Coker Vintage Tire Insight - CHP Insider
Corky Coker Of Coker Tire Explains The Art And Technology Behind Designing Vintage Treads.
From the January, 2010 issue of Chevy High Performance
By Stephen Kim
Photography by Courtesy of the Manufacturer
There's good reason why his friends call him the Indiana Jones of the tire business. That's because until Corky Coker came along, collector car enthusiasts were in a real pickle. With big-name tire manufacturers having long abandoned the vintage car market, enthusiasts had nowhere to go to get tires for their restoration projects. Corky recognized this void, and began expanding his company's antique tire division in 1974. After convincing large tire companies, such as Firestone and Michelin, that reproducing vintage tires was a good idea, Corky obtained the licensing rights necessary to start manufacturing them. Due to the global nature of the tire business, Corky literally traveled the world hunting down antique tire molds. The hard work paid off, and today Coker Tire has over 1,000 different part numbers, and has grown from a 500-square-foot shop into a 100,000-square-foot empire in Chattanooga, Tennessee. Interestingly, although Coker's reproduction tires resemble their old-school counterparts, they feature the latest in modern tire innovations. To find out more about what goes into designing everything from whitewalls for street rods to bias-plies for muscle cars, Corky was kind enough to let us pick his brain. During our talk, we even covered some of the most basic yet commonly misunderstood aspects of tire design as well.
"Coker Tire Company was founded by my father, Harold Coker, in 1958. Harold dreamt of making rare and obsolete tires commercially available to antique car collectors. Having collected and restored cars for years, Harold recognized the need for this specialty area that his fellow hobbyists had so often demanded. I took over the responsibilities of the antique tire division in 1974. At the time, antique tire sales represented only 5 percent of the company's total business. Much of what we did over the next 20 years or so would actually define the vintage tire industry. The first obstacle was figuring out how to produce tires that were no longer being manufactured or supplied, which sizes would be most popular, and how to market and distribute them. We realized early on that we'd have to be our own best source of vintage treads. We bought molds from original tire makers if they still had them, and literally searched the world for old tire molds. Furthermore, we brokered deals with major tire producers that secured Coker Tire the worldwide licensing agreements and exclusive distributorships to big-name vintage brands including BFGoodrich, Firestone, Michelin, and U.S. Royal. To grow our customer base in an industry with no recognized method of distribution, we went straight to our customers. On the weekends, we loaded up a small van with tires, and worked car shows across the country, sleeping in the back to save money. Show travel became, and still is, the mainstay of Coker's commitment to its customers.
"As the era of mail order came into full bloom, aggressive advertising efforts targeted to car collectors and enthusiasts put the company's catalog in the hands of thousands of new potential customers. Perhaps the key component to Coker's success lies in the mail order aspect of the business that emphasizes customer service. We established the 'No Sweat' return policy that simply states that the customer is always right. Coker Tire's antique tire division started with one employee in 1974, and today has grown to more than 50. The company's web page is now a full e-commerce site with complete online ordering capability. All inventory has recently been consolidated to a separate 100,000-square-foot warehouse in Chattanooga, Tennessee. Our restoration shop and private museum opened in 2008 at the company's Chestnut Street headquarters."
Old Meets New
Although Coker's line of classic car tires-such as bias-plies for period-correct muscle car restorations and whitewalls for street rods-may look similar to tires produced back in the '30s, they feature the latest in modern tire design. According to Corky, tire technology has evolved tremendously through the decades, and Coker's designs resemble the originals in appearance only. All of the company's products are designed from the ground up to be classic car tires. "We don't take a modern tire, grind up the sidewall, and cure a whitewall on it. They're designed from the start to be classic tires," Corky explains. "Even when we make a bias-ply tire for a '65 Chevelle that needs to look just like the original tire, we use the most modern compounds, cord angles, and carcass designs. Likewise, treads stock today are much better than they were in the '60s. With traditional looks and modern technology, it really is the best of both worlds."
"When we set out to resurrect vintage tires that had already been out of production for decades, it was not only a novel concept, but also a monumental undertaking. Over the years, sourcing original tire molds and equipment has been the biggest problem. As tire companies became larger and more global, they didn't care about specialty tires produced in low volumes. Big companies don't have an interest in nostalgia, so as the old equipment started piling up they often threw away the molds. Although companies changed tire sizes just about every year on each model, sometimes tire manufacturers stored molds for some reason or another. We were successful in finding some of these molds, but they wouldn't just release them to anyone. Consequently, we first had to convince tire companies that there was genuine value in having us produce these tires once again. Next, we developed licensing agreements with companies like Firestone, Michelin, BFGoodrich, and Uniroyal before we were able to acquire the molds. The global nature of the large tire companies meant that we looked for molds overseas as well, because they have plants in places like Costa Rica, Colombia, New Zealand, the Philippines, Canada, and Australia. When original molds weren't available, we made new ones from the original drawings, so it's not completely accurate to call them reproductions. Since the '70s, I've traveled all over the world looking for molds, leading some people to call me the Indiana Jones of the tire industry. Today, Coker Tire has over 1,000 different part numbers, and now when companies discontinue a tire, they send us a list of molds to pick from. In fact, we just purchased 1,500 molds from Michelin for '80s and '90s high-performance cars."
Big-name tire companies such as Firestone, Michelin, BFGoodrich, and Uniroyal aren't in the business of producing classic car tires. Consequently, while vintage car tires might have Firestone or BFGoodrich logos imprinted on their sidewalls, they're actually manufactured by Coker. "It was by no means an easy task, but we went directly to tire manufacturers in the '70s and informed them that there were large numbers of potential customers that wanted to buy tires they no longer produced. Since hot rodders are so passionate about their cars, we got the tire manufacturers to realize that these cars would show up on covers of magazines and on TV shows, maximizing their exposure," Corky recalls. "After recognizing the value in having their vintage treads brought back to market, companies like Firestone, Michelin, BFGoodrich, and Uniroyal gave us permission to reproduce their original tire designs. We have to pay them a royalty, which is why they're more expensive to produce. As part of the licensing agreement, the tire companies first study how you're going to make a tire to ensure that it's up to their standards."
Instead of just riding on its reputation, Coker Tire is extremely involved in attending various enthusiast events throughout the year. Corky says the decades-old tradition is as much about pleasure as it is business. "I grew up around cruise nights and tours, so if I'm not in the office, I'm in the shop restoring one of my cars or at a show. We're all car guys, and attend over 70 events a year," he explains. "We believe you have to interact with your customers through all mediums, and talking to them face-to-face is extremely important. In fact, that's where we get our best ideas for new product development. People approach us at shows all the time and ask 'Did you ever think about making tires for this kind of car?' A simple encounter like that often leads to a new product in our catalog"
A tire's speed rating represents the maximum speed at which it can be safely operated, but the method used to establish those ratings can lead to some confusion. While the U.S. DOT came up with the Uniform Tire and Quality Grade (UTQG) standards to rate tires on their traction, temperature, and treadwear characteristics, speed ratings started in Europe. The lab tests used to determine speed ratings involves pressing a tire against a metal drum at a specified load, then running it up to a certain speed. For instance, an S-rated tire must hold together at 112 mph, while H-, V-, W-, and Y-rated tires must endure a sustained 130, 149, 168, and 186 mph, respectively. "The rating system is a bit misleading because the test involves running a tire at speed for hours at a time, and most people don't drive their cars at such high speeds for hours at a time," Corky explains. "Also, speed ratings don't necessarily equate to grip. For instance, a V-rated tire can handle higher speeds than an H-rated tire, but that doesn't mean it will have more grip."
Most modern tires are sized based on the P-Metric system that was introduced in the United States in the late '70s. The method is based on a uniform engineering formula to determine a tire's load capacity, and reflects a tire's section width, sidewall aspect ratio, and diameter. For instance, a P245/50-16 tire has a 245mm section width, a sidewall height that's equivalent to roughly 50 percent of the section width, and a 16-inch diameter. Most muscle cars were built before the P-Metric sizing system was introduced, however, when the Numeric and Alpha Numeric systems were more common. The Numeric system used through much of the '60s measured a tire's section width and diameter, and most featured an 80- or 90-series aspect ratio. For example, a 6.95-14 tire had a section width of nearly seven inches and a 14-inch diameter. The Alpha Numeric system introduced in the late '60s used a letter to describe a tire's load rating, followed by numbers that represented a tire's aspect ratio and diameter. An F60-15 tire used on a second-gen Camaro, for instance, specified a 60-series aspect ratio and a 15-inch diameter. Obviously, the older sizing methods aren't as precise, so trying to convert them to an equivalent tire size on the P-Metric scale can get a little tricky. Corky says the easiest way to do this is to call up Coker's tech support line, or refer to the conversion charts in its catalog. "Tires have evolved tremendously over the years, and so have the standards used to size them," Corky explains. "There have been times in the past when tires were measured by their overall diameter and section width, but the rim size wasn't even specified. Due to all the variations over the years, it's best to consult with a tire expert to see what tire size is right for your car when upgrading to modern P-Metric tires."
Section vs. Tread Width
A tire's section width is the distance between the widest points of the inner and outer sidewall. Tread width, on the other hand, is the actual footprint of a tire from crown to crown. According to Corky, all tires must be mounted on a wheel that's neither too wide nor too narrow to optimize the tire's contact patch and performance. "The Rubber Manufacturers Association and Tire and Rim Association have a recommended range of rim widths a tire should be mounted on," he explains. "The tread must be flat to perform correctly. If too wide, a tire's shoulder will wear, and if too narrow, the center will wear. When operating within the recommended width range, a good rule of thumb to follow is that a difference of 1/2 inch of rim width equates to a 2/10-inch change in section width."
While Coker manufactures its own line of tires, the company started out as a tire distributor. Consequently, it still offers a full line of tires from a diverse range of manufacturers. "We've been in business for over 50 years, and our goal has always been to be a one-stop shop for tires," says Corky. "In addition to our reproduction tires, we carry the entire catalog from BFGoodrich, Michelin, Firestone, Uniroyal, and Phoenix and M&H slicks. Coker also offers steel and wire wheels for antiques and muscle cars, as well as vintage tire related apparel and collectibles."
"When most people build cars, the tires are the last thing they put on their car. Most hot rodders probably know more about what goes into building an engine than what goes into making a tire. However, since tires are the only thing holding your car to the road, you should first figure out the stance, suspension setup, and what tires to run. The hardness or softness of a compound is important to ultimate grip, but that's not the complete story. They may look simple, but tires are highly engineered products. The first step during the design phase is to determine the handling and wear characteristics you want to achieve. To put it succinctly, the tread width, aspect ratio, chaffing materials in bead, compound, sidewall design, cord angles, and the number and type of plies all impact grip. Additionally, chemical engineers have to develop a rubber compound that has good grip and runs cool, since a tire runs best when it isn't overheating. The pressure and temperature used during the curing process is also very important."
Just like clutches and brake pads, new tires can benefit from following a break-in procedure. During the curing process, a release lubricant is applied to the tire to prevent it from sticking to the mold. The lubricant often remains on the tread until it is worn away, compromising traction. "Taking it easy for the first 500 miles or so with gentle acceleration, braking, and cornering will help maximize a tire's performance and ride quality after break-in," says Corky. "This also enables the different layers of steel, rubber, and fabric to start working together properly."
Don't Mix & Match
It might not seem like a big deal to mix radials and bias-ply tires on a car, but Corky adamantly advises otherwise. "I see it done all the time on hot rods, but you should never do it since it could lead to a severe understeer or oversteer condition," he explains. "Not only do radials and bias-plies grip the road differently, rims designed for bias-ply tires can crack due to the extra stress placed upon them by radials. People think it's OK to because some guys at the dragstrip might get away with it, but it's never something you want to do in a street car that will have to go around corners."
Racers have been inflating tires with nitrogen instead of regular compressed air for quite some time, and now this practice has started trickling down to the mainstream. Keep in mind that ambient air is already 78 percent nitrogen, but pure nitrogen has its benefits nonetheless. "The biggest benefit of nitrogen is that it maintains air pressure better, improving wear and potentially increasing gas mileage. Rubber is porous, so over time air will escape through it," Corky explains. "Nitrogen molecules are bigger than oxygen molecules, so they're less likely to escape through the sidewall. Also, the nitrogen used to fill tires is free of humidity, which reduces tire corrosion from the inside out, and pressure fluctuations."
For daily driven cars, the amount of tread remaining on the tires can be a good gauge of wear. According to Corky, that principle doesn't necessarily apply to collector cars that don't see much time on the road. Regardless of tread depth, Corky suggests replacing any tire that's over 10 years old. "In the past, tires were built from natural rubber, but the newer synthetic compounds used today don't rot, which helps tremendously," he explains. "Nonetheless, if you see oxidation on the outside of a tire, it should be replaced. High or low spots in the tread indicate that the balance is off or a wheel is bent, which needs to be corrected. Furthermore, any time a car is stored for a year or more, it should be placed on jack stands to take the pressure off of the tires."
Muscle Car Tires
Many prefer a more traditional stock-like appearance. Fortunately, Coker has a full line of reproduction tires for that period-correct look. "For muscle car fans, we offer a complete line of BFGoodrich Radial T/A's ranging from 14- to 16-inch sizes. They have raised white lettering and a vintage tread design, but with radial construction and the latest in modern tire technology. We also carry vintage whitewall, redline, and goldline tires. If your wheels have seen better days, Coker offers a complete catalog of muscle car wheels as well. It's often cheaper to buy new Rallye wheels than trying to restore the originals. If you buy a set of wheels and tires from us, we'll mount, balance, and fill them up with nitrogen for free."