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Old 25 July 2008, 07:07   #1
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correct tyre pressure for trailer?

hi
tried a search but cant find anything about trailer tyre pressure not sure what the correct pressure should be the tyres are 4.8 /4.00-8 its says max load 760lbs at 90psi its a 4 metre seardier withmerc 50 2 stroke
thanks
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Old 25 July 2008, 08:50   #2
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If you are nowhere near maximum load then having the tyres too hard will cause the trailer to bounce around a lot and cause uneven wear on the tyres.

I usually do them until they until they look and feel right. If they are too sqaushed on the bottom they need more air.

If you have a trailer or a car with different tyres to normal one way of finding out the correct pressure is to put a line of paint across the tyre and watch how it wears - worn away in the middle - pressure too high - worn away at the edges - pressure too low.
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Old 25 July 2008, 09:57   #3
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thanx for that think the paint is a good idea
Dino
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Old 25 July 2008, 11:27   #4
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Hi Dino

When I tried to find this info for my trailer a few years ago I came across this info which seemed to work for me.

1: First inflate the tyres to the pressure recommended by the manufacturer of the trailer or the tyre you are using. Secondly, tow your trailer for a distance of 100 km, preferably on a highway.

2: Recheck the tyre pressures immediately after pulling over and compare them with the pressures you had at the start of your run. If the pressures are right, the hot readings should be 4 psi (28 kPa) higher than the cold readings.

3: If there is a greater than 4psi (28 kPa) difference between these pressures, the tyre temperature is too high and the pressure needs to be increased. If there is less than 4 psi (28 kPa) difference, the pressure needs to be lowered.

4: Large 4WD tyres will have a differential of 6 psi (42 kPa).

5: Be sure to use the same accurate gauge for both readings.

Another way to find out approximately what pressure you should run is from a simple formula derived from the tyre specifications:

max tyre pressure divided by max load rating times actual load per tyre

example (450Kpa / 950kg) x 450kg = 213kpa (30psi)

Keith
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Old 25 July 2008, 12:32   #5
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thanks i have inflated to just over 40 psi and will see what happens on the journey the tyre doesnt look to bad at that ! believe i heard some one once say 60psi same as a caravan but that looks rock hard to me! but a bit of trial and adjustment should get there
thanx
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Old 25 July 2008, 14:23   #6
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Quote:
Originally Posted by kwil View Post
Another way to find out approximately what pressure you should run is from a simple formula derived from the tyre specifications:

max tyre pressure divided by max load rating times actual load per tyre

example (450Kpa / 950kg) x 450kg = 213kpa (30psi)
Hmmm. That would imply that if you ran the trailer empty, you'd only need around 10 psi? I don't think your formula works, except for loads in the upper range of the load limit. Required pressure does not extend to 0 psi, so you'd have to fudge in some unknown minimum starting pressure.

Personally, I run the pressure stated on the tire sidewall, or a bit less (like 4 to 8 psi less) if nowhere near the rated load on the tire.

jky
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Old 25 July 2008, 15:52   #7
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Quote:
Hmmm. That would imply that if you ran the trailer empty, you'd only need around 10 psi? I don't think your formula works, except for loads in the upper range of the load limit. Required pressure does not extend to 0 psi, so you'd have to fudge in some unknown minimum starting pressure.
I take you point but as I said it is not my formula it is one I found whilst doing similar research, which does seem to work with a loaded trailer, which after all is all you are really interested. I cannot remember the figures from my working out but results gave 56psi which has proved suitable upto now.

Keith
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Old 29 July 2008, 13:03   #8
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re tyre

this was posted a few weeks ago by Bern Hanreck

http://www.iwt.co.uk/tyre_pressure.htm

seems imformative

Andy
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Old 29 July 2008, 16:18   #9
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Could be.

Quote:
Originally Posted by jyasaki View Post
Hmmm. That would imply that if you ran the trailer empty, you'd only need around 10 psi? I don't think your formula works, except for loads in the upper range of the load limit. Required pressure does not extend to 0 psi, so you'd have to fudge in some unknown minimum starting pressure.

Personally, I run the pressure stated on the tire sidewall, or a bit less (like 4 to 8 psi less) if nowhere near the rated load on the tire.

jky
I had a Westfield 7 a while ago. Four 185 section tyres that were probably rated for 450kg each. Max pressure probably 40 - 45 psi.

The car weighed about 650kg and tyre pressures were 16-18psi.

With my trailers over the years I normally inflate until they look right and then check the temperature by hand after a few miles on the motorway. If hot they need more air. If cold then they're not too soft - if the boat's not bouncing than that pressure is suitable.

I guess from a tyre what we're looking for is for it to be as soft as possible to give the boat the best ride without heating up through flexing too much.
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Old 29 July 2008, 19:09   #10
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Quote:
Originally Posted by Searider View Post
I had a Westfield 7 a while ago. Four 185 section tyres that were probably rated for 450kg each. Max pressure probably 40 - 45 psi.

The car weighed about 650kg and tyre pressures were 16-18psi.
my westfield is running on yokohama 205s at 18psi but its a v8 so probably about 30kilo heavier than a 4 cyl, certainly makes bikers stare when they are leaning hard on an island and you overtake them on the outside, it just seems to grip more when you apply more power, good fun when you can afford fuel for it
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