Apologies for another tyre inflation query.

[brian_c]

Following on from my previous post where I was concerned about wheel hubs taking different tyre widths.
I have today finally got a new set of tyres.
I used a mobile service from a well known company. I ordered the tyres on line based on the hand book information. But reducing the width to 165.
Well a couple of days ago the fitter arrived with the tyres and promptly told me that they were not really suitable for the van.
I had ordered Continentals with a load factor of 86.

He said it wouldn't be a problem to change them. He rang back to base and told me that they could source more suitable tyres.
Well he arrived today and fitted them balanced etc so all is well. He says we will get the difference refunded via our card transaction.

The first ones I ordered were 165. 70. R13. Load index 86

These are Hankook R8. 165 R13 C. 94/92

So finally getting to my question.

I understand that the tyres don't need to be inflated to their max. When the load is reduced. But don't really know how to work it out except by a good guess. Which in this case would be around 40 PSI.

(The max pressure for full load on the tyres is 65PSI) they are capable of 670kg

The MTPLM of our caravan is. Only 1000kg

So I'm wondering if someone could give me the formula I've looked on the charts but can't find my specific example.

Best regards to all
Brian

 

[WoodlandsCamper]

Ratio of half MTPLM (500 kg) divided by max tyre rating (670 kg) times max pressure (65 psi) equals 48.5 psi.

The above assumes a single axle van.

 

[Sproket]

Brian

It's explained in more detail in this link on how to work it out either way, Sir WC must have used the same formula :lol:

 

[Dustydog]

Brian

It's explained in more detail in this link on how to work it out either way, Sir WC must have used the same formula :lol:[/quùote]

Sir Sprocket.
In the original post the Prof made the point that a twin axle may at various times have all or most of the weight on one or other of the two axles. Does that make the TA formula on your link correct?
I'm bringing the Wyoming home tomorrow and will check each axle loading plate.
OMG! I only want to go on holiday :silly:

 

[brian_c]

Thank you to one and all again.
I really need to attend one of the Woosie club gatherings and thank you all in person one day. Mind you drinks all round on me would take a bit of saving up for with the amount of people I'm indebted to?
Just need the mover fitting now and we can get the van on the road for our first trip with it.
Meanwhile I've always fancied a good look around the historic Ship yard at Portsmouth along with the other exhibits like the Victory and Warrior and Mary Rose.
My wife thinks it would be like watching paint dry. So come this Sunday I'm off!
I have borrowed my Daughters tent, booked myself onto a C&CC. CS Site located near to Nutbourne Station close to Chichester and scrounged a camping stove and an air bed. At least I don't need a television nowadays.
Unable to hear it.

I intend all being well to abandon the car when I get there and use the train for a Daily commute into Portsmouth.
Mind you it could take me two days to erect the tent it's got to be thirty years since I last slept in one.
Thank you all again
Best wishes Brian

 

[Sproket]

Sir Sprocket.
In the original post the Prof made the point that a twin axle may at various times have all or most of the weight on one or other of the two axles. Does that make the TA formula on your link correct?
I'm bringing the Wyoming home tomorrow and will check each axle loading plate.
OMG! I only want to go on holiday :silly:

Hmm

You need the tyre information to work it out , but in saying that what does the plate in the middle of the axle state ??
Will both axles be rated at 1800kg ? so that it would be possible for one axle to carry all of the load ? if so each tyre will need to be capable of carrying 900kg and on that basis the tyre pressure would be the same as a single axle...

But it won't be ..... but if your tyres were max psi @ 65 and the load was 900kg well ...

65 / 900 = 0.7222
0.7222 x 1800 = 130
130 / 4 = 32.5psi

 

[ProfJohnL]

Hello Dusty,

I still stand by my post - but it does need a bit more explanation:-

In much the same way the tow bar assembly is actually capable of handling dynamic loads somewhat greater than the static nose load, the strength of the axle is also capable of withstanding dynamic loads greater than the static design limit. So whilst each of the static axle load limits on the TA may be less than the MTPLM, the designers should have allowed for the dynamic variations that will occur in normal towing, which should include the kerb riding weight transfer.

I would expect the static ratings of each axle to be a little greater than half the MTPLM.

 

[Gafferbill]

Meanwhile I've always fancied a good look around the historic Ship yard at Portsmouth along with the other exhibits like the Victory and Warrior and Mary Rose.

.......you can also take the Gosport Passenger ferry over to Gosport for the HMS Alliance submarine museum

...... and Fort Nelson where there is an interesting armouries museum in an old fort on Portsdown Hill with stunning views over Portsmouth and the Isle of Wight.

 

[Dustydog]

Hello Dusty,

I still stand by my post - but it does need a bit more explanation:-

In much the same way the tow bar assembly is actually capable of handling dynamic loads somewhat greater than the static nose load, the strength of the axle is also capable of withstanding dynamic loads greater than the static design limit. So whilst each of the static axle load limits on the TA may be less than the MTPLM, the designers should have allowed for the dynamic variations that will occur in normal towing, which should include the kerb riding weight transfer.

I would expect the static ratings of each axle to be a little greater tha5n half the MTPLM.

Prof.
I have no wish to harp but your previous post cogently said either axle on a TA must be able to support the whole MTPLM.
I will be checking the Al ko plates on the axles tomorrow.
Meanwhile I can tell you my Wyoming tyres run at half the pressure of a SA.
If what you say is true then in my doggy mind my tyres must be grossly under inflated if the are expected to support 1700kgs on one axle at any point in time .
:silly:

 

[brian_c]

Thank you for that Gafferbill I have discovered that a lot of the exhibitions whilst quite pricey on their own can be bought for an all in ticket price of £23 ( over 60 price) from Portsmouth city website. this gives unlimited visits for up to a year bank holidays and special events are the only restrictions. All the exhibits I mentioned are included as is the Submarine exhibition.
I've looked at google maps and was beginning to think I would need the car for that visit. I'll have a look on the internet regarding your suggestion re- the ferry.i need to research a bit now because I'm not so good at asking directions etc. well I am ok at asking just no good a hearing the answer.
The Overlord (D-Day) museum at Southsea isn't included but I intend looking at that whilst there as well. Being on my own I can cover more things, also being back in a tent will encourage me to spend more time away from site. It will do me good! Make me appreciate the caravan more!
Thank you for your comments I'm booked on site for a week so hope to cover quite a bit. I will look up the details from your link Re-Fort Nelson as well.
Just need a good chippy near the site now.

Best wishes Brian

 

[ProfJohnL]

Hello Dusty,
I used the word "support", I didn't say its rated limit should equal the MTPLM. The difference between the safe working load and the margin of safety that such designs will have.

However regardless of the words I may have used, or the way you may have interpreted them, you can be sure the chassis manufacturers will have taken such matters into account when agreeing the correct axles for the caravan.

.

 

[Dustydog]

http://www.practicalcaravan.com/forum/technical/51214-daft-question-about-axles#399868
Hi Prof.
As a true dog I am a bit confused
Due to my knee op I can't get down to check the Al-ko axle plates.
I'll do it tomorrow with help from Mucky pup.
Forgive me for re quoting your original above.
I am very curious now to know if Bailey got it wrong hmy:

Can we all have a spoof type game and suggest what the loading rate per axle is on my TA 1700kgs MTPLM before I check tomorrow :silly: :huh: :evil:

 

[Sproket]

http://www.practicalcaravan.com/forum/technical/51214-daft-question-about-axles#399868

Can we all have a spoof type game and suggest what the loading rate per axle is on my TA 1700kgs MTPLM before I check tomorrow :silly: :huh: :evil:

My guess is 1000kg per axle

 

[Dustydog]

http://www.practicalcaravan.com/forum/technical/51214-daft-question-about-axles#399868

Can we all have a spoof type game and suggest what the loading rate per axle is on my TA 1700kgs MTPLM before I check tomorrow :silly: :huh: :evil:

My guess is 1000kg per axle

Sir Sproket
I am offering a prize of a heavy duty Milenco self levelling mechanical device for the winner. Prize to be awarded at this years Woosiefest. . Value £50 plus.

 

[Gafferbill]

.......1300kgs/ axle :blink:

 

[Gagakev]

....1250kgs /axle

 

[Dustydog]

Well my fellow dogs.
I've shuffled under the Wyoming and read the Al-ko load plate.
I can tell you each of the four tyres run at 29 psi.
The MTPLM is 1700kgs.
One of you is spot on.
Any more bids for the self leveller kit?
Tomorrow I will reveal the truth which I expect will set more hares racing!

 

[Sproket]

Well my fellow dogs.
I've shuffled under the Wyoming and read the Al-ko load plate.
I can tell you each of the four tyres run at 29 psi.
The MTPLM is 1700kgs.
One of you is spot on.
Any more bids for the self leveller kit?
Tomorrow I will reveal the truth which I expect will set more hares racing!

Will be interesting to know the tyre size and load rating with the max psi and max load ( in the small text on the tyre wall ) to work out what the over load amount would be for when all its weight is being carried by one axle .... @ 29 psi hmy: ie: like driving over the extended length speed humps but just for that short amount of time 1700kg on what ???

 

[ProfJohnL]

Hello dusty,

I think I will also take a stab at the answer, I'll estimate the rated static axle load will be 900 to 1000kg per axle, But I'll be interested in what you do have.

 

[Dustydog]

Sir Sproket

Trailermaxx tyres x4.
185/65 R14
6PR 93/91N
S 650kgs
D 615kgs
@max pressure 55psi cold.

recommended tyre pressure at MTPLM= 29 psi.

Any more offers before I reveal the answer B)

 

[Sproket]

29 psi @1700kg ?? bet they are flat at the bottom :silly: :silly:

55 / 650 = 0.0846
0.0846 x 1700 = 143
143 / 4 = 35.96 psi

55 / 615 = 0.0894
0.0894 x 1700 = 152
152 / 4 = 38 psi

They will get warm when rotating ( mine increase by 10 psi as shown on my tyrepal tyre monitor i put the back one's on the van & the front stay on the truck's front wheels ) so maybe that is taken into account by the manufacturer when working it out ??
So in that theory 29 psi will increase to 39 psi or there about's :dry:

Going back to when there is a possibility of it being all on one axle ....
But even the max loading of the tyres for a single axle is only 1300kg bit of a difference by 500kg. hmy:

 

[colin-yorkshire]

1275kg give or take 25kg
a twin axle boat trailer has each axle rated at 50% above half the total MAM so 1700kg +50% = 2250kg / 50% = 1275kg.
that's my guess. what I think is missing here is the axle dynamics true as the prof said each axle may initally carry the whole load, in fact it is possible one wheel could carry the whole load but only for a split second as the the other axles would drop to contact the road as each suspension strut is independant, bit like the towbar load set it at 100kg static but under tow could be anything from minus 200kg to plus 400kg but the bar does not fail.

 

[Dustydog]

Brace yourselves my boys.
Here's the answer taken from the Al-ko axle plate. Both front and rear are rated the same.
Type: B1030-3
Date: 9.Nov 07.
Customer: Bailey
Rated over 25kph.
Capacity 1000 E kgs.

Looks like Sir Spoket wins the levellers .
So now I have to ask did Bailey get it wrong?
Am I towing a time bomb waiting to go off the rails.
The details here appear to contradict the Prof's original statements but how sure can I be that Bailey haven't under engineered my caravan hmy:

 

[ProfJohnL]

Hello Dusty,

I seem to have sparked quite a debate about the all load on one axle thing. :dry:

It needs a slightly wider perspective than just looking at the rating plates.

If the suspension units had used all their compliance when load to their rated maximum, whenever the caravan encountered even a minor bump, it would already be on its suspension stops causing major problems.

The rated load will deflect the suspension system to its median running position. There is still further compression available to cope with the dynamic effects of towing and bumps.

The same is true for tyres, whilst they have a rated load, they can in fact sustain moments when the load is several times greater than their rated capacity. :cheer:

For both the axles and the tyres its this designed overload capacity that ensures the systems will cope with the rated load under dynamic conditions.

The other factor is that these high load events are usually of short duration. In the case of the caravan traversing a speed bump or a kerb is these usually do occur at low speeds when the tyres and axles are not under other dynamic events and stresses.

Your time Bomb has a very very long fuse. :woohoo:

 

[Sproket]

Thank you

Anyway thinking that quite a lot of twin axle vans will come into this weight range i presume Alko will just re-position & fit caravan chassis mounting plates to them ( makes it cost effective ) more so for the caravan manufacturer as one set fit's most van's :dry: the next weight range will come in for the heavier vans & the others will be for large trailers.... where as there appears to be quite a larger selection for the single axle vans ....

Hmmm :S

Wonder if i could do a weight upgrade from 1600kg to 1800kg ...... :dry: