The 1956 Armstrong-Siddeley Sapphire came from a period when British luxury and sporting saloon design often balanced formal styling with surprisingly capable road manners. For owners today, that character makes tire choice more than a maintenance detail, because the car’s stance, steering feel, and visual presentation are closely tied to the correct fitment. The 1956 Armstrong-Siddeley Sapphire uses different tire sizes depending on whether it is a Sapphire 234 or Sapphire 236, with both bias-ply and radial fitments appearing across 15-inch and 16-inch applications. That opens the door to choices in construction, sidewall style, and period-style presentation. The right selection starts with confirming the exact sub-model and wheel diameter before comparing brands or considering a radial alternative.
Which Tire Size Is Right for The 1956 Armstrong-Siddeley Sapphire
The 1956 Armstrong-Siddeley Sapphire uses four primary tire sizes, and the correct one depends first on the exact sub-model and wheel diameter. The Sapphire 234 uses 15-inch fitments, while the Sapphire 236 uses 16-inch fitments, with each sub-model appearing in both a bias-ply and a radial size. Before choosing a tire, confirm whether the car is a 234 or 236 and verify the wheel diameter actually on the vehicle.
185R15 is a Euro-metric radial size in which 185 indicates nominal section width in millimeters, the R identifies radial construction, and 15 is the wheel diameter in inches. On the 1956 Armstrong-Siddeley Sapphire, this size belongs to the 15-inch Sapphire 234 fitment and gives buyers a modern radial-format choice within the proper wheel diameter. Available options include blackwall, narrow whitewall, and redline presentations from brands such as Michelin, Avon, Coker Classic, and Universal Vintage Tire. This size is the one to evaluate if the car uses 15-inch wheels and the goal is radial construction with period-minded styling choices.
640-15 is a numeric bias-ply size, with the 640 code representing an approximate 6.40-inch nominal section width and the 15 indicating a 15-inch rim. For the 1956 Armstrong-Siddeley Sapphire, this is the bias-ply fitment tied to the 15-inch Sapphire 234 setup and is the traditional-style choice for owners who want to stay with vintage construction. Product choices include blackwall, narrow whitewall, and wide whitewall versions from BFGoodrich, Firestone, Avon, and Excelsior across several bias-ply series. This size deserves close attention when appearance, wheel compatibility, and a restoration-oriented presentation matter as much as simple diameter match.
185R16 is a Euro-metric radial size that uses a 185-millimeter nominal section width and a 16-inch rim diameter, with the unstated profile conventionally associated with an 80-series-style radial format. On the 1956 Armstrong-Siddeley Sapphire, this radial size belongs to the Sapphire 236 and keeps the fitment within the correct 16-inch wheel family. Blackwall options are available from Michelin, Avon, and Vredestein in classic-style radial series. This is the size to compare when a Sapphire 236 is already running 16-inch wheels and the owner wants radial construction without moving outside the established fitment range.
670-16 is a numeric bias-ply size, where 670 refers to an approximate 6.70-inch nominal section width and 16 identifies the wheel diameter. For the 1956 Armstrong-Siddeley Sapphire, this size is the 16-inch bias-ply fitment used with the Sapphire 236 and suits buyers who want a traditional construction on that wheel diameter. Available choices are blackwall bias-ply tires from Firestone and Avon in distinct vintage series. This size should be chosen only after confirming the car is a 236 or otherwise fitted with the proper 16-inch wheel setup, since matching rim diameter is critical here.
Sub-model fitment matters on the 1956 Armstrong-Siddeley Sapphire because the Sapphire 234 and Sapphire 236 do not share the same wheel diameter or tire sizes. Identifying the exact sub-model is the first step before comparing bias-ply versus radial construction or narrowing the choice by brand and sidewall style.
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1956 Armstrong-Siddeley Sapphire 234
The 1956 Armstrong-Siddeley Sapphire 234 uses 15-inch fitments, with a choice between 640-15 bias-ply and 185R15 radial sizing. That makes the tire decision less about diameter changes and more about whether the car should retain a traditional bias-ply presentation or move to a radial in the same wheel family.
The 1956 Armstrong-Siddeley Sapphire 236 uses 16-inch fitments, centered on 670-16 bias-ply and 185R16 radial sizing. Tire selection here starts with confirming the 16-inch wheel setup, then deciding whether the car’s intended use favors a period-style bias-ply look or a classic radial alternative.
Bias-Ply to Radial Tire Conversion for the 1956 Armstrong-Siddeley Sapphire
The original 640-15 tire size has three radial-equivalent options. Those alternatives are 175R15 as an 80-series metric radial, P175/75R15 as a 75-series P-metric radial, and P185/70R15 as a 70-series P-metric radial. Each option keeps the conversation within the 15-inch wheel category, but they differ in sizing convention and profile family rather than simply being the same tire in another construction. A recommended rim-width range of 5 to 6 inches applies to these equivalents, so wheel width, overall dimensions, and vehicle clearance should be checked before converting.
Modern Radial Equivalents
175R15
Equivalent 80-series Metric Radial (640-15)
P175/75R15
Equivalent P-metric 75-series Radial (640-15)
P185/70R15
Equivalent P-metric 70-series Radial (640-15)
Important Considerations When Replacing Bias Ply With Radial
Compare overall diameter and section width carefully to ensure proper fit.
Verify recommended rim range (5-6 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.
Best 1956 Armstrong-Siddeley Sapphire Tires for Sale
Available 1956 Armstrong-Siddeley Sapphire tires span both bias-ply and radial construction across 15-inch and 16-inch sizes. Buyers can compare brands including Michelin, Avon, Firestone, BFGoodrich, Vredestein, Coker Classic, Universal Vintage Tire, and Excelsior, along with blackwall, whitewall, and redline sidewall treatments where offered.
Owners of a 1956 Armstrong-Siddeley Sapphire usually need to sort out sub-model fitment first, then compare 15-inch versus 16-inch sizing, bias-ply versus radial construction, and the appearance choices available within each correct tire size.
Tire Size & Fitment
What tire size fits a 1956 Armstrong-Siddeley Sapphire?
The 1956 Armstrong-Siddeley Sapphire does not use one universal tire size across all versions. Sapphire 234 models use 640-15 in bias-ply form or 185R15 in radial form, while Sapphire 236 models use 670-16 in bias-ply form or 185R16 in radial form.
That means the first step is identifying whether the car is a 234 or 236 and then confirming the wheel diameter actually installed on the vehicle. Many collector cars have had wheels or tires changed over time, so the safest path is to match the sub-model, construction preference, and wheel size before comparing brands or sidewall styles.
What size rim does a 1956 Armstrong-Siddeley Sapphire use?
A 1956 Armstrong-Siddeley Sapphire uses either a 15-inch or 16-inch rim, depending on the sub-model. The Sapphire 234 uses 15-inch fitments with 640-15 bias-ply or 185R15 radial tires, and the Sapphire 236 uses 16-inch fitments with 670-16 bias-ply or 185R16 radial tires.
Rim diameter should be confirmed before anything else, because a 15-inch tire and a 16-inch tire are not interchangeable even when the car looks similar externally. Once diameter is verified, compare wheel width, the chosen tire construction, and clearance around steering and suspension components so the new tire choice stays aligned with the car’s actual setup.
Do all 1956 Armstrong-Siddeley Sapphire sub-models use the same tire size?
No. The 1956 Armstrong-Siddeley Sapphire 234 and 236 use different tire-size families. The 234 is tied to 15-inch sizes, using either 640-15 bias-ply or 185R15 radial, while the 236 is tied to 16-inch sizes, using either 670-16 bias-ply or 185R16 radial.
That difference matters because the tire decision starts with the sub-model, not just the make and model name. A buyer who skips that step can end up comparing the right-looking tire in the wrong diameter. Checking the model designation on the car and measuring the wheel diameter is especially important when the vehicle has been restored, modified, or stored for long periods.
Bias-Ply & Radial Options
Is 640-15 a bias-ply or radial tire for the 1956 Armstrong-Siddeley Sapphire?
640-15 is a bias-ply tire size on the 1956 Armstrong-Siddeley Sapphire, specifically within the Sapphire 234’s 15-inch fitment range. It uses the older numeric sizing system rather than modern metric radial sizing, and it appears in traditional bias-ply product lines with blackwall, narrow whitewall, and wide whitewall choices.
That makes 640-15 the more traditional construction path for a 15-inch Sapphire 234. Owners considering a change to radial construction should not assume that any 15-inch radial is automatically comparable, because wheel width, overall dimensions, and clearance still need to be checked even when staying within the same rim diameter.
What radial tire sizes are equivalent to 640-15?
Radial equivalents for 640-15 include 175R15, P175/75R15, and P185/70R15. Those represent three different radial approaches to the same 15-inch fitment conversation: an 80-series metric radial, a 75-series P-metric radial, and a 70-series P-metric radial.
A recommended rim-width range of 5 to 6 inches applies to those equivalent sizes, which is useful when evaluating an actual wheel on the car. Even with a recognized equivalent, the final choice should still be checked against wheel width, vehicle clearance, and the owner’s preference for traditional appearance versus a more modern radial-style presentation.
What should I check before converting my 1956 Armstrong-Siddeley Sapphire from bias-ply to radial tires?
Start by confirming the exact sub-model, because the Sapphire 234 uses 15-inch fitments and the Sapphire 236 uses 16-inch fitments. Then verify the wheel diameter and width, since a radial conversion only makes sense when the chosen radial size matches the wheel and remains appropriate for the car’s available clearance.
The next step is comparing the car’s actual setup, including steering travel, fender clearance, suspension condition, and any changes made during restoration or long-term ownership. Construction choice also affects the car’s visual character, so owners often balance road-use goals with period-style appearance rather than treating radial conversion as a purely technical decision.
Choosing the Right Tire
What should I consider when choosing a tire for a 1956 Armstrong-Siddeley Sapphire?
The biggest decision is not brand first, but fitment first. A 1956 Armstrong-Siddeley Sapphire can use either 15-inch or 16-inch tires depending on whether it is a Sapphire 234 or 236, and each sub-model also presents a choice between traditional bias-ply sizing and radial sizing within that wheel diameter.
Once the sub-model and wheel diameter are confirmed, the choice narrows to construction, sidewall style, tire series, and wheel-width compatibility. A restoration-oriented owner may favor the visual character of bias-ply or whitewall options, while a road-use-focused owner may prefer a radial in the correct size family without stepping outside the car’s established fitment.
What sidewall styles are available for 1956 Armstrong-Siddeley Sapphire tires?
Sidewall choices for the 1956 Armstrong-Siddeley Sapphire include blackwall, narrow whitewall, wide whitewall, and redline, depending on the tire size selected. The broadest variety appears in the 15-inch fitments, where both radial and bias-ply products offer different visual treatments across several brands and series.
That makes sidewall style an important part of the final decision after the correct size and construction are settled. A blackwall usually gives the most restrained look, while whitewall and redline options change the car’s visual character more noticeably. Appearance should be weighed alongside wheel compatibility and intended use rather than treated as a separate decision.
What brands offer tires for the 1956 Armstrong-Siddeley Sapphire?
Brands available for the 1956 Armstrong-Siddeley Sapphire include Michelin, Avon, Firestone, BFGoodrich, Vredestein, Coker Classic, Universal Vintage Tire, and Excelsior. The exact brand options depend on whether the car uses a 15-inch or 16-inch fitment and whether the goal is a bias-ply tire or a radial tire.
Brand comparison makes the most sense after the correct size is confirmed, because the assortment changes from one fitment family to another. Buyers can then compare tire series, sidewall styles, rim-width ranges where stated, and load figures where given, rather than trying to choose a brand before narrowing the fitment to the car’s actual setup.
Restoration & Appearance
Which tire should I choose for a period-style 1956 Armstrong-Siddeley Sapphire?
A period-style 1956 Armstrong-Siddeley Sapphire usually starts with the correct size family for the sub-model, then leans toward bias-ply construction if the goal is a more traditional visual presentation. That means 640-15 for a Sapphire 234 or 670-16 for a Sapphire 236 are the natural starting points when appearance and era-appropriate character matter most.
The final choice still depends on how closely the owner wants to follow the car’s restoration direction. Whitewall or blackwall treatment can change the overall look significantly, and exact originality questions are best checked against marque references or vehicle-specific historical material. Tire selection should support the restoration, not compete with it.
How does tire construction affect the appearance of a restored 1956 Armstrong-Siddeley Sapphire?
Tire construction changes more than ride characteristics on a restored 1956 Armstrong-Siddeley Sapphire; it also changes the car’s visual stance and overall period impression. Bias-ply tires in 640-15 or 670-16 give the car a more traditional presentation, while radial sizes such as 185R15 and 185R16 tend to reflect a later replacement style.
That difference is especially noticeable on a formal mid-1950s saloon, where sidewall shape and tread presentation contribute to the finished look. Owners who prioritize show-field appearance often begin with construction and sidewall style together, then compare brand and series details. Those planning regular road use may still choose a radial while keeping the fitment visually sympathetic.
Fitment, Maintenance & Road Use
Can modifications affect tire fitment on a 1956 Armstrong-Siddeley Sapphire?
Yes. Modifications can change tire fitment on a 1956 Armstrong-Siddeley Sapphire even when the tire size appears correct on paper. Aftermarket wheels, suspension alterations, ride-height changes, brake conversions, or bodywork repairs can all affect whether a 15-inch or 16-inch tire has adequate space during steering and suspension movement.
That is why the wheel actually on the car matters as much as the catalog size. Owners should verify wheel diameter, wheel width, and visible clearance at the fender, inner wheelhouse, and steering components before changing construction or profile. A collector car that has changed hands several times may no longer reflect its original wheel and tire setup.
What should I inspect before driving a 1956 Armstrong-Siddeley Sapphire on new tires?
Before road use, inspect the wheel condition, valve stems, tire pressure, and the basic clearance around suspension and steering components. It also makes sense to check that the chosen tire size matches the sub-model and rim diameter, because the Sapphire 234 and 236 use different fitment families.
A road test should begin cautiously, with attention to rubbing, steering feel, vibration, and any sign of uneven contact. On a long-stored car, the tire installation is only part of the preparation; wheel bearings, alignment, brake condition, and suspension wear can all influence how the car behaves once the new tires are mounted and inflated.
How should tires on a collector 1956 Armstrong-Siddeley Sapphire be maintained?
Collector-car tires on a 1956 Armstrong-Siddeley Sapphire should be checked regularly for pressure loss, tread wear, sidewall cracking, bulges, cuts, and signs of aging. Even when the car sees limited mileage, tires still deteriorate with time, storage conditions, and long periods of sitting in one position.
Proper storage helps preserve both appearance and service life, especially when the car is kept away from prolonged sunlight, heat, moisture, and ozone sources. Periodic movement, clean wheels, and routine visual inspection are worthwhile for any low-use saloon. Owners should also recheck pressures before driving, since collector vehicles often sit long enough for air loss to go unnoticed.
