Wheel size markings 26x52/56 seem abnormal
From the WTB Website:
GMS Global Measuring System The current industry standard for specifying the actual inflated size of a bicycle tire does not account for subtle variation in tread and casing size. To address this problem and provide you with more information for comparing tires, WTB has introduced the Global Measuring System (GMS) for tire measurement.
The GMS uses a two-number system: the first number is the width of the casing, and the second number is the width of the tread, both in millimeters. These measurements are taken on a rim which is 20mm wide at the bead-capturing point, with a tire inflated to 60psi and maintained for 24 hours.
In addition to being able to accurately size a tire, knowing the actual casing size and tread width provides an indication of air volume, tread characteristics and tread contact area; all of which provide you with a more concise idea of what ride characteristics to expect from each of WTB's tires. WWhat this means in the simplest terms is a nominal 26x2.1 inches.