I cut these sleeves from a new piece of 12" HDPE DR11 pipe from WL Plastics.

Inner Diameter
Inner Circumference
Wall Thickness
Outer Diameter
Sleeve Width
Weight
Hardness
Text
10.432"
32.773"
1.159"
12.75"
6"
156 Ounces Each
60 Shore D
IPS 12" DR 11 WL PLASTICS SD PE 4710 PE 445574C PC200/200PSI AWWA C906 ASTM D 3035/F714 FM1613

The most accurate way to measure a tire is by circumference. Wrap a fabric measuring tape (typically used for sewing) around the outside of the tire. Measure the tire twice, deflated and inflated. The inner circumference of these sleeves is 32.773" which should be in between your two tire measurements (deflated & inflated).

Wider sleeves are more slippery.
Skinny sleeves are more sticky.
Clean edges are better for racing and cornering.
Round edges are better for drifting and 360s.
PVC is harder and more slippery.
HDPE is softer and more sticky.

Sparky Sleeves are hand made by Scott Blake in Saint Paul, Minnesota.