How to Measure a Trailer Axle 3
Replacing a trailer axle starts with two critical dimensions: hub face and spring center. You must also identify the axle capacity, suspension type, brake or idler configuration, bolt pattern, spring position, and wheel-end components before ordering.
Quick Answer: The Two Measurements Most Replacement Axles Require
- Hub Face (HF): Distance from one wheel-mounting surface to the other wheel-mounting surface.
- Spring Center (SC): Distance from the center of one spring seat to the center of the opposite spring seat.
Axle sizes are often written as Hub Face / Spring Center. For example, 95/80 means a 95-inch hub face and an 80-inch spring center.
Step 1: Find the Axle Label or Serial Number
Before measuring, inspect the center portion of the axle tube—especially the rear-facing side—for a manufacturer label, identification tag, or stamped serial number. A readable Dexter label may identify the serial number, customer or model number, axle configuration number, capacity, hub face, spring center or outside-of-bracket dimension, torsion start angle, and a Nev-R-Adjust brake callout when applicable.
Photograph the complete label before cleaning it. Even a partially readable serial number or description number may help identify the original axle.
What If the Label Is Gone?
Axle labels are exposed to water, road debris, corrosion, paint, and years of use, so missing or unreadable labels are common. If the label cannot be used, continue through this guide and identify the axle from a complete set of measurements, component details, and photographs.
Step 2: Measure the Hub Face
The hub-face measurement is the distance between the two wheel-mounting surfaces—the flat faces where the backs of the wheels contact the hubs or brake drums. Do not measure from grease cap to grease cap, spindle tip to spindle tip, or outside edge to outside edge.
- Park the unloaded trailer on a firm, level surface and secure it from moving.
- Remove the wheels if they prevent access to the mounting surfaces.
- Place the end of a tape measure against one wheel-mounting surface.
- Measure straight across to the matching wheel-mounting surface on the opposite hub.
- Record the measurement to the nearest practical fraction of an inch and repeat it for verification.
Step 3: Measure the Spring Center
On a leaf-spring axle, spring center is measured from the center of one welded spring seat to the center of the spring seat on the opposite side. This dimension positions the axle on the trailer’s leaf springs and must match the suspension mounting arrangement.
- Locate both spring seats welded to the axle tube.
- Identify the centerline of each seat.
- Measure from the center of one seat to the center of the other.
- Record the dimension and verify it a second time.
Spring center is often close to the trailer-frame width, but do not assume a fixed offset or calculate it from frame width alone. Measure the actual axle and suspension.
Step 4: Identify the Axle Capacity
Use the manufacturer label, etched serial number, trailer certification label, original build information, or manufacturer lookup whenever possible. If those records are unavailable, tube size, bolt pattern, brake size, bearings, seal, spindle, and hub configuration can help narrow the likely axle family—but no single feature establishes the rating by itself.
Common Axle Beam and Wheel-End Reference
The following combinations are common on many light- and medium-duty trailer axles. Use them to narrow the possible axle family, then verify the complete axle before ordering.
← Swipe left/right to see the full table →
| Common Axle Rating | Common Round Beam Outside Diameter | Typical Wheel-End Clues |
|---|---|---|
| 2,000–2,200 lb | Varies; commonly smaller than 2-3/8 inches | Often idler hubs with 4- or 5-lug wheel patterns |
| 3,500 lb | Approximately 2-3/8 inches | Commonly 5 on 4.5 with 10 x 2-1/4-inch brakes when equipped |
| 5,200–6,000 lb | Approximately 3 inches | Commonly 6 on 5.5 with 12 x 2-inch brakes |
| 7,000 lb | Approximately 3 inches | Commonly 8 on 6.5 with 12 x 2-inch brakes |
| 8,000 lb | Often approximately 3-1/2 inches | Commonly 8 on 6.5 with heavier hubs, bearings, brakes, and spindles |
Confirm the Wheel Bolt Pattern
The bolt pattern must match the trailer wheel. Record both the number of wheel studs and the bolt-circle diameter. These are common axle and hub combinations:
- 3,500 lb axles: Most commonly 5 lug on a 4.5-inch bolt circle, although other 5-lug patterns and some 6-lug configurations are available.
- 5,200 lb axles: Commonly 6 lug on a 5.5-inch bolt circle.
- 7,000 lb axles: Commonly 8 lug on a 6.5-inch bolt circle.
Five-lug hubs require special attention because several different bolt circles exist and they can be difficult to distinguish visually. Use our How to Measure a 5-Lug Trailer Axle Bolt Pattern guide for the correct measurement method.
Select any diagram to open the full-size image.
Step 5: Identify the Complete Axle Configuration
Hub face and spring center determine basic fit, but they do not describe the entire axle. Record each of the following before ordering:
- Axle type: leaf-spring or torsion
- Wheel end: idler hub, electric brake, hydraulic drum brake, or disc brake
- Spindle: straight or drop; record the exact drop amount
- Spring position: overslung (springs above the axle) or underslung (springs below the axle)
- Spring type: double-eye or slipper
- Brake size: backing-plate diameter and shoe width when known
- Bolt pattern and stud size
- Lubrication system: standard grease, Dexter E-Z Lube, Posi-Lube, Dexter Nev-R-Lube, oil bath, or another system
- Wheel and tire size, offset, and load rating
Overslung vs. Underslung
An overslung axle has the springs above the axle tube; an underslung axle has the springs below it. This changes ride height and clearance. Photograph the U-bolts, tie plates, spring seats, and complete suspension before disassembly.
Single, Tandem, and Triple Axles
On multi-axle trailers, measure and identify every axle rather than assuming they are identical. Record hub face and spring center for each axle, axle-to-axle spacing, hanger condition, equalizer type, spring type, tire clearance, and whether the front and rear axles use the same brake and hub configuration.
Dexter and Rockwell American Resources
For Dexter identification terminology and manufacturer measurement diagrams, use Dexter’s axle-measurement guide and axle-label guide.
If your axle is Rockwell American, our Rockwell American Axle Service Manual and Maintenance Guide provides brake, hub, bearing, seal, suspension, Posi-Lube, and replacement-parts references.
Measuring a Bent Axle or an Axle With Missing Hubs
The most reliable replacement measurements come from a complete, undamaged axle. If the tube is bent, a spindle is damaged, or one or both hubs are missing, use every remaining reference point and compare the results with the trailer frame, suspension, wheel clearance, and manufacturer information.
If the axle is bent between the spring seats, do not rely on the damaged tube to establish spring center. Measure laterally between the corresponding suspension mounting lines on the trailer and confirm that the hangers, frame, and suspension have not shifted or been damaged before using that dimension.
One Hub Is Missing
If the axle is symmetrical and one complete side remains, measure from the spring-center line to the remaining hub face. The remaining hub-face overhang multiplied by two, plus the spring-center measurement, can provide an estimated hub face: Spring Center + (One-Side Overhang × 2) = Estimated Hub Face. Confirm the result against the trailer frame, fenders, wheel position, and tire clearance before ordering. Do not assume symmetry if the axle has an unusual or custom configuration.
Both Hubs Are Missing
Brake-flange spacing, spindle dimensions, bearing numbers, and overall beam length can help identify the axle, but fixed add-or-subtract formulas are not universal. Hub, drum, brake, and spindle designs can change the distance between these reference points and the final hub face. Contact the axle manufacturer or Johnson Trailer Parts with photographs and all available measurements before ordering.
Replacement Trailer Axle Ordering Checklist
Gather the information below before contacting a supplier or placing an order. Start with the first group, then provide the additional configuration and identification details that are available.
Information Needed to Select or Order an Axle
- Hub face
- Spring center or torsion outside-of-bracket
- Axle capacity
- Number of axles needed
- Leaf-spring or torsion suspension
- Idler or brake axle, including brake type and size
- Bolt pattern and stud size
Important Configuration Details
- Straight or drop spindle, including the exact drop amount
- Overslung or underslung spring position
- Double-eye or slipper springs
- Standard electric or Dexter Nev-R-Adjust self-adjusting brakes, if applicable
- Wheel and tire size and wheel offset
- Required frame, tire, and fender clearance
- Photos of the axle label, both wheel ends, suspension, and complete axle
Helpful for Identification or an Exact Match
- Manufacturer and serial or part numbers
- Axle-tube shape and diameter
- Bearing and seal numbers
- Lubrication system: standard grease, E-Z Lube, Posi-Lube, Nev-R-Lube, or oil bath
Shop trailer axles and running gear from Johnson Trailer Parts.
Trailer Axle Measurement FAQs
How do I measure trailer axle hub face?
Measure between the two wheel-mounting surfaces where the backs of the wheels contact the hubs or brake drums. Do not measure from grease cap to grease cap, spindle tip to spindle tip, or outside edge to outside edge.
How do I measure trailer axle spring center?
Measure from the center of one spring seat to the center of the other spring seat. If the axle is bent between the seats, measure between the corresponding suspension mounting lines on the trailer and confirm that the hangers, frame, and suspension have not shifted or been damaged.
Where is a Dexter axle serial number located?
Dexter states that its axle label is normally on the rear-facing side of the axle tube. Many axles also have a nine-digit serial number etched near the center of the rear side of the beam. Chalk may help reveal a faint engraving.
How can I determine what capacity trailer axle I have?
Start with the axle label, etched serial number, trailer certification label, or original build records. If those are unavailable, use the axle-tube diameter and shape, brake size, bearings, seal, spindle, hub, and bolt pattern together to narrow the likely axle family. No single measurement or component proves the axle capacity by itself.
Is hub face the same as overall axle length?
No. Hub face is measured between the two wheel-mounting surfaces. Overall axle length may include spindle ends, threads, or other features and is not the standard replacement-axle width.
Can I calculate spring center from the trailer-frame width?
Spring center may be close to the frame width, but mounting arrangements vary. Measure the actual centers of the axle’s spring seats rather than relying on a fixed formula.
What measurements are needed for a torsion axle?
Torsion axles commonly require hub face, outside-of-bracket dimension, bracket orientation and profile, start angle, capacity, brake or idler configuration, and wheel-end specifications. Follow the axle manufacturer’s terminology and order form.
Can a higher-capacity replacement axle increase my trailer’s GVWR?
No. Replacing the axle does not automatically change the trailer manufacturer’s GVWR. Capacity remains limited by the complete trailer design and its lowest-rated applicable component.
Will my existing wheels fit the replacement axle?
Only if the wheel bolt pattern, stud size, hub-pilot requirements, wheel offset, load rating, tire size, and available frame and fender clearance are compatible. Matching the hub-face measurement does not automatically mean the old wheels and tires are correct for the new axle.
Why does my axle tube bow upward in the middle?
Many axles are manufactured with upward camber to compensate for deflection under load. This can be normal. Have the axle inspected if it has impact damage, abnormal tire wear, damaged spindles, alignment problems, or an unusual change in camber.
Need Help Identifying a Replacement Axle?
Johnson Trailer Parts can help review your measurements and axle information. Before contacting us, gather the hub face, spring center, axle capacity, bolt pattern, brake size, suspension configuration, label or serial number, and clear photographs of the axle and wheel ends.
Call or Text: (602) 292-9690
Email: sales@johnsontrailerparts.com
My axel where the wheel hub goes measured, using calipers, 1.05 inches. Would this be considered a 1 inch axel?
When using calipers to measure your axle spindle, if the measurement is 1.05 inches, this generally indicates a 1-inch spindle. Spindle sizes are typically nominal (rounded) measurements, and slight variations like 1.05 inches are still considered within the tolerance for a 1-inch axle spindle.
My axle measures at 1.65″ in diameter. Having such a hard time finding this size. Is that considered 1.75 or 1.5?