1979 Mercury Tire Fitment Guide

1979 Mercury vehicles used a wide range of alphanumeric sizes, and the correct one depends on the model. Bobcat sizes are A78-13, BR78-13, and BR70-13; Capri uses B78-13, C78-13, BR78-14, CR78-14, and C78-14; Cougar uses HR78-14, GR78-15, and HR78-15; Marquis uses FR78-14, GR78-14, and HR78-14; Monarch uses DR78-14, ER78-14, and FR78-14; Zephyr uses CR78-14, DR78-14, B78-14, and C78-14. Rim diameters span 13, 14, and 15 inches across the full 1979 Mercury range.

That spread means year and make alone are not enough to choose a tire correctly. A Bobcat owner will be working with 13-inch fitments, a Cougar may require either 14-inch or 15-inch wheels, and several midsize and full-size Mercury models share 14-inch radial families while still using different exact sizes. Start with the model name on the car, then verify the wheel diameter already on the vehicle before narrowing the size choice.

A78-13 is an older alphanumeric bias-ply size used on the 1979 Mercury Bobcat. In that format, the letter-and-number combination identifies the tire’s relative size class within the bias-ply system, while the final 13 means the tire mounts on a 13-inch wheel. Unlike a radial code, there is no R in the size, which is one of the easiest ways to recognize that A78-13 belongs to the bias-ply family.

For a Bobcat owner, that matters because A78-13 points you toward a more period-style tire choice than the model’s BR78-13 or BR70-13 radial alternatives. If you are trying to preserve a late-1970s original look, the size code itself is already telling you a lot about the tire’s character. Before choosing one, confirm that the car is actually using the 13-inch wheel setup intended for that size.

Sizes such as BR78-13, CR78-14, or HR78-15 use the alphanumeric radial system that was common on many American cars in the 1970s and early 1980s. The R in the code tells you the tire is radial, and the final number gives the wheel diameter in inches, so BR78-13 fits a 13-inch wheel while HR78-15 fits a 15-inch wheel. The letter prefix places the tire within a relative size range rather than giving a direct modern metric width in millimeters.

On a 1979 Mercury, that format appears across much of the lineup, especially on Cougar, Marquis, Monarch, and the radial-equipped Capri and Zephyr applications. It is a useful code to recognize because a tire can look era-correct while still being a radial rather than a bias-ply construction. The practical step is to match the exact code to the model and wheel diameter instead of assuming that one radial letter-series size can substitute for another.

No, 1979 Mercury models do not use one common tire size across the range. Bobcat stays in 13-inch sizes, Capri mixes 13-inch and 14-inch applications, Cougar uses both 14-inch and 15-inch radials, and Marquis, Monarch, and Zephyr each carry their own combinations of 14-inch sizes. A few sizes overlap between models, such as CR78-14 for Capri and Zephyr or FR78-14 for Marquis and Monarch, but those shared sizes are the exception rather than the rule.

That makes model identification the first fitment step, especially on cars that have changed hands, been restored, or had wheels swapped over the years. If you know only that you have a 1979 Mercury, you still have not narrowed the search enough. Check the model badging, verify the wheel diameter on the car, and then compare the exact size code before choosing between bias-ply and radial options.

For a 1979 Mercury Bobcat, A78-13 and BR78-13 represent two different construction approaches on the same 13-inch wheel diameter. A78-13 is a bias-ply size, while BR78-13 is a radial size. That means the choice is less about basic wheel fit and more about whether you want the older construction style associated with original presentation or the radial format that better reflects the driving direction the market was taking by 1979.

A restoration aimed at factory-era appearance will usually lean toward the bias-ply A78-13, especially if visual authenticity matters more than regular-use comfort. A Bobcat that sees more routine road miles will often point the owner toward BR78-13 instead. The key is to keep the decision tied to the Bobcat itself rather than treating it as a generic 13-inch Mercury tire question, because the lower-profile BR70-13 also exists in that same model family.

On the 1979 Mercury Capri and 1979 Mercury Zephyr, C78-14 and CR78-14 share a 14-inch wheel diameter but differ in construction. C78-14 is a bias-ply size, while CR78-14 is a radial size. That makes the decision a classic late-1970s choice between a more traditional period-style build and the radial layout many owners prefer when the car will spend more time on the road.

If your Capri or Zephyr is being restored with a stronger emphasis on original-era appearance, C78-14 is the more natural direction. If the goal is to preserve the right 14-inch alphanumeric look while favoring radial construction, CR78-14 is the better fit for that use. Either way, make sure the car actually belongs to the Capri or Zephyr group that used those sizes rather than one of the neighboring 13-inch or alternate 14-inch applications.

1979 Mercury fitments span many alphanumeric sizes, but the exact brand choices depend on the specific size and model. A Bobcat owner searching for A78-13 will not necessarily see the same brand mix as a Cougar owner looking for HR78-15 or a Marquis owner using FR78-14. The meaningful comparison is always by exact size code first, because brand coverage follows the size family rather than the Mercury badge alone.

That is why it helps to settle the fitment question before getting drawn into brand preference. Once the model and size are confirmed, you can compare the available makes within that size for construction type, sidewall appearance, and any product-specific details that matter to your project. Trying to choose a brand before choosing the correct 1979 Mercury size usually creates confusion, especially in a model year with both bias-ply and radial options across several wheel diameters.

Inner-tube requirements on 1979 Mercury tires depend on the exact tire product and the wheel it is being mounted on, not just on the Mercury model name. Bias-ply and radial alphanumeric sizes from this era can appear in tube-type or tubeless forms depending on the specific tire, and original wheels may also influence the proper setup. The safest approach is to match the tire’s sidewall marking and construction with the condition and design of the wheel you plan to use.

That matters most when a 1979 Mercury is being restored with original steel wheels, older rims, or wheel finishes that may not behave like a modern airtight tubeless wheel. Before final mounting, verify whether the specific tire calls for a tube and inspect the wheel carefully for sealing condition, valve-stem compatibility, and overall serviceability. If there is any doubt, a restoration shop or marque specialist can help keep the setup true to the car and safe to use.

Original 1979 Mercury wheels cannot be assumed to work with all sizes across the full Mercury lineup because the model range used 13-inch, 14-inch, and 15-inch tire diameters. A Bobcat’s 13-inch applications are separate from Cougar’s 15-inch sizes, and many 14-inch fitments belong only to specific Capri, Zephyr, Monarch, Marquis, or Cougar combinations. Wheel diameter has to match the tire code exactly, so a 15-inch GR78-15 cannot be mounted on a 14-inch Mercury wheel.

Even within one diameter, it is wise to confirm that the wheel is appropriate for the exact size being considered. A 14-inch Mercury wheel may still differ from one model to another, and decades of owner changes can blur what is original to the car. Treat the existing wheel as something to verify rather than assume, especially if the car has been restored, modified, or passed through several owners over the years.

A stored 1979 Mercury should be kept in a cool, dry, dark space away from direct sunlight, electric motors, battery chargers, furnaces, and other ozone-producing equipment. Clean tires and wheels before storage, keep inflation pressures checked, and move the car periodically so one section of the casing is not carrying the load for months at a time. Bias-ply tires on 1979 Mercury models such as some Bobcat, Capri, and Zephyr applications are more prone to temporary flat-spotting during long static storage than radials.

If the car will sit for an extended season, many collectors either roll it occasionally or support it in a way that reduces prolonged load on the tires. That helps preserve ride quality, sidewall appearance, and casing shape. Storage habits matter just as much as mileage on a low-use collector Mercury, especially when the car is driven infrequently but expected to be ready for shows, cruises, or a long spring awakening.

Tires on a 1979 Mercury are usually judged more by age than by tread wear, because collector cars often accumulate limited mileage. A good rule is to begin evaluating them closely once they reach the 5-to-7-year range and to treat around 10 years as a strong point for replacement consideration, even if the tread still looks respectable. The DOT date code on the tire is the starting point for that timeline, and visible cracking, hardening, vibration, or repeated pressure loss can shorten it further.

That age-based approach is especially important on a car that sees seasonal use, indoor storage, and occasional show duty. A 1979 Mercury can seem fine on short local trips while the tire rubber is quietly aging out. If you have recently purchased the car and do not know the tire age, checking the date code is one of the most valuable first maintenance steps you can take before any meaningful road use.

Tires on a 1979 Mercury should be inspected before every drive, with extra attention before any longer outing. Look for sidewall cracking, cuts, bulges, uneven tread wear, embedded debris, and signs that the tire is losing pressure between uses. If the car uses a tube-type setup, include the valve stem, valve core area, and any slow-leak behavior in the inspection routine, because pressure retention becomes part of the health check as much as tread condition.

A second, more thorough inspection a few times each season is a smart habit for collector ownership. That is the right time to check inflation against your chosen operating pressure, inspect the spare, and look over the wheel itself for rust or damage that could affect the tire. Frequent inspection is cheap insurance on a 1979 Mercury that may spend long stretches parked and then return to service with little warning.

The 1979 Mercury Bobcat used A78-13, BR78-13, and BR70-13 tire sizes, with both bias-ply and radial constructions appearing in the model’s fitment range. That mix is historically believable for the late 1970s, when American manufacturers were transitioning from older bias-ply conventions toward wider radial adoption. The exact original fit on an individual Bobcat could depend on equipment level, wheel package, and market-specific details, but the correct starting point remains within those Bobcat-specific 13-inch sizes.

For an authenticity-minded restoration, that means you should first determine which of those three sizes belongs to your car before worrying about brand or sidewall appearance. A build intended for strict originality may lean toward the size and construction that best matches the car’s original wheel and trim configuration, while a driver restoration may make a different choice. For event-level confirmation, Mercury literature and marque clubs are still the best tie-breakers.

Correct tire fitment does matter when showing a 1979 Mercury, especially if the event values originality. Judges and knowledgeable enthusiasts often notice whether the car wears the right size family, the correct construction type for its restoration goal, and a sidewall presentation that matches the era. A 15-inch Cougar radial, for example, belongs to a different visual and fitment context than a 13-inch Bobcat bias-ply, and crossing those boundaries can make an otherwise strong restoration look less convincing.

The practical standard is to think in three layers: correct size code, correct wheel diameter, and correct construction style for the way the car is being judged. A driver-oriented car can still look highly appropriate with a radial, but a show field focused on originality may view that differently on a model that also carried bias-ply options. Check the rules of the event and the expectations of the Mercury club or judging body before finalizing the tire choice.

The 1979 Mercury Cougar used HR78-14, GR78-15, and HR78-15 sizes, and all three are radial fitments. That aligns with the Cougar’s position as a late-1970s personal luxury car, where radial construction had become a natural part of the market. The main originality question on a Cougar is therefore less about bias-ply versus radial and more about which of those radial sizes belongs to the specific car and wheel package you are restoring.

That distinction matters because the Cougar spans both 14-inch and 15-inch wheel diameters in 1979. A restoration that uses the wrong wheel diameter will usually look off before anyone even starts discussing tread or sidewall details. If your goal is authenticity, confirm the wheel size on the car and compare it with factory literature or Mercury club guidance so the radial size and stance remain true to the way the particular Cougar was equipped.

A properly chosen, properly maintained tire can make a 1979 Mercury suitable for normal highway use, but safety depends on more than just having tread left. The model range includes both bias-ply and radial applications, and that alone changes how the car will feel at speed, on crowned roads, and during sudden lane changes. A Bobcat on a bias-ply setup and a Cougar on 15-inch radials will not deliver the same highway behavior, even when both are fitted with correct-size reproduction tires.

The important point is to view the tire as one part of the whole car. On a 1979 Mercury, suspension condition, steering play, brake performance, alignment, wheel integrity, and tire age can matter as much as the size code on the sidewall. If the car is roadworthy overall and the tires are the correct type and age for the application, highway driving is realistic, but collector-car caution and reasonable speeds should always guide the experience.

Inflation pressure for a 1979 Mercury should be matched to the specific tire size, the actual tire manufacturer’s guidance, and the factory recommendation for the exact model. Because the 1979 Mercury range spans 13-inch, 14-inch, and 15-inch tires in both bias-ply and radial constructions, one pressure number should never be copied from one size to another as a blanket rule. The right pressure for a Bobcat’s 13-inch fitment may differ substantially from what suits a Cougar or Marquis radial setup.

The best routine is to begin with the original Mercury specification for the car, then compare it with the tire maker’s rated inflation guidance for the reproduction or replacement tire you are using. If the tire and vehicle recommendations point in slightly different directions, use the manufacturer guidance as the operating framework while keeping the car’s weight and intended use in mind. Recheck pressure regularly, especially on collector cars that sit between drives.

Before taking a 1979 Mercury on a longer drive, inspect all four tires and the spare for cracking, cuts, bulges, unusual wear, and proper inflation. Confirm that the valve stems are in good condition, and pay extra attention to stem sealing and pressure retention if the car uses a tube-type setup. Wheel condition matters too, especially on older original rims that may have corrosion, old paint buildup, or previous repairs hidden by wheel covers.

A longer outing is also a good reason to think beyond the tires. On a late-1970s Mercury, age can affect belts, hoses, cooling, charging, brakes, and suspension components just as much as the rubber. If the tires pass inspection but the car has been sitting, take a short test drive first and feel for pull, vibration, brake response, and heat buildup. A calm shakedown run often reveals problems before they become roadside interruptions.