1957 Armstrong-Siddeley Tire Fitment Guide

1957 Armstrong-Siddeley vehicles use four sizes, all on the Sapphire: 185R15 and 640-15 for 15-inch wheels, plus 185R16 and 670-16 for 16-inch wheels. The radial choices are 185R15 and 185R16, while the bias-ply choices are 640-15 and 670-16. Rim width ranges vary by size and product, with 185R15 commonly covering roughly 4.5 to 6.5 inches, 640-15 covering about 4.0 to 5.0 inches, 185R16 covering about 4.5 to 6.5 inches where listed, and 670-16 covering about 4.5 to 5.0 inches where listed.

Wheel diameter is the first thing to confirm before anything else, because a 15-inch tire and a 16-inch tire are not interchangeable. Once the wheel diameter is settled, the next decision is whether your Sapphire is being kept in a more original-style bias-ply presentation or driven on radial tires for more contemporary road feel. Checking the actual wheel on the car is especially important on long-owned British cars, since replacement wheels may have been fitted at some point in their lives.

A 640-15 size on a 1957 Armstrong-Siddeley is a classic numeric bias-ply code. The 6.40 refers to the tire’s nominal section width in inches, and the 15 refers to the wheel diameter in inches. On the Sapphire, 640-15 is one of the 15-inch options and sits alongside the radial 185R15 as the traditional-construction alternative. Available versions include wide whitewall and narrow whitewall styles from BFGoodrich and Firestone.

That matters because 640-15 is not just a measurement; it also signals the tire’s period construction and overall character. Owners restoring a mid-1950s British luxury car for authentic stance and appearance often gravitate toward the numeric bias-ply size, especially when whitewall presentation is part of the look. Before choosing one, confirm that your wheel width falls within the listed range for the exact product you want, since different 640-15 offerings do not all share the same approved rim-width window.

A 185R15 or 185R16 size on a 1957 Armstrong-Siddeley is a Euro-metric radial code. The 185 is the nominal section width in millimeters, the R indicates radial construction, and the final number is the wheel diameter in inches. In classic European sizing like this, the absence of a written aspect ratio generally implies an 80-series profile. On the Sapphire, 185R15 fits 15-inch wheels and 185R16 fits 16-inch wheels.

The practical takeaway is that these sizes represent the radial side of the Sapphire’s fitment choices, not just a different way of writing dimensions. Radials in these sizes are offered by brands such as Michelin, Avon, Vredestein, and Coker Classic depending on diameter, with sidewall treatments ranging from blackwall to redline and narrow whitewall on certain 15-inch products. It is still worth checking the exact sidewall marking, because speed ratings and tube designations can differ between individual tires within the same nominal size.

The 640-15 and 185R15 both fit 15-inch wheels on a 1957 Armstrong-Siddeley Sapphire, but they represent two different construction philosophies. The 640-15 is a bias-ply size with traditional mid-century proportions and available whitewall styling, while the 185R15 is a radial metric size offered in blackwall, redline, and narrow whitewall forms. Within 185R15, speed ratings also vary by product, reaching H or V depending on the tire.

If your priority is original-era look and feel, the bias-ply 640-15 is the more authentic direction for a 1957 luxury saloon. If your priority is a more modern radial driving character while staying on a 15-inch wheel, the 185R15 is the more natural choice. Neither decision should be made by size code alone, though, because the wheel’s actual width and the sidewall style you want can narrow the field further within the same diameter.

1957 Armstrong-Siddeley tires are available in several sidewall presentations depending on size. The 185R15 radial range includes blackwall, redline, and narrow whitewall options, while 640-15 bias-ply tires include wide whitewall and narrow whitewall versions. The 185R16 radial and 670-16 bias-ply selections are blackwall offerings in the currently listed products. That gives Sapphire owners a meaningful visual choice in addition to the construction choice.

For a 1957 British luxury car, blackwall is usually the safest visual baseline unless you are deliberately pursuing a market-specific or personal-period look. Whitewall width can noticeably change the character of the car, and a redline creates a more specialized appearance than many owners expect on a formal saloon. Choosing sidewall style is partly a restoration question and partly an aesthetic one, so it helps to decide whether you are matching an existing presentation or refining the car’s finished look before selecting the tire itself.

Several brands cover 1957 Armstrong-Siddeley fitments. In 185R15, the available names are Coker Classic and Michelin; in 640-15, BFGoodrich and Firestone; in 185R16, Michelin, Avon, and Vredestein; and in 670-16, Firestone and Avon. Those brands span both radial and bias-ply construction and include sidewall treatments from blackwall to whitewall and redline depending on the size.

Brand choice on a Sapphire is often tied to the kind of finished result you want rather than simple compatibility. Some buyers want a European-flavored radial offering in the 16-inch sizes, while others want a classic American bias-ply presentation in 15-inch form with a visible whitewall. The easiest way to narrow the list is to settle the wheel diameter first, then decide whether authenticity, sidewall appearance, or radial road use matters most in the way you use the car.

Rim width requirements for 1957 Armstrong-Siddeley tires depend on the size and, in some cases, the exact product. For 185R15, listed fitments run from 4.5 to 6.5 inches depending on brand and version. For 640-15, the published ranges run from 4.0 to 5.0 inches depending on the tire. For 185R16, listed products cover 4.5 to 6.5 inches where rim width is specified, and 670-16 products with published widths cover 4.5 to 5.0 inches.

That means wheel diameter alone is not enough to make a sound choice on a Sapphire. A tire may match the diameter of your wheel but still fall outside the preferred width range for the exact casing design you select. Measuring the wheel already on the car or confirming its specification before purchase helps avoid avoidable issues with tire profile, appearance, and mounting suitability, especially when comparing a narrow bias-ply against a wider-approved radial in the same general diameter class.

Inner-tube requirements on 1957 Armstrong-Siddeley tires depend on the exact size and product. The 185R15 products shown are tubeless. In 185R16, one Michelin X Radial is marked TT, meaning tube type, while the Avon and Vredestein listings do not carry the same marking, so tube status varies by product within that size. The 640-15 and 670-16 bias-ply listings do not all carry a tube designation in the sidewall code shown here, so the individual tire marking and the wheel itself should guide the final setup.

That distinction matters because original-style wheels and modern reproduction tires do not always line up the same way in tube practice. A wheel condition issue, riveted wheel design, or a tube-type sidewall marking can change what the installation should be even when two tires share the same nominal size. The safest approach is to inspect the wheel, confirm the sidewall designation on the exact tire, and treat tube use as a setup question for the specific combination rather than a blanket rule for every Sapphire.

A 1957 Armstrong-Siddeley should be stored in a cool, dry, dark space with the tires kept away from direct sunlight, electric motors, battery chargers, furnaces, and other ozone-producing equipment. Tire pressures should be kept at a sensible maintenance level, and the car should either be moved periodically or supported in a way that reduces long static loading. Bias-ply tires are especially prone to temporary flat-spotting after long periods of inactivity, while any older-style sidewall can suffer if it sits near heat and ozone sources.

Collector-car storage is really about preserving the whole assembly, not just the tread. A Sapphire that sits for months at a time will benefit from occasional rolling, clean dry floors, and routine visual checks for cracking before it returns to service. If the car wears whitewalls or redlines, cleaning products should be chosen carefully so the sidewall finish stays presentable. Good storage habits do more to preserve expensive reproduction tires than low annual mileage ever will.

Tires on a 1957 Armstrong-Siddeley are usually judged by age and condition more than by miles. A prudent collector-car rule is to begin evaluating tires closely once they reach about five to seven years from their date code, and to give serious replacement consideration as they approach ten years regardless of tread depth. That applies to both radial and bias-ply construction, because rubber aging, internal deterioration, and long periods of inactivity often matter more than visible wear on a lightly used Sapphire.

The key is not to let a nice-looking old tire create false confidence. A luxury saloon that sees occasional touring, long idle periods, and infrequent maintenance can still be riding on rubber that has aged out even if the tread looks respectable. Checking the DOT date code where present, watching for sidewall cracking, and considering the age of the spare along with the road tires will give you a more realistic picture of whether the car is ready for continued use.

Tires on a 1957 Armstrong-Siddeley should be inspected before every drive, and more thoroughly before any extended outing. Look for sidewall cracking, tread separation, cuts, bulges, uneven wear, and any sign that the tire is losing pressure between uses. On tube-type or potentially tube-equipped combinations, the valve stems and tube condition deserve extra attention, especially if the car has sat for a long period or the tires were mounted years ago.

Routine checks matter more on a collector car than they do on a regularly driven modern vehicle, because problems can develop while the car is simply sitting. A Sapphire may spend weeks or months parked, and that makes pressure loss, casing aging, and wheel-seat corrosion easier to miss until the next drive. A short walk-around and pressure check before departure is simple insurance, and it is especially worthwhile before motorway travel or an event that keeps the car farther from home.

A 1957 Armstrong-Siddeley Sapphire would have been associated first and foremost with period bias-ply practice, since radial adoption was still uneven across markets and manufacturers in the 1950s. On today’s replacement market, the Sapphire is served by both bias-ply sizes, 640-15 and 670-16, as well as radial alternatives in 185R15 and 185R16. That means a restorer can stay close to period construction with the numeric bias-ply sizes or choose a radial while keeping the proper wheel diameter.

For an originality-minded restoration, construction type, sidewall treatment, and wheel diameter all matter more than simply finding a tire that fits. A show car may need a specific look that matches period photos, club guidance, or a surviving original car rather than a modern interpretation. Marque clubs and Armstrong-Siddeley specialists remain the best source for market-specific confirmation, especially if your Sapphire has an unusual history, replacement wheels, or export-market details that affect how authentic the final presentation should be.

Correct tire fitment does matter when showing a 1957 Armstrong-Siddeley, especially in events where authenticity is part of the judging. Judges and knowledgeable enthusiasts often notice whether the car wears a period-appropriate size, the expected construction type for the era, and a sidewall style that suits the vehicle’s class and market character. A radial with a modern-looking sidewall on an originality-focused car can attract the same attention as an obviously incorrect whitewall width or wheel diameter.

That does not mean every Sapphire has to wear bias-ply tires, but it does mean you should choose deliberately. Touring-oriented owners may accept a less original construction in exchange for driving preference, while concours-minded owners usually narrow the field toward a more era-appropriate size and appearance. Event standards vary, so if the car is being prepared for judged competition, it is wise to compare your intended tire against club expectations and period imagery before finalizing the setup.

Within the 185R15 radial choices for a 1957 Armstrong-Siddeley, the Michelin XVS and Coker Classic offerings differ in sidewall presentation, speed marking, and published wheel-width coverage. Michelin XVS appears in blackwall and narrow whitewall forms, with H-rated and V-rated versions, while the Coker Classic entry is a redline radial with a listed maximum load of 1355 pounds at 35 psi. The Michelin 185HR15 narrow whitewall is listed for 4.5 to 6-inch rims, while other 185R15 radial options extend to 5.0 to 6.5 inches.

That makes the choice as much about the finished look as the basic size. A buyer wanting a more understated European-style appearance may lean toward the Michelin blackwall or narrow whitewall, while a redline creates a more stylized visual statement. The published speed ratings are also worth noting if you are comparing products closely, but the actual road decision should still account for the Sapphire’s age, condition, and intended use rather than focusing on the tire rating in isolation.

1957 Armstrong-Siddeley tires can be suitable for highway use when they are correctly sized, properly mounted, in sound condition, and operated within the speed capability marked on the tire. Among the listed products, 185R16 includes S-rated versions at 112 mph and V-rated versions at 149 mph, 185R15 includes H-rated versions at 130 mph and V-rated versions at 149 mph, and the Avon 670H16 carries an H rating at 130 mph. A standard 670-16 bias-ply listing without a visible speed symbol should be treated according to the manufacturer’s own guidance for that tire.

On a 1950s Armstrong-Siddeley, the tire’s speed rating is only one part of the equation. Brakes, suspension condition, steering, wheel integrity, and the simple realities of an older saloon often matter more than the published ceiling on the sidewall during ordinary highway use. The best safety practice is to match the tire to the car’s real-world use, keep pressures correct, and avoid assuming that a high speed letter turns a mid-century luxury car into a modern high-speed machine.

Inflation pressure for a 1957 Armstrong-Siddeley should follow the vehicle manufacturer’s recommendation for the original fitment and the tire maker’s limits for the exact product you choose. Among the listed reproduction tires, 640-15 appears with load-and-pressure figures such as 1190 pounds at 32 psi and 970 pounds at 32 psi depending on the product, 670-16 appears at 1130 pounds at 30 psi on one version, 185R15 is listed at 1355 pounds at 35 psi on one version, and one 185R16 carries 1,433 pounds at 51 psi.

Those numbers are maximum load-and-pressure references for the tire itself, not a blanket instruction to run every Sapphire at the same inflation. A reproduction radial and a classic bias-ply can have very different casing behavior even when they fit the same wheel diameter. The sensible approach is to begin with the car maker’s intended operating pressure where applicable, then confirm that the chosen tire’s own rated limits and usage guidance are being respected rather than transferring a pressure figure from one size or construction to another.

Before taking a 1957 Armstrong-Siddeley on a longer drive, inspect every tire for cracking, cuts, bulges, irregular wear, and proper inflation, and make sure the spare is serviceable as well. Check that the valve stems are sound, especially if the car uses or may use tube-type assemblies, and look for any sign of bead leakage or wheel-seat corrosion on long-stored rims. On a car of this age, the tire inspection should be part of a broader pre-drive review rather than a separate task.

A Sapphire intended for touring should also have its brakes, steering, cooling system, wheel fasteners, and basic fluid levels checked before departure. Tires are the most visible part of the car’s readiness, but they are only one link in the chain on a late-1950s British saloon. Taking a few extra minutes to inspect the whole chassis and carrying forward-looking awareness of the car’s age will do more for peace of mind than simply seeing that the tread still looks deep.