How to Attach Trailer to Bike | Rear Axle Hitch Setup

Attaching a trailer to a bike means mounting the hitch hardware to the rear axle, then connecting the trailer arm and securing the safety tether.

For the full breakdown, see our best Aluminum Bike Trailer guide.

Whether you’re hauling kids, groceries, or camping gear, the connection between bike and trailer is the one part you can’t get wrong. A trailer that detaches mid-ride is a hazard, and a hitch installed on the wrong axle side can damage your frame.

Here’s what the attachment process actually looks like, step by step, for the most common setups.

Know Your Axle Type First

Before touching any tools, identify whether your bike has a quick-release skewer or a thru-axle. Burley’s hitch guide makes this the very first step, and for good reason: the hitch hardware physically replaces or wraps around part of the axle, so the axle type dictates which parts you need.

Quick-release bikes use a hollow skewer with a lever on one end; thru-axle bikes use a solid bolt that threads directly into the frame. If you have a thru-axle bike, you’ll likely need a specific thru-axle adapter — Burley notes its standard Steel Hitch fits most bikes, but some specialty frames need an additional adapter.

A quick check: look at the rear dropout where the wheel meets the frame. A lever with a spring on one side means quick-release. A hex bolt head flush with the frame means thru-axle.

Mounting the Hitch on the Rear Axle

Once you’ve confirmed compatibility, the mounting process follows the same logic across brands. For Thule’s ezHitch system, the instructions are explicit: remove the nut and washer(s) from the left end of the axle — that’s the side opposite the sprockets and chainring — then place the ezHitch on the left side of the axle and reinstall the hardware, tightening to your bike manufacturer’s recommended torque.

Burley’s Steel Hitch follows the same left-side placement. The hitch must sit flush against the dropout; if it doesn’t, or if the axle becomes too short after installation, you need an adapter. Burley is blunt about this: never force the installation. A hitch that sits crooked will fail under load.

After tightening, check the clearance: If your setup sits lower, the trailer arm will drag on driveways and curbs.

Connecting the Trailer Arm and Securing the Tether

With the hitch mounted, you connect the trailer’s arm. For Thule trailers, insert the hitch arm into the left VersaWing — the receiver on the trailer frame — hold the button, and slide until the large pin snaps into place. Then verify with a sharp pull to confirm the pin is fully seated.

Burley trailers use a Flex Connector that clicks onto the hitch ball. If you have an older Burley trailer with the Classic Hitch, you’ll need the Steel Hitch (part number 960116) plus the correct Flex Connector: 950037 for round tow bars, 950038 for square ones.

Every brand’s procedure ends the same way: clip on the backup tether or safety strap. This is the redundant strap that keeps the trailer attached even if the primary connection somehow releases. Thule instructs users to inspect the hitch arm for wear or damage before each use, and the tether is not optional.

That’s the downward force on the hitch ball itself, not the trailer’s total weight — but it’s a reminder that the tongue weight can’t be excessive.

Common Mistakes That Cause Trailer Failures

The most frequent errors are using the wrong axle type, failing to retighten the axle hardware, skipping the safety tether, and assuming universal fit without checking brand-specific compatibility.

Here’s what each one looks like in practice:

• Wrong axle type. A quick-release hitch forced onto a thru-axle bike won’t seat properly and can shear under load. Check before you buy.
• Loose axle hardware. Reinstalling the nut or thru-axle to finger-tight is not enough. Use a torque wrench to the bike manufacturer’s spec, and re-check after the first ride.
• Skip the backup tether. This is the single safety component that catches failures. If the hitch ball disengages mid-ride and there’s no tether, the trailer detaches completely.
• Assuming universal fit. Even within one brand, older trailers need conversion parts. Burley’s Steel Hitch is included with newer trailers, but older ones require the part plus the correct Flex Connector.

One more overlooked detail: the left-side mount. Both Burley and Thule specify the left side of the rear axle (opposite the drivetrain) because mounting on the right interferes with the chain and derailleur.

Torque specs vary by bike brand, so consult your bike’s manual. If you can’t find a torque spec, a snug, consistent tightening with a torque wrench set to the wheel’s axle spec is the safe baseline.

When the connection is done right, the trailer tracks straight behind the bike, the hitch sits level, and the tether hangs loose but connected. That’s the setup that survives a full season of rides.