Bias Ply or Radial Drag Tire: Which Tire is Right for Your Car

Dragzine

Does your car need a bias ply, or a radial tire? Image courtesy of Dragzine

When it comes to tires for your car, you have two choices—other than flat or not flat. You can choose either a radial or a bias-ply tire. It’s no surprise that radial tires outsell bias plies for standard street use, but what about for those of us who go racing? For years, Mickey Thompson’s conventional race tire has been a bias ply construction. But now, with the introduction of the radial “slick”, which one is actually better for use on your car?

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A bias-ply tire will allow the sidewall to wrinkle when a car launches.

When you’re at your local drag strip, bias ply tires are typically what you see on most cars that are racing. When the car launches, the sidewalls wrinkle as the tire grips the track surface. The construction of the bias-ply tire allows the sidewall to wrinkle, which in turn helps absorb the shock of the launch. Bias-ply tires are constructed using nylon strings in a crisscross pattern within the side wall. This design is strong enough to make a safe tire, yet pliable enough to allow the tire to buckle when launching. Keep in mind, this trait makes them a terrible choice when cornering is encountered, as this flex, can cause the tire to roll under the wheel in extreme cases. When at the track, these tires generally operate at around 10 to 15 psi of air pressure. A drag radial on the other hand, will not wrinkle, and is not as forgiving to a hard “hit” at the launch. John_Mustang_Launch

When the drag radial was introduced, it was looked upon as a fad. No one expected them to take the sport by storm. Guess what, they did. But as good as they are, there are instances when a drag radial might not be best suited for a car. For starters, the sidewall of a drag radial is not as forgiving as that of a bias-ply race tire. The sidewall doesn’t wrinkle when you launch. This stiffer sidewall also makes the tire best suited for cars using an automatic transmission. This is because an automatic transmission applies power less aggressively than a manual transmission-equipped car, and does not typically “hit” the tire as hard–transbrake not withstanding. This softer “hit” allows the tire to react accordingly. There are plenty of guys using a drag radials on cars equipped with a manual transmission, but those cars have well thought out suspensions, and use modern clutch technology. They’re not your average daily driver car.

Another thing to consider is that a drag radial will not “grow” as you go down the track. When a car with bias-ply tires gains speed going down the track, the bias ply might increase in size as much as one inch. The taller the tire gets, the lower the gear ratio becomes, allowing for a higher achievable top speed. This means that rear gear selection must be made accordingly. A definite plus to a drag radial is reduced rolling resistance. When compared to a bias-ply racing tire, the drag radial will take less energy to move.

The marks on the left are from an under-inflated tire. Notice the dark lines where just the outer edges of the tire are making contact. On the right, the dark center-only stripe shows over inflation.

Air pressure does not have as big as an effect on a drag radial as it will on a bias ply. If you add air to a drag radial, the tread will still retain a contact patch—within reason, the sidewall will just get stiffer. With a bias-ply racing tire, the proper air pressure is paramount. Adding too much air pressure simply to reduce sidewall flex can have an adverse effect on the car’s launch. Adding too much air will cause the tread will bulge, reducing the contact patch. Too little air, and the center will not even contact the road surface.cth73

 

Neither a bias-ply or drag radial tire will require a long, smoky burnout. In reality, both the ET Street and Street Radial need only a short burnout to prep the tires, because they heat up quickly.

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About the author

Randy Bolig

Randy Bolig has been working on cars and has been involved in the hobby ever since he bought his first car when he was only 14 years old. His passion for performance got him noticed by many locals, and he began helping them modify their vehicles.
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