If a modern Corvette needs a new set of tires, it may be as simple as calling your local tire store and ordering the OE size. Your only big decisions consist of the tire brand, and a possible sizing increase. For vintage Corvettes, the decision can be a little more complicated, even if you're going back to a stock appearance. You have the choice of bias ply or radial, and then you have the very important choice of whitewall, redline, gold line, raised white letter, or blackwall. With all of these options, where should you begin?
The first thing to take into consideration is the style of your build. There are so many ways to get creative with a vintage Corvette and you can really change the personality of the car with a different set of tires and wheels. If you're going the modified route with your early Corvette, there are plenty of options for tire sizing, such as if you want to go bigger or stagger the front and rear sizes for an aggressive look.
The bias ply versus radial debate is always at the forefront when you're dealing with cars built prior to 1973. Authentic tires for a '53-'72 Corvette restoration would feature bias ply construction, but swapping to radial tires is a popular upgrade for improved ride quality and handling. There are pros and cons to both types of tire construction, but it's important to know the differences to help make your decision.
The term bias ply refers to the internal construction of the tire. In a bias ply tire, the cords (plies) run at a 45 degree angle from bead to bead. This diagonal pattern is crisscrossed with each layer of ply cord, and creates a very rigid structure. In the vintage car market, bias ply tires feature a narrow tread profile with a sharp shoulder that usually has a piecrust appearance. The narrow tread pattern and the fact that most bias ply tires mount to narrow wheels makes for a sidewall bulge that is easily identifiable and adds to the authentic appearance of most early Corvettes. Some of the early C3 cars (1968-1972) had bias ply tires, but they had a 70-series aspect ratio, which gave them a wider tread pattern and a shorter sidewall than the tall and skinny bias ply tires from year's prior.
Bias ply tires are strong, but the rigidity offers some interesting handling characteristics if you're accustomed to driving on radial tires. The rigid construction means that bias ply tires do not conform to the road surface as efficiently as a radial tire. This creates a “wandering” sensation as the tires tend to follow the ruts and breaks in the pavement. This wandering is not necessarily dangerous, but it definitely requires the driver to pay more attention, especially at highway speeds.
The major advantage to a bias ply tire that completely overrides the finicky handling is the authenticity. For instance, a '57 Corvette came from the factory with 6.70-15 tires, so the fact that you can get a brand-new set of 6.70-15 tires with appropriately sized whitewalls is a huge win for the restoration crowd. The same can be said for the popular 7.75-15 sizing that ran from 1965 to 1967 and the F70-15 sizing that ran from 1968 to 1972. Authentic brands, such as BFGoodrich and Firestone are available, and authentic sidewall Corvette-specific sidewall treatments are also on-the-shelf items at companies like Coker Tire.
The folks at Coker Tire gave us plenty of information about tires (and wheels) when we approached them about tire availability for classic Corvettes. One of the coolest details that we gleaned from the information we got from Coker Tire is that their bias ply tires are made from original molds. Of course, they refurbish the mold and update it if necessary, before it goes back into the production line, but the fact that these molds are the same ones that made the original Corvette tires is pretty cool. The level of authenticity goes way up when you consider that detail. All of the products from Coker Tire (even the radial tires) are built from day one to feature a custom sidewall treatment so the white, red, or gold rubber is added to the tire carcass in the early stages of the manufacturing process. Then, reveals in the mold provide a crisp breaking point between the black rubber and the special color.
Radial tires are a popular upgrade for vintage Corvettes, as the more modern construction offers great improvements, including ride quality, wet weather traction, and tread life. The advantages are created by the tire's construction, which consists of ply cords that run 90 degrees in relation to the bead. This radial orientation of the cords allow for a more flexible design, which conforms to the road surface, and allows the tires to skim across the ruts and breaks in the surface. This makes for a pleasant ride quality, even on rough roads, which would cause the wandering sensation with bias ply tires.
In most cases, a radial tire will have a wider footprint, even if it is the equivalent size to a bias ply tire. For instance, a 6.70-15 tire (OE size for 1953-1964 Corvettes) has the P-metric radial sizing equivalent to a 205/75R15 tire. However, the radial equivalent features a wider tread surface by more than one inch. This increased contact patch offers more traction and more stability, while the rounded shoulder provides additional traction in hard cornering situations. Radial tires also feature tread siping, which helps evacuate water from the tread surface, and thus, increases wet weather traction. The drawback to the wider footprint is the lack of an authentic shape and profile. However, you can get any of the sidewall treatments that were original for Corvettes in a modern radial equivalent. On top of that, Coker just introduced a new American Classic bias-look radial tire, available in 6.70R15 sizing. The new tire is available in wide whitewall and blackwall, and it's a very nice piece that keeps the authentic appearance, but provides the driving characteristics of a modern radial.
So, you've decided on a set of tires, and possibly a set of wheels for your classic Corvette. What's the next step to ensure you can get out and enjoy your car? The mounting and balancing process is crucial for any old car, so it's important that you pay close attention when your tire shop is doing the work. When we spoke to Coker Tire about this matter, it was mentioned that any customer who buys tire and wheels together gets free mounting and balancing. Coker's specialty is vintage style tires and wheels, so you can expect to see great results from taking advantage of its tire and wheel combo deals. However, if you choose to keep your original wheels, and have the tires mounted and balanced at the local tire shop, always request lug-centric balancing, as opposed to hub-centric balancing. The lug-centric attachment provides the most accurate balancing, as it doesn't rely on the center hole of the wheel, which isn't always perfectly true with the outside diameter of the wheel.
If the tires cannot be installed on the car immediately, always be sure to place a piece of cardboard between the tires (this applies only to whitewalls, white letter, redline, and gold line) as the black rubber can leave stains on the white, red, or gold rubber. If the tires came with plastic wrapping, keep the wrapping on the tires, until they are ready for installation. For whitewall and white letter tires, you can usually expect to see a blue coating on the white rubber, which protects it during transit. The blue coating washes off with soap and water, and the white rubber can be cleaned as often as you see fit. Coker Tire suggests a citrus-based cleaner, such as “Wide White,” as opposed to bleach-based cleaners, which are too harsh in most cases.
For cars that don't see many miles on the road, you'll likely develop flat spots on the tires if the car sits on a concrete floor for long periods of time. Bias ply and radial tires are susceptible to this condition, but flat spots in a radial tire are usually a bit more permanent because of the steel belting that rides beneath the tread surface. The only way to prevent flat spots is to lift the tires off the concrete by storing the car on jack stands, but our favorite preventative measure is to get out and drive it as often as possible! It's much better to replace your tires because of worn out tread instead of flat spots or dry rot. No matter what tire and wheel combination makes the cut for your classic Corvette, put them to use every chance you get!