Tyre Pressures ?

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Whameller Whameller
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Tyre Pressures ?

Does anyone have any idea about the correct range of tyre pressures for 400 x 8 tyres ?

I ask because I had a blowout on the M4 in South Wales on Tuesday evening with this trailer and boat:

Moonfish 14 'Blue Streak' on Trailer

The tyres (virtually brand new - less than 300 miles - 4 ply tubeless inflated to about 45psi) showed signs of monstrous tread wear and the one that didn't blow is barely fit to be used as a spare.  I had been driving for about 1 1/2 hours at between 55 and 60 mph.

'Blue Streak' weighs between 70 and 80kg; the trailer is a pretty lightweight refurbished 1960s number.

I've ordered a couple of new 6 ply (= slightly heavier load rating) wheels and tyres - strangely cheaper than buying tyres on their own - but want to make sure that they are correctly inflated.  I can't afford a repeat performance on the way to Beale Park, as the boat has an appointment with the Watercraft ABBA competition !

Any suggestions very gratefully received.

Nick

alopenboat alopenboat
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Re: Tyre Pressures ?

First, check the tracking, then lift the wheels and see if they run
true. That amount of wear suggests significant problems somewhere. My
tyres usually die from perishing rather than wearing out.

Blow-outs usually occur when the pressure is too low. The tyre walls
flex and overheat then burst.

However, if the pressure is too high then the tread will wear in the
middle and the ride will be harsh, not good for the boat.

Not knowing what pressure to use for my own boat I started with a
relatively high pressure (max pressure is printed on the tyre). After
driving for 10 miles I stopped and felt the tyre walls. As they were
still quite cool I dropped the pressure by 5 psi and repeated the 10
miles. Once the tyres began to get hot I knew the limit below which I
shouldn't go. Remember to take a pump as now you have to put some
back in.


On 28 May 2015 at 7:46, Whameller [via UK HBBR Forum] wrote:

>
>
> Does anyone have any idea about the correct range of tyre pressures
> for 400 x 8 tyres ?
>
> I ask because I had a blowout on the M4 in South Wales on Tuesday
> evening with this trailer and boat:
>
> <http://uk-hbbr-forum.967333.n3.nabble.com/file/n4028819/MF_Tlr.jpg>
>
> The tyres (virtually brand new - less than 300 miles - 4 ply tubeless
> inflated to about 45psi) showed signs of monstrous tread wear and the
> one that didn't blow is barely fit to be used as a spare.  I had been
> driving for about 1 1/2 hours at between 55 and 60 mph.
>
> 'Blue Streak' weighs between 70 and 80kg; the trailer is a pretty
> lightweight refurbished 1960s number.
>
> I've ordered a couple of new 6 ply (= slightly heavier load rating)
> wheels and tyres - strangely cheaper than buying tyres on their own -
> but want to make sure that they are correctly inflated.  I can't
> afford a repeat performance on the way to Beale Park, as the boat has
> an appointment with the Watercraft ABBA competition !
>
> Any suggestions very gratefully received.
>
> Nick
>
>
>
>
>
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--
Sail when you can, row when you must, motor
when you have to be at work in the morning.

Alastair Law
Yeovil, England.
<http://www.little.jim.freeuk.com>


Timmo Timmo
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Re: Tyre Pressures ?

In reply to this post by Whameller
http://www.ntta.co.uk/law/trailers/load_pressure.aspx  is a site that does seem to suggest a much higher pressure.

Others will be more expert than me at this, but that degree of tyre wear sounds seriously excessive even if the pressures were low. The load doesn't seem anywhere near the limit of 540kg. Those tyres should have gone on till they perished of old age.

Hopefully it was just a duff pair of tyres. I know you've checked the wheels are tracking true, rolling easily and nothing's rubbing them (even when it bounces on it's springs.)

Look forward to seeing that very nice boat safely displayed at Beale.

Tim.

On 28 May 2015, at 15:46, Whameller [via UK HBBR Forum] <[hidden email]> wrote:

Does anyone have any idea about the correct range of tyre pressures for 400 x 8 tyres ?

I ask because I had a blowout on the M4 in South Wales on Tuesday evening with this trailer and boat:

Moonfish 14 'Blue Streak' on Trailer

The tyres (virtually brand new - less than 300 miles - 4 ply tubeless inflated to about 45psi) showed signs of monstrous tread wear and the one that didn't blow is barely fit to be used as a spare.  I had been driving for about 1 1/2 hours at between 55 and 60 mph.

'Blue Streak' weighs between 70 and 80kg; the trailer is a pretty lightweight refurbished 1960s number.

I've ordered a couple of new 6 ply (= slightly heavier load rating) wheels and tyres - strangely cheaper than buying tyres on their own - but want to make sure that they are correctly inflated.  I can't afford a repeat performance on the way to Beale Park, as the boat has an appointment with the Watercraft ABBA competition !

Any suggestions very gratefully received.

Nick




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momist momist
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Re: Tyre Pressures ?

In reply to this post by Whameller
I'm not at home just now and can't look it up, but I recently saw a web site that lets you calculate optimum pressure based on tyre size and load and max pressure printed on the tyre.
Ian
Port-Na-Storm Port-Na-Storm
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Re: Tyre Pressures ?

A few years ago I put a new set of tyres on my trailer, drove from Southampton to the Norfolk Broads and by the time I got back they were too bald to be legal.
I was running them at 40psi, I run the replacements at about 30 and haven't had any problems so far.
If you are doing long distances at motorway speeds its worth considering 10” or even 13” wheels.
It is cheaper to buy tyres on wheels than have them fitted, crazy. Getting rid of the old ones can be a problem.
Graham.

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I'm not at home just now and can't look it up, but I recently saw a web site that lets you calculate optimum pressure based on tyre size and load and max pressure printed on the tyre.
Ian


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Jeremy Jeremy
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Re: Tyre Pressures ?

I'll lay money on the rolling tracking being way out.  

Wear at that rate isn't tyre pressure, it's almost certainly excessive toe-out as the tyre drag moves the wheels back and angles them out.  Checking them when stationary will most probably show them to be OK, but for stability trailer wheels should be set to slightly toe-in when static, so that tyre drag flexes them out on the suspension compliance when they are rolling.

I run the same size wheels an tubeless tyres on a light trailer and it's covered a couple of thousand miles now with no signs of tyre wear.  The tyres are run at 30 psi, because I only have a very light load on them, and they are set with about 1.5 deg toe-in when static.
Whameller Whameller
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Re: Tyre Pressures ?

Many thanks for all your thoughts.

I'll try the 'start at highest pressure then gradually reduce' method.

I suspect that there may be something in the tracking point as well.  The trailer has a somewhat weird leading arm suspension arrangement (shown here as originally purchased off fleabay and before fitting new wheels, tyres, bushes & shock absorbers):



Static, there is no measurable toe in or out but I suspect that the forces exerted by forward movement will force some toe out.

But how does one adjust tracking on a trailer with no visible means of adjustment ?
Paul (admin) Paul (admin)
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Re: Tyre Pressures ?

Tony,

I can see the tyres have worn at high pressure, only in the centre. So drop down to 30psi...but like Al said I found with MilliBee at least 30 psi was needed to keep tyres cool (about 350kg all up). But also modern tyres have the recommended and maximum pressures written on the side.

I suspect the wheels toe out/in at speed. I've seen an MOT examiner test with a long metal pole to lever the joints to check for excessive wear.

With a trolley jack (buy one if you don't have one) lift one wheel free, then grab it at the sides and check for movement. First maybe a slight mechanical knock from the bearing, then with more force it might move. If it moves by hand the swing arm pivot joint is knackered...which means a new axle if it has rubber suspension.

-Paul
Say NO to Brexit. Kick it into the long grass
Paul (admin) Paul (admin)
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Re: Tyre Pressures ?

In reply to this post by Whameller
Whameller wrote
But how does one adjust tracking on a trailer with no visible means of adjustment ?
Look for packing pieces, slivers of metal somewhere near a bolt or joint mounting point. Different thickness's of packing pieces adjust the toe angle. Also look for non-concentric circles, where rotation moves a bolt in or out. Again rotation then clamping gives the correct toe angle. These things might be hidden away so a good clean and degrease makes it easier to work on.

cheers
-Paul
Say NO to Brexit. Kick it into the long grass
momist momist
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Re: Tyre Pressures ?

If you need extra packing a good source is cut up drinks cans. Don't mix alloy and steel though. Some premium beers can still be found in steel  cans, take a magnet shopping with you. :-)
alopenboat alopenboat
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Re: Tyre Pressures ?

In reply to this post by Paul (admin)
If you really can't find any way to easily adjust the tracking, and
you decide that is your problem (look for scuffing on the tread after
a few miles) then it may well be cheaper to get a new trailer than to
keep on paying for new tyres.

Old dodgy trailers are a false economy.


On 29 May 2015 at 5:21, Paul (admin) [via UK HBBR Forum] wrote:

>
>
> Whameller wrote
> > But how does one adjust tracking on a trailer with no visible means
> > of adjustment ?
>
> Look for packing pieces, slivers of metal somewhere near a bolt or
> joint mounting point. Different thickness's of packing pieces adjust
> the toe angle. Also look for non-concentric circles, where rotation
> moves a bolt in or out. Again rotation then clamping gives the correct
> toe angle. These things might be hidden away so a good clean and
> degrease makes it easier to work on.
>
> cheers
> -Paul
>
>
>
> -----
> Sail when you can, motor when you can't http://www.millibee.com
> _______________________________________________
> If you reply to this email, your message will be added to the
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> 05/29/15

--
Sail when you can, row when you must, motor
when you have to be at work in the morning.

Alastair Law
Yeovil, England.
<http://www.little.jim.freeuk.com>


Jeremy Jeremy
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Re: Tyre Pressures ?

All except one my trailers have been home made, so I have always bolted the suspension units on to the mounting plates at a deliberate toe-in, as all the rubber-in-torsion units toe-out with drag, even when new.  A little bit of toe-in also makes the trailer track a bit better.

I'm not sure how you can adjust your trailer, but my guess would be that the leading arm pivot has developed a bit of play.  If it has, and it's a rubber bush type pivot, then you may be able to find replacement bushes by hunting around.  Lots of older motorcycles have rubber pivots like this on the rear forks.
Whameller Whameller
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Re: Tyre Pressures ?

As some of you saw at Beale Park, I think I have solved this problem by converting the suspension to a trailing arm setup.  I just swopped the entire suspension units from side to side.

The only (minor) challenge was repositioning the mudguards.  Luckily the stays (although handed for the original leading arm setup) allowed for this, so it just required re-drilling the mounting holes in the rubber mudguards.

Pictures to follow.

Using Al's 'start high and gradually lower the tyre pressures' method, I've ended up with 40psi as a seemingly comfortable setting.

So far, I've only done the return trip to BP (about 70 miles in total) - with no sign of any unnatural wear on the tyres.  The major test will be 180 miles back down to Pembrokeshire next month !

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