(Note: Semi trailers and simple trailers have no front axle set)
Axle: | Axle number (from front) for which data is required. | |
Tyre Size: | Size of tyres fitted on the axle. Select from drop down list. | |
Tyre Configuration: | Single, Single Large, Single Mega or Dual. Select from drop down list. |
Mixed Freight: | assumes that the payload consists of a mixture of items which have been sensibly loaded so that 70% of the load mass is in the bottom half of the load space and 30% of the mass is in the top half. This would include container trucks, curtainsiders and van body vehicles. |
Uniform Density: | applies to vehicles which can be loaded from the load bed to the load height with a uniform density load. It also assumes that payload Cg is midway between the load bed and the load height. This category includes logs , stock, liquid tankers, tipper bodies, chip liners etc. Car carriers can be certified using this load type as this will underestimate their SRT and be conservative. |
Other: | is for loads not covered by the previous two categories. In this case the user needs to calculate the height of the payload Cg. This category includes large single item loads such as heavy machinery and stockfeed hopper vehicles with triangular crossection tanks. |
Gross Mass: | Gross mass carried by the axle group in kgs. |
Tare Mass: | Unladen vehicle mass carried by the axle group in kgs. |
Payload Mass: | Payload mass carried by the axle group in kgs. |
Notes:
Load Bed Height from the ground: | Height of the load bed from the ground in metres. |
Load Height from the ground: | Max height of the load from the ground in metres. |
Payload Cg Height from the ground: | Height of the payload centre of gravity from the ground in metres. |
Notes:
Suspension type: | Select from Generic Air - low roll stiffness type, Generic Air - high roll stiffness type, Generic Steel or User Defined. Fill in remaining fields using manufacturer-supplied data if user defined option selected. |
Suspension Brand: | Brand and Model ID of suspension used. |
Total Roll Stiffness / axle: | Roll stiffness per axle in Newton metres per radian. |
Spring Stiffness / spring: | Spring stiffness per spring in Newtons per metre. |
Suspension Track Width: | Spacing between spring centres in metres. |
Axle lash: | For a steel spring as the load changes from compression to tension there is a small range of axle displacement for which there is minimal resistance. This is called the lash (mm). With air suspensions there is minimal resistance in tension until the dampers or retaining straps prevent further movement. Thus the lash is large, typically 300mm or more. |
Roll Center Height: | Measured from axle centre in metres. Positive is above the axle and negative below. |
Notes:
Suspension Name and Model Number |
Suspension spring stiffness (N/m) |
Suspension track width (m) |
Total roll stiffness per axle (Nm/radian) |
Suspension lash (mm) |
Roll centre height from axle (m) |
Generic - steer axle | 185000 | 0.8 | 130000 | 15 | -0.02 |
Generic steel | 1000000 | 0.97 | 520000 | 30 | 0.2 |
Generic air - low roll stiffness type | 350000 | 0.97 | 280000 | 300 | 0.2 |
Generic air - high roll stiffness type | 350000 | 0.97 | 780000 | 300 | 0.2 |
Suspension Parameter |
Units used by supplier |
Units required by SRT Calculator |
To convert multiply by |
Spring stiffness | lb/in | N/m | 175 |
Roll stiffness | in-lb/degree | Nm/radian | 6.47 |
Roll stiffness | Nm/degree | Nm/radian | 57.3 |
Lash | in | mm | 25.4 |
Roll centre, track width | in | m | 0.0254 |