The 1968 Sunbeam Imp belongs to a distinctive era of compact British motoring, when small-displacement cars balanced economy, nimble road manners, and unmistakably period styling. Its light, city-friendly character makes tire choice especially important, because the tire has a visible effect on both stance and driving feel. For the 1968 Sunbeam Imp, fitment centers on two 12-inch tire sizes: 5.50-12 in bias-ply form and 155R12 in radial form. That gives owners a meaningful choice between a more traditional vintage-style construction and a later radial-style fitment. The right direction depends on whether the goal is restoration-minded appearance, everyday road use, or a careful balance of both.
Which Tire Size Is Right for The 1968 Sunbeam Imp
The 1968 Sunbeam Imp uses two primary tire sizes, both on 12-inch rims: 5.50-12 in bias-ply construction and 155R12 in radial construction. Because the Base model can use either size, the key decision is not identifying a different trim, but deciding whether a traditional bias-ply presentation or a radial-style setup better suits the car's appearance, driving use, and wheel compatibility.
The 155R12 size uses a Euro-metric radial format, with 155 indicating nominal section width in millimeters, R identifying radial construction, and 12 indicating the rim diameter in inches. On a 1968 Sunbeam Imp, this size represents a radial fitment choice for owners who want a more modern construction while staying with the proper 12-inch wheel diameter. Its sizing format will feel more familiar to later compact-car owners than older numeric tire codes. This is a useful size to evaluate when road use and radial construction matter as much as keeping the car's overall proportions appropriate to the vehicle.
The 5.50-12 size is a numeric bias-ply designation, with 5.50 referring to the nominal section width in inches and 12 identifying the rim diameter. That older sizing convention suits the 1968 Sunbeam Imp's period character and gives the car a more traditional vintage tire presentation. Bias-ply construction also aligns with the way many small British cars of the era were originally equipped and restored in appearance. This size deserves close consideration when the goal is a restoration-oriented look, a more authentic side profile, or a tire choice that reflects the car's original-era tire language.
Sub-model fitment is straightforward for the 1968 Sunbeam Imp covered here, because the Base model can use the same two 12-inch tire sizes. The main choice is deciding between radial and bias-ply construction rather than sorting through different trim-specific wheel diameters.
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1968 Sunbeam Imp Base
The 1968 Sunbeam Imp Base can be fitted with either a 155R12 radial or a 5.50-12 bias-ply tire, both built for 12-inch rims. That gives the owner room to choose between a more traditional period-style tire presentation and a radial-style setup that should still be checked against the car's actual wheels and overall condition.
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
Common questions for the 1968 Sunbeam Imp usually come down to understanding the two 12-inch tire sizes, choosing between bias-ply and radial construction, and checking wheel fitment, appearance goals, and basic road-use readiness before the car goes back into service.
Tire Size & Fitment
What tire size fits a 1968 Sunbeam Imp?
The 1968 Sunbeam Imp uses two primary tire sizes: 155R12 in radial construction and 5.50-12 in bias-ply construction. Both sizes are associated with the car's 12-inch wheel diameter, so the fitment question is less about wheel size and more about which tire construction and sizing style best matches the car.
That means the next step is confirming the actual wheels on the car and deciding whether the Imp is being kept closer to a period-style setup or driven with a radial-oriented approach. On an older compact car, aftermarket wheels, prior restorations, or long ownership history can affect what is mounted today.
What size rim does a 1968 Sunbeam Imp use?
The 1968 Sunbeam Imp uses a 12-inch rim diameter with both of its primary tire sizes, 155R12 and 5.50-12. Even though the tire constructions differ, both fitments center on the same rim diameter, which simplifies the first stage of narrowing down the correct tire.
Rim diameter is only part of the fitment picture, so it still helps to confirm the wheel width and the actual wheel installed on the car before choosing a tire. That matters even more on collector vehicles that may have had replacement wheels fitted over the years.
What does 5.50-12 mean on a 1968 Sunbeam Imp?
A 5.50-12 tire is a vintage numeric bias-ply size. The 5.50 refers to the tire's nominal section width in inches, while the 12 identifies the rim diameter. On a 1968 Sunbeam Imp, that code points to the traditional bias-ply fitment choice rather than the later-style 155R12 radial format.
For an owner, the practical takeaway is that 5.50-12 reflects an older sizing system and a different construction style, not just a different way of writing the same tire. It is best suited to buyers focused on vintage presentation and period-style fitment rather than simply choosing the most modern-looking sidewall code.
Bias-Ply & Radial Options
Is 5.50-12 a bias-ply or radial tire for the 1968 Sunbeam Imp?
On a 1968 Sunbeam Imp, 5.50-12 is a bias-ply tire size. It uses a vintage numeric size format and represents the more traditional construction option offered for this car, while 155R12 is the radial alternative within the same 12-inch rim diameter.
That distinction matters because construction changes the tire's visual character as well as the overall setup of the car. Anyone moving from 5.50-12 to a radial should confirm wheel compatibility, compare the installed tire's proportions, and make sure steering and body clearance remain appropriate for the actual vehicle.
Should I use bias-ply or radial tires on a 1968 Sunbeam Imp?
The 1968 Sunbeam Imp can be fitted with either 5.50-12 bias-ply tires or 155R12 radial tires, so the decision depends on how the car is being used and presented. Bias-ply suits a more traditional period-style look, while 155R12 gives the car a radial-format tire choice on the same 12-inch rim diameter.
Owners focused on restoration appearance often start with the bias-ply option, while owners planning more regular road use may prefer to evaluate the radial fitment. Either way, the car's actual wheel setup, suspension condition, and available clearance deserve a careful look before changing construction type.
What should I check before converting my 1968 Sunbeam Imp from bias-ply to radial tires?
A conversion from 5.50-12 bias-ply to 155R12 radial starts with confirming that the Imp is still running the correct 12-inch wheels and that the wheel width suits the intended radial tire. It also helps to compare the current tire's installed dimensions and inspect how much clearance the car has at the fenders and steering points.
Beyond size, the condition of the suspension and steering should not be overlooked on a vintage small car. Older components, worn bushings, or previous modifications can influence how a different construction behaves, so a careful inspection before the switch is just as important as choosing the new size itself.
Choosing the Right Tire
What should I consider when choosing a 5.50-12 tire for a 1968 Sunbeam Imp?
Choosing a 5.50-12 tire for a 1968 Sunbeam Imp starts with confirming that the car is being kept on its 12-inch wheel setup and that a bias-ply construction suits the owner's goals. This size is the traditional numeric bias-ply option, so appearance, period character, and overall vehicle presentation usually guide the decision.
A buyer should also look closely at the actual wheel on the car, especially if the Imp has changed hands or seen restoration work over time. Matching the tire to the intended use matters too, since a car shown for originality-minded presentation may call for a different choice than one driven more often.
What should I consider when choosing a 155R12 tire for a 1968 Sunbeam Imp?
Selecting a 155R12 tire for a 1968 Sunbeam Imp means choosing the car's radial-format option while staying with the correct 12-inch rim diameter. The main considerations are whether the car's wheels are suitable for that radial fitment and whether a radial construction matches the owner's driving plans and visual expectations.
Because many older cars have seen wheel changes, suspension work, or long periods of storage, it is wise to inspect the actual setup before finalizing the choice. The 155R12 format can be a practical path for road use, but it still needs to be evaluated against the car's present-day condition and clearance.
How do I choose between the available 12-inch tires for a 1968 Sunbeam Imp?
The 1968 Sunbeam Imp's two 12-inch tire paths are 5.50-12 bias-ply and 155R12 radial. The simplest way to choose between them is to decide whether the car is being kept closer to a period-style presentation or set up around a radial-format tire while remaining within the original wheel diameter.
Once that decision is clear, confirm the wheels currently on the car and inspect the surrounding hardware before committing to one size. A small British car can be sensitive to wheel and tire changes, so verifying the actual setup is more useful than relying only on what might have been fitted years ago.
Restoration & Appearance
Which tire should I choose for a period-style 1968 Sunbeam Imp?
For a period-style 1968 Sunbeam Imp, the 5.50-12 bias-ply tire is the more traditional starting point. Its vintage numeric sizing and bias-ply construction better reflect the tire language associated with small cars of the era, making it a natural choice when the vehicle's visual presentation matters as much as simple fitment.
That does not automatically make every 5.50-12 tire the right restoration answer, especially if originality is being judged at a very high level. Buyers pursuing exact historical accuracy should compare the tire choice against marque-specific references and the car's own restoration goals rather than assuming any one vintage-style option settles the matter.
How does tire construction affect the appearance of a restored 1968 Sunbeam Imp?
Tire construction changes the appearance of a restored 1968 Sunbeam Imp because bias-ply and radial tires carry a different visual character even when they share the same 12-inch wheel diameter. A 5.50-12 bias-ply presents the car in a more traditional vintage style, while a 155R12 radial gives the Imp a later-looking tire format.
That visual shift can influence how the car sits and how authentic the finished restoration feels to the owner. Anyone restoring the Imp for period flavor will usually pay close attention to that difference, while an owner balancing appearance with regular road use may accept a more modern-looking radial presentation.
Fitment, Maintenance & Road Use
Can modifications affect tire fitment on a 1968 Sunbeam Imp?
Yes, modifications can affect tire fitment on a 1968 Sunbeam Imp even though both primary tire choices use a 12-inch rim diameter. Changes such as aftermarket wheels, altered wheel width, suspension work, or body repairs can all influence how either a 5.50-12 bias-ply or 155R12 radial sits on the car.
That is why the car itself should be checked before choosing a replacement tire, especially on an older vehicle with a long service history. Clearance at the fenders and steering points matters, and the actual wheels on the car are more important than assumptions based on age alone.
What should I inspect before driving a 1968 Sunbeam Imp on new tires?
Before driving a 1968 Sunbeam Imp on new tires, inspect the wheels for correct diameter and general condition, then check the suspension and steering for looseness or wear. It also makes sense to look over the old tires for uneven wear patterns, since those can hint at alignment or mechanical issues that new tires alone will not cure.
Air pressure, lug hardware, and visible clearance should be confirmed once the new tires are installed. A brief slow-speed road check is useful as well, because a collector car that has been stored or only lightly used may reveal vibration, rubbing, or steering issues only after it is back on the road.
How should tires on a collector 1968 Sunbeam Imp be maintained?
Tires on a collector 1968 Sunbeam Imp should be maintained with regular pressure checks, routine visual inspection, and attention to age-related condition even if the car is driven only occasionally. Sidewall cracking, bulges, cuts, flat spotting, and persistent air loss all deserve prompt attention on a lightly used vintage car.
Storage conditions matter almost as much as mileage, so the car benefits from being kept away from prolonged heat, direct sunlight, excess moisture, and ozone sources. Periodic inspection before every outing is a sensible habit, particularly because collector vehicles often accumulate time in storage faster than they accumulate miles.
