Tyre pressure on a trailer?

S

steve yates

Well-Known Member
Joined
16 Oct 2014
Messages
4,113
Location
Benfleet, Essex/Keswick, Cumbria
Visit site
Lifted my new boat out last night, when loaded into the trailer there was a noticeable bulge on thevtyresxat the bottom outside edge. They were at 31 psi, used a little compressor which could only get them up to 38. That's better but still a slight bulge.
All up the weight is approx 1000kgs, the tyre walls say max pressure is 44 psi.
Is a slight bulge on a loaded trailer normal or not? Should I pump them to the max or is a blowout more likely at full pressure?
The boat is going350 miles
Thanks.
 
Does the trailer plate not have tyre pressures marked thereon? When you say "new boat" do you mean new to you or brand new? If brand new then suggest you speak to the dealer. Sounds like you may have normal car tyres on the trailer whereas commercial rated tyres may be the better option.
 
It always used to say the max weight tyres can take, on the wall - do yours have this info? In general terms, the higher the weight on a tyre, the higher the pressure should be, therefore in your case, if the max is close to 500 kg, you'll need to inflate to close to the max pressure. Inflating to the max permitted will not increase the risk of blowout (but overloading tyres will).
An easy but approx test to see if pressures are about right is to drive for a few miles, and then see how hot the tyres are. Warm to the touch is fine, but if they feel hot, they need more air. Also note that as they warm up, the measured pressure will increase, however tyre pressures are always quoted for cold tyres......
 
I had a lot of problems with the tyres on a Hunter 19 trailer until I contacted a tyre agent who told me my blowouts were caused by side wall failures and that I should always inflate to the maximum pressure if the trailer is near its maximum loading. Also use tyres with more plies as they'll take a higher pressure.
 
Age of the tyres is also a factor. Caravan and trailer tyres don't tend to wear the tread much (if they do then a differnt issue), but the side walls and tread rubber deteriorates.
If over 5-7 years old I would suggest replacing with new tyres, van/commercial rated as proposed above.

We had a carav an tyre blow out due to age at under 6 years - perfectly pumped up and correct weight load, but could have been interesting at 60mph on M6 if we hadn't fitted Tyreon bands which kept the tyre on the rim.
A ton an a bit balanced on one wheel can get interesting if a blowout at speed
 
My load is 1.2te and tyres are at 50psi (as indicated on tyre). Below that and the tyres have an obvious bulge and dont track as well as when properly inflated.
 
If the tyres are underinflated the sidewalls bulge out a lot, the weight is taken on the outsides of the tread and the inside barely touches the road. If the tyres are overinflated the sidewalls don't bulge out at all, the tread curves out and the weight is taken on the middle with the edges off the ground.

Solution: experiment with inflation until the whole tread is evenly on the ground, at which point the sidewalls will bulge out a little, but not much, near the bottom. Note the pressure. Check that it's below the tyres' limit. If so, use in future. If not, get tougher tyres and start again.
 
Don't forget that trailer tyres are often crossply, so may bulge a bit more than radials.
I used to run a dinghy trailer at quite low pressure, because it was about 250kg loaded on tyres rated for over a tonne.

I'd agree that aged tyres can be an issue.
I'm careful about that now!

IF the bulging seems unreasonable with the rated pressure, it may be that the boat is heavier than you think?
Plod or Highway Wombles will see the bulge and haul you off to a weighbridge if they stop you, or spot you at the side of a road.

Also, don't trust the pressure gauge on el-cheapo 12V compressors, some are badly wrong.
 
Most trailers on this side of the pond are fitted with passenger- or light truck tyres. The number of layers (ply) indicate the load capacity, commonly also designated by 'XL' (for eXtraLoad) on the side.

It is completely normal that tyres bulge under load. Look at your car, for example.

The tyre will tell you a lot:
Reading-your-tyre.gif


The load index must match the total weight of the trailer (shared between the 2 or 4 Wheels).

If you have no indication of pressure recommendation use 90% of max rated. If the trailer tend to bounce when laden the pressure most likely is too low and allows the tyres to act as air springs.
 
I believe the difference is between suspension capability and tyre pressure. It is not IMO, it's plain experience:

When laden and tyres act as springs, the solution is to increase pressure. Maybe that forces the axle to take up more movement, but at least it stopped the constant bounce that eventually made it's way to the tow and into the car rear.

Different trailers may perforem diffrently. My 2-ton twin axle cargo trailer never bounces, regardless of load etc.

I guess the OP should make own tests, starting with 90% of the max rated pressure.
 
steve yates said:
Lifted my new boat out last night, when loaded into the trailer there was a noticeable bulge on thevtyresxat the bottom outside edge. They were at 31 psi, used a little compressor which could only get them up to 38. That's better but still a slight bulge.
All up the weight is approx 1000kgs, the tyre walls say max pressure is 44 psi.
Is a slight bulge on a loaded trailer normal or not? Should I pump them to the max or is a blowout more likely at full pressure?
The boat is going350 miles
Thanks.
Click to expand...

You have not given any details of the tyres. Type, size , number of plies etc.
 
Check the maximum load and pressure written on the sidewalls of the tyres. Work out what load each tyre is carrying (1/2 or 1/4 of total weight of trailer and boat). Then inflate the tyres to the maximum pressure x actual weight / maximum load. In other words, if your total weight per wheel is half the maximum load then use half the maximum pressure.
 
One of the most useful devices I bought to help me out with not only my boat trailer tyre pressures but also the way it is loaded was a small temperature gun which I picked up cheap off Ebay. Yes you do need to inflate the tyres to the correct pressure and the information on the sidewalls will give you a maximum (and obviously the weight limit for each tyre should also be observed) but you also need to make sure the tyres are carrying an even load, especially if it's a two axle trailer.

Tow the trailer for about ten miles then stop and take the temperature off each tyre. They should all be somewhere around 30 degC, if they are much hotter then you probably need more pressure in them (sidewall flex causes heat to build up and that's what eventually leads to the failure), and if the tyres on one axle are hotter than the other you need to look at your tow hitch height. If the front axle is hotter than the rear then it's to low, if the rear is hotter then it's to high.

It's also extremely useful for checking for binding brakes or tight/dry bearings, especially if like me you dunk the trailer in the sea every time you go sailing. I just stop after a few miles of every trip and run around with the gun checking each hub and wheel.
 
Spi D said:
I believe the difference is between suspension capability and tyre pressure. It is not IMO, it's plain experience:

When laden and tyres act as springs, the solution is to increase pressure. Maybe that forces the axle to take up more movement, but at least it stopped the constant bounce that eventually made it's way to the tow and into the car rear.

Different trailers may perforem diffrently. My 2-ton twin axle cargo trailer never bounces, regardless of load etc.

I guess the OP should make own tests, starting with 90% of the max rated pressure.
Click to expand...

My opinion is based on my experience.
 
The idea of running tyres at the maximum pressure is wrong and dangerous. The pressure needs to be adjusted to suit the tyre size and the load. The tyres on my car say max 50 psi but the car manufacturer says 34 psi. If I pumped them up to 50 I would have much poorer roadholding and the centre of the tread would wear faster. I have a kit car which uses the same tyres as the donor vehicle. The correct pressure for the kit is 19 psi whereas those for the much heavier donor are 26/30. If I ran the kit at 50 psi I wouldn't make it round the first corner.

All tyre walls are designed to flex and to show a bulge at the bottom. If you pump them up to eliminate the bulge you might as well have solid tyres.

Here is a table of sizes/loads/pressures- http://www.ntta.co.uk/law/trailers/load_pressure.aspx

Incidentally, the table shows max speeds of 60 and 80. From what I see on the roads, an awful lot of trailer owners don't know that there is a blanket trailer limit on all roads of 60.
 
snowleopard said:
From what I see on the roads, an awful lot of trailer owners don't know that there is a blanket trailer limit on all roads of 60.
Click to expand...

From what I read on here someone doesn't know the speed limit for a car towing a trailer on a single carriageway road is 50mph.......:)


sorry, couldn't resist!


Two hulls good, three hulls better.
 
You must log in or register to reply here.

Share this page

Top