1974 GMC Tire Fitment Guide

1974 GMC vehicles used 22 different tire sizes across six model lines: 700-15, G78-15, L78-15, H78-15, 700-16, LR78-15, 875-16.5, 950-16.5, 750-16, 800-16.5, 10-16.5, E78-15, F78-15, F78-14, G78-14, G70-14, GR70-14, H78-14, 700-14, E78-14, 670-15, and HR78-15. Wheel diameters span 14, 15, 16, and 16.5 inches, so there is no single fitment that covers the full 1974 GMC range. Where rim-width guidance is available, it varies by size, from narrow 14-inch passenger applications to heavier-duty 16.5-inch truck and van tires.

That means a buyer should start with the exact model, then confirm the wheel diameter already on the vehicle before comparing brands or sidewall styles. A C/K Pickup or Suburban may share some sizes, for example, while a Sprint or Vandura can use completely different size families. Treat year and make as the starting point, not the final fitment decision.

On a 1974 GMC tire, 700-15 is a numeric bias-ply size. The 700 portion is the traditional nominal width designation, and the 15 identifies a 15-inch wheel diameter. Within the 1974 GMC line, 700-15 appears on the C/K Pickup, Jimmy, and Suburban, and available versions include blackwall and wide whitewall bias-ply tires from brands such as Firestone, BFGoodrich, and STA.

Numeric bias-ply sizing predates modern metric nomenclature, so the code is more about period size class than the exact dimensional style modern buyers expect from a P-metric tire. If your GMC still uses a 15-inch wheel and you are matching an original-style truck or utility fitment, 700-15 is part of that traditional vocabulary. It should not be treated as interchangeable with every other 15-inch GMC size without checking the actual application.

No. 1974 GMC models do not all use the same tire size, and several sizes are tied to only one model or a small group of models. The Sprint stays in 14-inch car-based fitments, the Jimmy centers on 15-inch truck and SUV sizes, the C/K Pickup and Suburban span 15-, 16-, and 16.5-inch applications, and the Vandura and Rally mix passenger-van and truck-style sizes depending on setup.

That variation matters because it affects more than appearance. It changes wheel diameter, rim-width range, available sidewall styles, and whether a radial alternative exists. If you are unsure whether your GMC is carrying its original wheels, check the tire sidewall and wheel diameter directly before choosing a replacement. That one step avoids the most common ordering mistake on broad year-and-make pages like this.

For a 1974 GMC, the LR78-15 is the radial-format choice that appears on select C/K Pickup and Suburban applications, while sizes such as 700-15, G78-15, H78-15, and L78-15 stay in the traditional bias-ply family. LR78-15 is available as a Firestone bias-look radial, which keeps a vintage visual feel while changing the internal construction. The bias-ply sizes remain the more traditional route for period-style restoration work.

The decision is usually about how you want the vehicle to present and behave, not simply what will mount on a 15-inch wheel. A show-focused restoration often leans toward the original-style bias-ply family, while a regularly driven truck or Suburban owner may prefer the radial option where it is appropriate to the vehicle. Confirm the exact size family already used on your GMC before switching between them.

1974 GMC tires span a wide sidewall range depending on size. Whitewall choices include wide whitewall and narrow whitewall treatments on sizes such as 700-15, L78-15, 700-16, 750-16, 670-15, and others. Sportier 14-inch Sprint-oriented sizes add redline, raised white letter, pin white stripe, and dual-white-stripe options, while many truck and van-oriented 16.5-inch sizes stay blackwall.

The right sidewall usually follows the personality of the model and the kind of restoration you are doing. A Sprint can legitimately wear bolder performance-era styling cues, while a work-focused C/K, Suburban, or Vandura often looks most natural in blackwall or restrained whitewall form. If you are building toward judged authenticity, size, construction, and sidewall treatment should all agree with the vehicle's intended presentation.

Brands covering 1974 GMC applications include Firestone, BFGoodrich, Coker Classic, STA, Lester, Avon, Goodyear, US Royal, and Universal Vintage Tire. Coverage varies by size: 700-15 includes Firestone, BFGoodrich, and STA; 700-16 includes Lester, Avon, BFGoodrich, and Firestone; 670-15 includes Firestone, US Royal, Coker Classic, and Universal Vintage Tire; and several 16.5-inch truck sizes center on STA.

That brand spread gives GMC owners room to match the vehicle's purpose as well as its look. Some sizes lean toward classic passenger-car styling with multiple whitewall choices, while others skew toward truck, military, or highway-service character. Once you know your exact size, compare brands within that size rather than assuming every brand covers every 1974 GMC application.

Rim width on 1974 GMC tires depends entirely on the size. Examples include 700-15 at 5.00 to 5.50 inches, G78-15 at 5.00 to 7.00, L78-15 and LR78-15 at 5.50 to 8.00, H78-15 at 5.50 to 7.00, 700-16 at 4.50 to 5.50, 750-16 at 5.00 to 6.00, 950-16.5 at 6.50 to 6.75, 800-16.5 at 6.00 to 6.50, and 10-16.5 at 8.25 inches. Several 14-inch sizes also vary, from 4.50-inch minimums on some E78-14 applications to 6.50 to 7.00 inches for G70-14.

Those differences are why wheel diameter alone is not enough. Two tires may both fit a 15-inch rim yet expect different rim-width ranges. Before finalizing a tire, measure the wheel you actually have or confirm its stamped width. That is especially important on trucks, vans, and long-owned collector vehicles that may have received wheel swaps decades ago.

Tube use on 1974 GMC tires depends on the exact product and size. E78-14 includes at least one tubeless-marked STA Traxion version, so tube status can vary by product within that size. Many other tires in the 1974 GMC range do not carry an explicit tube marking in the size line, which means the buyer should verify the individual tire's sidewall designation and pair that with the wheel type being used.

The wheel matters just as much as the tire. A tire designed for tubeless service may still need a tube if it is being mounted on an original wheel that does not seal well enough for modern tubeless use. Conversely, some reproduction-style tires are intended to be run as they are marked. Check the exact sidewall and your wheel condition before mounting, especially on older truck and van wheels.

No single original wheel can be assumed to cover all 1974 GMC tire sizes because the year spans 14-, 15-, 16-, and 16.5-inch rims, plus multiple rim-width requirements within each diameter. A 15-inch Sprint or Jimmy wheel is not automatically suitable for a 16-inch or 16.5-inch C/K, Suburban, Rally, or Vandura application. Even within one diameter, sizes such as 700-15 and L78-15 can call for different rim-width ranges.

Original wheels can absolutely be used when they match the correct diameter and width for the chosen tire. The safe approach is to verify the wheel diameter first, then check the tire's approved rim-width range before mounting. That preserves the original look while avoiding avoidable fitment problems, especially on GMC trucks and vans that may have served in fleets or heavy utility use.

A stored 1974 GMC should be kept out of direct sunlight, away from ozone sources such as electric motors and welders, and in a dry space with stable temperatures. Clean tires before storage, maintain inflation, and move the vehicle periodically if possible. Bias-ply tires can flat-spot more readily during long static storage, while any vintage-style tire can suffer from age cracking if it sits in a hot, bright, or ozone-rich environment.

That matters even more on collector trucks, vans, and utilities that spend long periods parked between events or seasonal drives. If the GMC will sit for months, consider using stands or at least rolling it enough to change the contact patch. Good storage habits preserve ride quality, appearance, and service life far better than simply covering the vehicle and leaving it untouched.

Tire life on a 1974 GMC is usually judged more by age than by mileage, because many surviving examples are collector vehicles that see irregular use. A sensible rule is to begin evaluating tires carefully around five to seven years of age and to consider replacement around the ten-year point regardless of tread depth. The DOT date code on the tire is the starting point for that timeline.

A low-mileage GMC can still have tires that are too old for confident road use. Sidewall cracking, hardening, repeated air loss, or visible flat-spotting may justify replacement sooner. If the vehicle has been in storage or changes hands without a clear service history, checking age before the next long drive is just as important as inspecting the brakes or fuel system.

Tires on a 1974 GMC should be inspected before every drive and again before any longer highway outing. Look for cracking, bulges, punctures, unusual tread wear, and signs that the tire is not holding pressure consistently. On truck and van applications, pay close attention to valve stems and to any tire-and-wheel combination that may use a tube or older-style rim.

Frequent inspection is especially important because collector vehicles often sit long enough for problems to develop between drives. A GMC that feels fine on a short local trip can still have age-related tire issues that become obvious only at speed or under load. Making tire checks part of every pre-drive routine helps catch those issues before they become roadside problems.

A 1974 GMC C/K Pickup would have been associated with bias-ply construction in many of its original-style fitments, including sizes such as 700-15, G78-15, H78-15, L78-15, 700-16, 750-16, and several 16.5-inch truck sizes. A radial option appears in LR78-15 for select applications, reflecting the transitional character of the mid-1970s. The exact original size depended on the pickup's configuration, wheel package, and intended duty level.

For a restoration, the safest path is to confirm the truck's existing wheel diameter, any surviving placard or manual information, and the expectations of the club or show circuit you care about. Size family and construction type are usually more important than chasing a specific original brand name. If the truck is especially rare or highly optioned, a GMC or truck-marque specialist is worth consulting.

Yes, correct tire fitment matters when showing a 1974 GMC, especially in judged restoration classes. Judges and knowledgeable enthusiasts typically notice whether the tire's size family, construction type, sidewall treatment, and overall stance fit the period and the model. A modern-looking radial or an aggressively incorrect sidewall style can stand out quickly on a vehicle being presented for originality.

That does not mean every GMC must wear the same tire. A Sprint with redlines or raised white letters can make sense in a performance-era presentation, while a work-oriented Vandura or C/K may look more authentic in blackwall form. Event standards vary, so if trophies matter, compare your planned tire against marque-club guidance and the class rules before the vehicle reaches the show field.

For the 1974 GMC Sprint in G70-14, Firestone Wide Oval and Goodyear Custom Wide Tread both stay within the period-correct bias-ply performance theme, but they differ in presentation and wheel fitment range. Firestone versions appear in redline, raised white letter, and pin white stripe styles with a 6.50 to 7.00-inch rim range, while the Goodyear redline version carries a broader 6.0 to 8.0-inch rim range. Both show similar 1620-pound load ratings at 32 psi.

The practical difference is usually visual and wheel-related more than mechanical. If you are matching a specific Sprint-era appearance, sidewall style may decide the choice. If your wheels sit near the wider or narrower edge of the fitment window, the approved rim-width range becomes just as important. Either way, this is a model-specific decision rather than a general 1974 GMC rule.

1974 GMC tires can be suitable for highway driving when the correct size is used, the tires are in sound condition, and their speed rating matches the intended use. Most bias-ply offerings here do not carry a modern speed-letter marking in the size line, while one 700-16 Avon version is marked L, which corresponds to a 75 mph ceiling. Collector-era GMC trucks, vans, and utilities also have their own braking, steering, and suspension limits that matter just as much as the tire itself.

For that reason, highway confidence comes from the whole setup rather than from the tire alone. Check age, inflation, load condition, wheel integrity, and overall vehicle readiness before sustained road use. If your GMC will regularly see modern traffic speeds, be especially deliberate about choosing the correct construction type and avoiding aged-out tires that may still look usable at a glance.

Inflation pressure on 1974 GMC tires depends on the exact size and tire. Examples include 700-15 at 1700 pounds at 32 psi, G78-15 at 1620 pounds at 32 psi, L78-15 at 1970 pounds at 32 psi, H78-15 at either 1770 pounds at 32 psi or 1830 pounds at 45 psi depending on product, 750-16 at 1660 pounds at 40 psi or 1850 pounds at 48 psi depending on product, and 950-16.5 at 2780 pounds at 60 psi. Those figures are tire ratings, not a blanket recommendation for every 1974 GMC application.

Use the vehicle's original manual or placard as the baseline for factory intent, then compare that with the reproduction tire's own rated pressure and load information. Do not transfer a pressure from one size to another just because both fit the same model. A Sprint on G70-14 and a Suburban on 950-16.5 live in completely different operating ranges.

Before a longer drive in a 1974 GMC, inspect each tire for sidewall cracking, cuts, punctures, bulges, irregular wear, and proper cold inflation. Check that the spare is usable, and give extra attention to valve stems and any tube-type or older wheel combinations that may be more sensitive to long periods of storage. On trucks, vans, and Suburbans, also think about how much load the vehicle will carry on the trip.

Tires are only one part of the pre-trip check, but they are the part that meets the road. On a 1974 GMC, that means pairing tire inspection with a wider check of brakes, steering, wheel bearings, suspension, lights, and fluids. A careful once-over before departure is far easier than troubleshooting a heavy vintage truck or van at the roadside.