Running Gear Capacity and Axle Application
- Determine running gear capacity from all component ratings.
- Evaluate hitch load, lateral balance, and Torflex application.
- Inspect tire clearance, axle orientation, and suspension movement.
- Portable wheel-load scales — Measure individual wheel loads to evaluate axle loading and side-to-side distribution in the intended loaded condition.
- Tape measure — Measure axle spacing and tire clearance; compare the installation with the tire manufacturer's maximum diameter.
- Spirit level — Check trailer attitude while coupled in its intended towing configuration.
- Inspection light and mirror — Read component identification and inspect axle orientation, spring eyes, equalizers, and mounting areas.
- Jack and rated support stands — Safely support the trailer when access or suspension movement checks require lifting; never work beneath a trailer supported only by a jack.
A running gear assembly is limited by its lowest-rated component, not simply by the axle beam rating. Dexter illustrates this with components rated for 4,000 pounds per axle: two wheels rated at 1,500 pounds each reduce assembly capacity to 3,000 pounds, and two tires rated at 1,400 pounds each reduce it further to 2,800 pounds. The trailer manufacturer remains responsible for evaluating, specifying, and testing the complete combination.
Gross Axle Weight Rating includes the wheels and tires and describes capacity at the tire-ground interfaces. When selecting axle capacity, subtract hitch load from gross vehicle weight and consider the final load distribution. The load on the heavier side must not exceed half the rated capacity of the axle or axles.
Torflex suspensions use natural rubber cords supporting steel inner bars and torsion arm/spindle assemblies. Trailers with these non-equalized suspensions must travel level to distribute axle loads properly. Dexter identifies #12T, #13T, and #14T as Torflex models designed for triple-axle applications; the listed conventional models are not recommended for that arrangement.
Axle spacing must provide at least 1 inch between tires under every loading condition. Use the tire manufacturer's maximum diameter when determining spacing, and allow additional clearance if tire chains require it. Wider axle spacing can increase tire scrubbing and stresses on axle components and mountings.
Dexter axles are directional: their front must face forward and their top must face upward. Leaf-spring eyes and equalizers must rotate freely rather than bind. Springs mounted below the axle tube lower frame height, while springs mounted above it raise frame height. Dual wheels must not be used as singles unless the hubs are specifically designed for that application.
How It Works
Capacity follows the weakest component
The running gear assembly is limited by its lowest-rated component, so the axle beam rating alone cannot establish usable capacity. Dexter's example reduces a system with components rated for 4,000 pounds per axle to 3,000 pounds with two wheels rated at 1,500 pounds each, then to 2,800 pounds with two tires rated at 1,400 pounds each. The trailer manufacturer remains responsible for evaluating, specifying, and testing the complete combination; dual wheels must not be used as singles unless the hubs are specifically designed for that application.
Load distribution matters as much as total load
Gross Axle Weight Rating includes wheels and tires and describes capacity at the tire-ground interfaces; subtract hitch load from gross vehicle weight when selecting axle capacity, then evaluate the final distribution. The heavier side must not exceed half the rated capacity of the axle or axles, because an acceptable total can conceal an overloaded side. Torflex rubber cords support the inner bars and torsion arm/spindle assemblies without an equalizing linkage, making level towing important for axle load distribution; Dexter identifies #12T, #13T, and #14T as models designed for triple-axle applications.
Clearance and geometry control stress
Axle spacing must maintain at least 1 inch between tires under every loading condition, using the tire manufacturer's maximum diameter and allowing additional clearance when chains require it. Wider spacing can increase tire scrubbing during turns because the tires resist following different paths, adding stress to axle components and mountings. Axle fronts must face forward and tops upward, spring eyes and equalizers must rotate freely, and spring placement below or above the axle tube respectively lowers or raises frame height.
Step-by-Step Procedure
0/6 doneApplication Limits and Examples
| Minimum clearance between tires | 1 inch under every loading condition |
| Maximum load on the heavier side | One-half of rated axle capacity |
| Example with two 1,500-pound wheels | 3,000-pound assembly capacity despite other components rated at 4,000 pounds |
| Same example with two 1,400-pound tires | 2,800-pound assembly capacity |
Diagnostic Chart
| Symptom | Check | Spec / Expected | Likely cause & fix |
|---|---|---|---|
| The axle beam rating appears adequate, but assembly capacity is uncertain. | Identify the axle, suspension, wheel, and tire ratings. Compare each component's contribution to assembly capacity rather than comparing a single wheel rating directly with an axle rating; verify hub suitability if dual wheels are being used as singles. | Assembly capacity is limited by the lowest-rated component. Dual wheels must not be used as singles unless the hubs are specifically designed for that application. | Lower-rated wheels or tires can limit an otherwise higher-rated assembly; an unsuitable hub and wheel application is not validated by beam capacity. Basis: applications-manual-(lit-008-00) |
| Total axle load appears acceptable, but loading is concentrated on one side. | Account for hitch load, measure the final wheel loads, and compare the heavier side with the applicable rated axle capacity. | Maximum load on the heavier side: One-half of rated axle capacity. | Uneven cargo or equipment placement can overload one side while leaving the opposite side lightly loaded. Basis: applications-manual-(lit-008-00) |
| A Torflex trailer shows uneven axle loading or has an uncertain triple-axle configuration. | Verify level towing in the intended loaded and coupled condition. Identify the Torflex model rather than assuming every model is suitable for the arrangement. | Non-equalized Torflex trailers must travel level. #12T, #13T, and #14T are designed for triple-axle applications; the listed conventional models are not recommended. | An unlevel trailer can distribute load unevenly across non-equalized axles, and the selected model may be unsuitable for the configuration. Basis: applications-manual-(lit-008-00) |
| Tires contact each other, scrub excessively, or suspension movement appears restricted. | Evaluate clearance using maximum tire diameter and all loading conditions, including chain needs. Check axle direction and free rotation of spring eyes and equalizers; do not assume wider spacing is automatically better. | Minimum clearance between tires: 1 inch under every loading condition. Axle front faces forward, top faces upward, and spring eyes and equalizers rotate freely. | Insufficient spacing can allow contact; excessive spacing increases scrub and stress, while incorrect orientation or binding violates installation requirements. Basis: applications-manual-(lit-008-00) |
At the Bay: Diagnose the Case
CASE 1 / 4
The axle beam rating appears adequate, but assembly capacity is uncertain.
- Test
- Compare
- Correct
Select the next check
Basis: applications-manual-(lit-008-00). A likely cause is a hypothesis; confirm it with the applicable service procedure before repair.
Common Bay Mistakes
- ✕ Treating the axle beam rating as the complete assembly rating.
- ✕ Using total axle weight to overlook an overloaded side.
- ✕ Assuming every Torflex model supports triple-axle use.
- ✕ Checking tire clearance only with the trailer unloaded.
Quick Check
Practice only — not scored.
Plan the Service Sequence
Planning practice only. Follow the applicable manufacturer's instructions, employer safety program and qualified supervision on real equipment.
Plan the first action. Compare the service steps with the bay mistakes.
Hands-on: Shop Test Equipment
Dial Indicator — Bearing End Play
Magnetic-base dial indicator (0.001 in) on the hub face, spindle nut adjustment
🛠 Equip your bay for this test →Symptom: Bearing service — set end play after repack.
Spec limits used
- 0.001–0.010 in — Allowable end play, double-nut wheel end (Dexter 9-15K service manual, p.64)
- 0.008 in — Nev-R-Lube 50 mm max axial end play (Dexter 059-831-00)
- illustrative only — Face runout limit (General shop practice)
Simulated readings for practice. Always follow the manufacturer's procedure and values on a real trailer.
Source: applications-manual-(lit-008-00) — 2-14