I first got interested in white letter tires when I started to study the tires on the 1970 Mustang Milano. One picture had Firestone Sports 500 tires and another picture had B.F.Goodrich T/A Radials. I was trying to figure out how to dupicate these in 1/25 scale.
   At first I searched the web for pictures of these tires and found that the tire photos on eBay etc. were rather poor quality and low resolution. Then I thought, just go out around town and photograph them myself. So it all began, I look for tires the WL white letters or OWL outlined white letters. I get the camera down to axle height and take a picture, nothing to fancy. I have learned that taking the picture on the shadow side of the car helps to avoid highlights on the black rubber.
In PhotoShop I rotate the image so that the logo is horizontal at the top of the tire. Then I scale to make the outer edge of the lettering is 506 pixels diameter. Then crop to 640x640. Next, use threshold to change to black and white only. Finally, touch up with the a one pixel pencil.
I later began creating original designs. Starting with the Firestone Sports 500 tire. I don't even know if that was ever manufactured or if it too was just a concept.  I found a suitable 'Firestone' font and created the Sports 500  using Photoshop. Then ideas started coming, such as "HotWired", "WildFire" and my favorite "RoyalSport" for those fantasy cars.
All these and many more are available at
ModelMayhem They are at 640x640 resolution in the tire photo album.!