GMC C20 Spare Tire Sizes
The GMC C20 has used a 6x5.5" bolt pattern for all models from 1978 to 1988 along with tire diameters ranging from 28.6" to 31.8" tall. Using a temporary spare tire with a diameter close to the standard tire has many benefits, especially for modern vehicle applications. Tire diameter as well as wheel diameter clearance have been taken into account for the specific GMC C20 years and options. In this case, using a non-temporary Full-Size tire as your spare, is the recommendation for all applications.