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Technical Information

how to read a tyre

Tyre Designations - How to read a tyre (300-4)

DIMENSIONS EXPLANATION
300-4 Tyre width 300 / Rim Diameter 4"
10x3 Former designation in inches:
Tyre Width 3” / Tyre diameter 10” ( =3” x 2 + 4”)
260x85 Designation in millimetres:
Tyre diameter 260mm / Tyre width 85mm
The former designation in inches converted to mm:
10” x 25.4 = approx. 260mm
3” x 25.4 = approx. 85mm
85/100-4 This is how the designation would be, had it been a passenger car tyre.
Tyre width 85mm / Profile 100% / Rim diameter 4”.
10x3.00-4 American designation, mainly used for low proflie and turf tyres:
Tyre Diameter 10” / Tyre Width 3” / Rim diameter 4”


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OFFSET

The offset is the distance from the centre-line to the back side of the wheel disc (Where the wheel is fitted to the hub). The off set can be positive (+) or negative (-). A positive offset results in a narrower track width, i.e. Brings the wheel closer to the machine body. A negative offset will result in a wider track width, thus taking the wheel further away from the machine body. The following drawings illustrate positive and negative offsets.

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Wheel offset

LOAD AND SPEED RATINGS

On the sidewall of a tyre you can find the load index and Speed Symbol following the key sidewall size markings.
 
  • The Load Index is a numerical code associated with the maximum load a tyre can carry
  • The Speed Symbol indicates the speed at which the tyre can carry a load corresponding to its load index.
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technical knowledge tyre sml

HUB FITTING WHEELS AND RIM TERMS

Hub fitting wheels have a bore and a number of stud holes to suit the hub to which it is being attached. When fitting the wheeks to the hub, it is very important to tighten at the correct torque in order to prevent nuts from working loose. It is also important to check after a short period of use and on a regular basis thereafter. The correct nut must be used to suit the wheel seating eg. conical or spherical.

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hub fitting  

A = Bore (mm)
B = Pitch circle Diameter (PCD) mm
BD = Back depth (mm)
ET = Offset (mm)
E = stud hole diameter (mm)
= Rim diameter (Inches)
G = Rim width (Inches)

Common Stud Patterns

NO. STUDS PCD INCHES PCD METRIC STUD TO STUD TYPE
4  4"  101.6mm  71.84mm  Mini
4¼"  108mm  76.33mm  Escort/Cortina
4½"  114.3mm  80.82mm  Most Japanese
4¾"  120.65mm  85.31mm  
4¼" 108mm 63.45mm  HT Holden
4½"  114.3mm  67.18mm  Falcon/Toyota
4¾"  120.65mm  70.92mm  Holden HQ
5" 127.00mm  74.65mm Delta Alloy
5   140mm  82.29mm Ag
5½"  139.7mm  69.85mm Landcruiser

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