When we picked up our Runner in March 2025, it had a nice set of BFGoodrich Silvertown radial tires wrapped around the factory wheels. The 235/70R15 tires had less than 1000 miles on them, but they were over thirty years old. Because of our desire for more factory-appearing tires and our concern with the age of the current radials, we contacted Coker Tires for a set of “bias-look radials” Firestone Wide Oval, FR70-15 tires.
Although Coker has a wide selection of bias-ply and belted bias-ply tires that would fit our Road Runner, we opted for a set that combines the vintage look with the advantages of modern radial construction. This choice offers the best of both worlds.
Above: Our Road Runner came with belted bias-ply tires in 1968. We wanted the look of a bias tire but the performance, reliability, and comfort of a radial. Coker Tires had what we needed: a bias-look radial tire with all the sidewall markings, tread pattern, and redline of the bias tires of yesteryear, but in a radial construction.
Tire designs can be broken into three construction designs that have been used on vehicles from the late 1800s to modern-day vehicles: bias-ply, belted bias-ply, and radials. Each has pros and cons, but our choice stands out for its unique blend of classic aesthetics and modern performance.
Bias-ply tires were the first pneumatic tires used on automobiles. The design was used through the mid-1970s. Its construction consisted of nylon or polyester plies laid diagonally from bead to bead, typically at 30–40° angles. Each layer crisscrossed over the previous one, with no steel belts. The sidewall and tread functioned as a unit.
Above: The bias-look radials are replicas of the Firestone Wide Oval tire of the late 1960s. The side markings are the correct design from that era. However, additional markings on the tires would not have been around in 1968 but are required for modern tires. For instance, our tires are FR70-15 94S M+S tires, which designates a 70-series radial with a 15-inch rim, a load capacity of 94, an S speed rating, and the tires are mud and snow traction. The original tire would have an F70-15 on the sidewall. Additionally, the DOT number on the sidewall was not required by law until 1971.
Pros of the bias-ply design are durability on rough terrain, strong sidewalls (a benefit for trucks and trailers), and period-correct for restorations (like a 1960s muscle car). Yet, the cons are a less flexible sidewall (harsher ride), poor traction and handling compared to modern designs, and they generate more heat. The construction is less forgiving than other designs regarding tread wear concerns.
The belted bias-ply tire debuted in the late-1960s, representing a significant step in tire evolution. Similar to a bias-ply with a diagonal-ply construction, its design was a bridge between the traditional bias-ply and the more advanced radial designs. Additional stabilizing belts (fiberglass or steel) were strategically placed beneath the treaded area of the tire, enhancing stability and wear characteristics.
Above Left: All the particulars of the Coker Tires radial tire are listed on the sticker on the tire. Above Right: The tread pattern from the bias tires is similar to a highway tread rather than the modern tire with ribs, tread blocks, grooves, sipes, and shoulders.
The addition of the stabilizing belts improved the tread stability and wear characteristics over a bias-ply construction. A second pro is the belted bias-ply offers a smoother ride and subjectively better handling. Unfortunately, belted bias tires retain most of the limitations found in a bias-ply design. The tire was a transitional technology (between bias and radials) and is nearly obsolete today.
Above: The BFGoodrich tires on the Runner looked good. They had just under 1000 miles on them but were also thirty plus years old. The age of the tires and the fact that they did not have a period-correct appearance were the primary reasons for us to remove them.
Today’s tire standard construction is the radial design. Although the radial structure has existed since the mid-1940s and was used sporadically in Europe since the 1950s, it did not gain traction in the U.S. until the mid-1970s. Plies run radially from bead to bead at a 90° angle to the tread. Radials are stabilized with steel belts running under the tread (around the circumference). Although physically attached, the tread and sidewall act independently of one another.
Through extensive testing by tire and auto manufacturers, it was discovered that radial tires, among many benefits, improve fuel economy. With the oil embargos of the early seventies, better MPG was high on the list of new car buyers and those shopping for more fuel-efficient tires, so the radial was moved to the forefront.
Above Left: The BFGoodrich tires were P235/70R15, slightly taller than the new FR70-15 tires. The tire load capacity is minimally greater than the new Firestone tires, but everything else remains the same. Above Right: Although somewhat challenging to view, the last three digits of the DOT information are 461, which is the week and year of the tire’s construction. This tire was week 46 of year 1 (1991). In 2000, the DOT number was amended to four digits XX (week) and XX (year). Because our tires have a three-digit number, we know they were constructed prior to 2000.
We may not recognize the positives of radials since nearly all of us have driven/ridden in vehicles with them for years. The list includes superior ride comfort, boosted fuel economy, better handling, grip, and tread life, lower rolling resistance (especially the low-rolling-resistance tires on hybrids and EVs), and reduced heat buildup.
Radials have a few drawbacks, which include less sidewall stiffness (they may flex more under load), increased expense due to greater manufacturing complexities, and, in the case of the Road Runner, not being period-correct for classic restorations.
Above: Depending on your Mopar, the lug nuts are left and right side specific through the 1970/71 model years. The studs are labeled with an “R” or “L” to denote the thread type.
In 1968 (the year of the Road Runner), most passenger car tires in the U.S., including those on performance and muscle cars, were still primarily bias-ply in construction. However, belted bias-ply tires were also gaining popularity around this time.
The Firestone Deluxe Champion and the Goodyear Power Cushion were popular bias-ply tires of the era. Conversely, our Road Runner was likely fitted with belted bias-ply tires, specifically Goodyear Polyglas F70-15s. Goodyear and Firestone (Wide Oval) introduced the belted bias tires in 1967.
Above: We are lucky to have our own rim clamp tire machine (right) and balancer (left). While not the top-dollar units found in cutting-edge tire shops, they work well. Beissbarth, a German company, builds both. The air pressure gauge on the tire machine has kPa as the major scale with PSI on a smaller scale.
While the classic bias-ply Goodyear Polyglas tires were an option for the Runner, we were drawn to a more versatile choice. Opting for the radial-designed Firestone Wide Oval tires, we were confident in our decision.
These tires not only replicate the appearance of the original bias-ply version, with the same sidewall shapes, tread patterns, and sidewall engravings but also feature a distinguishing red stripe, adding a touch of originality to our Road Runner.
Above Left: All four wheels were in excellent condition. Each was a 15×5.5-inch Kelsey Hayes steel wheel. Above Right: The wheels were painted Matador Red on both sides, which is likely incorrect. The wheels should have been black and painted red on the front to match the body color. They would not have been taped off, so red paint would pass through the wheel at each opening, leaving a red overspray on the black inner side.
The installation of the Coker tires was a thorough and careful process. With the Runner on the car lift, we removed the wheels (remember the left-side lug nuts are left-hand thread). Each tire was removed from its wheel using our Beissbarth tire machine. We replaced all four valve stems before installing the Firestone tires to ensure the best performance.
We lubed the bead of the first Firestone tire. After feeding the beads onto the wheel, we lined up the faint yellow mark on the outer bead with the valve stem. By orienting the tire on the wheel, the valve stem lined up with the big “O” on the sidewall.
With the tire lined up and the valve stem core removed, we filled the tire, reinstalled the valve stem core, and adjusted the air pressure to 32 psig. We followed the same procedure for the other three tires.
Above Left: Since the tires were over thirty years old, we figured the valve stems were at least the same age, so we removed them. We cut the underside of the stem and pulled it through to the outside of the wheel. Above Center: The new valve stems were pulled through from the inside of the wheel to the outside. We used high-leverage pliers pulling on the threaded area of the stem. We used a paper towel to protect the painted wheel. Above Right: The new valve stems fit correctly. We chose mid-length stems for our Runner.
With our Beissbarth wheel balancer, we elected to static balance the wheels as they had been with the BFGoodrich tires. Chek-Chart’s Automotive Steering, Suspension, & Wheel Alignment textbook defines static balance as:
“When a wheel and tire assembly that lacks static balance hangs freely on the spindle, it rotates until the heavy spot is at the bottom because gravity pulls the heavy spot down as far as possible. If the wheel and tire assembly is balanced, gravity affects it equally at all points, so it does not spin if hung freely.”
Additionally, by placing the weights on the inner plane only, it prevented us from scratching the outer lip of our body-colored wheels.
Above: The Firestone tire was significantly narrower than the BFGoodrich tire. Also, it was shorter in height. We will have to check the speedometer gear in the transmission to see if it is the correct size for the new tires. If not, we will need to swap it for the proper gear. Otherwise, our speedometer will be incorrect.
Each wheel/tire assembly balanced without difficulty except one. One wheel would not balance, so we broke down the assembly and rotated the tire 180° on the wheel. After seating the bead and adjusting the tire pressure, we attempted to balance the wheel again. Just like our previous attempt, we struggled to find the balance.
Above: The Firestone tire looks excellent regardless of the angle. The red wheel with the 3/8-inch redline looks great.
After careful consideration, we broke down the tire again and rotated it an additional 90°. With the wheel/tire assembly inflated, we attempted to balance the assembly one last time. This time, we succeeded on the first attempt, highlighting the need for perseverance.
With all four wheels balanced, we reinstalled the wheels. Each lug nut was torqued to 75 ft-lbs. After torquing the lug nuts, we tapped on the dog dish hub caps, lowered the Road Runner, and checked the appearance. The tires looked outstanding.
Above Left: There is something remarkable about the tread pattern of a bias tire. Maybe it is just the distinct, nostalgic design, but it definitely throws us back to our youth when the tires were on everything from muscle cars to grocery-getters. Above Center: The front tires fit well with clearance all around. Conversely, the driver’s front 235/70R15 tire had hit the inner splash shield, leaving a groove. Above Right: Once on the ground, the tires had a slight sidewall bulge, consistent with a radial tire. From a short distance away, nobody will notice.
We backed the Runner out of the garage and took a short trip up and down the street. The car rode smoothly, and the tires were quiet. Stepping out of the Road Runner, we observed the tires. They looked like they were installed from the factory. The tire tread appears perfect, and all the markings on the tires and the flawless redlines set off the Runner’s Matador Red paint.
Above: The Road Runner has slipped back into the sixties with the Wide Oval tires. The tires are subtle but stand out simultaneously because of their unique appearance. The first thing everyone seems to notice is the “old tires” on the Runner.
The new FR70-15 tires were much narrower (tread width) than the BFGoodrich tires. Also, the Firestone tires were slightly shorter than the BFGoodrich tires, so when we service the transmission, we will see which speedometer pinion gear is installed and adjust it as needed to get our speedometer as accurate as possible.
On our test drive, we observed the steering wheel was noticeably off-center. We know the previous owner had recently replaced the idler arm, which could have changed the front toe and caused a non-centered steering wheel. To ensure the new Firestones operate effectively for years, we will perform a thrust alignment on the Runner before we seriously start driving it.
Above: Although we do not feel the Road Runner is ready for a long drive, we did take a spin through the neighborhood, and the tires provided a smooth ride. We noticed the steering wheel was off-centered, so a thrust alignment will be necessary before any trips are planned to minimize any tire wear concerns.
If you drive a vintage Mopar on the open road, purchasing a set of bias-ply look radial tires should be a strong consideration. However, if the radials are not what you desire or a period-correct design is required, Coker Tires has an unbelievable inventory of tires for nearly every application.
Above: Another step in our “restoration” of the Runner is complete. While there is still plenty to accomplish, the tires have provided our progress’s most significant visual impact.
In addition, although we had the factory wheels we love on the Runner, Coker is now offering kits that include tires, wheels, trim rings, center caps, and lug nuts. So, regardless of your needs, Coker Tires has everything you need for your Mopar’s rolling stock.
