Originally Posted by AtomicNo13
Bias ply tires lack the steel belt that acts as a shredder in a failure. There is just the tread carcass attached with a ribbon of nylon.
A blowout cannot be as disastrous to the wheelwell or skins. I think I'm going with bias ply 15" next season on my 34' classic. Coker tire is just one place with a wide variety.
I hope Atomic will not think I am picking on him just because I chose his quote to reply to. There's a lot of mis-understanding being expressed in this thread and his is just the last one.
First, the difference between a bias tire (sometimes called a cross ply or a diagonal) and a radial tire is the direction of the ply cords. In radial tires, the cords are at basically a 90° angle to the circumference of the tire (the "radial" direction), while bias tires are at a substantial angle - 30° to 40°. This makes the casing of a radial tire much more flexible as the plies do not fight each other when the tire is distorted - all other things being equal. (however, things aren't equal and I will explain that in a moment.)
Some tires have belts - a layer of cord (typically 2 steel wire layers) in the tread area - that stiffens this area and improves the wear and traction of the tire. However, that comes at the sacrifice of ride quality.
When a belt is added to a bias ply tire, it becomes a bias-belted tire. Because radial tires don't work without a belt, not only will you not find non-belted radial tires, but it is common just to call them "Radials" - and assume they are also belted.
Tire stiffness? Inflation pressure has much more affect on tire stiffness that does the tire itself. So a person may be able to sense the difference in stiffness in an uninflated tire, but that difference is overwhelmed by affect inflation pressure has.
Besides, in a radial (belted) tire, you can stiffen a particular part of the sidewall so much, while leaving another part quite flexible, that the overall stiffness is greatly increased, but it seems more flexible when picked up because if that very flexible portion. You can do the same thing to a bias or bias belted tire, but in practice bias and bias belted tires aren't stiffened in this way.
So be careful. Tire stiffness is complex and there is overlap.
Blowout? First, the term is used for 2 quite different failure modes.
1) A rapid release of inflation pressure. This is usually caused by encountering an object such that the casing is damaged (by cutting, tearing, or breaking cords) This escaping air can cause a lot of damage, and there have been fatalities just from exploding tires.
This is the correct use of the term - although people analyzing tire failures never use it. They generally use a description that points to the cause.
2) Incorrectly, the term is also used to describe a "belt separation", where the belt and the tread rubber over the belt, separate as a unit from the rest of the casing. There are several kinds, but the most common is a "belt-leaving-belt separation". In the separation sequence, the normal hoop-like configuration of the belt is split between belt wires and a flap is created by the centrifugal forces. This flap can damage anything near the failing tire.
Normally, the rest of the casing is undamaged and would still be inflated, but because the casing would be exposed to road debris, it is not usual for the casing to be damaged in the failure sequence. This makes distinguishing between this kind of failure and #1 above much more difficult.
Since bias tires do not have belts, they can not have this kind of failure. However, they do have an analogous failure where the tread comes off, but usually, this is in smaller chunks and the damage is more isolated and less severe.