1981 GMC Trucks K2500 Sierra Classic Tires

The 1981 GMC Trucks K2500 Sierra Classic uses either 8.75R16.5 or 950-16.5, depending on the sub-model. Standard Sierra Classic configurations use the 8.75R16.5 radial, while Bonus Cab front and rear fitments use the 950-16.5 bias-ply size.

That means the truck cannot be sized correctly by year, make, and model alone. The useful first step is confirming whether the vehicle is a standard Sierra Classic or a Bonus Cab, then checking that it still carries the correct 16.5-inch wheels and has not been changed to a different wheel or tire setup over the years.

Both primary tire fitments for the 1981 GMC Trucks K2500 Sierra Classic use a 16.5-inch rim diameter. That applies to the 8.75R16.5 radial fitment and the 950-16.5 bias-ply fitment used on Bonus Cab applications.

Rim diameter is only one part of fitment, but it is the first number to verify on an older truck because many have been converted to more common 16-inch wheel packages. A 16.5-inch tire requires a true 16.5-inch wheel, so checking the wheel before choosing a tire helps avoid ordering the right size for the truck on the wrong rim.

The size difference comes from sub-model variation within the 1981 GMC Trucks K2500 Sierra Classic lineup. Standard Sierra Classic versions use the 8.75R16.5 radial, while Bonus Cab front and rear positions use the 950-16.5 bias-ply size.

That distinction matters because the two sizes are not simply alternate labels for the same fitment path. One is a radial truck tire size and the other is a traditional numeric bias-ply truck size, so the buyer should confirm the exact truck configuration first and then make sure the wheel diameter and present-day wheel setup still match the intended tire.

Start by confirming that the truck is a Bonus Cab application, since 950-16.5 belongs to that fitment and not to the standard Sierra Classic radial setup. Within 950-16.5, the available choices are bias-ply STA truck tires with Blackwall styling, including the Traxion and Super Transport series.

The real comparison is series character, wheel compatibility, and how the tire suits the truck’s intended role and presentation. Both available products use a 16.5-inch rim and a 6.50 to 6.75 inch rim-width range, so it is worth checking the actual wheel before deciding, especially on a truck that may have seen wheel or suspension changes.

For the 950-16.5 Bonus Cab fitment, the available products come from STA. Those choices cover two different tire series, giving the buyer more than one period-style truck tire option within the same size and construction category.

Brand alone is not the full decision on an older three-quarter-ton truck. It still makes sense to match the tire to the correct sub-model, confirm the wheel is truly 16.5 inches in diameter, and compare series details such as intended appearance, rim-width compatibility, and load specification before settling on the tire that best suits the truck.

In the 950-16.5 Bonus Cab fitment, the available series are STA Traxion and STA Super Transport. Both are Blackwall bias-ply truck tires in the same size, so the series name helps distinguish the style of tire rather than changing the basic fitment.

That makes series selection a matter of intended use and presentation once the size has been confirmed. A restoration-minded owner may focus on traditional truck appearance, while another buyer may be more concerned with matching the existing setup across the axle, preserving 16.5-inch wheel compatibility, and keeping load capacity appropriate for the vehicle.

A period-style choice starts with using the correct size for the exact truck configuration. Standard Sierra Classic versions use the 8.75R16.5 radial, while Bonus Cab front and rear positions use the 950-16.5 bias-ply, so appearance decisions should begin only after that fitment difference is settled.

Construction has a visible effect on how an older heavy-duty GMC sits and presents itself. Buyers aiming for a restoration-oriented result usually benefit from matching the truck’s original-style size and construction path first, then consulting marque-specific references or historical vehicle documentation if exact appearance details matter beyond basic fitment.

Tire construction changes the visual character of the truck as much as the driving setup. On this GMC, the standard Sierra Classic fitment uses a radial 8.75R16.5, while Bonus Cab applications use a 950-16.5 bias-ply, and those two construction types create different period impressions.

A restoration-minded owner should think about whether the goal is to preserve the truck’s original-style configuration for that specific sub-model or simply maintain a traditional heavy-duty look. Sidewall treatment also matters, and the available 950-16.5 options use Blackwall styling, which keeps the presentation straightforward and appropriate for a truck-oriented application.

Yes, modifications can change tire fitment on a 1981 GMC Trucks K2500 Sierra Classic even when the original size is known. Wheel swaps, suspension lifts or lowering, brake changes, and axle or hub conversions can all alter the space and wheel specifications that the truck’s tires must work with.

That is especially important on a truck that originally uses 16.5-inch wheels, since many older pickups have been converted to different diameters. A useful check includes actual wheel diameter and width, front steering clearance, rear clearance under load, and whether the truck still matches the sub-model-specific fitment that belongs on it.

Before road use, inspect the wheels, valve stems, lug hardware, and overall tire condition after mounting. It also helps to confirm that the truck is wearing the correct sub-model fitment, that the tires are seated properly on the 16.5-inch rims, and that inflation matches the tire’s intended service.

An older three-quarter-ton truck deserves a broader walk-around before serious driving. Check for suspension wear, steering looseness, rubbing at full lock, uneven stance, and any signs of interference under compression. A short test drive followed by a second inspection can reveal clearance issues, vibration, or air loss before the truck is put back into regular use.

Collector-truck tires should be inspected regularly for cracking, bulges, cuts, uneven wear, and pressure loss, even when the truck is driven only occasionally. Older heavy-duty GMCs often spend long periods parked, and low annual mileage does not stop rubber from aging or wheel hardware from needing attention.

Good maintenance includes keeping the truck stored away from prolonged sunlight, excess heat, moisture, and ozone-producing equipment when possible. It also helps to move the vehicle periodically, maintain proper inflation, and recheck wheel condition before each driving season, especially if the truck uses older 16.5-inch wheels or carries a restoration-era tire setup.