QuickAxle Calculator

Heavy Duty Trailer Axle Calculator

Estimate heavy-duty trailer axle fit-up details including overall tire width, axle beam capacity, and air brake configuration before contacting QuickAxle.

Important: This calculator is for estimating and fit-up support only. Final axle, brake, wheel-end, tire, suspension, and GAWR approval must be verified by the vehicle manufacturer, final-stage manufacturer, alterer, or qualified technician. Final GAWR may be limited by the lowest-rated component in the axle, suspension, brakes, hubs, bearings, wheels, tires, or other wheel-end equipment.
Step 1

Overall Width and Tire Clearance

Estimate inside tire width and outside tire width from axle track, tire width, and wheel configuration.

Tire width is populated from the selected tire size and wheel configuration. Actual dimensions vary by manufacturer, model, rim width, inflation, and load.
This value can be overwritten if you have the exact tire manufacturer's published section width or overall width.
For dual wheels, this is wheel offset (O). The calculator derives wheel spacing as S = 2 x O. Wheel offset, outset, and inset are reference values. Verify the exact wheel part number before relying on calculated width or beam capacity.

Width Results

Axle track (T): Not calculated yet

Tire width (W): Not calculated yet

Wheel spacing (S): Not applicable

Tire track (TT): Not applicable

Outside tire width (OTW): Not calculated yet

Inside tire width (ITW): Not calculated yet

Formula used: Not calculated yet

Step 2

Axle Beam Capacity

Calculate estimated axle beam capacity from axle track, beam center, moment arm, and selected axle family.

Wall thickness may be listed on the axle tag, suspension documentation, or axle part number information. If you are not sure, send QuickAxle photos before relying on the calculated capacity.
Moment arm is calculated as (axle track - beam center) / 2.

Beam Capacity Results

Beam configuration used: Not calculated yet

Axle track: Not calculated yet

Beam center: Not calculated yet

Moment arm: Not calculated yet

Moment limit used: Not calculated yet

Beam capacity: Not calculated yet

Calculation status: Not calculated yet

Step 3

Brake Capacity - Friction Material

Estimate friction material brake capacity from the published friction rating, rated AL factor, actual AL factor, and static loaded radius values.

Use the published friction material rating for the selected brake lining or pad. Ratings depend on the tested brake size, AL factor, and static loaded radius.
Standard heavy-duty trailer axle default is AL 180, based on a Type 30 chamber and 6.0 inch slack adjuster.
Chamber type is treated as the service-side effective area for AL factor estimating.
Actual AL factor is calculated as chamber effective area x slack adjuster length.

180

Assumes rated SLR and actual SLR are the same unless specified otherwise.

Friction Material Results

Brake type: S-cam drum brake

Brake size: 16.5 x 7.0 drum brake

Friction material rated capacity: 23,000 lb

Rated AL factor: 180

Actual AL factor: 180

Rated SLR: 20.8 in

Actual SLR: 20.8 in

Friction material brake capacity: Not calculated yet

Calculation status: Waiting for valid friction material inputs.

Axle Fit-Up Summary

Review the calculated width information, beam capacity, friction material brake capacity, calculated axle rating, and limiting factor.

Estimated outside tire width: Not calculated yet

Estimated inside tire width: Not calculated yet

Beam capacity: Not calculated yet

Friction material brake capacity: Not calculated yet

Calculated axle rating: Needs beam and brake capacity calculation

Limiting factor: Cannot determine until beam and brake capacity are calculated

Need Help Confirming the Correct Axle?

Send QuickAxle your axle measurements, tire and wheel information, brake details, and photos of the axle or suspension tags.

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