What’s the Difference Between Bias Ply and Radial Tires? How Does That Affect Alignment?
The difference between bias ply and radial tires is that bias ply tires are constructed of layers of fabric that are woven at a diagonal angle, while radial tires have cords that run directly from the wheel to the tread.
This difference affects tires alignment because a bias ply tire will distort more than a radial tire when it is being inflated. As a result, if you try to align a car with bias ply tires using the factory settings, it will not be correctly aligned. You will need to adjust the alignment parameters and wheel balancing to account for the distortion caused by the bias ply tires.
Bias Tires
Bias tires are made by crisscrossing cords of polyester and nylon belts at a 30 to 45-degree angle to the tread’s centerline. Whereas Radials are constructed with crisscrossing steel belts underneath the tread and increase structural integrity. Check out the old school Carlisle video below.
When it comes to your standard driving tires, “bias ply” isn’t a familiar term to describe the latest and greatest tires coming out on high-performance cars. In the racing, trailer, and even motorcycle worlds we still see bias ply but, even then, it’s quickly being eliminated.
Bias Ply
The treads wear faster and exhibit more rolling resistance. This means you’ll get flat spots if you allow a bias ply tire to sit on the vehicle’s weight for too long. You’ll also feel like you’re wandering due to cracks, ruts, and bad road surfaces.
While the tread isn’t directional, the way you rotate bias ply tires for maintenance is specific to them. You’ll take a left rear tire and move it to the left front, left front to the right rear, right rear to the right front, and right front to the left rear.
Radial Tire
A radial tire, however, has its plies in a 90-degree pattern from the direction of travel from bead to bead.
What makes the radial superior to bias ply tires (outside of high-load capacity) is that those radial cords allow better flex. It makes a tire act more like a spring and improve riding comfort even as load capacity rating increases. This also increases tire life as the flexing required is easier than bias ply, which would resist and begin to overheat the tire.
The areas where bias ply dominated are no longer solely for them. Radials have become an acceptable replacement. As ply and rubber technology continues to improve, the need for any type of bias ply will be left for those who are just in it for numbers-matching correct restoration.
Bias Ply Vs Radial for Alignment
Experts tell us that caster is the most difficult of the 3 major alignment angles. For an ultimate demonstration of what happens when a massive dose of positive caster is at work, consider the road grader. There is so much positive caster built into these behemoths that the front tires actually tilt over (camber roll) on their sides as they work. Road grader manufacturers designed them this way so they would have enough side force to allow the blade to push dirt.
Positive caster occurs when the imaginary steering axis line intersects the ground in front of the tire contact patch. Negative caster is when the line intersects the ground behind the contact patch.
Explained in everyday language, caster is easier to understand. During the past 30 years car makers have gotten better at it, to the point that 21st century drivers float along with almost no sense that their vehicle may have an alignment problem caused by a caster.
That’s why you are more likely to hear about handling complaints from vehicle sensitive purists who enjoy driving, who love their cars and appreciate good handling. For these drivers, too much positive caster can deliver over responsiveness and handling jitters at higher speeds. This may be ideal for autocross, but not a daily driver.
Now, if you have bias ply tires, you will have a difference in caster settings over the radials. Specs that work best for radials are slightly different from those for bias ply tires. Radials like as much caster as you can get.
Radial tires do not have the same kind of self-centering feel provided by bias ply tires. So, when power steering became more prevalent, more positive caster was designed into the suspension at the automotive factory to improve responsiveness and self-centering or on-center-feel. Factory-added caster also allowed vehicles to handle better. Your bias ply tires will, typically, not have the higher amount of positive caster as radials.
Using a QuickTrick System
If you are using a QuickTrick System with bias ply tires and do not have access to the recommended specs for your vehicle, give us a call so we can help find the correct settings for your vehicle and tires. We are a reliable name in the world of portable wheel alignment and DIY wheel alignment tools.
