I had Diamondback on my 67.
Was not so happy with the color of the redline.
They looked great for a few years, and then they turned dark.
Diamondback said i could sand them down, as it was red all the way through the bead.
But, even then - they just never looked right. (More Like a dark maroon)
I took them off and sold them with a this car pictured.
Now that being said - I bought them in 97, so maybe they are better now.
I have had DB redlines on my 69 Camaro for more than five years now, 100% happy, especially if you drive alot. Lots of sizes aviallable because there made from off the shelf DOT tires, I think mine are Dayton Daytonas ??
As far as maintaining the Red stripe, I have also used this on white letters, take some mineral spirits based solvent on a damp rag and go over the red or white rubber a few times a year. Terry towl works good.
Tires oxidize and on the white letter tires the black seems to stain the white letters after awhile. The solvent seems to cut in and remove the top layer of crud, leaving freash rubber. I have even used enamal reducer. Also works to clean you wiper blades on you drivers, you will be suprised at the crud that caomes off on the rag.