This article is going to compare bias ply tires with radials. While I will be referencing passenger car tires, the comparison would apply to any type of tire. There’s a summary at the bottom of the page, but read the introductory paragraphs first. They explain how I am organizing this.
Everyone needs to be aware that each of the properties listed below can have a wide range of values. It is quite possible to design a tire of one type to exceed the other type in a certain property just by careful selection of materials and design elements. Hydroplaning is one such property as hydroplaning is almost exclusively about the tread pattern – grooves and such.
Modern radial passenger car tires have a steel belt.
A belt is at least 2 plies of some sort of fabric under the tread, about the same width as the tread, with the strands oriented at a slight angle to circumferential. 15º is typical.
Radial tires need that belt because the only other thing holding the tire together circumferentially is rubber, which is fairly weak.
After trying belts made of various materials including the same fabric as the body plies, the industry has settled on steel wire.
A bias ply tire doesn’t have a belt. If it did it would be called a bias belted tire, which has a combination of the best and the worst properties of both worlds!
I will not be comparing bias belted tires as you hardly see these nowadays.
Sometimes bias tires have breakers, which are similar to belts except that breakers have the same angle as the body plies. Breakers are usually the same fabric as the body plies, but occasionally other materials are used, such as steel wire. For the purposes of this article, the comparison will be to bias tires without breakers.
This is not going to be a completely apples to apples comparison as I am going to compare steel belted radial tires to bias ply tires without breakers. There are even more differences in modern tires. Radials are usually made of polyester body plies, steel belts, and if they have them, nylon cap plies. I am not including cap plies in any of the comparisons.
By contrast, bias ply passenger car tires – when they are made (Rarely!!) – would have nylon body plies. So I am going to make 2 comparisons:
An apples-to-apples comparison (same materials, except for the steel belt in the radial), which I am going to call the “Apples” Comparison, and a comparison to the way modern tires are built, which I will call the “Modern” Comparison. With all that in mind, here goes:
Treadwear:
This is where the radial really excels. That belt really stiffens the tread area, so the tread rubber wears very slowly compared to a bias tire. This is especially true for the modern comparison as the modern radial can use a much longer wearing tread compound than the bias tire
| Treadwear | Apples to Apples | Modern Constructions |
| Radial | + + | + + + |
| Bias | – | – |
Dry Traction:
That stiffening belt works here as well, just not as much.
| Dry Traction | Apples to Apples | Modern Constructions |
| Radial | + | + + |
| Bias | – | – |
 | Wet Traction (Not Hydroplaning): This follows dry traction as the tire thinks it is on a slightly more slippery surface. I will deal with the water surface tension (hydroplaning) next. |
| Wet Traction (Not Hydroplaning) | Apples to Apples | Modern Constructions |
| Radial | + | + + + |
| Bias | – | – |
| Hydroplaning: That stiffening belt doesn’t really affect things as hydroplaning is more affected by tread pattern, water depth, vehicle speed, and tread depth. |  |
| Hydroplaning | Apples to Apples | Modern Constructions |
| Radial | Same | Same |
| Bias | Same | Same |
 | Snow Traction: This property is mostly about the tread pattern – and as such isn’t different between construction types. EXCEPT The belt in radial tires allows for a more aggressive tread pattern with the loss of treadwear still being better than a bias tire. This is done by careful selection of the tread rubber compound. |
| Snow Traction | Apples to Apples | Modern Constructions |
| Radial | Same | + + |
| Bias | Same | – |
| Ice Traction: This is mostly about the tread rubber compound – and just like snow traction isn’t different between constructions BUT just like snow traction, the belt allows for the tread compound to work betterIce TractionApplesModernRadialsame+Biassame- |  |
| Ice Traction | Apples to Apples | Modern Constructions |
| Radial | Same | + |
| Bias | Same | – |
 | Rolling Resistance: Another place where radials greatly exceed bias ply tires. Rolling resistance is the biggest reason radials got adopted so quickly – because of the 1973 OPEC oil embargo. (Goggle it for more information.) |
| Rolling Resistance | Apples to Apples | Modern Constructions |
| Radial | + + | + + + |
| Bias | – | – |
| Ride Quality: Here it’s the radial plies that help. The crisscross bias plies in the sidewall stiffen the sidewall. |  |
| Ride Quality | Apples to Apples | Modern Constructions |
| Radial | + | + |
| Bias | – | – |
 | Handling: This is how the car feels and how quickly the tire responds to steering input – and the bias tire with its stiff sidewalls does this better. |
| Handling | Apples to Apples | Modern Constructions |
| Radial | – | – |
| Bias | + | + |
| Ease of Manufacture: Radials require additional equipment. Some of that equipment is for building and applying the steel belts to the partially completed casing, while some of that equipment is part of the mold. The belt doesn’t like being stretched, so it has to be applied separately from the body plies, and the mold is segmented so the tread pattern moves INTO the tread rubber. The photo to the right shows a segmented mold laid out to show the segments and the bottom bead/sidewall ring. There’s one peculiar thing about manufacturing bias ply tires – and it’s that because the ply material is cut at an angle, there is a limit on how high of an angle can be cut and how wide of things the building machine can accommodate. What that means is that bias ply tires are extremely difficult to make with low aspect ratios. |   |
| Ease of Manufacture | Apples to Apples | Modern Constructions |
| Radial | – | – – |
| Bias | + | + |
| Radial Low Aspect Ratio | + | + |
| Bias Low Aspect Ratio | – | – – |
 | Cost to Manufacture: In addition to the extra equipment, the materials used in a radial tire have to perform at a higher level. |
| Cost to Manufacture | Apples to Apples | Modern Constructions |
| Radial | – | – – |
| Bias | + | + |
| Repairs: Bias ply tires are fairly tolerant of repairs – both plugs and patches. By contrast, radial tires have 2 areas where repairs don’t work as well as they should – the edge of the top belt and the entire sidewall. The edge of the belt is where the highest stress is. Repairs in that area could cause a separation – very dangerous. The sidewall in a radial tire goes through a very complex movement as the tire rolls through the contact patch. Bias tires spread that same movement over a larger area. Further, plugs sometimes don’t seal at the outside surface, so it’s possible for water to find its way to the steel belts.RepairsApplesModernRadial—-Bias++ |  |
| Repairs | Apples to Apples | Modern Constructions |
| Radial | – – | – – |
| Bias | + | + |
 | Durability: This is how susceptible the tire is to a structural failure. The good news is that radial tires have improved so much, that there is only a slight advantage for bias tires. When we tire engineers use the term “durability”, we never mean wear resistance. |
| Durability | Apples to Apples | Modern Constructions |
| Radial | – | – |
| Bias | + | + |
| Speed Capability: While radials can be made with very high speed capability, it requires cap plies (the higher the speed, the more cap plies). It’s the belt trying to be thrown off by the centrifugal forces. I am not doing that comparison! By contrast, a bias tire, while affected by those same centrifugal forces, resists a bit better because they don’t have that additional mass. |  |
| Speed Capability | Apples to Apples | Modern Constructions (S rated to S rated) |
| Radial | – – | – |
| Bias | + | + |
 | Flatspotting: Modern bias ply tires use nylon – and nylon is prone to flatspotting. That’s because nylon has a glass transition temperature in the operating temperature range of a tire, so when the tire cools down after operating, it takes the shape it is in – with a flat spot at the contact patch. Modern radial tires only use nylon for cap plies, so they are also prone to flatspotting, but since they use less of it, the effect is smaller. The good news is that unless the tire sits for a long time, nylon flatspotting is temporary. In the case of the Apples to Apples Comparison, I’m assuming the same materials, so no nylon involved. In the case of the Modern Construction comparison, I am comparing S rated to S rated. |
| Flatspotting | Apples to Apples | Modern Constructions |
| Radial | Same | – – |
| Bias | Same | – – – |
| Sensitivity to Toe: Because of the belt, radial tires are more sensitive to toe than bias tires. Only a few car manufacturers have recognized this and adjusted their alignment tolerances. On a personal note, I think the toe on a passenger car should be within 0.1º (1/32 of an inch). Please note that the chart below reflects that sensitivity to toe is bad. |  |
| Sensitivity to Toe | Apples to Apples | Modern Constructions |
| Radial | – | – |
| Bias | + | + |
 | Sensitivity to Camber: Because of their naturally soft sidewalls, radial tires are not as sensitive to camber as bias tires. Many car manufacturers take advantage of this by aligning their vehicles with a lot of camber. On a personal note, many car manufacturers overdo the camber and it causes one sided wear especially if there is excessive toe. I think anything over 1º is excessive for wear purposes.Sensitivity to CamberApplesModernRadial++Bias— |
| Sensitivity to Camber | Apples to Apples | Modern Constructions |
| Radial | + | + |
| Bias | – | – |
Summary Please note that this chart is organized differently than the charts above AND a positive sign means better for performance. This is particularly important in the last 2 entries, as sensitivity to alignment is a bad thing. Also, if there is no difference between radials and bias, I’ve used “same” in both columns. |
| Property | Apples to Apples Radial | Apples to Apples Bias | Modern Construction Radial | Modern Construction Bias |
| Treadwear | + + | – | + + + | – |
| Dry Traction | + | – | + + | – |
| Wet Traction (Not Hydroplaning) | + | – | + + | – |
| Hydroplaning | Same | Same | Same | Same |
| Snow Traction | Same | Same | + + | – |
| Ice Traction | Same | Same | + | – |
| Rolling Resistance | + + | – | + + + | – |
| Ride Quality | + | – | + | – |
| Handling | – | + | – | + |
| Ease of Manufacture | – | + | – | + |
| Ease of Manufacture Low Aspect Ratio | + | – | + | – |
| Cost to Manufacture | – | + | – – | + |
| Repairs | – – | + | – – | + |
| Durability | – | + | – | + |
| Speed Capability | – | + | – | + |
| Flatspotting | – | – | – – | – – – |
| Sensitivity to Toe | – | + | – | + |
| Sensitivity to Camber | + | – | + | – |