Steer, Drive, and Trailer Axle Weights Explained

Contents

• Steer axle
• Drive axles
• Trailer axles
• What causes each group to be heavy
• Common mistakes
• Sources

Steer axle

The steer axle is the single front axle of the tractor. It carries the weight of the cab, engine, and the share of trailer load transferred forward through the fifth wheel.

• On a loaded tractor-trailer, steer axle readings commonly fall between 10,000 and 12,000 lb, but the legal limit depends on the applicable axle rule, tire load ratings, and manufacturer specifications — not on what is typical.
• Fifth-wheel position directly affects steer weight. Sliding the fifth wheel forward (toward the cab) adds weight to the steer; moving it back reduces it.
• The steer axle check involves the axle weight limit, tire ratings, and registration. Do not assume a familiar target number is the legal limit in every state.

Drive axles

Drive axles sit under the rear of the tractor. A standard tractor has a tandem drive group — two axles sharing the same housing — which is usually the heaviest group on a loaded combination.

• The federal Interstate tandem limit is 34,000 lb. State limits on non-Interstate roads should be checked separately using the state page.
• Drive tandem weight is affected by both fifth-wheel position and trailer tandem position. Moving the fifth wheel back or sliding trailer tandems forward typically increases drive weight.
• When the drive tandem reads near or above 34,000 lb, check the bridge formula for the actual axle spacing. Spacing affects the allowable weight beyond the simple tandem figure.

Trailer axles

Trailer axles carry the rear portion of the load. Most semi-trailers have a tandem group that slides along a rail on the trailer frame, which gives the driver a tool for adjusting weight distribution.

• Sliding trailer tandems toward the rear of the trailer moves weight from the drive group to the trailer group. Sliding them forward moves weight back to the drives.
• The federal Interstate tandem limit of 34,000 lb applies to the trailer group in the same way it applies to the drive group.
• After any tandem slide, re-weigh before treating the adjustment as complete. The second ticket is the confirmation that the intended group changed by the intended amount. Read How to Slide Tandems for the step-by-step workflow.

What causes each group to be heavy

When a group is heavy, the fix depends on which group and whether the cause is distribution or total weight. Distribution problems can sometimes be corrected by adjusting cargo position, fifth-wheel slide, or tandem position. A total-weight problem requires reducing the load or obtaining a permit.

Common mistakes

Only checking gross weight. Gross is one of four checks — steer, drive, trailer, and gross all need to pass independently. An axle group can fail even when total weight is well under the gross limit.

Assuming the same rules apply on every road. Federal Interstate limits are a baseline. State statutory limits, bridge postings, and permit conditions can set different requirements on non-Interstate routes.

Moving tandems without re-weighing. Sliding tandems changes distribution, but without a re-weigh there is no confirmation that the right group changed by the right amount. The second ticket is the evidence.

Read Gross Vehicle Weight vs. Axle Weight for the broader distinction between gross and axle checks.

Sources

This page uses FHWA size and weight material and FHWA bridge formula context.