It helps greatly if the tire you are using has a circular molding line in the sidewall at a radius that allows its use in aligning the stripe as did the red lines on my GTX.
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On these blue lines there wasn’t one in the vicinity of where I wanted the stripe so I laid down a 1/4” masking tape line around the nearest molding line and then another 1/4 tape line next to it to space the blue line 1/2” off of the molding line. This is a lot more tedious and prone to slight hiccups in creating an accurate circle with the stripe if not done very carefully. Mockup below.
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Most tires have radial molding lines extending out across the sidewalls. Those have to be ground down flush where the strip runs to prevent humps in the stripes. I use a Dremel with a fine drum sander bit which works very well.
The stripes of course protrude from the sidewall rather than being recessed in the sidewalls in a groove. This didn’t bother me any.
The butt connection joint has to be done with great precision to make it virtually invisible. I have an old Craftsman cutter for cutting hoses and so forth that did an accurate job.
The adhesive has to be carefully spread on the back of the stripe to ensure 100% coverage. I worked o about 3-4” increment and after applying the adhesive and then spread it thinly over the entire surface with a popcycle stick to avoid it squeezing excess adhesive out. If any did squeeze out I tried to wipe it off quickly with a little PrepSol or Acetone on a paper towels. After the adhesive and stripe had set for a couple minutes I used an old wallpaper seam roller to roll the stripes down good. I followed the kit instructions carefully on surface prep and cleaning.
I have about $105-110 in each tire so it’s far cheaper than $260-350/tire from Coker or Diamondback. I can’t hardly stand to throw away a $1400 set of tires after 10 years with maybe 5-6,000 miles on them.