1958 Armstrong-Siddeley Tire Fitment Guide

1958 Armstrong-Siddeley vehicles in this range use two tire sizes, both for the Sapphire: 185R16 and 670-16. Both sizes mount on 16-inch rims, but they differ in construction. The 185R16 options are radial tires, while the 670-16 options are bias-ply tires. Approved rim-width ranges are listed at 4.50 to 6.00 inches or 5.0 to 6.5 inches on available 185R16 products, and 4.50 to 5.00 inches on listed 670-16 products.

That means the basic fitment question is straightforward at the year-and-make level: you are choosing between two constructions on the same rim diameter, not between different wheel diameters for different models. Before selecting a tire, compare your actual wheel width to the specific product you want to use. That step matters because a 16-inch rim alone does not confirm that every 16-inch tire is appropriate for your particular wheel.

On a 1958 Armstrong-Siddeley, 185R16 is a radial tire size. The 185 refers to a nominal section width of 185 millimeters, the R identifies radial construction, and the 16 is the rim diameter in inches. Because no aspect ratio is printed in the size itself, this type of Euro-metric radial is conventionally treated as an 80-series design.

That decoding helps explain why 185R16 feels like a later sizing convention than 670-16, even though both fit the same 16-inch wheel diameter. For a Sapphire owner, the practical takeaway is that 185R16 points you toward radial products from Michelin, Avon, and Vredestein. If you are comparing tires for appearance as well as use, the size code is often the quickest clue to whether you are looking at a modern-style radial or a more traditional period format.

On a 1958 Armstrong-Siddeley, 670-16 is a numeric bias-ply size. The 6.70 portion refers to the nominal section width in inches, and the 16 identifies the rim diameter in inches. Unlike a radial code, there is no R in the size because the available tires in this fitment are bias-ply constructions.

That makes 670-16 the more traditional-looking format for a late-1950s British luxury saloon such as the Sapphire. A buyer choosing this size is usually prioritizing original-style construction and presentation rather than simply matching wheel diameter. It is still important to verify the individual tire against the wheel, because the listed 670-16 products are aimed at narrower approved rim widths than some of the available 185R16 radial choices.

For a 1958 Armstrong-Siddeley Sapphire, the choice between 185R16 and 670-16 is mainly a choice between radial and bias-ply construction. The 185R16 options are radial blackwalls from Michelin, Avon, and Vredestein, while the 670-16 options are bias-ply blackwalls from Firestone and Avon. Both sizes fit 16-inch rims, so the decision is less about wheel diameter and more about the kind of driving feel and presentation you want.

A buyer restoring a Sapphire for period character will often gravitate toward the 670-16 bias-ply format because it matches the era more closely. A buyer who expects more regular touring or wants a radial offering with published S or V speed ratings may prefer 185R16. Either way, compare the specific tire's approved rim-width range to your wheels before finalizing the choice, because that detail can narrow the field even when the diameter is correct.

1958 Armstrong-Siddeley tire options in these sizes are available as blackwalls. The 185R16 radial choices from Michelin, Avon, and Vredestein are blackwall tires, and the 670-16 bias-ply choices from Firestone and Avon are also blackwalls. No alternate sidewall style appears in this fitment range.

That consistency simplifies the decision for a Sapphire owner who wants a restrained, formal appearance appropriate to an upper-market British saloon of the late 1950s. Since sidewall treatment is not the variable here, your choice comes down more to construction, brand preference, and wheel compatibility. For show-minded owners, a blackwall presentation is also the most natural place to start when keeping the car visually in period.

Four brands cover the available 1958 Armstrong-Siddeley fitments here. The 185R16 radial size is offered by Michelin, Avon, and Vredestein, while the 670-16 bias-ply size is offered by Firestone and Avon. Avon is the only brand represented in both size families, but it appears in different series for the radial and bias-ply applications.

That spread gives Sapphire owners room to choose within each construction type instead of being forced into a single-brand solution. If your goal is to stay with a bias-ply format, your path is narrower than it is in the radial size. If your goal is to compare radial options, 185R16 provides the broader brand field, and the next step is to sort by speed marking, tube marking, and wheel-width compatibility rather than brand name alone.

Rim-width requirements for 1958 Armstrong-Siddeley tires depend on the size and the specific product. Available 185R16 radial tires list approved rim widths of 4.50 to 6.00 inches on one product and 5.0 to 6.5 inches on another. Available 670-16 bias-ply tires list an approved rim-width range of 4.50 to 5.00 inches on a listed product. All of them share a 16-inch rim diameter.

That difference matters because a wheel that accepts one 16-inch tire may still fall outside the ideal width range for another. If your Sapphire still carries its original-style wheels, measure the actual inside bead-seat width before making a final selection. Doing that will help you avoid choosing a tire that technically matches diameter but is not approved for the wheel width you have.

Inner-tube requirements on 1958 Armstrong-Siddeley tires vary by product. One 185R16 radial option is explicitly marked TT, meaning tube type, while the other 185R16 products are not marked the same way in their size descriptions. The 670-16 bias-ply listings also do not all carry the same visible tube marking pattern in the size field, so tube status should be checked on the exact tire you intend to use.

A Sapphire owner should treat tube fitment as a product-by-product question rather than assuming every tire in a size family is identical. Wheel design also matters, especially on vintage applications where original rims may have been intended for tube-type service. Confirm the sidewall marking and wheel construction together before installation so the tire, tube choice, and wheel type all match.

The original-style 1958 Armstrong-Siddeley wheels can usually be considered for both listed sizes because both 185R16 and 670-16 mount on 16-inch rims. Diameter compatibility is the easy part here. Width compatibility is the part that needs confirmation, since listed 185R16 products can require a broader approved rim-width range than the narrower 670-16 bias-ply products.

That means a Sapphire owner should not assume that every original 16-inch wheel is equally suited to both constructions without measuring first. If your wheel falls within the approved range for the specific tire you want, the shared diameter works in your favor. If it does not, the safer path is to choose a tire that matches the actual wheel rather than trying to force the wheel to suit the tire.

A 1958 Armstrong-Siddeley should be stored in a cool, dry, dark space away from direct sunlight, electric motors, welders, furnaces, and other ozone-producing equipment. Keep the tires clean and properly inflated, and move the car periodically if it will sit for long stretches. Bias-ply tires such as 670-16 are generally more prone to taking a temporary flat spot during static storage than radial tires such as 185R16.

For a Sapphire that spends much of its time parked, thoughtful storage often matters more than mileage. If the car will be inactive for an extended period, some owners use stands or slightly increase movement intervals to reduce prolonged load in one spot. The goal is to preserve sidewall condition and casing shape so the tires remain pleasant and predictable when the car goes back on the road.

Tires on a 1958 Armstrong-Siddeley should be evaluated by age as much as by tread depth. Collector vehicles often accumulate very little mileage, so a tire can look usable while still aging out. A sensible rule is to inspect carefully once tires reach the five- to seven-year range and to treat around ten years from the date code as a point where replacement deserves serious consideration, even if wear appears light.

That approach is especially important on a Sapphire, where low annual use can hide the real effect of time, storage, and environmental exposure. If you do not know the age of the tires currently on the car, start by checking the date code and the overall condition of the sidewalls and tread area. Reproduction and specialty tires should be judged by the same age-based standard as any other road tire.

Tires on a 1958 Armstrong-Siddeley should be inspected before every drive and again before any longer outing. Look for sidewall cracking, tread separation, uneven wear, cuts, bulges, and pressure loss. If your chosen tire setup involves tube-type service, include the valve stems and any signs of tube-related leakage or heat history in the inspection routine as well.

A quick inspection is one of the easiest ways to prevent trouble on an older touring car such as the Sapphire. Vintage cars often spend long periods parked, and that pattern can reveal issues only when the car is finally driven. Building a habit of checking pressure, visual condition, and the spare before departure makes the tire part of your normal pre-drive routine instead of an afterthought.

A 1958 Armstrong-Siddeley Sapphire would have been associated with period bias-ply practice in its era, which makes the 670-16 format the closest match to original-style construction among the available choices here. The radial 185R16 options reflect a later construction approach, even though they fit the same 16-inch wheel diameter. No original-equipment brand should be assumed from the current replacement range alone.

For a restoration, that means 670-16 is the natural starting point if your goal is to stay visually and mechanically aligned with how a late-1950s luxury saloon would typically have left the period. If your car has market-specific history, export delivery differences, or prior wheel changes, a marque club or Armstrong-Siddeley specialist is the best place to confirm what was correct for that individual Sapphire.

Correct tire fitment matters on a 1958 Armstrong-Siddeley because judges and knowledgeable enthusiasts often notice size format, construction type, and sidewall presentation quickly. A blackwall appearance is consistent across the available options here, but a radial 185R16 and a bias-ply 670-16 still present differently in both specification and character. On an originality-focused Sapphire, modern radial construction can stand out even when the wheel diameter remains correct.

That does not mean every event uses the same judging standard. Some shows reward drivability and presentation broadly, while others look much more closely at whether the tire matches period practice. If you plan to show the car seriously, check the rules of the specific event and use marque-club guidance so the size, construction, and overall appearance line up with the standard you will actually be judged against.

For a 1958 Armstrong-Siddeley in 185R16, the Michelin X Radial and Vredestein Sprint Classic share blackwall styling, radial construction, and a 26-pound listed weight, but they differ in markings and fitment details. The Michelin is marked 185R16 92S TT, which adds a tube-type designation and an S speed rating of 112 mph. The Vredestein is marked 185VR16 93V, carries a V speed rating of 149 mph, lists a maximum load of 1,433 pounds at 51 psi, and shows an approved rim width of 5.0 to 6.5 inches.

Those differences matter if you are sorting through details rather than choosing by brand alone. The Michelin may appeal to an owner working around a tube-type setup, while the Vredestein gives you a different speed marking and a clearly stated broader wheel-width range on the larger side. On a Sapphire, either tire stays within the radial side of the fitment picture, so the comparison comes down to markings, wheel compatibility, and the exact setup you plan to run.

1958 Armstrong-Siddeley tires can be appropriate for highway driving when they are the correct size, properly fitted to the wheel, in sound condition, and used within their rated limits. The available 185R16 radial products include S- and V-rated examples, corresponding to 112 mph and 149 mph, while the available 670-16 range includes an H-rated bias-ply example at 130 mph. Those published ratings are well above normal U.S. highway speeds.

On a Sapphire, tire condition and overall vehicle condition often matter more in real use than the headline speed letter alone. A late-1950s luxury saloon brings its own braking, suspension, steering, and age-related considerations, so the tire should be treated as one part of the broader roadworthiness picture. If the car will be driven regularly, many owners prefer to compare the radial options closely, but any choice still needs to match the wheel and the car's intended use.

Inflation pressure for 1958 Armstrong-Siddeley tires should be matched to the specific tire and then checked against the vehicle's original recommendations. Within the available range, one 670-16 bias-ply tire lists a maximum load of 1130 pounds at 30 psi, and one 185R16 radial tire lists a maximum load of 1,433 pounds at 51 psi. Those figures are tire ratings, not universal running pressures for every product in the fitment.

Use the original owner's manual or factory service guidance for the Sapphire's operating pressure target, then make sure the tire you choose is being used within the manufacturer's limits. Do not transfer a pressure figure from 185R16 to 670-16, or from one brand to another, simply because the wheel diameter matches. Pressure choice should reflect the actual size, construction, tire specification, and how the car will be driven.

Before taking a 1958 Armstrong-Siddeley on a longer drive, inspect all four tires and the spare for cracking, cuts, bulges, irregular wear, and proper inflation. Check that the tires are seated correctly on the rims, and pay close attention to valve stems and any tube-type components if your chosen setup uses them. A long-stored collector car should also be checked for age-related hardening even when tread depth looks generous.

A Sapphire prepared for a proper road trip deserves more than a quick walk-around, because tire readiness is only one part of an older car's reliability. After the tire inspection, continue with the broader mechanical basics that matter on a 1950s touring car: brakes, steering, cooling, fluids, and lights. Starting with the tires is smart because they are the car's contact with the road, but the safest long drive comes from treating the whole vehicle as a system.