maximum tyre pressure

Submitted: Friday, Jan 30, 2009 at 12:51
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I was wondering about using a spare tyre as a "tank" to inflate other tyres. Does anyone know the maximum pressure I can safely inflate a LT265 75 x 16 that will not be under load, but will be in the sun.
thanks
Ian
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Reply By: Sir Kev & Darkie - Friday, Jan 30, 2009 at 13:07

Friday, Jan 30, 2009 at 13:07
There should be a max pressure noted on the side wall of the tyre. I would keep the max pressure to about 10 PSI less than stated.

Cheers Kev
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Follow Up By: ian - Friday, Jan 30, 2009 at 17:28

Friday, Jan 30, 2009 at 17:28
thanks for your reply Kev
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Reply By: Robin Miller - Friday, Jan 30, 2009 at 13:39

Friday, Jan 30, 2009 at 13:39
This has come up a few times before Ian.

Those tyres don't state a maximum pressure - if you look closely they state something like Max load xyz kg at minimum 65psi.

I.E. if you put less than 65 in them then they are unable to carry the load.

The typical garage uses 10 psi above that to carry the load in case there guage etc in a bit off i.e. 75psi.

As a spare tyre this 75 is a very safe pressure to use and is what I use except say in a competion where I use 100psi.

I used BFG AT as the example above.

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Follow Up By: ian - Friday, Jan 30, 2009 at 17:38

Friday, Jan 30, 2009 at 17:38
thanks Robin,
I will check the writing on my tyres.
Ian
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Follow Up By: Peter_n_Margaret - Saturday, Jan 31, 2009 at 00:12

Saturday, Jan 31, 2009 at 00:12
Robin, I have never seen "at MINIMUM....psi on a tyre"
Show us a pic?

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Peter
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Follow Up By: Robin Miller - Saturday, Jan 31, 2009 at 10:10

Saturday, Jan 31, 2009 at 10:10
Hi Peter

Nor do any of my current tyres.

They don't refer to max pressure either.

The actual writing on BFG is Max load at 65 psi.

However it is the clear and unambigous meaning as you can read off there inflation/load charts that minimum pressure is always required.








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Follow Up By: Peter_n_Margaret - Saturday, Jan 31, 2009 at 11:50

Saturday, Jan 31, 2009 at 11:50
I don't agree Robin.
The word is AT.
AT 65psi (cold) does NOT mean MINIMUM 65psi(cold).
My inflation/load charts show lower inflation pressures for lower loads and lower speeds, but never do they indicate that the appropriate pressure (cold) for MAXIMUM load can be exceeded.

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Peter
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Follow Up By: Robin Miller - Saturday, Jan 31, 2009 at 17:36

Saturday, Jan 31, 2009 at 17:36
Hi Peter

Its a straight out mathemacitcal relationship so it must.

However I appreciate that some might require more than me just saying so , so a add the following Toyo Tire note cut from the rv website which give substance to my asseration that typical use is
rated load pressure + 10

Robin


--------------------------------------------------------------------------------------
It is important to note that the inflation pressure molded on the side wall of a passenger-car tire is the maximim air pressure for that tire. That is not the case, however for light-truck tires.

The inflation pressure molded into the sidewall of light-truck tire is the minimum (that's right, the minimum) air pressure required for that tire to carry the maximum weight molded into the sidewall of that tire. Using less air pressure means the light-truck tire must carry a lighter load.

While the tire-load rating molded into the sidewall of a light-truck tire should not be exceeded, it is generally recommended that the tire be inflated to the minimum pressure required to carry the load plus an additional 5 - 10 psi. The extra pressure will help the tire run cooler. It also acts as a reserve to offset normal loss of air pressure. But the extra pressure will not add to the tire's load carrying capability. Just keep in mind that the maximum air pressure for a light-truck tire is the minimum air pressure molded into the side of the tire plus 10 psi.
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Follow Up By: Peter_n_Margaret - Saturday, Jan 31, 2009 at 19:14

Saturday, Jan 31, 2009 at 19:14
So, Robin, you will use an unsubstantiated quote from an un-named RV website in the USA talking about Toyo LT tyres to detirmine what is best for your AT BFGs?

That's too long a reach for me.
Frankly no US forum has much credibility on any subject that I have noticed yet.
Why don't you ask BFG?
I will stick with what Michelin says about my size and model of Michelin tyres.

Cheers,
Peter
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Follow Up By: Robin Miller - Saturday, Jan 31, 2009 at 19:36

Saturday, Jan 31, 2009 at 19:36
Peter , you should know from previous posts that all mine can be substainiated , you only needed to ask.

But if your prepared to write off the US as well because they don't agree with you then there is little point in trying to explain the basic physics any further.









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Reply By: Geoff (Newcastle, NSW) - Friday, Jan 30, 2009 at 13:56

Friday, Jan 30, 2009 at 13:56
I used to regularly wack 100psi or even 120psi if the compressor could do it in my 7.50 x 16's when I had my FJ40.

I made up a hose with a clamp chuck on one end and a plain air chuck on the other.

It was great for pumping the tyres up when you came off the beach!

Geoff
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Follow Up By: ian - Friday, Jan 30, 2009 at 17:41

Friday, Jan 30, 2009 at 17:41
Thanks Geoff,
what type of shop sells the chucks and suitable hose?
rgds
Ian
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Follow Up By: Geoff (Newcastle, NSW) - Friday, Jan 30, 2009 at 18:06

Friday, Jan 30, 2009 at 18:06
Hi Ian,
I made the hose up well over 25 years ago!

I got the air chucks from a company here in Newcastle called Rema-TipTop I think they are still running in various parts of Australia, just no longer here! They were a supplier to the tyre industry.

A quick Google just turned them up! I'm impressed: Rema-TipTop

The hose came from I think Dunlop-Flexhide.

You should be able to find the air chucks these days at I'd guess either Repco or Supercheap.

The hose could be bought from someone such as Blackwoods or most any of those industrial suppliers.

Hope that helps,

Geoff
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Follow Up By: Geoff (Newcastle, NSW) - Friday, Jan 30, 2009 at 18:15

Friday, Jan 30, 2009 at 18:15
Hi Ian,

I just remembered something else, air chucks come in two types, open and closed end.

The open end is just that, open it has a pin which pushes the valve stem in the tyre to let the air in or out but it does not stop air flow when not on a tyre.

The one you require at least on the end you are going to use to inflate the road tyres is the closed end type. It has a valve that only opens and allows air to flow when it is connected to a valve stem.

The clip on chuck for the reservoir tyre end can be of either type but an open end is probably the best as it will vent your hose to atmosphere when you take it off the tyre.

I was just wandering around the Rema-TipTop site and found the chucks: Chucks etc

The one I used on the reservoir tyre end is about halfway down the page an "Air Chuck 315 Clip-on"

Hope all that helps,

Geoff

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Reply By: Michael ( Moss Vale NSW) - Friday, Jan 30, 2009 at 14:04

Friday, Jan 30, 2009 at 14:04
Ian,

Check out my post 60998. I use my spare as a tank and now have a cut off switch set at 65 PSI, i have the switch located next to the RYCO chuck so as soon as i start taking air from the spare, it creats a pressure drop instantly and the compressor cuts in and start adding to the spare again. The whole thing works brilliantly. So you just pull up, grab the hose, plug it into the chuck that is located in the centre of the spare and start using it,. it works great with an air gun also with 100 litre tyre as a tank. . pics attached to the original post. Michael
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Follow Up By: ian - Friday, Jan 30, 2009 at 17:40

Friday, Jan 30, 2009 at 17:40
Thanks Michael,
I will go to that post now.
Ian
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Reply By: Member - Oldplodder (QLD) - Friday, Jan 30, 2009 at 18:47

Friday, Jan 30, 2009 at 18:47
Like Ian and Geoff, I have set up a similar idea using the spare as a reservoir for my blue tongue pump.

My 235/85/16 LT 10 plies says max load @ 80 psi, so I run 80 psi in my tyres.

Geoff reckons you could go higher, but if I am putting 15 psi in each tyre , say 20 to 35, it works fine. By the time I walk around and do it, the pump is topping up the spare between each tyres.

Got my parts from Industrial Fitting Spares (IFS) here in Brisbane.

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Follow Up By: donks1 - Friday, Jan 30, 2009 at 21:27

Friday, Jan 30, 2009 at 21:27
Hi there

How exactly do you do that ??

Do you have two valves on the "reservoir tyre".... 1 in 1 out?

I like the idea but have never thought of it.

Have however got a truck with stuck brakes ( blown air lines ) out of trouble by using the air from the spare tyre. But that was only to get it out of an intersection

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Follow Up By: Michael ( Moss Vale NSW) - Saturday, Jan 31, 2009 at 11:16

Saturday, Jan 31, 2009 at 11:16
Donks, you dont need an in and out, just a tee piece, it is basically an accumulator.. See my post that i mentioned above. Michael
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