Tyre presure dilema

[Gary_5075845]

Hello again,

I have a bit of an issue here. Our caravan is only small and weighs in at about 950K fully loaded. We have just had some new tyres fitted but I'm finding it difficult to find the correct presure. The hand book isn't the exect one for my van but comes extremly close and they state a presure of 36psi. I've read on a link all about tyre(see below) that the pressure for my tyre should only be at 28psi for the weight of the van. I tried 28psi but the tyres seem very bulged at the bottom so I don't feel comfortable with this so I tried 36psi and they look buch better but could this be too much. The tyers we have a budget and the specs are 175R13C 95/97 6ply.

Can someone help me please as I'm off to the blue dolphin on saturday and it's quite a journey.

Thank you in advance

Gary

 

[Lutz]

A higher tyre pressure always improves stability of the outfit. The only reason for not taking it to the limit is that it increases wear in the middle of the tread and consequently reduces the useful mileage you would get out of the tyre. However, for caravans, this is rarely an issue as their tyres usually need replacing due to old age long before the tread is fully worn. For this reason I would recommend you to go for a higher tyre pressure, especially as you say that they are bulging heavily at 28psi.

 

[PaulIrons]

I know its down to tyre size and the sort of caravan it is but 28 psi does seem a bit low, our tyres need a pressure of 62 psi with a fully laden caravan.

 

[Lutz]

This chart may be of use:

http://www.iwt.co.uk/tyre_pressure.htm

 

[rayc]

Gary, I have the same tyres fitted to a 1350kg 5 berth. They are light commercial vehicle tyres and the pressure for my van is 54 psi.

 

[Gary_5075845]

36 PSI seems about right then acording to the chart supplied by Lutz but what is the difference between 175R13 4PR and 175R13R. Plus my tyres are of the 'C' type which I believe means light commercial and I've also read somewhere that the 'C' type tyres often require more inflation that the not 'C' type.

Gary

 

[PC_5041701]

You really should talk to the tyre manufacturer on this. However, you probably haven't got time to do it before you set off so I can offer you information that I had from Avon. They supplied me with a table of pressures against max. speed against load for their 175R13C6PR Supervan tyres. From that table, an axle load of 963Kg would require a tyre pressure of 36psi.

Regards

PC

 

[ProfJohnL]

Hello Gary.

COntrary to PC's advice, the tyre manufacture will not know anything about your caravan. On the other hand the Caravan manufacture should know, and perhapse a telephone call to them might give you the information your requie.

It is generally safer to slightly over inflate a tyre than to run it under inflated. Under inflation increases side wall flexing and thus generates more internal heat.

What is certain is that your tyre will have moulded into it two vital bits of information, the maximum load, and the maximum pressure. Neither of these figures should be exceeded.

Be aware that although your caravan may have a maximum weight of 950Kg, the weight may not be equally distributed from side to side, so it is quite possible to have 550Kg on one side and only 400Kg on the other.

 

[Lutz]

A difference of 150kg from side to side on a caravan that only weighs 950kg in total is a recipe for an instable outfit.

 

[ProfJohnL]

A difference of 150kg from side to side on a caravan that only weighs 950kg in total is a recipe for an instable outfit.

Hello Lutz,

Yes Perhapse 150Kg may be excesive, but considering that most caravans have the cooker & fridge on the same side there is certainly going to be 75 to 100Kg potental differnce side to side.

 

[rayc]

Gary, I have checked the chart at the link Lutz sent you.The nearest tyre to the one you are quoting is 165R13C 6PR which has a figure of 54psi. The only difference to yours is that your is a 175. As I said in my previous reply my tyres are the 175's and the caravan manufacturers pressure is 54psi so I believe this is the pressure you should be using. I do not see what the actual weight of the caravan has got to do with the pressure which is based on the maximum load at max speed rating.

 

[PC_5041701]

In response to John L, the tyre manufacturer may not know anything about Gary's caravan but they should know about the tyres they produce, which is the subject of the query. I'm sure John L will be aware of the problems encountered with this particular tyre specification which has been the subject of lengthy investigations with the Caravan Club and tyre manufacturers. As I'd experienced three catastrophic blow outs with this size of tyre at 54psi (all less than 4 years old and removed over winter) I asked for advise from the Club and Avon Tyres and was told that generally the caravan manufacturer will quote a tyre pressure suitable for the caravan at maximum load. If the load is less than maximum, tyre pressures should be reduced. That's why Avon supplied me with a table of pressures against axle load and speed. The advise was welcome, haven't had a problem since. Sorry John L, it would be tyre manufacturer every time for me. Looking at the varied advise given to Gary, don't suppose he's much the wiser but hope he enjoys his holiday.

 

[rayc]

PC, it's reallly strange that some people including yourself have had problems with this size of tyre. Goodyears were fitted to my 2000 van when new, pressure always 54psi and I never had any problem with them. I replaced them a month or so ago as they were 5 years old ( no discernable wear or damage). The choice of replacement was very limited with only two makes apparently available in the UK, the Avons and maxmileres with a Korean sounding name. I have towed 1500 continental miles, at up to 60mph, since fitting with no problems but will certainly keep an eye on things.

Did you ever explore the technical possibility of changing the wheels and tyres for 14 inch?

 

[alyson_5075411]

We have found the Camping and Caravanning club guide to trailer wheels and tyres helpful. On page 3 it has a chart giving tyre size, load index, max axle load and pressure psi. It also gives advice on wear, tyre construction, care etc. You download it as a pdf file and you dont have to be a member. They have a section on information sheets on their website.

 

[PC_5041701]

PC, it's reallly strange that some people including yourself have had problems with this size of tyre. Goodyears were fitted to my 2000 van when new, pressure always 54psi and I never had any problem with them. I replaced them a month or so ago as they were 5 years old ( no discernable wear or damage). The choice of replacement was very limited with only two makes apparently available in the UK, the Avons and maxmileres with a Korean sounding name. I have towed 1500 continental miles, at up to 60mph, since fitting with no problems but will certainly keep an eye on things.

Did you ever explore the technical possibility of changing the wheels and tyres for 14 inch?

Ray, apparantly the problem lay with tyres bearing the letter "C" in the specification which denoted a commercial rating. According to the Caravan Club the failures were not specific to any particular tyre manufacturer. Like yourself, I'd covered a lot of continental miles with two of the tyres before they burst (in France) but the third was a 4 year old unused spare which burst within 100 miles of fitting. I finished up keeping records of the age of each tyre I had (using the date code moulded into the tyre)and changing them at 4 years. Also, this size of tyre was not available in France and had to be flown out to me by the Club. My tyres which burst were 6 ply, the last I had to buy had been uprated to 8 ply. In answer to your question, I didn't consider changing up to 14" wheels, changed the van instead and now have 15".

 

[rayc]

Ray, apparantly the problem lay with tyres bearing the letter "C" in the specification which denoted a commercial rating. According to the Caravan Club the failures were not specific to any particular tyre manufacturer. Like yourself, I'd covered a lot of continental miles with two of the tyres before they burst (in France) but the third was a 4 year old unused spare which burst within 100 miles of fitting. I finished up keeping records of the age of each tyre I had (using the date code moulded into the tyre)and changing them at 4 years. Also, this size of tyre was not available in France and had to be flown out to me by the Club. My tyres which burst were 6 ply, the last I had to buy had been uprated to 8 ply. In answer to your question, I didn't consider changing up to 14" wheels, changed the van instead and now have 15".

PC, Many thanks. Ray

 

[ProfJohnL]

In response to John L, the tyre manufacturer may not know anything about Gary's caravan but they should know about the tyres they produce, which is the subject of the query. I'm sure John L will be aware of the problems encountered with this particular tyre specification which has been the subject of lengthy investigations with the Caravan Club and tyre manufacturers. As I'd experienced three catastrophic blow outs with this size of tyre at 54psi (all less than 4 years old and removed over winter) I asked for advise from the Club and Avon Tyres and was told that generally the caravan manufacturer will quote a tyre pressure suitable for the caravan at maximum load. If the load is less than maximum, tyre pressures should be reduced. That's why Avon supplied me with a table of pressures against axle load and speed. The advise was welcome, haven't had a problem since. Sorry John L, it would be tyre manufacturer every time for me. Looking at the varied advise given to Gary, don't suppose he's much the wiser but hope he enjoys his holiday.

Hello PC.

Thank you for your clarification and reasoning. I am sorry to hear of your own experience with these tyres, I was unaware of a problem with them. I am reasonably confident that a tyre manufacture would not release an inherently bad design, so my suspicion is that you may have experienced either a batch problem, or a manufacturing fault. This does not of course offset the bad experience you have had, and you are right to make any checks you feel you need to make.

In your case I would also suspect a number of other possible influences:

If the blow-out always occurred on the same wheel, I would also suspect Caravan axle alignment - I have recently heard of a case where an axle stub was 7 degrees out of alignment from new. Or check for a binding brake. Both the additional load generated by the braking effect and the heat transfer from drum to wheel and tyre would be detrimental.

Tyre pressure gauge inaccuracy - Garage forecourts should have a calibration certificate for their systems, it is unlikely that a domestic unit could receive the same level of confidence.

I would agree that caravan manufactures will quote the pressure for a fully laden van, but realistically most vans in motion will be close to their theoretical maximum laden weight.

It is of course best to inflate the tyres to match the actual load, but in the absences of a weigh bridge it should be acceptable to use the caravan manufactures figure.

It is generally accepted that under inflation causes more side wall flexing, which not only generates more internal heat but also will fatigue the side walls quicker, than running at correct or slightly over pressure. So using the caravan manufactures maximum figure and running slightly under weight should not cause a stability problem, or increase the danger of thermally induced blowouts.

 

[Martin4]

After two blow outs on busy French motor ways, I have become sensitive to the pressure issue. In both cases, our Tyron bands saved our bacon. The first blow out was self inflicted, I had not appreciated the extent to which tyres deteriorated with time. The second was (according to the tyre dealer who inspected it) the result of under inflation.

The Lunar Ariva 2 berth van is now ten years old, the original Dunlop tyres had been replaced with a continental make but I continued to use the caravan handbook pressures. When I again replaced the tyres in France, the tyre man was adamant "You tell me the weight, I fit the tyres to the wheels and tell you what pressure to use". In this case 3 bar - rather higher than the handbook value.

 

[mkej100]

Gary...you don't state what make and model incl. the year your van is,i have a huge wealth of info that i have collected to help us during servicing if you let know these details i can probably tell you what they should be.

Contary to what some are advising you MUST only ever replace the tyres and set them to the pressure inaccordance to what is recommended by the manufactuer.

And don't forget to torque up the wheel nuts/studs correctly we lost a van just last week for this very reason.

Mike.

 

[rob_jax]

Gary,

If your caravan is an Eriba, take a look at www.eriba-amiga.co.uk, and look at the on-the-road section.

But even if not, a 175R13 is a common tyre size fitted to the mid-sized Eriba Touring vans, which have a max weight of 1000kg, and the recommended inflation pressure is 2.5 bar - about 37 psig. This is consistent with the value of 36 psig for your 950kg max weight.

Robert

 

[Brian_5062637]

All tyre manufacturers have load and inflation tables and ALL tyres should be inflated to the pressure suitable for the load being carried. The sidewall max pressure and load figures are a legal requirement for the North American market only. However, the original query indicates that the tyre was a bit OTT for the van! The pressure in a commercial tyre is much higher than the same size car tyre but is, of course, designed to carry a much higher load. So, if the load is lighter than the design weight the pressure can be reduced to suit, down to a minimum ,which, then, may be still too high to give a good ride. It is better to choose a tyre to suit the vehicle weight with a margin to spare than to "overtyre" and get a poor ride.

 

[Gary_5075845]

Hi all,

Thank you all for your response on this one. I have been and returned from the Blue Dolphin and we had a fantastic time. I can't wait to get hitched up and back on the road again. I think I'm addicted.

Anyway, I went for the 36psi, the tyres looked fine and the caravan performed outstandingly. No swaying at all. I did buy myself a torque wrench from argos at a cost of about