Single Axle Tyre Pressures

[sgtangel]

Hi all,
Reading some of the other posts on the forum got me thinking about tyre pressures (specifically a comment made on the single axle / twin axle discussion - a forum member stated he had tyre pressures upwards of 60psi on his SA van)

The manual for my SA 1993 Swift Diamond Corvette states the tyre pressures (175R13) should be 3.0 bar (42 psi), although I think that they appear under inflated at this pressure when the van is loaded for travelling.

My query is this - Should tyre pressures be increased if the van is fully laden, or is the tyre pressure stated in the manual the figure to be maintained regardless of load ?

As always, many thanks

 

[Damian]

http://www.tyresafe.org/tyre-safety/caravan-tyre-safety/load-and-inflation-tables
Look here for your tyre size and load rating, and pressures

 

[ProfJohnL]

Hello SA,

By all means follow Damian's link and if you are prepared to weigh the caravan before each trip and make adjustments then there is nothing wrong with that, apart from the impracticality of it all.

I am not a tyre expert, but what is clear from all the information that car and caravan manufacturers provide about tyre pressures is that a recommended pressure is capable of carrying a modest weight range without the need for continual pressure changes.

In the context of a caravan, the difference in weight of a caravan from empty to maximum load is typically about no more than about 15 to 20% of the total weight. As caravans are far more frequently run closer to fully loaded than empty setting the tyre pressures for the MTPLM seems sensible.

It is safer to have a tyre set up for its maximum load and occasionally run it slightly light, rather than have tyre under inflated for the load it's carrying.

So the general practice of following the manufacturers pressure guidelines is usually all that's needed .

If you are concerned about tyre wear, again its most common to find that caravan tyres are not worn away because of the comparatively low milage they do, but more often start to show signs of age. The tyre and caravan manufacturers recommend changing tyres at about 5 years of age regardless of the milage they have done.

 

[JonnyG]

Hi all,
Reading some of the other posts on the forum got me thinking about tyre pressures (specifically a comment made on the single axle / twin axle discussion - a forum member stated he had tyre pressures upwards of 60psi on his SA van)

The manual for my SA 1993 Swift Diamond Corvette states the tyre pressures (175R13) should be 3.0 bar (42 psi), although I think that they appear under inflated at this pressure when the van is loaded for travelling.

My query is this - Should tyre pressures be increased if the van is fully laden, or is the tyre pressure stated in the manual the figure to be maintained regardless of load ?

As always, many thanks

a lot depends on conversion from which, bar to psi or psi to bar,as 1 bar actually equals 14.5 psi . so if the quoted pressure was in bar then converted to psi, 3 bar is equal to 43.5 psi .[44 psi]

 

[sgtangel]

http://www.tyresafe.org/tyre-safety/caravan-tyre-safety/load-and-inflation-tables

Look here for your tyre size and load rating, and pressures

Quite a difference from the handbook guide pressure to that quoted on this chart.
For a 175R13 light commercial tyre (Which I assume is a caravan tyre ????) the tyre pressures are stated as 4.5 bar or 65 psi - that is a huge difference to what I am running them at just now.

Can anyone advise if they have noted a difference of this scale with their own vans, and if so, what pressures they chose to run at. That figure certainly would give the appearance of being correctly inflated (as I say, the tyres appear under inflated just now, although are at the correct pressures as per the handbook)

Last thing I want to do is induce instability or increase the risk of a blow out when travelling.

Thanks for all your views so far

 

[Gafferbill]

........this is a common problem with caravans of your vintage.
They were sold from the factory with reinforced tyres which were sometimes designated by ply rating and the handbook provided with the caravan stated the correct tyre pressure should be 42-44 psi.
Obviously this was correct at the time but tyres have changed since then.

What tyres are fitted to your caravan now?

I own a 1995 Swift and the handbook contains similar information to yours, as when I bought it new, it was fitted with reinforced tyres and the information was correct.
It is now fitted with 175x13C light commercial tyres and the tyres at a MTPLM of 1150kgs are at a recommended pressure of 51psi.
These tyres would be suitable up to a MTPLM of 1460kgs if they were inflated to 65psi.
My caravan axle is rated to 1300kgs with a MTPLM of 1150kgs for the caravan .........so there is not the need to inflate them to the full 65psi that is their maximum allowable pressure.

 

[sgtangel]

........this is a common problem with caravans of your vintage.
They were sold from the factory with reinforced tyres which were sometimes designated by ply rating and the handbook provided with the caravan stated the correct tyre pressure should be 42-44 psi.
Obviously this was correct at the time but tyres have changed since then.

What tyres are fitted to your caravan now?

I own a 1995 Swift and the handbook contains similar information to yours, as when I bought it new, it was fitted with reinforced tyres and the information was correct.
It is now fitted with 175x13C light commercial tyres and the tyres at a MTPLM of 1150kgs are at a recommended pressure of 51psi.
These tyres would be suitable up to a MTPLM of 1460kgs if they were inflated to 65psi.
My caravan axle is rated to 1300kgs with a MTPLM of 1150kgs for the caravan .........so there is not the need to inflate them to the full 65psi that is their maximum allowable pressure.

Thanks for that response Gafferbill...
The tyres fitted are Avon Supervan 175R13C, and the tyres are marked

"load range 94/92N max load single 1475lbs at 54psi (670kg at 375kpa)"

They were fitted by the dealer when we bought the van last June.

The plate on my van states Max authorised weight (which I think is now MTPLM) of 1060kg
and allowable payload of 220kg

Given all of the information, I think I could probably increase my pressures slightly, and remain both safe and stable ?

 

[Gafferbill]

Hi ..........those Avons are good tyres ..........I had them on for my last set..........changed them at 6years old for Hankook Ra08 light commercial tyres............I ran them on my caravan at 51psi.

Your caravan is 90kgs less MTPLM than mine and I would run your tyres at 48psi.

 

[ProfJohnL]

Going back to the original post,

Hi all,
...............The manual for my SA 1993 Swift Diamond Corvette states the tyre pressures (175R13) should be 3.0 bar (42 psi), although I think that they appear under inflated at this pressure when the van is loaded for travelling...................

If the tyre you have fitted is the same as the ones in the manufacturers specification, then you should not judge the tyre by the way it looks, but by the actual inflation pressure. The manufacturers information will allow for the caravans MTPLM.

If you seriously believe the tyre is "under inflated" when it is actually at the recommended pressure, then you need to check the actual weight of the caravan to make sure its not over loaded.

 

[Gafferbill]

If the tyre you have fitted is the same as the ones in the manufacturers specification...........

........the OP has clearly told us that they are not.

 

[JonnyG]

OP stated.."Last thing I want to do is induce instability or increase the risk of a blow out when travelling" far too many mis conceptions flying around.frankly your risk is far far higher to both your concerns from having tyres that are under inflated. . as for the term "over inflated" it seems to be a term that is used far too often and totally out of context to what actually an over inflated tyre is...

 

[Len_Cuff]

On my Adria they have markings on the wheel arch stating 65PSI so that's what I go with and never had any problems - yet!!

 

[sgtangel]

I appreciate all of the responses.

Going back to the original post,

If the tyre you have fitted is the same as the ones in the manufacturers specification, then you should not judge the tyre by the way it looks, but by the actual inflation pressure. The manufacturers information will allow for the caravans MTPLM.

If you seriously believe the tyre is "under inflated" when it is actually at the recommended pressure, then you need to check the actual weight of the caravan to make sure its not over loaded.

Prof, I cannot say whether the tyres currently fitted are the same as the original specification, as I have nothing to reference other than the handbook, which merely quotes a size. I suspect they are not a reinforced tyre, certainly there are no markings to suggest this.

I had considered the possibility of the van weight being high, but have weighed the majority of the big items I carry, and use a basic spreadsheet to "roughly" track the payload. Certainly I am at the top end of my allowable amount, and I suspect my gross mass would certainly be at or very near 1000kgs, if not slightly above.

I am relatively new to this whole game, and with safety in mind (wife, 2 kids, and now 2 dogs in car when towing), am trying to make an informed decision.

As a driver for 20 yrs, both socially and for work, ( but never having towed) I do think the tyres look underinflated, although this is when stationary.
In addition, when driving I feel like i am having to "pull" much more than i thought would be required ( if you see what i mean) as if the tyres arent running at the correct pressure ( a slight feeling of dragging, but not actually)

I am now considering persuading the wife to overcome her fears, drive with the van on, and I will follow in another car and see how the tyres look, actually running.

 

[ProfJohnL]

If the tyre you have fitted is the same as the ones in the manufacturers specification...........

........the OP has clearly told us that they are not.

Hello Gaffer,

Up to your post , the OP had not " clearly told us that they are not" as per originals. so my comment was pertinent.

And since when is it sensible to judge the inflation pressure of a tyre by sight alone?

Don't just treat a symptom, as you can too easily mask the underlying cause. Find out what the cause is and put that right first.

In this case tweaking the pressure is the wrong next step. The only proper and logical way is to measure the pressure and check the applied load is not bigger than it should be.

SA, something else that you wrote earlier on also concerns me. your stated you had found the MTPLM and it had a 200kg loading margin. The way you wrote it suggested you might believe you have the MTPLM and can add the 200kg load on top of it.

Sorry but no. the MTPLM is the absolute heaviest the caravan can legally be. It already has the load margin included and it.

 

[colin-yorkshire]

hi all, with reference to Gafferbill's post, 175R13c [94] is exactly the same tyre I had on the ranger, MTPLM 1052kg or 526kg per wheel,
I had a tyre chart that gave relative pressures to the actual load [not just the max] based on load index. I cannot find it on lap top so it must be on the other computer but it gave the pressures for a 94 index tyre with a load of 530kg @46psi that is what mine were set at so Bills 48psi is not far off, [yes they looked a little under inflated] but it was the correct pressure, I never had any tyre issues even while using the mover. so I suggest you start there.

oh and ps, dont forget light commercial tyres have a stiffer side wall than 175r13 so if they are too hard ie at max for such a light weight it will cause the van to bounce around under tow [emptying the top cupboards all over the floor].
been there got a T shirt.

 

[sgtangel]

I think a logical next step would be to get a definitive weight for the van, and go from there.
Time to find a weighbridge !

 

[Gafferbill]

..........to me this topic is a road safety matter which is why I have joined in and posted.
I have expertise on this exact topic which was raised by the OP.

The problem which is out there is that caravans like mine and that of the OP's (early1990's vintage) were sold with handbooks that TODAY will likely be giving the WRONG information as to tyre inflation pressures ........if the information is blindly followed.
This is because tyres subsequently fitted to such a caravan are likely to be of a different construction and MUST operate at different pressures for a given amount of load.

I find it worrying that other posters are telling the OP to consult his handbook which is normally the correct thing to do but would be dangerous in this specific case.
This is because my expertise on the specific tyre that the OP has fitted, shows that such advice would lead to under inflation of his caravan tyres.
The OP has a suspicion his tyres are under inflated...... but if they are inflated to 42psi then I know for a fact that they are under inflated.

Several years ago before the advent of the Swift Talk forum.... Swift themselves used to post on this PC forum.
This exact same topic came up and I gave exactly the same advice as I have given in this topic.
Again posters gave varying advice and again in the interests of safety I advised the OP to ask Swift for a definitive answer as to what the tyre pressure should be for their caravan with the tyres currently fitted.
On that occasion Swift gave the exact same advice as I gave.

If stangel contacts Swift on the Swift Talk forum I am sure Swift will provide him with a definitive answer.

 

[ProfJohnL]

Hello Gaffer,

That is a positive post. and it offers sensible advice, which is to get the facts before making adjustments on unknown equipment. which is what I have been stressing for so long.

As you well know, one of the difficulties with forums like PC''s is that contributor use pseudonyms, and we have no way of knowing what a poster's experience, knowledge or qualifications are or what their agenda may be. So in all fairness to to the OP as a relatively new member to the forum he would have no justification to give more credence to your information over anybody elses.

Give good reasons and where possible sources so that readers can have the chance to verify the information they receive, and that not only helps the reader but enhances the credibility of forum and its contributors.

 

[JonnyG]

A very good post prof..but i have one question can we assume you too will heed that advice?
i have an example with no prejudiced given your to quote "on forum credibility." .you see underneath is a quote by you it has no verifying evidence or good reason..
..
"I have looked on the WWW, and so far I have not found the Elgrand listed as using 215/60/17's 16 & 18's yes but not 17's. Probably like me Graham has only found a tyre pressure listed for
2.2Bar. My Renault Espace grand only has R15 rears at 2.1 for normal running and 2.3 for heavy load and motorway running, so the 2.2 does not seem too far out of kilter"..end quote.

anybody with any decent knowledge on tyres would ask how did you come to that answer without knowing the tyre index..nobody questioned you about it,at first as it was merely your opinion..
i only pionted it out very much later when you deemed it fit to "advise" against adding a few psi to a tyre again having done the same sort of thing on this thread .

We know now from that earlier thread that the OP, tyre pressure should have been 2.9!bar which is a lot more than the advice you gave of 2.2 bar! which possibly had the tyres dangerously under inflated!
Gaffabill has now had to explain his reasoning on this tyre thread because you have queried his response .although from past posts from the likes of people like gaffabill it should be clear they have
a decent knowledge on said subject...Now me,you will never read a post regarding things like carver heaters. well i suppose i could post don't touch it you'll break it and it could catch fire if its thingy gets too hot. which thinking about it actually is sound advice,but as useful as a nine bob note.....my point? well it hasn't changed on topics regarding tyres, if it looks flat and you cannot see a reason for it, pump it up a few psi its a lot safer a few psi over than a few psi under.and if nothing else is known at the time that is the best advice one can give..then seek professional help as soon as poss,although if you know your tyre index and the weight of your
vehicle,then you yourself can be the professional help..

 

[Gafferbill]

Hello Gaffer,

As you well know, one of the difficulties with forums like PC''s is that contributor use pseudonyms, and we have no way of knowing what a poster's experience, knowledge or qualifications are or what their agenda may be. So in all fairness to to the OP as a relatively new member to the forum he would have no justification to give more credence to your information over anybody elses.

I could equally write the same about your posts Prof........but I haven't ever done so

 

[ProfJohnL]

Hello Jonny

The wording I used in the reply you have quoted ended with:-

"does not seem too far out of kilter".

The reason I used that wording was because I recognised the equipment in question MAY be different and therefore the values I quoted should not be taken as exact more of a generalised comparison based on a similar size of vehicle.

This is not the place to reopen that thread.

 

[colin-yorkshire]

hi all, I really don't know why it is that simple questions get so side tracked, complicated and converluted,[new word]
if you read the information given by the OP. a 4year old could work out the correct pressures.
he stated in the opening post that, the handbook stated the original tyres were 175Rx13's and the recommended pressures were 3bar or 42psi, but the tyres looked "under inflated". when loaded for travelling.
My query is this - Should tyre pressures be increased if the van is fully laden, or is the tyre pressure stated in the manual the figure to be maintained regardless of load ?
the simple answer is no set for max load and leave them.
however in a later post he said "Quite a difference from the handbook guide pressure to that quoted on this chart.
For a 175R13 light commercial tyre (Which I assume is a caravan tyre ????) the tyre pressures are stated as 4.5 bar or 65 psi - that is a huge difference to what I am running them at just now.
well yes it would be!!! because a 175Rx13c is not the same tyre as was fitted originally the tyre construction is different, a normal 175Rx13 would only have a load index of around 86, max axle load 1060kg at 42psi, [as stated in hand book].
but a "C" tyre has a load index of 94 max load 1460kg at 65psi. the tyre chart only gives the the tyre pressures at max load ie 42psi for the original and 65psi for the new one that is why the difference.
if the 175Rx13c tyres are fitted to a trailer with a max load lower than the 94rating [1460kg] the pressures must be reduced according to the weight carried,
he also informed us that "The plate on my van states Max authorised weight (which I think is now MTPLM) of 1060kg and allowable payload of 220kg
the maximum authorised weight [MAM] is 1060kg but this includes the user payload of 220kg and is NOT extra.weight, [can be confirmed by looking at the MIRO on plate]

so from the information given it is easy to calculate the tyre pressures.
175Rx13C tyres carrying 1060kg = 46psi. simple.
to answer the OP question YES your tyres are under inflated by 4psi.

 

[JonnyG]

deleted .

 

[Dustydog]

Excellent post Colin.
Time for another caravan maybe :silly:

 

[Gafferbill]

............to answer the OP question YES your tyres are under inflated by 4psi.

Well Colin that makes two people who have actually answered the OP's question that know what they are talking about