The history of car tires sounds rather dull to most, even to automotive enthusiasts. The earliest ‘tires’ were really just wagon wheels, with the first real tires being solid rubber. Then came pneumatic tires, with their separate inner tubes; these used belts of reinforcing materials, like rayon or nylon, that were wound in the direction of the tire’s tread. Finally, radial tires appeared in the 1970’s. And there you have it, right?
Well, kind of, but we’re leaving out a ton of interesting and relevant facts. Maybe it’s a bit like saying that the novel Moby Dick is about whaling. True, but deceptively simple.
The all-important material we know as rubber was known to residents if the Americas many centuries ago. It was Robert Goodyear who in the mid 19th century discovered that heat treating rubber could greatly enhance its hardness, resilience and longevity. This was vulcanization, named after the Roman god of fire. The vulcanization process uses heat and Sulphur.
Let’s Fill Them With Air!
Pneumatic tires were initially developed for bicycles, which were hugely popular in the late 19th century. The names of Robert Thomson and John Boyd Dunlop are strongly associated with the early development of these tires. Interestingly, both Dunlop and Thomson were Scottish. (Hey, I have nothing against the Scottish! It’s just that, well, you know.)
Toward the end of the 19th century Frenchman Andre Michelin emerged as a pioneer of applying this new technology to automobile tires.
Natural rubber is neither black nor white, but tends to have an off-white color. It was determined that adding zinc oxide to rubber strengthens it, with a secondary benefit of making the tires appear truly white.
We’re used to our tires being black, even if they have white sidewalls. Tires are black because of the inclusion of carbon black which is added to increase durability of rubber. So tires transitioned from whitish, to white, and then to black. Then came the whitewalls.
Whitewall Tires
I’m not sure if or how the earlier all-white tires played a part in this, but in the 1920’s it was realized that a black tire with white sidewalls could be darned attractive. Thus was born the white sidewall tire. The white sidewalls remained fairly wide throughout the ’50’s, becoming a bit narrower as the decade ended. Perusing my issue of Standard Catalog of American Cars 1946 – 1975 leads me to believe that 1962 was about the time that white sidewalls became the narrow ones we were familiar with in the 1960’s and ’70’s.
Korean War Shortage
The war in Korea started in mid 1950 and lasted for three years. During the war there were shortages of certain metals and chemicals containing metals, as well as rubber itself. This meant that tires were difficult to come by, and white sidewall tires were not to be had. I don’t know if this was due to a shortage of zinc (for zinc oxide) or if so many tires went to the war effort that a separate line for whitewalls just didn’t make sense.
In the 1950’s you could buy white discs that would simulate wide white sidewalls on your black tires. These were held in place between the wheel rim and the tire bead. Some automakers made these available as options.
The wide white sidewalls that reached all the way to the wheel rim gave way to those with a white stripe, often about one inch wide. Throughout the 1960’s and ’70’s it was almost difficult to find a car that didn’t have tires with these white stripes. The exception would be primarily the sporty cars that had raised white letters.
This type of tire was super popular in the ’60’s and ’70’s.
These were the tires to have in the later ’60’s. Cars like the 1970 Dodge Challenger had tires such as these from the factory. If your sporty car didn’t come factory equipped with these, I have to believe that they would be at the top of the list when it came to buying replacement tires.
The tires with a narrow red, blue or gold stripe were influenced by European sport car tires. Your 1967 Corvette could have been outfitted with these from the factory for a mere $46 and change extra ($468 2020$).
If red or blue weren’t cool enough, you could get gold stripe tires, too.
Tire Construction
Radial tires have their cord threads wound differently and have belts beneath the tread. The sidewalls are therefore more flexible, allowing a larger contact patch between the tire and the roadway. They also allow the manufacture of tires with low aspect ratios, such as 45, 40, 35, or even 20. The radial construction also provides a flatter contact with the road, where a bias ply tire tends to have a stiffer tread area that doesn’t conform to its surface as well.
Radial tires offer less rolling resistance than bias ply tires and suffer less from heat generation. Even the big semi tractor and trailer tires today are of radial construction.
Radial tires were invented about a half century before they really started to surpass the bias ply tires. Lest you think that I’m making up crap (again), here’s an image from the patent issued in 1916 to one Arthur W. Savage. This is the same man who founded Savage Arms!
Tire Aspect Ratio
Lest my OCD get triggered, I have to point out that the formula above will yield numbers such as .60, .70, etc. You must multiply by 100 to get the number you’re familiar with. There.
In the muscle car days the majority of cars had tires with a 70 or 78 aspect ratio, with some performance cars using 60 series tires. It should be obvious that lower aspect ratio tires will allow a car to experience more lateral force when cornering relative to a tire with the same width but a higher aspect ratio.
Bias Ply and Steel Belts?
Yes, there was a period of time, prior to the widespread introduction of radial tires, that some bias ply tires were manufactured with steel belts. This greatly improved the robustness of these tires. Bias ply tires were and are more suitable than radials for certain applications, such as off roading. Reproduction tires for your vintage muscle car, pre-war car or post-war car are available, being constructed as bias ply like the original factory tires.
All Those Freakin Numbers and Letters!
Specifying a certain size tire has always resulted in a flurry of letters and numbers. Some are familiar and easily understood; others not so much. Let’s look at a sampling of tires from the 1950’s, ’60’s and ’70’s.
Generally speaking, the larger and heavier the vehicle the larger the tires it tends to have, with these tires having higher load limits than smaller tires. The smaller tires with lower load limits are prefixed by letters earlier in the alphabet, with larger tires and their higher load capacities more towards the last third part of the alphabet. The modern system specifies the width of the tire in millimeters. With ten mm in a centimeter, you can estimate the size in inches by dividing by ten and then dividing by 2.5 (1 in. = 2.54cm). Take a 235/60R15 as an example. Dividing 23.5 by 2.5 in your head tells you that it’s less than 10 in. and slightly more than 9 in. The value is actually 9.25 in.
The cars of the 1940’s tended to have 16 inch wheels with widths of from 5.5″ to 7.5″ or so. These tires had separate inner tubes. The 1950’s and ’60’s saw 15 inch wheels being used for the larger cars and 14 inchers for midsize and smaller cars. Some of the early and mid ’60’s smaller cars used 13 inch wheels.
Those All-Present 14″ Wheels
The change to 14-inch wheels for all but larger cars was very intentional and had no functional purpose. It was to allow these cars to appear shorter! There was quite a bit of styling energy directed toward achieving this lowered look. 15-inch wheels would often still be used for larger cars and for some high-performance cars. Prior to the proliferation of 14-inch wheels the majority of cars had 15-inch, and prior to that they were typically 16-inch. This was, of course, the era of tubed tires.
What Happened to the Tubes?
Pneumatic tires had their air contained in an inner tube for the first several decades of their existence. This made technical and practical sense at the time. One of the shortcomings of this design was that a puncture would allow air to escape quickly from the tube, thus causing sudden tire failure (blowouts).
1955 was the key year for the transition to tubeless tires. By 1956 the transition was nearly or entirely complete. For a year or two some manufacturers offered the old tubed tires as an option. (“Who wants those darned new-fangled tubeless tires anyway?”)
Tire Sizing
This is a snapshot of what things looked like in 1960 regarding tire sizes. It should be obvious that the larger cars tended to have wider tires with higher load capacities. The sizing shown, such as “7.60 x 15”, is simply referred to as “numeric”.
A decade later and things look like this. Same trend of bigger cars having wider tires, and often 15 inch wheels. Yes, the tire rating system has changed by 1970, but the use of different sized tires has remained the same. Most of the entries reflect “alpha-numeric” naming.
Not Just a Single Size?
Something that doesn’t seem to be common knowledge is that multiple tire sizes will fit a given wheel size. Let’s say that your 1969 GTO needs some new tires and you want to know what your options are. The car was factory equipped with 14″ x 6″ wheels. Generally, you could vary the tire width by minus 16% / plus 24% (approximately) and the tires will still fit and function properly, other considerations accessed as needed. Keeping a tighter range (+/- 1.0″) is safer!
So, with 6″ being 152mm, you could consider 152mm -24mm / +36mm, or 128mm to 188mm. Realistically, I’m not sure why you would ever go down in width, unless certain unique circumstances occurred. So, for our 6″ wide wheels we’re looking at tire widths from 6″ to 7.4″, or up to 185mm in common sizes. This yields selections from: P185 55R14, P185 60R14, P185 65R14 and P185 70R14 for the widest tires. The tire diameter varies from about 22″ to nearly 25″, so that needs to be taken into account. If you wanted a lower profile tire for your classic ride and its factory wheels, you will then need to adjust your speedometer, or it will read high.
Tires Today
It’s worth knowing how tires of contemporary manufacture are rated. This section will tell you what the numbers and letters on your tires mean.
Your radial tires will have a speed rating letter on its sidewalls. As this table shows, this letter indicates the speeds a tire can safely maintain. Your ‘Q’ rated tires (100 mph) won’t explode if you surge up to 120 mph, but they are not suitable for sustained 120 mph operation.
Also, if you have a set of old tires, say, for example, ten years old, and you chose to bomb through a lonely Nevada highway at 140mph for twenty or thirty minutes, you might think again. Your older ‘V’ rated tires might not be up to the task, given their age. Plus, if it’s a 115-degree day, this combination of speed/tire age/heat might prove catastrophic.
Load Indexes
This tire has a load index of 101, and a ‘V’ speed rating. From the tables you can tell that this tire will support a weight of 1,819 lbs. and is rated for speeds of up to 149 mph.
What About the Temp, Traction, and Mileage?
We all understand these simple A, B and C ratings, right. Well, not so fast, Bunkie! There’s a bit more to it than that. These ratings are part of the Uniform Tire Quality Grading System (UTQG).
Mileage Rating
- 100–200: ~15,000–20,000 miles
- 250–350: ~25,000–35,000 miles
- 400–500: ~35,000–50,000 miles
- 600+: ~70,000–100,000+ miles
Traction rating
- AA – Best
- A
- B
- C – Least
Temperature Rating
- Measures heat resistance at sustained high speeds (A – best)
- Grades: A, B, C.
A sticky street performance tire might well have a lower mileage rating than a comparable tire with a harder compound. A speed-rated tire will tend to have a higher temperature rating than on otherwise comparable tire with a low-speed rating.
