The Difference between radials and rags tires.
The difference is the way the tires are constructed as well as the materials used. Bias ply tires have the plies (layers of rubberized nylon or polyester mesh) laid in at a 30 – 45 degree angle to the centerline of the tire and in alternating directions. There are usually fiberglass belts added for strength.
In the Radial design, Polyester cords are laid in and overlapped at 90 degrees to the centerline of the tire and then steel mesh belts are added. The Radial design prevents the point of contact (where the rubber meets the road) from deforming, unlike the Bias Ply, which does deform under load.
There are a number of benefits to the Radial design for the trailer operator.
1) Softer, smoother, quieter ride
2) Improved fuel economy
3) Flat, wider footprint for better tire wear
4) Runs cooler than a bias ply, minimizing risk of a blowout on the highway
5) Longer tire life
6) Better tracking – Improved sway control
The main benefit for the Bias-Ply design is that the sidewall is more rugged and bruise resistant, plus Bias-Ply tires are usually less expensive. This could be an important consideration in a trailer application because many trailers are used infrequently, minimizing some of the Radial’s benefits.
WHY SPECIAL TRAILER ‘ST’ TIRES?
‘Special Trailer’ (ST) tires have been constructed for better high speed durability and bruise resistance under heavy loads. Trailer tire construction varies substantially from automotive tires, therefore it is essential to choose the correct tire for your towing application. In general, trailer tires have the same load range (or ply) from bead to bead. This allows for a stiffer side wall which provides safer towing by helping to reduce trailer sway problems. The use of ‘Passenger Car’ (P) tires a on a trailer is not recommended because their construction, usually radial or bias belted, allows for more flexible side walls. This could lead to increased trailer sway and loss of control.
Proper selection is a very important component of your trailer gear system. When replacing your trailer tires and trailer rims it is critical that the proper size and load range be selected in order to match the load requirements of the trailer. The following characteristics are extremely important and should be thoroughly checked when replacing trailer tires.
TIRE CONSTRUCTION TYPE – Bias Ply vs. Radial
TIRE APPLICATION TYPE – (ST) Special Trailer vs. (P) Passenger Car vs.(R) Radial
TIRE SIZE – % of section height / section width Refereed to as ‘Aspect Ratio’
TIRE LOAD RANGE – Load carrying capacity and air pressure rating
RIM SIZE – Diameter and width must match tire
RIM BOLT CIRCLE – Diameter of bolt circle must match hub
Quite often consumers are uncertain how to read or interpret specifications on a tire side wall. This problem is compounded by the Trailer Tire Industry’s use of three different size identification systems on trailer tires. The following are examples and explanations of tire code.
THE NUMERIC SYSTEM – (4.80 X mostly used on smaller trailer tires, indicates the tire section width (4.80″), and the rim diameter (8″)
THE ALPHA NUMERIC SYSTEM – (B78 X 13 C) common on 13″-15″ trailer tires, indicates air chamber size (B), the ‘Aspect Ratio’ (78), the rim diameter (13″), and the load range (C)
THE METRIC SYSTEM – (ST205 75D 15) currently being phased in by trailer tire manufacturers, indicated the tire application type (ST-special trailer), the section width (205mm), the ‘Aspect Ratio’ (75), the construction type (D= bias ply), and rim dia.(15″)