Bias and radial are the two construction types used to make tires and is usually displayed as a “R” for radial or “D” or “B” for bias in the tire size sequence. The radial tire has dominated the market and the older bias ply tire design has been kicked to the curb for most uses.
But bias tires still have advantages over the radial tire design and are a better choice when you need strength over speed.
Bias Vs Radial Tires
Bias tires have a crisscross cord construction which gives it exceptional sidewall strength. This makes bias ply great for heavier loads and lower speeds.
Radial tires have a cord construction that runs opposite the direction of travel and gives them superior heat dissipation and flexibility. This makes radial best for highway speeds and comfort.
The stiffer sidewall of a bias ply tire makes it great for trailers that carry heavy loads, off-roading vehicles that need a sidewall that can resist punctures, and other situations where slow speeds reduce the need for improved heat dissipation.
Radial tires are almost exclusively used for cars and trucks while bias ply tires are almost exclusively used as trailer tires. But this isn’t always the case.
There are situations where radial tires are better for trailer use and reasons bias ply tires might be preferred on your car or truck.
Let’s take a closer look.
What Is A Radial Tire?
Radial is a term that describes the construction method used to align the layers of plies within a tire. Radial tires have the plies oriented radially or perpendicular to the direction of the tire’s rotation.
Radial tires are almost the only type of tire used on cars and trucks due to their performance benefits over bias ply tires.
Consumer Reports studied radial tires in the late 60’s and found them to be far superior to the common bias ply tires used at the time. This led to them overtaking the market completely within the following years.
Radial Construction
Radial tires are constructed with the main polyester plies of the tire running perpendicular to the direction of rotation of the tire. While the main construction uses the radial belt layers, there are steel belt layers on top of these. The steel belts run in diagonal directions beneath the tread for added strength.
They have more sidewall flex than than bias ply tires which improves shock absorption but reduces sidewall strength.
Radial Tires Pros And Cons
The radial tire may be the new king of the hill, but that doesn’t mean it’s perfect. Bias tires still have the radial tire beat in a few ways.
Radial Tire Pros
- Better heat dissipation
- Ability to be used at higher speeds
- Longer tread life
- Ride comfort
- Better traction and performance
- Lower rolling resistance
Radial Tire Cons
- More expensive
- Less load carry capability
- Less durable sidewall
What Is A Bias Ply Tire?
A bias ply tire is an older tire construction design the relies on diagonal nylon plies as opposed to the polyester plies and steel belts used in radial tires.
A bias ply tire used to be the standard for cars and trucks from the 1930’s to 1970’s but has been replaced by radial tires.
You can still find bias ply tires on motorcycles and trailers. They make great off-road tires for Jeeps, trucks, and SUVs for their improved traction on particularly rough terrain. They are also common agricultural tires for tractors and other farm equipment due to their improved puncture resistance.
Bias Ply Construction
Bias ply tires have multiple plies of nylon layers alternating in diagonal directions to the rotation of the tire. The plies are usually angled from 30 to 40 degrees diagonally. The number of plies range from only 4 and up to 10 though 4 is most common.
They do not contain steel belts and have more rigid sidewalls than those of radial tires which have much more sidewall flex.
Bias ply tires are more round and need more rubber to create the tread, shoulder, and sidewall when compared to radial tires.
Bias Ply Tires Pros And Cons
While no longer the default choice, bias tires still have a few advantages over radial tires that make them a great choice for certain applications.
Bias Ply Tire Pros
- Better sidewall puncture resistance
- Less trailer sway
- Able to handle heavier loads
- Less expensive
Bias Ply Tire Cons
- Can form flat spots when parked
- Difficult to balance
- Much shorter lifespan
- Poor ride quality
- Can wear unevenly
- Can be noisy
Belted Bias Ply Vs Diagonal Bias Ply
Belted Bias is the more contemporary version of a bias ply tire. The older style is Diagonal Bias. The difference between the two bias designs is the addition of belts.
Both have the same core structure of crisscross pattern cords, but belting improves the design by incorporating the steel belt design of radials to create a smoother ride and lower rolling resistance.
Difference Between Radial And Bias Tires
The key differences between radial and bias tires are:
- Better tread life of radials
- Better heat dissipation of radials
- Better sidewall strength of bias ply
These 3 differences make radial tires a significantly better choice for use at highway speeds where a bias ply tire will fail.
Not only that, but radial tires will dramatically outlast bias tires poor tread wear.
Bias tires are stronger due to the stiff sidewall design but this relegates them to use only as a workhorse type of tire.
Tire Construction Type Labeling
One of the designations within the tire size sequence is the construction type used to manufacture the tire. Radial tires are indicated with a “R” and bias ply tires are indicated with a “D” or “B”. No indication also means the tire is a bias ply construction.
Radial And Bias Ply Tires Used Together
During the transition of the average car owner switching from bias to radial tires in the 70’s there were lots of public service announcements to ensure people knew not to install both radial and bias tires on the same vehicle.
The dramatic difference in performance can cause an extremely unsafe situation. Without consistent grip at all four corners, you can easily end up in a situation that is very difficult to properly control your car or truck.
If you’re in a pinch and need to limp your vehicle over to a shop or some other location at a slow speed, it’s reasonable to do so. Otherwise, avoid mixing these two tire designs at all cost no matter what type of use they’ll be used. Even mixing on a trailer can be very dangerous.
Resources
Below are some links you may find helpful when learning about tires
Final Thoughts
The average consumer looking for a tire to use on their car or truck will choose a radial tire 99% of the time. Radial tire designs beat bias ply in almost every way aside from sidewall strength.
Even the situations where a bias ply design has traditionally been superior are beginning to get replaced by new and improved radial options. As technology progresses and radials become even more advanced, there will be even fewer jobs available for bias ply designs.
Good luck and happy motoring.
