Tire - Wheel (Rim) Calculator

Display Wheel/Tire Information

                  Tire Size         |  Wheel Width / Offset      
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Wheels:

  

Wheel Size

BackSpace
   

Tires:

  

Tire Size

Section Width
Side Wall
Diameter
Circumference

Revolutions per Mile
   

Backspace
Backspacing is the distance from the inside bolting surface (Hub mounting surface) of the rim to the outer edge of the inboard side of the rim.  To determine backspacing simply lay the wheel face down and lay a straight edge across the wheel.  Use a ruler and measure the distance from the bottom of the straight edge to the hub mounting pad.

Offset
Offset is the distance from a wheels hub mounting surface to the center line of the wheel.  There are three types of offset:

Zero:       Hub mounting surface is even with the center line of the rim.
Positive:  Hub mounting surface is towards the front side of the wheel's center line (more BS)
Negative: Hub mounting surface is toward the back side of the wheel’s center line (less BS)


 

An increase in POSITIVE offset will give you more BackSpace. For approximately every 6 mm you will get .25 (1/4) inches of additional BackSpace. Likewise for a decrease in offset will result in less BackSpace.
Example: A 7" wheel with 0 mm offset will result in 4.0" of BackSpace. A positive offset of +12 mm will result in 4.47" of BackSpace (Appox 1/2 inch)

Calculator Notes:

Result generated by this calculator is dependent on an accurate tire diameter. Actual tire diameter can vary quite a bit from brand to brand. The tire calculator should be close, but don't depend on it. Also rounding may make slight differences and noticed that different BROWSERS and/or version of JAVA produced slightly different results.

Some information may not be 100% accurate but it is what was found doing searches on the internet. If you have real proof or would like to add additional information please let me know.

 
© 2010 GB Janssen .... aka Black_Magic