Hang on, Adam..... I gotta go find where I put my flak jacket again..........
Maybe we can just get Rich to put something in the Grab Bag, this topic comes up so often.
First, the basic differences between radial and bias..... Let's look at the tires from the side - staring right down the axle - stripping away the rubber so that all we see are the cords underneath.....
Bias ply tires are exactly what the name says. You will see layers of cords starting at the rim on one side, running over the tread area and back to the rim on the other side. They don't run directly around but at an angle. The first layer will angle forward and the second layer will angle backward so that they criss-cross; kind of like if you were to lay the fingers of one hand over the fingers of the other hand at a 45 degree angle. This criss-cross pattern adds strength and rigidity to the tire. There are at least 2 layers, sometimes more, always in pairs. We use the term "ply" to describe the number of layers.
On a Radial tire, the cords run directly across from one rim to the other. No criss-crossing. There is usually only one layer. Strength comes from the composition of those cords; the term "ply rating" is used to describe the equivelant strength. The construction allows for flexibility and cushioning of the load.
Today, most bias ply tires are constructed with only two, opposing layers of cord. This allows for better dissipation of heat and longer tire life.
One exception to this is the "trailer tire". Here, because we are constantly cutting corners too short and scuffing the sidewalls, trailer tires are generally constructed of multiple layers to give additional safety. What we see most often on our trailers is a "C load range" or 4 ply construction.
About the time radials started to become popular some 30 years ago, the term "load range" was coined. This replaced "ply rating". "B load range" replaced "2 ply rating"; "C load range" replaced "4 ply rating"; and so on.....
IMPORTANT: The Air supports the Load; the Tires are merely Containers for the Air.
On the side of your tires you will see a "Maximum Inflation Pressure" - 35# for a B load range; 50# for C load range. You will also see a "Maximum Load Capacity" at that inflation pressure.
The 4 tires on my trailer are "C" load range radials and have a maximum capacity of 1,870# at an inflation pressure of 50#; I can safely carry up to 7,480#! More than TWICE what my boat and motor weigh! Theoretically, I could easily get by with just a single axle trailer and "C" load range tires.
At 50# pressure, I've got much more air than I need to carry the load - I'm "over-inflated". The tires will balloon out, wear in the center and give a harsh ride.
If I drop my inflation pressure in my RADIALS to about 35 or 40#, I will still have enough "air" to carry the load, I will get more even wear and more cushioning.
BUT STOP! If you're running "C" load range BIAS ply tires with the same set-up..... You remember the criss-cross of the plies..... You lower the inflation pressures to match the load and you're going to put an undo strain on the tire from the internal flexing of the cords against each other..... Heat will build up..... BOOM! You've lost a tire.
With bias ply tires, it is CRITICAL that you match the tire, ply rating and load you are carrying for maiximum performance overall.
Radials are far more forgiving.
I don't know if I've communicated what's in my head in an understandable manner..... It's a very complex issue..... When in doubt - keep your tires at the maximum pressure listed on the sidewall. You'll be safe that way.
me!
