Bicycle Trailer Guide (cont'd) - The Trailer Hitch - Bikes At Work
A good hitch should allow the bike to freely turn left or right, "pitch" (angle up or down relative to the trailer, such as when climbing over a curb), and lean left or right (if a two-wheel trailer). Some trailers use a piece of rubber hose inside a spring between the hitch and the trailer towbar to achieve this motion. This costs less than a universal joint or ball joint, but the hose is susceptible to fatigue cracking over time. Also, "flex hitches" don't provide truly independent freedom of motion, as rubber can only bend so far.
The trailer hitch can attach to the bike in one of three locations:
- the seatpost ,
- the rear axle , or
- the left seatstay and/or chainstay (i.e. the two frame tubes near the rear axle on the left side of the bike).
The higher the hitch attachment point is above the ground, the greater the torque exerted by the trailer on the bike when turning (see drawing). This can make a heavily-loaded seatpost-mount trailer difficult to control.
Less-expensive bicycle trailers often use easy-to-fabricate rear axle hitches. In our experience, rear axles aren't sufficiently strong to pull heavy loads and will break under use. Quick-release axles (i.e., the type with a locking lever on one end) are especially bad for this. We've broken several QR skewers in testing some early bike trailer hitch prototypes.
Our recommendation: If you plan to pull moderate to heavy loads (> 100 lbs [50 kg.]), choose a bicycle trailer with a ball-joint or U-joint hitch that mounts to the lower left side of the bicycle frame.
