The 1978 Mercury Bobcat belongs to the late-1970s compact-car era, when domestic small cars were balancing economy, practicality, and changing buyer expectations around ride quality. In Bobcat form, that meant a simple, usable platform that could appear as a Runabout or Wagon, with fitment differences that matter when it is time to replace tires. The 1978 Mercury Bobcat uses A78-13, B78-13, or BR78-13 tires depending on configuration, all on 13-inch rims, with both bias-ply and radial fitments represented. That opens the door to period-style bias-ply replacements on some versions and radial-oriented decisions on others. The key is confirming the exact sub-model and tire construction before choosing by size, appearance, or radial-equivalent direction.
Which Tire Size Is Right for The 1978 Mercury Bobcat
Three tire sizes apply to the 1978 Mercury Bobcat, and the right one depends on the exact sub-model. All of them use a 13-inch rim, but fitment varies between bias-ply A78-13 and B78-13 sizes and the radial BR78-13 setup. The first step is confirming whether the car is a Runabout 4 Cyl., Runabout V8, or Wagon before comparing tire style, construction, or equivalent options.
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 a 13-inch rim. On the 1978 Mercury Bobcat, this is a traditional bias-ply fitment used on certain Runabout 4 Cyl. applications. Buyers familiar only with modern metric sizing will notice that this older format is centered more on period sizing convention than current millimeter-based notation. It is the size to evaluate when maintaining an original-style bias-ply presentation and then deciding whether to stay with that construction or compare radial equivalents separately.
B78-13 uses the same vintage alphanumeric bias-ply sizing system, with the final 13 again denoting a 13-inch rim and the leading code identifying a different size class from A78-13. For the 1978 Mercury Bobcat, this size appears on certain Runabout 4 Cyl. configurations where a bias-ply tire remains the primary fitment. It also has a broader radial-equivalent path available, including metric, P-metric, and bias-look radial alternatives for buyers exploring a different construction while preserving a traditional look. Choosing B78-13 starts with confirming that specific Bobcat setup rather than assuming all Runabouts use the same tire.
BR78-13 is an alphanumeric radial size, and the presence of the R within the size designation marks it as radial construction rather than bias-ply. On the 1978 Mercury Bobcat, this size is used on the Runabout V8 and Wagon, making it the key fitment for owners whose cars were set up around a radial tire from the start. Modern buyers often recognize this format as a bridge between older alphanumeric sizing and later metric radial conventions. It is the size to focus on when the goal is preserving the Bobcat's radial-based fitment while still confirming wheel condition and overall compatibility.
Sub-model fitment matters on the 1978 Mercury Bobcat because tire size and construction are not the same across the range. The 4-cylinder Runabout uses bias-ply sizing choices, while the Runabout V8 and Wagon use a radial BR78-13 fitment, so identifying the exact version comes first.
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1978 Mercury Bobcat Runabout 4 Cyl.
The 1978 Mercury Bobcat Runabout 4 Cyl. uses bias-ply fitment, with A78-13 and B78-13 both appearing in this sub-model. That makes tire selection less about rim diameter and more about confirming which of the two bias-ply sizes is on the car before considering period-style replacement or a radial-equivalent path.
The 1978 Mercury Bobcat Runabout V8 uses the BR78-13 radial size on a 13-inch rim. For this sub-model, the focus shifts toward staying with the proper radial fitment and verifying the actual wheel setup if the car has been changed from its original-style configuration.
The 1978 Mercury Bobcat Wagon also uses BR78-13 radial tires, keeping fitment straightforward once the sub-model is confirmed. The buying decision centers on selecting the correct radial size and checking the wagon's present wheel and suspension setup before replacing aged or mismatched tires.
Bias-Ply to Radial Tire Conversion for the 1978 Mercury Bobcat
A78-13 and B78-13 each have radial-equivalent choices for buyers comparing modern sizing formats to the original bias-ply fitment. A78-13 corresponds to 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, with a recommended rim-width range of 4 to 5 inches. B78-13 corresponds to 175R13, P175/75R13, P185/70R13, and the 650R13 bias-look radial, with a recommended 4 to 6 inch rim-width range. Each option should be checked against wheel size, overall dimensions, and vehicle clearance before conversion.
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
These FAQs focus on 1978 Mercury Bobcat tire size differences by sub-model, 13-inch rim fitment, bias-ply versus radial construction, and what to inspect before putting a compact collector-era Mercury back on the road.
Tire Size & Fitment
What tire size fits a 1978 Mercury Bobcat?
The 1978 Mercury Bobcat uses three possible tire sizes: A78-13, B78-13, and BR78-13. The correct one depends on the sub-model. Runabout 4 Cyl. cars use the bias-ply A78-13 or B78-13 sizes, while the Runabout V8 and Wagon use the radial BR78-13 size.
Because all three sizes mount on 13-inch rims, wheel diameter alone does not answer the fitment question. The practical step is to confirm the exact Bobcat sub-model and then verify the tire size already on the car, especially if it has had wheel changes or older replacement tires installed over the years.
What size rim does a 1978 Mercury Bobcat use?
The 1978 Mercury Bobcat uses a 13-inch rim with its applicable tire sizes. A78-13, B78-13, and BR78-13 all share that same rim diameter, even though they differ in size designation and, in some cases, construction type.
That common 13-inch diameter helps narrow the search, but it does not mean every 13-inch tire is suitable. Buyers should still confirm the exact tire size for the sub-model and check the actual wheel width on the car, especially when comparing a bias-ply size to a modern radial equivalent.
Why does the 1978 Mercury Bobcat have more than one tire size?
More than one tire size appears on the 1978 Mercury Bobcat because fitment varies by sub-model and construction. The Runabout 4 Cyl. uses bias-ply A78-13 or B78-13 tires, while the Runabout V8 and Wagon use the BR78-13 radial size.
That means tire selection should begin with the exact version of the car rather than the Bobcat name alone. A buyer restoring a 4-cylinder Runabout may be comparing two vintage bias-ply sizes, while a V8 Runabout or Wagon owner should center the search on the proper radial-format BR78-13 fitment.
Bias-Ply & Radial Options
Is A78-13 a bias-ply or radial tire for the 1978 Mercury Bobcat?
A78-13 is a bias-ply tire size on the 1978 Mercury Bobcat. It is used on certain Runabout 4 Cyl. applications and follows the older alphanumeric sizing convention rather than a modern metric radial format.
That matters because a bias-ply tire affects both appearance and replacement strategy. Owners keeping a period-style look may want to stay with the original construction type, while anyone considering a radial alternative should compare wheel width, overall dimensions, and vehicle clearance instead of assuming any modern 13-inch radial is interchangeable.
What radial tire sizes are equivalent to B78-13?
Radial equivalents for B78-13 include 175R13 as an 80-series metric radial, P175/75R13 as a 75-series P-metric radial, P185/70R13 as a 70-series P-metric radial, and 650R13 as a bias-look radial. The recommended rim-width range for these equivalents is 4 to 6 inches.
Those options give a buyer several ways to move from a vintage bias-ply size into radial construction while choosing between traditional and more modern sizing formats. The right choice still depends on the wheel on the car and the available fender and suspension clearance, so the conversion should be checked carefully before installation.
What should I check before converting my 1978 Mercury Bobcat from bias-ply to radial tires?
Start by confirming the Bobcat's original tire size, then compare the intended radial equivalent against the actual wheel diameter and wheel width. A78-13 and B78-13 have different equivalent paths, so the correct conversion depends on which bias-ply size belongs on the specific Runabout 4 Cyl.
Next, inspect for clearance at the fenders, suspension, and steering range, and make sure the car is not running aftermarket wheels that change the fitment picture. A collector car that has seen decades of replacement parts can differ from stock, so the safest approach is to verify the entire wheel-and-tire package as a system.
Choosing the Right Tire
What should I consider when choosing a tire for a 1978 Mercury Bobcat?
Begin with the correct size for the exact Bobcat sub-model. The 4-cylinder Runabout uses bias-ply A78-13 or B78-13, while the Runabout V8 and Wagon use BR78-13 radial tires. Construction type is part of the fitment decision here, not just the sidewall marking.
After that, think about the goal for the car. A restoration-oriented Runabout may call for a period-style bias-ply presentation, while another owner may be comparing radial equivalents for road use. The wheel currently on the vehicle should also be checked so the chosen tire matches both the intended look and the actual hardware.
How do I choose between the available A78-13 and B78-13 tires for a 1978 Mercury Bobcat?
A78-13 and B78-13 should not be treated as interchangeable choices for the same Bobcat without first confirming which size belongs on the specific Runabout 4 Cyl. They are separate bias-ply fitments, and B78-13 also opens the door to a broader set of radial-equivalent alternatives.
Once the correct primary size is confirmed, the decision becomes one of construction and appearance. Some owners will want to retain the traditional bias-ply sizing and look, while others may compare radial-equivalent formats for a different driving setup. Wheel width and clearance remain important before moving from one path to the other.
What rim-width specifications should I compare when choosing 1978 Mercury Bobcat tires?
Rim width becomes especially important when comparing radial equivalents for the Bobcat's bias-ply sizes. A78-13 radial equivalents use a recommended rim-width range of 4 to 5 inches, while B78-13 radial equivalents use a recommended range of 4 to 6 inches.
That means the actual wheel on the car can influence which equivalent sizes are worth considering. Even with the correct 13-inch diameter, a wheel that is too narrow or too wide for the intended radial option can create an uneven result, so measuring the wheel is just as important as reading the sidewall size.
Restoration & Appearance
Which tire should I choose for a period-style 1978 Mercury Bobcat?
A period-style 1978 Mercury Bobcat usually starts with the primary tire size and construction used by its specific sub-model. That means A78-13 or B78-13 bias-ply for the Runabout 4 Cyl., and BR78-13 radial for the Runabout V8 or Wagon.
Construction choice plays a major role in how the car presents visually. A buyer focused on restoration character may prefer to stay with the original style of sizing and construction, while someone balancing vintage appearance with a different road-use plan may compare the radial-equivalent route after confirming wheel and body clearance.
How does tire construction affect the appearance of a restored 1978 Mercury Bobcat?
Tire construction changes more than ride and handling on a restored 1978 Mercury Bobcat; it also influences the car's visual stance and overall period impression. The Bobcat's fitment range includes both bias-ply and radial construction, depending on sub-model, so the construction choice is part of the restoration conversation.
A bias-ply setup tends to support a more traditional late-1970s replacement look on the 4-cylinder Runabout, while a BR78-13 radial keeps the V8 Runabout or Wagon aligned with its radial-based fitment. When exact originality matters, the vehicle's historical paperwork or marque-specific references are worth checking before final tire selection.
Fitment, Maintenance & Road Use
Can modifications affect tire fitment on a 1978 Mercury Bobcat?
Yes, modifications can affect tire fitment on a 1978 Mercury Bobcat even when the tire still carries the correct 13-inch rim diameter. Aftermarket wheels, changes in wheel width, suspension alterations, or body modifications can all change how an A78-13, B78-13, or BR78-13 tire sits on the car.
A Bobcat that has been lowered, widened, or fitted with nonstock wheels should be checked carefully at full steering lock and through suspension travel. Clearance at the fenders and inner wheelhouse matters just as much as sidewall size, especially when considering a radial equivalent for a car that originally used bias-ply tires.
What should I inspect before driving a 1978 Mercury Bobcat on new tires?
Before road use, inspect the wheels for damage, confirm the tire size matches the Bobcat's sub-model, and make sure the tires are mounted evenly and holding pressure. It also helps to check valve stems, lug hardware, and basic alignment condition so the new tires are not compromised immediately.
A collector-era compact that has spent time parked deserves a broader look as well. Examine suspension bushings, steering components, and brake condition, then look for rubbing marks that could signal a fitment issue. A short test drive followed by a second inspection can reveal clearance or pressure concerns before longer use.
How should 13-inch tires on a collector 1978 Mercury Bobcat be maintained?
Collector-car tires on a 1978 Mercury Bobcat should be checked regularly for air loss, tread wear, sidewall cracking, cuts, and bulges, even if the car is driven only occasionally. Low-mileage use does not prevent age-related deterioration, and older compact cars are often stored long enough for those issues to go unnoticed.
Storage conditions matter just as much as mileage. Keeping the Bobcat away from prolonged sunlight, heat, moisture, and ozone-producing equipment can help preserve the tires between drives. Periodic pressure checks and visual inspections before every outing are smart practice, whether the car uses bias-ply A78-13 or B78-13 tires or BR78-13 radials.
