The 1978 Pontiac Sunbird came from an era when compact American cars balanced everyday practicality with a sportier image than basic economy transportation. As one of Pontiac’s late-1970s small-car offerings, it appeals today to owners who want the right stance and period character without losing sight of real-world drivability. Tire fitment on the 1978 Pontiac Sunbird centers on 13-inch applications, with A78-13 or B78-13 bias-ply sizes depending on sub-model, and BR78-13 as a radial fitment. That creates an important choice between preserving a traditional bias-ply presentation and selecting a radial-style setup. The right decision starts with confirming the exact sub-model and then matching the tire to the car’s appearance goals and intended road use.
Which Tire Size Is Right for The 1978 Pontiac Sunbird
Three primary tire sizes apply to the 1978 Pontiac Sunbird, and the correct one depends on the exact sub-model rather than wheel diameter, since all of them use a 13-inch rim. Some configurations use a bias-ply size while others can use a BR78-13 radial, so the first step is confirming whether the car is a 4-cylinder, 6-cylinder, or wagon before comparing construction and tire style.
A78-13 is a vintage alphanumeric bias-ply size in which the letter identifies the tire’s size class, the 78 designates its profile family, and the 13 indicates the wheel diameter. On the 1978 Pontiac Sunbird, this size serves as a traditional bias-ply fitment for certain configurations and gives the car a distinctly period-style look and feel. Its modern counterpart choices are less about brand variation here and more about whether to stay with the original construction type or consider a radial equivalent. This size makes sense when maintaining a restoration-oriented appearance is part of the goal.
BR78-13 uses an alphanumeric radial sizing format, with the letter code identifying the tire class, the R marking radial construction, and the 13 calling for a 13-inch rim. For the 1978 Pontiac Sunbird, it represents a primary radial fitment used across multiple sub-models, making it especially relevant for owners who want a period-appropriate radial specification. Its role is different from the bias-ply sizes because the construction itself is part of the fitment decision. This size is worth close attention when the car’s current wheel setup and driving use favor retaining a radial configuration.
B78-13 is another vintage alphanumeric bias-ply size, using the letter-and-series format common to American cars of the period, with 13 designating the rim diameter. On the 1978 Pontiac Sunbird, it is the larger of the two bias-ply fitments used on several 6-cylinder and wagon applications, so it should not be confused with A78-13. This size also has clearly defined modern radial-equivalent paths, including metric and bias-look radial alternatives for buyers comparing appearance with road manners. It is the right place to start when the car calls for B78-13 and the owner wants to weigh traditional construction against radial options.
Sub-model fitment matters on the 1978 Pontiac Sunbird because tire size changes with engine and body configuration, even though all of the covered applications use a 13-inch rim. Identifying the exact sub-model first helps narrow the choice between the two bias-ply sizes and the BR78-13 radial fitment.
1
1978 Pontiac Sunbird 4 Cyl.
The 1978 Pontiac Sunbird 4 Cyl. uses either A78-13 bias-ply or BR78-13 radial tires, so construction choice is part of the fitment story for this version. That means the buyer should decide whether to retain a traditional bias-ply presentation or stay with a radial-type setup before comparing specific tire options.
The 1978 Pontiac Sunbird 6 Cyl. uses B78-13 bias-ply or BR78-13 radial tires, placing it on a different bias-ply size than the 4-cylinder car. Tire selection here starts with matching the car to the correct primary size and then deciding whether a bias-ply or radial approach better suits its current setup and use.
The 1978 Pontiac Sunbird Wagon 4 Cyl. uses B78-13 bias-ply or BR78-13 radial tires, sharing its basic fitment pattern with the other wagon and 6-cylinder applications. That makes it important to confirm the wagon configuration before choosing among period-style bias-ply tires or evaluating a radial-based alternative.
The 1978 Pontiac Sunbird Wagon 6 Cyl. also uses B78-13 bias-ply or BR78-13 radial tires on a 13-inch rim. Buyers looking at this sub-model should focus on preserving the proper size first, then checking wheel condition and overall vehicle setup before changing construction or moving to a radial equivalent.
Bias-Ply to Radial Tire Conversion for the 1978 Pontiac Sunbird
A78-13 and B78-13 each have four radial-equivalent paths to consider across the two bias-ply fitments. A78-13 can be matched to 165R13 as an 80-series metric radial, P165/75R13 as a 75-series P-metric radial, or P175/70R13 as a 70-series P-metric radial. B78-13 can be matched to 175R13, P175/75R13, P185/70R13, or 650R13 as a bias-look radial. The choices move from traditional metric radial sizing to lower-profile P-metric formats, with 650R13 offering a more vintage-style presentation. Recommended rim-width ranges are 4-5 inches for A78-13 equivalents and 4-6 inches for B78-13 equivalents, and wheel fit, overall dimensions, and clearance should all be checked before changing sizes.
Modern Radial Equivalents
165R13
Equivalent 80-series Metric Radial (A78-13)
P165/75R13
Equivalent P-metric 75-series Radial (A78-13)
P175/70R13
Equivalent P-metric 70-series Radial (A78-13)
175R13
Equivalent 80-series Metric Radial (B78-13)
P175/75R13
Equivalent P-metric 75-series Radial (B78-13)
P185/70R13
Equivalent P-metric 70-series Radial (B78-13)
650R13
Bias-look Radial Equivalent (B78-13)
Important Considerations When Replacing Bias Ply With Radial
Compare overall diameter and section width carefully to ensure proper fit.
Verify recommended rim range (4-6 in) and load needs match your vehicle specifications.
Check fender clearance, steering clearance, and stance before installation.
Consider suspension condition and intended road use when choosing equivalents.
Important Fitment Notes
The tire sizes listed on this page assume factory-standard vehicle configuration. The following modifications may affect tire fitment and are not reflected in this guide:
Suspension changes (lowering, lift kits, spring replacements)
Body alterations (fender modifications, custom bodywork)
If your vehicle has been modified from factory specifications, verify tire clearance before purchase.
Frequently Asked Questions
Owners researching 1978 Pontiac Sunbird tires usually need to sort out sub-model-specific sizing, 13-inch rim fitment, and the difference between bias-ply and radial choices. The questions below focus on exact tire size, radial equivalents, restoration appearance, and the checks worth making before road use.
Tire Size & Fitment
What tire size fits a 1978 Pontiac Sunbird?
A 1978 Pontiac Sunbird can use A78-13, B78-13, or BR78-13, depending on the exact sub-model. The 4-cylinder car uses A78-13 bias-ply or BR78-13 radial, while the 6-cylinder and both wagon versions use B78-13 bias-ply or BR78-13 radial.
That means tire selection starts with identifying the car’s engine and body style, not just the year and model name. Since the Sunbird has both bias-ply and radial primary fitments in this range, it also helps to confirm what construction is on the car now and whether the wheels and overall setup match the tire being considered.
What size rim does a 1978 Pontiac Sunbird use?
The covered tire fitments for the 1978 Pontiac Sunbird use a 13-inch rim diameter. That applies to A78-13, B78-13, and BR78-13, so the wheel diameter remains consistent even though the tire size and construction can change by sub-model.
Rim diameter is only the first checkpoint, because wheel width and the car’s actual current setup still matter when selecting a tire. A Sunbird with replacement wheels, a past radial conversion, or other modifications should be measured carefully so the chosen tire matches the wheel and clears the body and suspension as intended.
Do all 1978 Pontiac Sunbird sub-models use the same tire size?
No. The 1978 Pontiac Sunbird uses different primary bias-ply sizes by sub-model, and BR78-13 radial fitment appears across all of the covered sub-models. The 4-cylinder car uses A78-13 as its bias-ply size, while the 6-cylinder and wagon versions use B78-13.
That distinction matters because A78-13 and B78-13 should not be treated as interchangeable just because they share the same 13-inch rim diameter. A buyer looking for the right tire should confirm the exact sub-model first, then decide whether the goal is a traditional bias-ply setup or a radial-based configuration that matches the vehicle’s current wheels and use.
Bias-Ply & Radial Options
Is A78-13 a bias-ply or radial tire for the 1978 Pontiac Sunbird?
A78-13 is a bias-ply tire size on the 1978 Pontiac Sunbird. It is used on the 4-cylinder Sunbird as the bias-ply fitment, while BR78-13 is the radial size found across the covered sub-model range.
That difference is important because a bias-ply tire keeps a more traditional period-style construction, while a radial setup changes the construction approach even if the rim diameter remains 13 inches. Anyone moving away from A78-13 bias-ply should compare the alternate size carefully and check wheel width, clearance, and the overall condition of the suspension and steering components.
What radial tire sizes are equivalent to A78-13 and B78-13?
A78-13 has three radial equivalents: 165R13 as an 80-series metric radial, P165/75R13 as a 75-series P-metric radial, and P175/70R13 as a 70-series P-metric radial. B78-13 has four: 175R13, P175/75R13, P185/70R13, and 650R13, with 650R13 serving as the bias-look radial option.
These alternatives give Sunbird owners several ways to move from a vintage alphanumeric bias-ply size into modern radial sizing conventions. Even so, an equivalent should be treated as an alternative rather than an automatic substitution, so the wheel width, overall vehicle setup, and clearance around the fenders and suspension should all be checked before making the change.
Should I use bias-ply or radial tires on a 1978 Pontiac Sunbird?
The answer depends on which fitment applies to the car and what the owner wants from it. The 1978 Pontiac Sunbird has both bias-ply and radial primary fitments within its covered applications, so either construction can be relevant depending on the sub-model and the tire size being matched.
Bias-ply tires usually make the most sense when preserving a stronger period-style look is part of the plan, while radial choices may appeal to owners maintaining a radial-equipped setup or exploring an equivalent for regular road use. The best approach is to confirm the exact sub-model, verify the wheel dimensions, and avoid assuming that a construction change is trouble-free just because the rim diameter is the same.
Choosing the Right Tire
What should I consider when choosing a 1978 Pontiac Sunbird tire?
Start with the exact fitment: A78-13, B78-13, or BR78-13, depending on the Sunbird’s sub-model. Once the correct size is established, the next decision is whether the car should stay with its bias-ply or radial-type fitment, since the 1978 Sunbird range includes both constructions on 13-inch rims.
After that, the right choice comes down to the car’s purpose and presentation. A restoration-oriented Sunbird may call for a traditional bias-ply look, while a driver may be better served by staying with the radial fitment or considering an equivalent where one exists. Wheel condition, actual wheel width, and the vehicle’s current ride-height and suspension setup should all be part of the decision.
How do I choose between the available A78-13, B78-13, and BR78-13 tires for a 1978 Pontiac Sunbird?
Choosing between these sizes is less about preference and more about using the size that matches the sub-model. A78-13 belongs to the 4-cylinder bias-ply application, B78-13 belongs to the 6-cylinder and wagon bias-ply applications, and BR78-13 is the radial fitment used across the covered sub-models.
Once the proper size is narrowed down, compare the tire by construction and by the role the car plays. A Sunbird being preserved for a more original-looking presentation may point toward the correct bias-ply size, while a car already set up around radial use may call for BR78-13 or a radial equivalent tied to the proper bias-ply size. The goal is matching the tire to the vehicle, not forcing a favorite size onto it.
What tire series are available for the 1978 Pontiac Sunbird?
The 1978 Pontiac Sunbird uses three vintage size series within its primary fitments: A78-13 and B78-13 as alphanumeric bias-ply sizes, and BR78-13 as an alphanumeric radial size. Those series reflect the period sizing systems used on compact American cars of the late 1970s.
For a buyer, the important point is that the letter-and-number format is part of the fitment itself, not just old-fashioned labeling. A78-13 and B78-13 are different bias-ply sizes tied to different Sunbird configurations, while BR78-13 represents radial construction in the same general vintage format. Reading the sidewall carefully and matching the size to the exact sub-model helps prevent selecting the wrong series.
Restoration & Appearance
Which tire should I choose for a period-style 1978 Pontiac Sunbird?
For a period-style 1978 Pontiac Sunbird, the starting point is the correct original-format size for the specific sub-model: A78-13 for the 4-cylinder bias-ply application or B78-13 for the 6-cylinder and wagon bias-ply applications. Those sizes preserve the vintage alphanumeric look that suits a late-1970s compact Pontiac.
Construction matters as much as size when appearance is the priority. Bias-ply tires generally keep a more traditional presentation, while a radial equivalent or BR78-13 radial fitment may change the visual character even if the wheel diameter stays at 13 inches. Anyone chasing exact restoration accuracy should compare the car’s historical documentation and marque-specific references before settling on a final tire choice.
How does tire construction affect the appearance of a restored 1978 Pontiac Sunbird?
Tire construction changes more than road feel on a restored 1978 Pontiac Sunbird; it also affects the car’s overall visual character. The Sunbird’s bias-ply fitments, A78-13 and B78-13, carry a distinctly traditional late-1970s presentation, while BR78-13 and metric radial equivalents move the look toward a more radial-era stance.
That difference becomes noticeable when the goal is a restoration-oriented finish rather than simple drivability. A buyer does not need to assume one choice is universally right, but the selected tire should match the car’s intended story and the owner’s standards for authenticity. Using the proper size for the sub-model is still the first rule, regardless of which construction is chosen.
Fitment, Maintenance & Road Use
Can modifications affect tire fitment on a 1978 Pontiac Sunbird?
Yes, modifications can affect tire fitment on a 1978 Pontiac Sunbird even when the intended tire size is correct on paper. Aftermarket wheels, wheel-width changes, altered ride height, suspension work, or body modifications can all change how an A78-13, B78-13, or BR78-13 tire sits and clears.
A Sunbird that has been lowered, fitted with replacement wheels, or converted from one construction type to another deserves a careful check before new tires go on. Measuring the actual wheel dimensions and checking clearance at the fenders, steering, and suspension helps prevent surprises. That is especially important when considering a radial equivalent instead of the original bias-ply size.
What should I inspect before driving a 1978 Pontiac Sunbird on new tires?
Before driving a 1978 Pontiac Sunbird on new tires, inspect the wheels for damage or corrosion, confirm the wheel diameter and width, and make sure the tires are mounted in the correct size for the exact sub-model. Tire pressure, valve stems, lug torque, and visible clearance around the fenders and suspension also deserve attention.
A short test drive should include listening for rubbing and checking that the car tracks and steers normally. Collector cars that sit for long periods also benefit from a broader inspection of shocks, bushings, steering parts, and brakes before regular road use resumes. New tires work best when the rest of the chassis is ready to support them.
How should 1978 Pontiac Sunbird tires be maintained?
1978 Pontiac Sunbird tires should be maintained with regular pressure checks, periodic visual inspection, and close attention to age-related condition. Whether the car uses A78-13, B78-13, or BR78-13, the owner should watch for sidewall cracking, cuts, bulges, uneven wear, and any sign of air loss before routine driving.
Storage habits matter on collector-era cars because many spend more time parked than driven. Keeping the Sunbird away from prolonged sunlight, excess heat, moisture, and ozone sources can help preserve the tires’ condition, and moving the car occasionally can reduce flat-spotting concerns. Even low-mile tires should be evaluated regularly, since appearance alone does not guarantee safe road condition.
