1966 Amphicar Tires

The 1966 Amphicar uses two primary tire sizes: 640-13 and 650-13. Both are bias-ply sizes for 13-inch rims, and the Amphicar Base is associated with both, so the vehicle does not point to just one universal size without checking the setup already on the car.

That makes wheel and existing tire confirmation especially important before ordering replacements. A collector Amphicar may have stayed with its long-time wheel setup or may have been changed at some point, so matching the mounted size, the wheel width, and the available clearance is the safest way to decide between the two primary fitments.

The primary tire sizes for a 1966 Amphicar are built around a 13-inch rim diameter. Both 640-13 and 650-13 share that same rim diameter, so the main fitment question is not wheel diameter change, but which of the two bias-ply sizes matches the vehicle's current wheel and tire arrangement.

Rim diameter alone is only part of the picture on a vintage vehicle. It still helps to verify actual wheel width before choosing a tire, since the available 640-13 and 650-13 products carry different rim-width recommendations and that can affect both how the tire sits on the wheel and how it clears the body and suspension.

Both 640-13 and 650-13 are vintage numeric bias-ply sizes. In that format, the first number refers to the tire's nominal section width in inches with the decimal omitted, so 640 means about 6.40 inches and 650 means about 6.50 inches, while 13 identifies the rim diameter.

That older sizing system is different from modern metric radial sizing, so it helps to read the code before comparing tires. On a 1966 Amphicar, understanding the size format keeps the focus on the correct vintage fitment first, then on details such as whitewall style, brand, wheel-width compatibility, or a carefully checked radial equivalent.

Both 640-13 and 650-13 are primary bias-ply tire sizes for the 1966 Amphicar. They use vintage numeric sizing rather than modern metric radial sizing, which is why the original-style fitment conversation starts with bias-ply construction on a 13-inch rim.

That matters because a buyer may be deciding between retaining the vehicle's traditional construction or considering a radial alternative for road use. Keeping the primary bias-ply format supports a period-style presentation, while any move to radial construction should include a check of wheel width, overall dimensions, and clearance rather than assuming automatic interchangeability.

Radial equivalents for both 640-13 and 650-13 include 175R13, P175/75R13, P185/70R13, and 650R13. That gives the Amphicar owner an 80-series metric radial, a 75-series P-metric radial, a 70-series P-metric radial, and a bias-look radial option tied to the original bias-ply sizes.

Those equivalents differ by sizing convention and profile family, not just by construction type. The 650R13 option is especially relevant when a more traditional visual presentation matters, while the other three move into modern radial sizing language. A 4-6 inch rim-width range is associated with these equivalents, and wheel compatibility and clearance should be confirmed before changing sizes.

A 650R13 bias-look radial is available as an equivalent for both 640-13 and 650-13 on the 1966 Amphicar. That makes it a notable option for owners who want radial construction while trying to preserve more of the traditional visual character associated with vintage tire sizing.

It should still be treated as an equivalent, not as an automatic replacement. Before making that change, check the actual wheel width against the associated 4-6 inch range and confirm that the mounted tire will work with the Amphicar's existing wheel, body, and steering clearances. That extra step matters on specialized collector vehicles with older or changed wheel setups.

Start by confirming whether the Amphicar is using 640-13 or 650-13, since both sizes are associated with this model year and both are bias-ply fitments on 13-inch rims. Once the size is verified, compare construction, wheel-width suitability, sidewall appearance, brand, and the tire series available in that size.

The strongest buying differences here are visual presentation and fitment details rather than broad category changes. Some owners will want the traditional look of a wide whitewall, while others may prefer a narrower whitewall treatment. Matching the tire to the vehicle's actual wheel setup and intended use keeps the decision grounded in fitment first, appearance second.

The available sidewall styles for the 1966 Amphicar are wide whitewall and narrow whitewall. In 640-13, the current product choice is a wide whitewall, while 650-13 opens up both wide and narrow whitewall options across different brand and series combinations.

That makes sidewall styling one of the key visual decisions once the correct size is established. A wide whitewall usually gives the Amphicar a stronger period-style presentation, while a narrow whitewall can create a slightly more restrained look. Since sidewall style varies by size and product line, it helps to settle the fitment question before comparing appearance.

BFGoodrich, Coker Classic, and US Royal all offer applicable tires for the 1966 Amphicar. BFGoodrich appears in 640-13 through the Silvertown Classic Bias Ply line, while 650-13 choices include Coker Classic Bias Ply and US Royal Classic Bias Ply offerings.

Brand comparison should stay tied to the exact size you need, because the assortment is not identical across both primary fitments. After confirming whether the Amphicar uses 640-13 or 650-13, compare each brand's available sidewall treatment, tire series, and wheel-width specification. That approach is more useful than choosing a brand first and trying to force the size decision afterward.

A period-style approach starts with the Amphicar's primary bias-ply sizing, which means choosing between 640-13 and 650-13 after confirming the wheel and tire setup already on the vehicle. Staying with a bias-ply construction preserves the vintage sizing language and the traditional sidewall profile associated with this unusual mid-1960s vehicle.

Appearance then comes down to details such as whitewall width and tire series. Wide whitewall and narrow whitewall choices create noticeably different visual impressions, especially on a compact collector vehicle like the Amphicar. If exact originality matters beyond general period style, it is worth checking marque references or restoration records before committing to one sidewall treatment.

Construction changes the look of a restored 1966 Amphicar as much as the handling feel. The original-style fitment is bias-ply, so keeping a 640-13 or 650-13 bias-ply tire maintains the vintage sizing format and a more traditional visual presence than a modern metric radial typically provides.

A radial equivalent can still be worth considering, especially if road use matters, but it shifts the presentation away from the original-style numeric bias-ply format. A bias-look radial such as 650R13 may help bridge that gap visually. The right answer depends on whether the project leans more toward historical appearance, regular driving, or a compromise between the two.

Yes, modifications can affect tire fitment on a 1966 Amphicar even when the tire size itself seems correct. Changes such as aftermarket wheels, altered wheel width, suspension work, or body adjustments can influence how a 640-13, 650-13, or radial equivalent sits in the wheel opening and clears surrounding components.

That is why a collector vehicle should be checked as it actually exists today, not only by the original-style size it was meant to use. Look at wheel diameter and width first, then inspect steering and fender clearance with the suspension loaded. A small size difference or wheel change can matter more on a specialty vehicle than the size code alone suggests.

Before driving a 1966 Amphicar on new tires, inspect the wheels for correct diameter and condition, confirm the tires are mounted in the correct size, and check inflation carefully. It is also wise to look over the steering and suspension for looseness, since tire behavior on a vintage vehicle depends heavily on the condition of the hardware underneath it.

A short local drive is a good way to verify that nothing rubs, wanders, or shows uneven contact. After that first outing, recheck pressure and look for any signs of sidewall scuffing or contact marks. On a collector Amphicar that may sit for long periods, regular inspection after installation is just as important as the initial fitment decision.

Collector-car tires such as 640-13 and 650-13 should be maintained with regular pressure checks, visual inspections, and careful storage habits. Even if a 1966 Amphicar is driven only occasionally, the tires still need to be checked for cracking, cuts, bulges, tread wear, and slow air loss before road use.

Storage conditions matter because long idle periods can age a tire without adding mileage. Keeping the vehicle away from prolonged sunlight, heat, moisture, and ozone sources helps preserve the rubber, and moving the car periodically can help avoid flat-spotting. Any tire that shows age-related deterioration deserves professional evaluation before the Amphicar goes back on the road.