1966 AC Tire Fitment Guide

1966 AC vehicles use three tire sizes: 550-16 for the AC Ace, and 640-15 or 670-15 for the AC Cobra and AC Grayhound. The Ace size mounts on a 16-inch rim, while the Cobra and Grayhound sizes mount on 15-inch rims. Rim-width guidance appears for several products within these sizes, including 3.25 to 4.00 inches for some 550-16 tires, 4.00 to 5.00 inches across 640-15 offerings, and 4.50 to 6.00 inches across 670-15 offerings.

That means year and make alone are not enough for a confident choice on a 1966 AC. Start by identifying the model, then verify the wheel diameter already on the car, and finally compare the wheel's actual width with the tire's approved range. That matters especially on Cobra and Grayhound applications, where both 15-inch sizes may appear correct at a glance but are not automatically interchangeable on every wheel.

On a 1966 AC, 550-16 is a traditional numeric bias-ply size. The 5.50 figure refers to nominal section width in inches, and the 16 identifies the wheel diameter in inches. There is no modern metric width or aspect-ratio format in this code, and the size belongs to the 1966 AC Ace rather than the Cobra or Grayhound.

That older numeric format is normal for mid-century British sports cars and should be read in period terms rather than compared too literally with modern radial sizing. If you own an Ace, 550-16 points you toward classic-style 16-inch tires, with blackwall and wide whitewall choices available depending on whether the goal is a sporting look or a more formal restoration presentation.

No, 1966 AC models do not all use the same tire size. The AC Ace uses 550-16, while the AC Cobra and AC Grayhound use 640-15 and 670-15. The split is significant because the Ace is on a 16-inch fitment and the Cobra and Grayhound are on 15-inch fitments, so the sizes are tied directly to model family.

For a buyer, that means the first job is simple identification. An Ace owner can move straight to 550-16 options, while Cobra and Grayhound owners need to confirm which of the two 15-inch sizes suits the car's wheels and intended presentation. If the car has been restored or modified at some point, checking the tire sidewall and measuring wheel diameter before replacing anything is well worth the time.

1966 AC tires are available in several sidewall styles depending on size. The 550-16 for the Ace comes in blackwall and wide whitewall form, the 640-15 for Cobra and Grayhound comes in wide whitewall and narrow whitewall form, and the 670-15 for Cobra and Grayhound comes in blackwall and wide whitewall form. All of these choices remain bias-ply constructions, so the visual difference is in the sidewall treatment rather than the basic tire type.

Sidewall style can change the entire personality of a car, especially on a small-volume British marque where details stand out. A blackwall usually gives a more sporting appearance, while whitewall variations can push the look toward a more formal period presentation. If show authenticity matters, compare the sidewall style already on the car with period photos, club references, or a known restoration standard before making your final choice.

Several brands cover 1966 AC fitments. The 550-16 Ace size is available from Excelsior, Avon, BFGoodrich, and Firestone. The 640-15 Cobra and Grayhound size comes from BFGoodrich and Firestone, while the 670-15 size is available from Firestone, US Royal, Coker Classic, and Universal Vintage Tire.

Brand choice on a collector car often comes down to the look of the sidewall, the wheel-width range that suits your wheels, and the kind of restoration you are pursuing. Avon, BFGoodrich, Firestone, US Royal, and the specialty vintage lines each speak to a different visual and historical flavor, so it helps to decide whether you are chasing a restrained sports-car appearance or a more formal whitewall presentation before narrowing the field.

For 1966 AC vehicles in 640-15, BFGoodrich and Firestone share the same 15-inch diameter and both are bias-ply tires, but they differ in sidewall presentation and rim-width coverage. The BFGoodrich version appears as a wide whitewall with a 4.00 to 4.50-inch rim-width range and a 1190-pound load figure at 32 psi. Firestone offers wide whitewall versions plus a narrow whitewall version, generally aimed at 4.50 to 5.00-inch rims, with load figures of 1190 pounds at 32 psi on some versions and 970 pounds at 32 psi on the narrow whitewall.

That makes the choice less about raw construction and more about visual style and wheel compatibility. A narrower original wheel may favor the BFGoodrich range, while a slightly wider 15-inch wheel may align more naturally with the Firestone fitment range. When two tires share the same nominal size but not the same approved rim span, wheel measurement matters just as much as the sidewall design.

Rim-width requirements for 1966 AC tires vary by size and, in some cases, by brand within the same size. The 550-16 size appears with a 3.25 to 4.00-inch rim-width range on certain products. The 640-15 size spans 4.00 to 5.00 inches depending on product, and the 670-15 size spans 4.50 to 6.00 inches across the available offerings.

Those ranges are one reason a same-size replacement should never be chosen by sidewall code alone. Measure the wheel that is actually on the car and compare it with the approved range for the exact tire you are considering. That is especially important on Cobra and Grayhound applications, where the broader 670-15 range may suit some wheels better than a narrower 640-15 option.

1966 AC tires in these sizes are all bias-ply products, but tube designation is not printed uniformly across every product naming convention. None of the three sizes carries a clear mixed TT and TL split in the available offerings, so the tube decision should be confirmed by the specific tire's sidewall marking and by the wheel type on the car. That is particularly important on older wire or riveted wheel designs, where the wheel itself may dictate tube use even when the tire construction looks straightforward.

The practical approach is to treat tube fitment as a tire-and-wheel system question, not just a tire-size question. Before finalizing a setup for a 1966 AC, check whether the wheel is suitable for tubeless service, inspect its condition at the bead seat, and match the valve hardware accordingly. If the car has older specialty wheels, a marque specialist can help confirm the correct setup without guesswork.

Original 1966 AC wheels cannot be treated as universal across all three tire sizes, because the Ace uses a 16-inch fitment and the Cobra and Grayhound use 15-inch fitments. Within the Cobra and Grayhound group, both 640-15 and 670-15 share the same 15-inch rim diameter. Rim diameter compatibility is only the first step, though, because approved wheel width still varies by the exact tire chosen.

That means an original 15-inch Cobra or Grayhound wheel may work with more than one 15-inch size, but only after you confirm its actual width. A 16-inch Ace wheel is a separate category entirely and does not cross over into the 15-inch Cobra or Grayhound fitments. On any restored car, it is wise to verify wheel dimensions directly rather than assuming the wheels are still factory-spec after decades of ownership changes.

A 1966 AC should be stored in a cool, dry, dark space away from direct sunlight, electric motors, welders, battery chargers, or any other ozone-producing equipment. Because the available fitments are bias-ply, long static periods can encourage flat-spotting and sidewall aging sooner than many owners expect. Keeping the tires properly inflated and moving the car periodically helps reduce stress where the carcass contacts the floor.

If the car will sit for an extended season, many collectors either reposition it occasionally or support it in a way that reduces sustained load on one contact patch. Clean the tires with mild soap and water only, and avoid dressings that leave a glossy chemical film. Storage habits matter just as much as mileage on a low-use AC, especially on a lightweight sports car that may spend long stretches parked between events.

Tires on a 1966 AC are usually judged by age and condition more than by tread wear. A sensible collector-car rule is to begin close inspection as tires move through the five-to-seven-year range and to think seriously about replacement as they approach roughly ten years, even if the tread still looks deep. The DOT date code, sidewall integrity, storage history, and how the car has been used all matter more than annual mileage alone.

That is especially true on a specialty car like an AC, where the car may see occasional spirited driving but relatively little total road time. A tire that looks fresh at first glance can still be aging internally. If you are unsure how old the current set is, check the date code, inspect for cracks or stiffness, and treat appearance as only one part of the evaluation.

Tires on a 1966 AC should be inspected before every drive and again before any longer outing or event weekend. Look for sidewall cracking, cuts, bulges, irregular tread wear, and pressure loss, and do not ignore an older spare just because it has not seen regular use. On a collector car, long dormant periods can age the tires even when the tread has barely been touched.

A brief inspection routine pays off because these cars often alternate between storage and occasional use rather than daily service. If the wheel-and-tire setup uses tubes, include valve stems and any signs of slow leakage in your check. Catching a small issue in the garage is far preferable to discovering it after the car has been driven long enough to generate heat in an already weakened casing.

The 1966 AC Ace belongs to an era when bias-ply construction was still the normal original fitment for many specialist British cars, and its 550-16 size fits that pattern squarely. That means a classic-style bias-ply tire is the right starting point for an authentic restoration approach. The available 550-16 choices include blackwall and wide whitewall styles, but original presentation could vary by market, owner preference, and the way the car was delivered or later restored.

For show-level work, size and construction should come first, then sidewall treatment. If you are trying to recreate a very specific period appearance, period photography, factory literature, and AC marque clubs are the best way to confirm whether a blackwall or whitewall look suits your particular car's history. Avoid assuming that one visual treatment was universal just because it is available in the correct size.

Correct tire fitment matters a great deal when showing a 1966 AC, particularly because AC was a low-volume marque whose details are often closely examined by knowledgeable enthusiasts. Judges and marque specialists typically pay attention to the tire size, the period-correct bias-ply construction, and whether the sidewall style suits the car's intended market and restoration theme. A mismatch in diameter, an obviously modern sidewall treatment, or a style that fights the car's era can distract from an otherwise strong presentation.

That does not mean every event uses the same standards, but authenticity is rarely helped by guesswork. A touring-oriented restoration may tolerate more flexibility than a concours class, while a historically focused show car may be expected to match period practice very closely. Before committing to a set, compare your plans with the rules of the events you attend and with advice from AC clubs or restoration judges familiar with the marque.

For the 1966 AC in 670-15, Firestone and Coker Classic share the same nominal size and bias-ply construction, but they differ in sidewall treatment, rim-width range, and load figure. The Firestone version appears as a blackwall with a 4.50 to 5.00-inch rim-width range and a 1450-pound load figure at 32 psi. The Coker Classic version appears as a wide whitewall with a 5.00 to 6.00-inch rim-width range and a 1550-pound load figure at 32 psi.

That contrast makes the choice straightforward if you think in terms of both appearance and wheel compatibility. A blackwall Firestone can support a more sporting visual theme on a narrower wheel, while the Coker Classic suits an owner who wants a whitewall presentation and has a wheel width that falls into its approved range. The tire that looks right is only half the answer; the wheel still has to match the tire's intended fitment envelope.

A properly selected and well-maintained tire can be suitable for normal highway use on a 1966 AC, but the answer begins with using the correct size and a tire in sound age and condition. These fitments are bias-ply rather than modern radial designs, so their on-road manners will feel more period-correct and less contemporary in tracking, ride response, and transient behavior. On many classic cars of this age, the vehicle's own brakes, steering geometry, and suspension condition can be just as important to road confidence as the tire itself.

Safe highway use therefore depends on the whole package rather than a sidewall code alone. Before extended driving, make sure the car is aligned appropriately, the pressures are set correctly for the specific tire, and the tires are free from cracking, damage, and age-related hardening. A freshly restored AC with old or mismatched tires is still compromised, while a mechanically sorted car on the correct, healthy tires is far more predictable.

Inflation pressure on a 1966 AC should be matched to the exact tire size and the product's own rated load-and-pressure relationship rather than borrowed from another size. Available examples include 840 pounds at 32 psi on one 550-16 tire, 1190 pounds at 32 psi on several 640-15 tires, and 1450 or 1550 pounds at 32 psi on certain 670-15 tires. Those figures describe the tire's capacity at that pressure, not a blanket factory recommendation for every AC application.

The best approach is to start with the original vehicle literature for factory guidance, then compare that with the reproduction tire's own specifications and the way the car is actually equipped. Do not transfer a pressure value from a Cobra or Grayhound tire to an Ace tire, or from one 15-inch size to another, simply because the numbers seem close. Pressure setting is a size-specific decision.

Before a longer drive in a 1966 AC, inspect each tire for cracking, cuts, bulges, embedded debris, and uneven wear, then verify cold inflation pressures and confirm that the spare is still usable. Pay close attention to the age of the tires and to the condition of the valve stems, especially if the wheels or tire setup are older. On a specialty British car, a tire that has sat for long periods can look acceptable yet still deserve a careful hands-on inspection.

That tire check should be part of a broader pre-drive routine that includes brakes, fluid levels, steering response, wheel fasteners, and basic electrical reliability. The farther you plan to go, the more important it is to avoid small assumptions. A 1966 AC rewards preparation, and a few extra minutes in the garage can make the difference between an enjoyable tour and a preventable roadside interruption.