HOW TO READ THE AG TYRE SIDEWALL MARKINGS?
The tyre sidewall has the necessary information of your tyre.
Let’s take a look at below picture, and see what these numbers and letters mean.
- 6.5/80-15 is the Tyre Size.
- 6PR means 6 Ply Rating for this tyre.
- TUBELESS indicates this tyre is a tubeless tyre. It could be used without tube inside.
- 82 A8
82 is a Load Index, tells you the max load the tyre could carry is 475kg (1047lbs).
A8 is a Speed Symbol. It limits the max speed you can drive with this tyre is 40km/h.
Well, guess you guys already have a question in your mind. Yes, there are a lot tyres outside that shows a very different symbol of tyre size.
Be patient, here comes the answer.
6 DIFFERENT TYRE SIZE DESIGNATION
Five Tyre Size Designation
TYRE WIDTH (W)
The linear distance between the outsides of the sidewalls of an inflated tyre excluding elevations due to labelling, decorations, or protective bands or ribs.
SECTION HEIGHT (H)
Half the difference between the overall diameter and the rim diameter.
ASPECT RATIO (ar)
One hundred times the ratio of the section height to the section width of the tyre on its theoretical rim.
ar = H/W
Construction Code ( – / R / B)
“ – “ means it is a BIAS or BIAS PLY tyre.
DIAGONAL (or BIAS PLY) describes a pneumatic tyre structure in which the ply cords extend to the beads and are laid at alternate angles substantially less than 90 degree to the centerline of the tread.
“ B “ means it is a BIAS BELTED tyre.
BIAS BELTED describes a pneumatic tyre structure of diagonal (bias ply) type, the carcass being restricted by a substantially inextensible circumferential belt.
“ R “ means it is a RADIAL tyre.
RADIAL describes a pneumatic tyre structure in which the ply cords extend to the beads and are laid substantially at 90 degree to the centerline of the tread, and carcass being stabilized by an essentially inextensible circumferential belt.
RIM DIAMETER (d)
It is a size code figure as indicated in the tyre and rim size designation.
OVERALL DIAMETER (D)
The diameter of an inflated tyre at the outermost surface of the tread.
D = H x 2 + d = (W x ar) x 2 + d
As you can see, there are only 5 tyre size designation above. But, I said 6, right?
Don’t worry, the 6th tyre size designation is quite different.
Here is an example for you:
Tyre Size: 31 x 15.5 – 15
Tyre Width: 15.5 inch
Tyre Height: 31 inch
Rim Diameter: 15 inch
PR = Ply Rating = Ply
Identifies different versions (load capacity, inflation pressure) of tyres having the same size designation.
The higher PR, the better load capacity.
TUBE TYPE (TUBELESS OR TT)
Tires specifically designed for fitment without an inner tube on appropriate rims.
Where no TUBELESS appears on the tire sidewalls, tires are intended for fitment with an appropriate inner tube.
LOAD INDEX & SPEED SYMBOL
The SPEED SYMBOL indicates the maximum speed at which the tyre can carry a load corresponding to its Load Index under service conditions specified by the tyre manufacturer.
Here is the Speed Symbol and the speed it means, for your information.
The LAOD INDEX is a numerical code associated with the maximum load a tyre can carry at the speed indicated by its Speed Symbol under service conditions specified by the tyre manufacturer.
Inflation pressure means the pressure taken with the tyre at ambient temperature and does not include any pressure buildup due to tyre usage.
Questions & Answers
Q1: How do I know the tyre height, according to the Width, Aspect Ratio & Rim Diameter?
A1: Theoretically, tyre height = Width x Aspect Ratio x 2 + Rim Diameter. And keep them in a same unit, like all inch or mm.
For example, tyre size 400/60-15.5
Tyre height = 400 mm (Tyre Width) x 60% (Aspect Ratio) x 2 + 15.5 inch (Rim Diameter) x 25.4 mm/inch = 873.7 mm
Here is another example, tyre size 11.5/80-15.3
Tyre height = 11.5 inch (Tyre Width) x 80% (Aspect Ratio) x 2 + 15.3 inch = 33.7 inch = 856 mm
Note: these are not the actual tyre height, just theoretical number for your reference. The actual tyre height depends on your tyre manufacturer, according to ETRTO Standard or TRA Standard.
Q2: Could I change the tyre size for my equipment as I wished?
A2: Yes, you can. However, there are several rules you should follow.
1st, the new tyre height should be close to the original one. Otherwise, it will not match your vehicle or equipment.
2nd, new tyre width should not be too wide. Because the wider tyre sidewall which face the vehicle, could scratch the vehicle and cause you in danger.
3rd, it might be difficult to get new wheel rims, once you change the rim diameter.
Anyway, check one more time with your tyre or wheel specialist(s), before you make your final decision.
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