What causes boat trailer tyres to wear on the inside, and how can I fix it?
Both tyres on my boat trailer are wearing along their inside edges, although the outer tread still looks good. It carries a 6-metre motorboat, and I'm unsure whether the problem is tyre pressure, wheel bearings or a bent axle. What should I check before fitting new tyres?
Answer
Inside-edge wear on boat trailer tyres usually means the wheels lean inwards at the top or point outwards because of overloading, a bent axle or worn suspension components. Check cold tyre pressures and the trailer's actual loaded weight first, then inspect bearings and wheel alignment before fitting replacement tyres.
Check pressure, load and tread
Inflate the tyres to the trailer manufacturer's specified cold pressure for the fitted tyre size and load. Do not use your tow car's pressure. If the trailer's figures are missing, follow the tyre manufacturer's load and inflation guidance for your measured loads, keeping within tyre and wheel limits.
Low pressure normally wears both shoulders rather than just the inside edge. It can worsen an existing alignment problem, but adding air will not straighten a bent axle.
Take the boat and trailer to a weighbridge in their normal towing condition, including fuel, batteries, anchor, outboard and cruising gear. Check the total against the trailer's plated maximum authorised mass and each axle load against its rating. On twin-axle trailers, an unsuitable hitch height can leave one axle carrying more weight than the other.
- Both inside edges worn smoothly: suspect excessive negative camber, often associated with overloading or axle damage.
- Feathered tread: tread blocks feel smooth in one direction and sharp in the other. Suspect incorrect toe alignment.
- One tyre affected: inspect that wheel's bearing, stub axle, suspension arm and spring mounting.
- Scalloped or patchy wear: check for bearing play, wheel imbalance, tyre damage and suspension movement.
Inspect bearings and suspension
Before working underneath or checking raised wheels, chock the trailer and support it on correctly rated axle stands at the manufacturer's approved support points.
Grip each raised wheel at 12 and 6 o'clock and rock it, then repeat at 3 and 9 o'clock. Watch whether movement comes from the hub bearing or the suspension. Spin the wheel and listen for rumbling. Slight brake contact can be normal, but investigate any grinding or roughness.
Many tapered roller bearings need a small specified end float; sealed cartridge bearings use a different arrangement. Do not tighten the hub nut until all movement disappears. Excessive preload can overheat and destroy a tapered bearing.
Inspect leaf springs for cracked leaves, worn eye bushes, damaged shackles, shifted axle seats and loose U-bolts. On rubber torsion suspension, compare arm positions and ride heights on level ground. A sagging or damaged unit may need specialist repair or replacement. If you launch in salt water, pay particular attention to corrosion around brackets and axle tubes.