Suspension Tyre Pressure Cold/Hot

Dean Anderson

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Feb 7, 2014
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What the??? I've never inflated any tyre above 38PSI (cold)...Van or Tug...

Just checked....My van placard is 345kpa (50PSI) maximum (cold). Four years on my tyres are great and the only puncture I've had was from a roo who punctured my brand new spare wheel (on the A-frame) with a rib bone.

Interesting to note that the vehicle manufacture has to state the required pressure without knowing what tyre may go on the vehicle. The 50PSI for the Savero tyres on mine may be because Savero is such a well trusted brand in high quality tyres. That is why they were put on by JAyco after all.

"The vehicle manufacturer selects the size and type of tyres for their vehicles. They perform the necessary testing to establish the vehicles' optimised operating tyre inflation pressures....." (BFGoodrich)

I'm confused..Never mind...it works...I'll stick with it.
 

Doc

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May 2, 2016
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What the??? I've never inflated any tyre above 38PSI (cold)...Van or Tug...

Just checked....My van placard is 345kpa (50PSI) maximum (cold). Four years on my tyres are great and the only puncture I've had was from a roo who punctured my brand new spare wheel (on the A-frame) with a rib bone.

Interesting to note that the vehicle manufacture has to state the required pressure without knowing what tyre may go on the vehicle. The 50PSI for the Savero tyres on mine may be because Savero is such a well trusted brand in high quality tyres. That is why they were put on by JAyco after all.

"The vehicle manufacturer selects the size and type of tyres for their vehicles. They perform the necessary testing to establish the vehicles' optimised operating tyre inflation pressures....." (BFGoodrich)

I'm confused..Never mind...it works...I'll stick with it.


Dean,
The manufacturer states the SIZE and construction of the tyre fitted at the vans manufacture. Based on that, they set the pressure. (That you have been running what appear at face-value to be underinflated tyres without incident - no conclusions can be drawn from that except that you appear to have been running underinflated tyres. That you haven't had a puncture or other incident does not mean that the pressures recommended on the placard were wrong - it simply means that you are fortunate in that apparent under inflation has UNTIL NOW not caused you any issues that you have been able to identify.)

Load and inflation tables are your friend. There is no particular mystery in tyre pressures, and ALL tyre manufacturers use the same baseline information for a size and rating of tyre. That is why load inflation tables exist - so that consumers can determine that for X sized tyre at Y load, then Z pressure is recommended by the manufacturer of the tyre. It is not complex.

The VAN manufacturer is able to say that X is the recommended size tyre, and Y is the load. They know both of these things ex-factory. They can therefore determine that (referring to the load inflation tables) Z is the required pressure for that tyre.

More generally (for the advice of all who read this), load inflation tables are the reference documents used by ALL tyre manufacturers to communicate recommended pressures to vehicle manufacturers, trailer manufacturers, and consumers. Tyre manufacturers do not use inaccurate methods such as the so-called "4PSI rule".
 
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Dean Anderson

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So why are my tyres the wrong pressure? Just cause they are not near the maximum?

I have even wear, good tyre life, and a more comfortable ride. I wouldn't say 38Psi is underinflated for 100km/hr with the loads involved in my situation.

The landcruiser actually has 33psi on the placcard, recommended pressure , not maximum pressure.

I would also say that if you need such high pressure to keep the tyre the right shape (round not massively bulged at the bottom), your load is probably too high.
 
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Doc

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Hi Dean,

I just re-read what I posted and I believe it is perfectly clear. I said "...what appear at face-value to be underinflated tyres...". Based on the information you provided, my statement is - in fact - correct.

You said "...I've never inflated any tyre above 38PSI..."

You also said "...My van placard is 345kpa (50PSI) maximum (cold)..."

So - at face value, your tyres appear to be underinflated - they are less than the pressure recommended by the van manufacturer. That is of course, if you believe the recommended pressures provided by the caravan manufacturer, as provided on the placard.

Out of interest - what method did you use to determine that 38PSI was the correct pressure for your van tyres? Did you cross reference the tyre size and loadings with the values in a load inflation table? Or did you use another method? I did not see that you had provided the tyre size (and construction) fitted to your van, nor the load on each tyre, so it is impossible to refer to the 'horses mouth' so to speak - load inflation tables provided by the tyre industry. In the absence of two critical pieces of information, the only valid course is to follow the recommendations of the van manufacturer.

A little background on my own situation:
  • The tyres fitted to my van are 235/75R15
  • GTM is 3022kg (for the sake of simplicity, lets say a load of 755kg per tyre)
  • Van manufacturer recommends 345kPa (~50PSI).
Referring to load inflation tables for the tyre size fitted to my van, LT construction tyres in that size carrying a 763kg load require a pressure of 40PSI. A 10PSI difference between what the VAN manufacturer recommends, and what the TYRE industry recommends. The Jayco-recommended pressure of 50PSI at max load equates to a load of 902kg according to the tyre industry. Personally - I run 40PSI. Well under the recommendation of the van manufacturer, but appropriate to the recommendation of the tyre industry. (FWIW, I think the tyre industry probably knows more about the product they build than Jayco does, and if I notice any undesirable wear appearing I may revisit the inflation pressures in future).

Anyway, long and circuitous route to get here but here it goes... According to all the available information - my tyres appear to be underinflated BASED ON THE PLACARD IN THE VAN (excuse the capitals - not yelling, trying to highlight the importance of a statement). However they are NOT underinflated when taken in the context of the tyre industry recommendations re: load inflation.

So based on the information you provided - in the absence of tyre size and load values - sorry, but the only valid conclusion I could possibly draw is that your tyres are underinflated.

(FWIW - my Y62 is somewhat like your LC in that it has what some may believe to be a low pressure recommendation - 35PSI. That is for the standard 265/70R18P tyres. Load inflation tables however show that for the weight of the vehicle, that recommended pressure is spot-on. Notably, the new tyres I fitted (285/65R18LT) have an identical load inflation recommendation, despite being both a different construction AND a different size.)

Sorry for the long post - I find this stuff interesting :)
 
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Dean Anderson

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Cruiser clearly says 33psi recomended in manual. Add 4psi roughly for high load or towing as stipulated by tyre manufacturer.

Van placard says 50psi maximum
Savero tyre says maximum 44psi at maximum load 925kg.
Van has 565kg per tyre maximum if I keep it legal. Way under maximum load of tyre, hence reduced pressure required.

Dual axle requires the sidewall to flex to turn corners. Pressure too high not good.
 

Dean Anderson

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I emphasis, van manufacturer (Jayco) states maximum tyre pressure, on most vans above 50psi and the van would probably shake to pieces before you get to your destination, and the van would be bouncing all over the road (tyres are a critical part of the suspension)...If not, excessive wear is occurring to the other suspension components...

I wonder if anyone changes tyre pressure every time they fill up the water tanks or empty the water tanks? 45kg (e.g.) difference per tyre .... I wonder if anyone changes tyre pressure due to ambient temperature? 7kpa per 10 degrees???..What is the specified temperature for tyre tables anyway? I'd assume 24-25 Celcius. With tyres everything is a compromise and you will never be able to get everything 100% right...200km of gravel road ahead should you change the tyre pressure? More right hand turns ahead better increase the pressure in the left hand tyres? If tyre tables are so critical why don't all the tyre manufacturers have them on their websites?

Formula one with all of the tyre specs and engineers and they have problems getting the tyres right (not that I have seen one towing a caravan:)).

The important thing is that you are at an acceptable pressure for the conditions that you are going to meet. 35psi or 42psi....is most probably not going to make much difference apart from ride and fuel economy...If the tyres are wearing right then I reckon the pressure is OK, but if there is a document out there that proves that the pressures I use are dangerous I'd love to see it and I will change my tyre pressures tomorrow.

I'd be more worried about all the people with mud terrain tyres on the car using a bitumen road and not altering their driving habits (especially in wet weather).....Same with All-Terrain tyres to a lesser extent. :behindsofa:
 
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Doc

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<snip>What is the specified temperature for tyre tables anyway?<snip>

Ambient.

Because no matter whether you are traversing the arctic tundra or crossing the Canning SR, you should be checking (and where necessary adjusting) your (cold) tyre pressures at regular intervals.

Cold pressures will vary little between a frosty morning in Canberra and the morning after a humid, difficult-to-sleep night in Darwin. That is why manufacturers always specify checking temps when cold and make no reference to checking pressures when hot.

Tyre pressures generally change about 1.4/1.5 PSI for every 10 degree Celsius change in ambient temperature. That is simply a scientific function of temperature changes and fixed volume affecting pressure.

As I said - interesting stuff. Well, I think so anyway, but that is the inner-science-nerd coming out in me.
 
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Doc

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<snip>The important thing is that you are at an acceptable pressure for the conditions that you are going to meet. 35psi or 42psi....is most probably not going to make much difference apart from ride and fuel economy...If the tyres are wearing right then I reckon the pressure is OK<snip>

(Dean - I posted this one separately because I think it merits being separately addressed - IMO you have raised some really good discussion point - well, things that I like to discuss anyway - and you deserve a well considered and thorough response)

I reckon you are pretty much spot on target with what you're saying.

I said in previous post/s that the only reason I thought your (van) tyres were underinflated was because that was based on the information available at the time. The further information you have provided (eg, the weight per tyre) shows that your tyres are likely NOT underinflated (although I am making assumptions on tyre size since I don't know what size you are running).

FWIW (and for the interests of all who may be interested in looking at such things) - inflation tables are industry standard and apart from a very few exceptions in some specialised cases, are common across all manufacturers and sizes. For example, the Toyo tables at the following link will provide exactly the same load inflation pressure recommendations as a set of tables from Michelin or Bridgestone.

https://toyotires-1524598101.netdna...ication_of_load_inflation_tables_20151020.pdf
 

Drover

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Following with interest, as I have a long association with the big round rubber things........................

Using the formula contained in an earlier link I posted I have made up a simple spreadsheet to calculate said data for a van tyre pressure, it seems to work. Cross referencing with tyre pressure tables and from my own experience using the formula I think it comes pretty close especially since you can input data that pertains to your van and tyre spec's, change tyres size/type and/or van weight , the pressure will vary.....
 

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Bellbirdweb

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Interesting, using the formula in the spreadsheet, I should be running at 53psi. Was going to bump them up a bit form the 40 I'm currently running.

Will try 45 and see how it feels
 
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Drover

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Just make sure you put the weights in whole Kgs and you use the single tyre max pressure on the tyre wall.........sounds a bit high though, Big Mal with 265 75R16 LR 112, max pressure cold at 80 psi and van weight of 2700kg only comes to 45 psi......................and they run nicely at that, but they are big mongrel wheels I can tell you.
 

Dean Anderson

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If anyone is changing tyre pressures above 42psi make sure you check your tyre construction. If it hasn't got LT on the tyre then it is not LT and Light Truck tyres are way different to standard passenger tyres.... My van has the original Savero tyres which are not LT. This means they should be at a lower pressure than LT tyres. The LT are designed to run at higher pressure and be capable of much higher loads. The P (passenger) are for running at lower pressure and be more comfortable.

The probable reason Jayco has the maximum tyre pressure of 50PSI is for people who change to LT tyres and up the pressure above what Jayco recommends for the vans ride comfort (to prevent the van from shaking to pieces). I would say don't go for LT unless you need the extra load carrying capacity, and if your load is within the compliance plate you shouldn't have to.

The doc supplied by Doc from Toyo tyres doesn't even have pressures above 42psi in the table....LT tyres on the other hand go all the way up to 80psi.
 

Drover

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I would say Jayco put 50 psi because it's a nice round figure and since they seem to use under rated tyres half the time or tyres that are very near their max loading then the high pressure is required but if like Big Mal you have a tyre which has plenty of loading then the higher pressure isn't required . I would prefer an LT tyre on a van especially as a single axle tyre can take a lot of stress and needs to be top line all the time where on a dual axle since very few rotate their rubber the rear axle gets screwed around a lot putting a lot of load on the tread area but once again a tyre which is not at or near it's max loading is going to need less air and will last longer, using non aggressive tread pattern also helps, they are lazy wheels no need for muddies on a van at all............and as I've said before the data on the compliance plate is usually incorrect and should be confirmed before using it.

@Bellbirdweb
Interesting, using the formula in the spreadsheet, I should be running at 53psi. Was going to bump them up a bit form the 40 I'm currently running.

What are the figures that you are using that gets it to come to that figure ???????
 

Bellbirdweb

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Jan 24, 2014
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@Bellbirdweb


What are the figures that you are using that gets it to come to that figure ???????

I'm using the Tyre pressure dual axle fields

Tyre load rating 975kg
Max tyre pressure 65psi
Van weight (as per the weighbridge yesterday) 3200

The 3200 is actually the ATM, I guess for tyre pressures I should really use the GTM, as its attached to the tug which is 2960.

When I reduce it to 2960, the pressure comes down to 49.3psi
 
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Drover

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Just using some guess work thats about what I'd figured, but basically I always reckon it gives you a base figure to work from. I've experimented with my Ute and the figure it gives is close to what I like putting in the tyres, a bit higher than the tyre placard but the rubber I have on at the moment seems mushy at the recommended pressure and I run it a few psi higher but then it's probably heavier than what they would call at empty anyway..................so long as the tyres wear even, all is good.
 
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Dean Anderson

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I reckon my case is interesting. I had the GTM increased by 100kg by Jayco...Here are picks of my tyres and compliance plates..Love to know where they get the figures from..
Tyre.JPG
Compliance Plate.JPG
I'd say there is no consistency between JAyco or the tyre manufacturers....All whom supposedly work off tables.....
 
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Drover

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Wonder what goes on sometimes don't you........................and on the pressure calculator it works out around the 27psi mark, sounds way too low but with a max tyre of 44psi ????????
 

mikerezny

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Hi @Drover,
thanks for providing the very helpful spreadsheet.

I am a complete newbie in this area and it seems very important that I get the pressure correct on the tyres of our Penguin.

One tyre looked a bit down. It was 25psi, the other was 38psi, the spare was 40psi. Never touched since it came back from its 3-month service. So I wanted to pump it up and check if it has a slow leak.

So here is what I have
GT-Radial ST6000 KargoMax 185R14C
Single Axle Max Load: 900kg
Max Pressure: 65psi, 450kpa

Penguin, Tare 964kg, ATM 1264kg.
Estimated load 250kg, measured Towball weight 127kg
Estimated weight on axles: 964kg + 250kg - 127kg = 1087kg

Plugging all the above into your spreadsheet gives a recommended pressure of 39.25psi.

Have I done this correctly?

If so, here are two questions:
The compliance plate on the van states 352kpa (51psi) to 414kpa (60psi) for max loading.
I gather that I should completely ignore this and go entirely on the tyre manufacturer's specifications and estimated load.
Is that correct?

Although the tyre clearly states a maximum pressure of 65psi, it also states "never inflate beyond 40psi"
This seems to be a complete contradiction. Have you any idea how to interpret this?
<<< EDIT >>>
my bad! Ignore this question. My anti-theft chain was covering the a key part of this information.
It actually states "never inflate beyond 40psi to seat beads"
<<< EDIT >>>

Although, the post is directed to Drover, I would be very happy for anyone else to also chime in.

kindest regards
Mike
 
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