Documentation/Engine/Units/accessory wheel data

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Revision as of 21:33, 24 February 2018 by Smarty (talk | contribs) (Added useful formulas for calculating the rolling radius/bb location)

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The accessory_wheel_data unit class is used to define wheels for most vehicle types, and tires for the player's vehicle. It defines the path to the visible model, the look used, whether it is paintable, and some physical characteristics of the tire (for playable vehicles). Units of this type are typically found in:

  • /def/vehicle/ai_wheel/*.sii (wheels used for AI vehicles)
  • /def/vehicle/f_tire/*.sii (front tires for playable trucks)
  • /def/vehicle/f_wheel/*.sii (front wheels for AI trucks)
  • /def/vehicle/r_tire/*.sii (rear tires for playable trucks)
  • /def/vehicle/r_wheel/*.sii (rear wheels for AI trucks)
  • /def/vehicle/tr_wheel/*.sii (wheels for trailers)


Many common attributes are inherited from accessory_data. Required attributes are bolded.

Name Type Default Value Description
model string Path to the descriptor (.pmd) of a valid wheel model. Valid wheel models have left and right variants and a bb model locator which sets the rolling/collision radius.
look token default Selects the look to be used.
paintable boolean false When true, enables the color picker on the garage, truck browser, etc screens. The paint color is applied to pieces of the model whose materials use the paint flavor.

Note: Unlike other accessories, wheel accessories do not inherit the paint color(s) of the vehicle they belong to.

default_color float3 (1.0, 1.0, 1.0) Sets the default color for the wheel accessory.
roll_resistance float 5.5 Tire rolling resistance in kg/t (EU Tyre Labelling Regulation 1222/2009)
wet_grip float 1.0 Tire wet grip performance (EU Tyre Labelling Regulation 1222/2009)
noise_volume float 73.0 Tire rolling noise in dB (EU Tyre Labelling Regulation 1222/2009)

EU Tire Label Letter Grades for Truck and Bus (C3) Tires

From ETRMA Industry Guidelines Version 4 (5 July, 2012)

Where numerical data is not available, the following tables are useful to translate letter grades from tire labels to the values used for roll_resistance and wet_grip.

Rolling Resistance

Class RRC in kg/t
A RRC ≤ 4.0
B 4.1 ≤ RRC ≤ 5.0
C 5.1 ≤ RRC ≤ 6.0
D 6.1 ≤ RRC ≤ 7.0
E 7.1 ≤ RRC ≤ 8.0
F RRC ≥ 8.1
G Empty

Wet Grip

Class G
A G ≥ 1.25
B 1.10 ≤ G ≤ 1.24
C 0.95 ≤ G ≤ 1.09
D 0.80 ≤ G ≤ 0.94
E 0.65 ≤ G ≤ 0.79
F G ≤ 0.64
G Empty

Calculating Rolling Radius from RPM or RPK

To get a correct rolling radius for accurate performance, it is possible to use the Revolutions per Mile (RPM) or per Kilometer (RPK) figure published by the tire manufacturer. This is used to set the position of the bb locator in the wheel model.

From RPM

The rolling radius in meters is given by:

rrolling = 1609.34 ÷ ( RPM × 2 × π )

From RPK

The rolling radius in meters is given by:

rrolling = 1000 ÷ ( RPK × 2 × π )

Related Classes