Rotate the Earth: Revisiting Drag Radial Tires Part 1

Wayne Scraba

30 Jan 2020

Click Here to Begin Slideshow Over six years ago, we presented a four-part series on drag race wheels and tires right here in these pages (check out “Wheeling & Dealing” parts I, II, III and IV – part III deals directly with tires). It was a detailed series, but time marches on and so does technology. Additionally, the use of “drag radials” on all sorts of cars is now even more common than it was a half-decade or so ago. And hey, even way back then drag radials were popular – they’re even more prevalent today. Given the passage of time and the advances in rubber, we figured it was high time to re-investigate the world of drag radials. This time around we’ll dig deeper into tire construction, the differences between bias ply and radial tires and other technical details. And once again, we’re going to focus upon tires from M&H Racemaster (PH: 800-299-8000; Website: MHRacemaster.com). Something we didn’t examine in detail before is the difference between a radial tire and a bias ply tire. In a bias ply tire, the construction is such that a ply cord runs in a criss-cross layout at an angle of 45 degrees to the tire bead. A radial tire incorporates a ply cord that runs at a 90-degree angle to the tire bead. With a bias ply tire, the sidewalls and the tread share the same plies. This construction layout allows the sidewall to flex. This flex is transmitted to the tread, which in turn causes it to deform and create tire spin. With a radial, the construction format creates a flat footprint on the ground. There is less contact patch distortion when compared to a bias ply tire. A radial design effectively allows the sidewall and the tread to function as two independent tire attributes. Because the bias ply tire is manufactured with multiple rubber plies that overlap each other, the tread and the sidewalls are essentially co-dependent. In a bias tire, the overlapped plies create a thick layer that is less flexible and is actually more sensitive to overheating. It can also make for a heavier tire when compared to a radial ply example. Fair enough, but stick shift cars and automatic cars exhibit different “preferences” when it comes to tire design. When properly set up, a radial tire car can effectively dead hook. But if the car turns the tire (wheel spin), the car will lose traction. Stick shift cars usually need wheel speed to work. When you combine a clutch with a radial tire, you usually end up with a car that either blows the tires off or simply bogs. Keep in mind, too, that a stick shift combination will have a pretty healthy first gear ratio and will often leave the line at an equally healthy RPM level. The key to making a radial tire work effectively with a stick shift combination is to figure out the clutch and the suspension. Sometimes this is far more difficult than you might imagine – even with infinitely adjustable clutch assemblies, double adjustable shocks and enormously adjustable suspension links. Factor in changes in track and weather conditions and you see how it can become a massive hurdle. That’s why the vast majority of stick shift racers prefer bias ply tires. In contrast, an automatic-equipped car is the perfect platform for a drag radial. First gear ratios are much lower. The hit to the tire is significantly less (particularly in a footbrake application) and the chassis setup can prove less complicated (when compared to what is needed for a stick shift car and radials). With a radial tire, the consistency from round to round tends to be better and the tires have less rolling resistance. Tire construction has an effect upon the rolling resistance of a radial, but so does tire air pressure. Typically, a radial combination can run a little bit more air pressure than a stick shift car. A radial is also more stable on the top end. Because a bias ply tire is less rigid than a radial, the sidewalls flex. That’s normal, but if you have big power (for example, a stick shift combination with a power adder), then there’s a pretty good chance you’ll have to run tubes in the tire. The tubes provide additional support for the sidewall of the tire. In turn, this can improve the contact patch grip. Because many bias ply and radial ply race tires are constructed with nylon (and/or fiberglass and polyester) cords, there is a possibility the cords can shrink over time. What this does is reduce the rollout of the tire (the height shrinks). Because of this, the tires should be matched to within a half-inch of roll-out of each other. That’s the reason many tire manufacturers, including M&H Racemaster, mandate you purchase two tires at a time. They’re matched in terms of rollout at the factory. In our next issue, we’ll re-examine tire growth, tire pressures, burnout procedures and more. Watch for it!

Rotate the Earth: Revisiting Drag Radial Tires Part 1 — Click Here to Begin Slideshow Over six years ago, we presented a four-part series on drag race wheels and tires right here in these pages (check out “Wheeling & Dealing” parts I, II, III and IV – part III deals directly with tires). It was a detailed series, but time marches on and so does technology. Additionally, the use of “drag radials” on all sorts of cars is now even more common than it was a half-decade or so ago. And hey, even way back then drag radials were popular – they’re even more prevalent today. Given the passage of time and the advances in rubber, we figured it was high time to re-investigate the world of drag radials. This time around we’ll dig deeper into tire construction, the differences between bias ply and radial tires and other technical details. And once again, we’re going to focus upon tires from M&H Racemaster (PH: 800-299-8000; Website: MHRacemaster.com). Something we didn’t examine in detail before is the difference between a radial tire and a bias ply tire. In a bias ply tire, the construction is such that a ply cord runs in a criss-cross layout at an angle of 45 degrees to the tire bead. A radial tire incorporates a ply cord that runs at a 90-degree angle to the tire bead. With a bias ply tire, the sidewalls and the tread share the same plies. This construction layout allows the sidewall to flex. This flex is transmitted to the tread, which in turn causes it to deform and create tire spin. With a radial, the construction format creates a flat footprint on the ground. There is less contact patch distortion when compared to a bias ply tire. A radial design effectively allows the sidewall and the tread to function as two independent tire attributes. Because the bias ply tire is manufactured with multiple rubber plies that overlap each other, the tread and the sidewalls are essentially co-dependent. In a bias tire, the overlapped plies create a thick layer that is less flexible and is actually more sensitive to overheating. It can also make for a heavier tire when compared to a radial ply example. Fair enough, but stick shift cars and automatic cars exhibit different “preferences” when it comes to tire design. When properly set up, a radial tire car can effectively dead hook. But if the car turns the tire (wheel spin), the car will lose traction. Stick shift cars usually need wheel speed to work. When you combine a clutch with a radial tire, you usually end up with a car that either blows the tires off or simply bogs. Keep in mind, too, that a stick shift combination will have a pretty healthy first gear ratio and will often leave the line at an equally healthy RPM level. The key to making a radial tire work effectively with a stick shift combination is to figure out the clutch and the suspension. Sometimes this is far more difficult than you might imagine – even with infinitely adjustable clutch assemblies, double adjustable shocks and enormously adjustable suspension links. Factor in changes in track and weather conditions and you see how it can become a massive hurdle. That’s why the vast majority of stick shift racers prefer bias ply tires. In contrast, an automatic-equipped car is the perfect platform for a drag radial. First gear ratios are much lower. The hit to the tire is significantly less (particularly in a footbrake application) and the chassis setup can prove less complicated (when compared to what is needed for a stick shift car and radials). With a radial tire, the consistency from round to round tends to be better and the tires have less rolling resistance. Tire construction has an effect upon the rolling resistance of a radial, but so does tire air pressure. Typically, a radial combination can run a little bit more air pressure than a stick shift car. A radial is also more stable on the top end. Because a bias ply tire is less rigid than a radial, the sidewalls flex. That’s normal, but if you have big power (for example, a stick shift combination with a power adder), then there’s a pretty good chance you’ll have to run tubes in the tire. The tubes provide additional support for the sidewall of the tire. In turn, this can improve the contact patch grip. Because many bias ply and radial ply race tires are constructed with nylon (and/or fiberglass and polyester) cords, there is a possibility the cords can shrink over time. What this does is reduce the rollout of the tire (the height shrinks). Because of this, the tires should be matched to within a half-inch of roll-out of each other. That’s the reason many tire manufacturers, including M&H Racemaster, mandate you purchase two tires at a time. They’re matched in terms of rollout at the factory. In our next issue, we’ll re-examine tire growth, tire pressures, burnout procedures and more. Watch for it!

There are a ton of sizes when it comes to drag radials. It’s also a good idea to check sizes. For example, not all P275-60R15 tires measure exactly the same.

With bias ply tire construction, a ply cord runs in a criss-cross layout at an angle of 45 degrees to the tire bead. In contrast, a radial tire is built with a ply cord that runs at a 90-degree angle to the tire bead.

The construction format of a radial creates a flat footprint on the ground. When compared to a bias ply tire, there is less contact patch distortion.

An automatic-equipped car is the perfect platform for a drag radial. First gear ratios are much lower. The hit to the tire is significantly less (particularly in a footbrake application) and the chassis setup can prove less complicated. See the text for more info.

With all tires (radial or bias), there is a possibility the cords can shrink over time. What this does is to reduce the rollout of the tire (the height shrinks). Because of this, the tires should be matched to within a half-inch of roll-out of each other.

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