Why do my boat trailer tyres keep blowing out?
I've had two tyres blow out on my boat trailer during motorway journeys, even though both still had plenty of tread. The boat carries its outboard, fuel and cruising gear when we tow. What should I check before fitting another pair?
Answer
Repeated boat trailer tyre blowouts usually result from heat caused by underinflation, overloading or excessive speed, or from rubber weakened by age. Check the specified cold tyre pressures and weigh the loaded trailer first, because another new tyre can fail if the cause remains.
Check cold pressure and load
Measure pressures before towing, with the tyres cold, using a reliable gauge. A tyre can look properly inflated yet run dangerously soft, particularly if it has stiff trailer sidewalls.
Use the trailer manufacturer's specified pressure for the approved tyre size and load rating. If replacement tyres differ from the originals, ask the tyre supplier to confirm the pressure against the manufacturer's load tables. The sidewall maximum alone does not establish the correct setting.
- Check every tyre, including the spare, before each long journey.
- Inspect valve stems for cracks and check valve cores for leaks with soapy water.
- Use valves rated for the required pressure, especially on high-pressure trailer wheels.
- Never bleed air from a hot tyre to bring it back to its cold setting.
Next, visit a weighbridge with the boat loaded exactly as you tow it. Include fuel, batteries, anchor chain, outboard, water and equipment. Brochure boat weights often exclude much of this.
Check the trailer's total permitted weight, axle ratings, wheel ratings and tyre capacities separately. A single axle carrying 1,600kg puts an average of 800kg on each tyre, for example, but an uneven boat load can put considerably more on one side. Individual wheel weights give the best check. Do not assume tandem axles share weight equally.
Check specification, age and speed
Match the approved size, construction, load index and speed rating. UK and European boat trailers commonly use commercial tyres marked C, while American trailers often specify ST tyres. Fit the specification approved for your trailer rather than choosing by diameter alone. A higher load rating cannot increase the trailer's permitted carrying capacity.
Read the manufacturing date where a four-digit date code is provided. The code 2323 means week 23 of 2023. Inspect the inner sidewalls as well as the visible outer faces for cracking, bulges, cuts and exposed cords.
Boat trailer tyres often deteriorate before their tread wears out because they stand for months in sunlight or under load. Follow the tyre maker's replacement guidance. At around five years old, arrange a careful assessment and plan replacement rather than relying on tread depth. Replace any tyre with a bulge or structural cracking immediately.