.
It turns out that the reason why is because of an antiozonant compound that they put in the rubber to protect it called
N-Isopropyl-N′-phenyl-1,4-phenylenediamine known as
IPPD.
IPPD reacts with ozone faster that the rubber does and therefore protects the rubber. However, IPPD also turns brown when it oxidizes.
The comments about brake cleaner working made me go look at the solubility of IPPD. It is practically insoluble in water and slightly reactive with chlorine. However, it it highly soluble in Acetone.
To confirm the hypothesis that the IPPD oxidized residue is the culprit, I took some acetone and an old tooth brush and scrubbed the “A” on my T/A tires for 15 secs and then wiped it off.
Hypothesis confirmed.
View attachment 1715265305
This explains why brake cleaner seems to work also since it contains solvents similar to acetone.
Now everyone should easily be able to clean their white letters with just some acetone and mild scrubbing. I know I will!
