Tyre Pressures in Trailer Tyres.

[Tim Falce]

I've always run my trailer tyres at around 35-40psi pressure. I recently got a couple of tyres for someone and the sidewall figures said 90psi, these were 12 inch 8 plys. I've just bought myself a pair of 6 ply 13 inch and the figures read at 65psi, the tyres I've taken off say run at 45psi.

So should I be running the pressure at the amount it states on the sidewall or a bit lower as I am not loading them to the maximum amount? The sidewall states maximum weight of about 680kg
Twin axle trailer probably grossing about 1800 kg maximum, except when I load it with hay and then it may go to over 2 tons.

[Dave Brand]

The pressure marked on the sidewall is the maximum pressure to which the tyre should be inflated. Optimum pressure for a given application will vary & will always be lower than the permissible maximum.

[Al Weyman]

Tim take this advise from someone who mulled no less than 3 tyres in one trip a few months ago and fortunately I have a 6 wheel trailer or lord alone knows how I would have got home. I made the same assumption looked at the sidewalls 90psi, got a heavy car so thought way to go 80psi in each. On the way homeI lost two tyres where the rubber valve had literally blown out under the pressure as I am sure they increased as it was a hot day and did the third one in pulling out of a garage after having to stop every few miles to top up pressures. Its only then I realised the original tyres fitted by Brian James had metal bolt in valves so the moral is you must use these if you are going to run high pressures. I have now dropped down to 45psi with rubber valve stems and have had no further problems and they dont look under inflated at all.

[Pure Fiater]

Size, type and load on the tyre govern optimin pressure.
I have a plate on my trailer (BJT) which tells me what to run at for
a selection of tyres. Which is usefull. 35 psi is what I use.

[andrewc]

We had a spate of tyre problems with a Motor Shuttle until we upped the pressure to about 80psi.

If the manufacturer of your trailer still exists, talk to them.

[GORDON STREETER]

I use 8ply caravan tyres on my race box inflated to 45psi never had a problem, running road tyres at 80psi is asking for trouble if it is "handling" wrong then it is loaded wrong !

[GORDON STREETER]

There is a formula for working out tyre pressures, on the side of your tyres there will be a " maximum load single " at a maximum psi .

Lets say for example , it states 1460kg at 65psi on your tyre , and your trailer or caravan weighs 1075kg . What you do is 65 divided by 1460 = 0.0445

Then , times 0.0445 by 1075 = 48psi




.

[Tim Falce]

Gordon, the weights stamped on the tyres are per tyre not gross weight, in my tyres case It's 640kg per tyre and 65psi

[GTRMagic]

I dont like 38psi in my road car as its too hard, imagine what 90psi would do in a trailer

You would have to imagine the trailer would bounce a bit (lot), having very little give in the sidewalls at that pressure to absorb even the slightest bump...

[andrewc]

Use the right tyres for the job, and run the pressures recommended by the tyre or trailer firm.

[Tim Falce]

Originally Posted by andrewc

Use the right tyres for the job, and run the pressures recommended by the tyre or trailer firm.

BJ recommend 36.2psi for my original tyres on my trailer which the sidewalls state 45 at full load. My new tyres have a stated pressure of 65 psi at full load and while I wouldn't run that high I think 36 will be too low.

[Dom]

a simple rule of thumb is the trailer tyres needs to be inflated for the weight of itself and the car its carrying. On my 4 wheel trailer with a fiesta on board, i would put pressures equivilent of say a road going focus (35ish psi) - certainly not 80-90 psi which is dangerously overinflated.

[Al Weyman]

I dont think its dangerously over inflated if you have tyres built for the job and bolt in valves. The 10inch tyres on my 6 wheeler have 95psi stamped on the side as max so I am sure they must be safe at that with the obligatory bolt in valves (see my previous post), don't forget the BJ 6 wheelers is designed to take a fully loaded LWB sprinter in fact I have a customer who has a recovery firm and he has had to turn jobs down with his fleet where this trailer would have coped. Again though for carrying my 1400kgs Camaro I won't use them at anything like that pressure.

[Tim Falce]

Originally Posted by Dom

a simple rule of thumb is the trailer tyres needs to be inflated for the weight of itself and the car its carrying. On my 4 wheel trailer with a fiesta on board, i would put pressures equivilent of say a road going focus (35ish psi) - certainly not 80-90 psi which is dangerously overinflated.

The tyres on my truck are supposed to be inflated to 115psi doubles and 125psi single I certainly don't let air out when I run empty so if the tyre states 80psi then surely that's what it should be, or close to it. Don't forget these are van tyres not standard car tyres.

[morninggents]

For many years I've run a 4 wheel trailer on 145/80 X 12 tyres and always run at 45 lbs pressure.

I always now carry 2 spares as many years ago I was taking a friends race car to him in Harrogate and I must have run over something on the kerbside as both nearside tyres disintigrated at the same time.

[haggispeed]

One question being missed here, are you running commercial tyres or road tyres ? 8 ply are commercial trailer tyres so would expect to run them at higher pressures than the equivilant 6 ply road tyres.