Jump to content

High Tyre Pressure


ericfield

Recommended Posts

Looking at Swift's latest offerings I see that the cold tyre pressures on some models are as high as 64psi. ..just 1psi below the tyres 65psi max rating.

 

My question to more knowledgeable tyre experts is. ... Given the inherent inaccuracy and variability of service station air compressors (my two local garages are 3psi different on my cars 30psi tyre pressures!) is there any danger of tyre failure if the actual tyre pressure is (say) 68psi. ..when the pump is set to 64psi?

 

I confess to being surprised that tyre inflation rates on these caravan should be so close to the manufacturers max limit. There is little room for operator or equipment error.

 

The load ratings on Swifts tyre choice seem correct for the caravan weights. It's just this high pressure thing that's a tad worrying. ..to me at least.

Link to comment
Share on other sites

Simply on the basis of answering the question, no problem, the stated maximum would be at least 50% below it's ultimate maximum pressure.

I would also expect, as new, 50% is on the conservative side, but as the tyre ages will reduce considerable, this leads to the advice to not fully load caravan tyres and leave an extra 10%. From your example this would appear to be ignored, however one or two sizes of tyre are rated at 69psi maximum

gary1s.gif

 

Arc Systems are specialist Carver caravan product repairers, committed to providing a comprehensive service as well as spare parts for these popular heaters.

Link to comment
Share on other sites

Simply on the basis of answering the question, no problem, the stated maximum would be at least 50% below it's ultimate maximum pressure.

I would also expect, as new, 50% is on the conservative side, but as the tyre ages will reduce considerable, this leads to the advice to not fully load caravan tyres and leave an extra 10%. From your example this would appear to be ignored, however one or two sizes of tyre are rated at 69psi maximum

Thanks for the reply Gary. I am being a little thick this afternoon - didnt quite grasp your last sentence.

 

If I understand you correctly you suggest that the REAL maximum for the tyre (when new and in good condition) is likely to be signifcantly higher than the stated maximum . ..such that a 2 or 3 extra psi variation due to guage inaccuracy shouldnt be an issue.

 

But aiming for the 64psi would still be the goal.

Link to comment
Share on other sites

Yes I agree, poorly worded, nevertheless you have it correct, aim for 64psi and a couple either side is near enough

gary1s.gif

 

Arc Systems are specialist Carver caravan product repairers, committed to providing a comprehensive service as well as spare parts for these popular heaters.

Link to comment
Share on other sites

Yes I agree, poorly worded, nevertheless you have it correct, aim for 64psi and a couple either side is near enough

 

Many thanks for the reassurance.

Link to comment
Share on other sites

The very high tyre pressures dictated these days by caravan manufacturers does concern me and it always has done ever since they started going for ever higher pressures, the reason being that a hard tyre is far easier to damage and far easier to puncture.

 

If my memory serves me correctly when I bought a Sprite 450EB new back in 1994 it had very reasonable pressures of 46psi.

 

Now at the same time in 1994, a lot of cars ran around on pressures of 24 to 26 psi and the tyres weren't the modern idiom of the low to ultra low profile variety of modern cars and oh didn't they all have such a comfortable absorbing ride?

 

But since 1994 (and earlier) caravan tyres have mostly remained of a fairly high profile and yet the pressures have gone relentlessly higher and for what reason I know not why ?

 

A tyre is as important to the safety and stability of a caravan as any other part of the suspension system and yet by running them at ever increasing pressures the rigidity of the sidewall effectively removes the tyres from the overall suspension equation and yet the woefully ineffective suspension fitted to the vans is almost exactly the same as it was then back in 1994 or indeed earlier!

 

Possibly a singing and dancing tyre expert can shine some light on this matter.

Link to comment
Share on other sites

The very high tyre pressures dictated these days by caravan manufacturers does concern me and it always has done ever since they started going for ever higher pressures, the reason being that a hard tyre is far easier to damage and far easier to puncture.

 

If my memory serves me correctly when I bought a Sprite 450EB new back in 1994 it had very reasonable pressures of 46psi.

 

Now at the same time in 1994, a lot of cars ran around on pressures of 24 to 26 psi and the tyres weren't the modern idiom of the low to ultra low profile variety of modern cars and oh didn't they all have such a comfortable absorbing ride?

 

But since 1994 (and earlier) caravan tyres have mostly remained of a fairly high profile and yet the pressures have gone relentlessly higher and for what reason I know not why ?

 

A tyre is as important to the safety and stability of a caravan as any other part of the suspension system and yet by running them at ever increasing pressures the rigidity of the sidewall effectively removes the tyres from the overall suspension

 

 

It is the air pressure that supports the load and the tyre construction contains that pressure. . Bigger caravans require tyres capable of carrying those loads hence the reinforced and 8PR tyre with 'thicker' sidewalls. Low profile tyres as used on cars these days give a much stiffer ride as most of us know. Caravan tyres have remained, generally, as standard 80 series profile to provide the softest ride.

I did have a 1500 kg Buerstner on 205/65 x 15 tyres at a relatively low pressure by comparison with the current 185 x 14 8PR at 65 psi.

Link to comment
Share on other sites

One problem with these high pressures is what happens when you have a blow out.

Ours caused a lot of damage to the wheel arch and ripped out all the waste pipes. We changed to a TA of the same weight but the tyre pressures are only 34psi.

Toyota Landcruiser and Fleetwood Heritage 640 ES(T)

Link to comment
Share on other sites

One problem with these high pressures is what happens when you have a blow out.

Ours caused a lot of damage to the wheel arch and ripped out all the waste pipes. We changed to a TA of the same weight but the tyre pressures are only 34psi.

 

Most "blow outs" are the result of a tyre slowly losing pressure and overheating leading to the failure of the tyre carcass. But even with a rapid pressure loss caused by an object the damage is almost certainly caused by the flailing tread after a tyre fails not the "explosion" of released air.

Link to comment
Share on other sites

I worked on a bit of machinery that used a standard tyre to drive a roller system and it was allowed +/-10% on max pressure at cold (72psi ) and after a hard day it was very hot and up around 90psi.

if you are not sure of the garage readings use a decent tyre pressure guage and the machine as a guide.

Link to comment
Share on other sites

Looking at Swift's latest offerings I see that the cold tyre pressures on some models are as high as 64psi. ..just 1psi below the tyres 65psi max rating.

 

My question to more knowledgeable tyre experts is. ... Given the inherent inaccuracy and variability of service station air compressors (my two local garages are 3psi different on my cars 30psi tyre pressures!) is there any danger of tyre failure if the actual tyre pressure is (say) 68psi. ..when the pump is set to 64psi?

 

I confess to being surprised that tyre inflation rates on these caravan should be so close to the manufacturers max limit. There is little room for operator or equipment error.

 

The load ratings on Swifts tyre choice seem correct for the caravan weights. It's just this high pressure thing that's a tad worrying. ..to me at least.

 

I would also check the tyresafe website for the CORRECT details for any size and type of tyre and the weights it is designed to carry. Coachman rec psi of 65 for my van when in actual fact that pressure is for a weight of 1700kg when my all up weight is 1465 kg and with the type and spec of tyre fitted the CORRECT pressure is 54psi. So check your van weight, size and type of tyre you should have a weight carrying margin of at least 10% over the 2 axles.

 

Jt

Coachman Pastiche

Link to comment
Share on other sites

 

I would also check the tyresafe website for the CORRECT details for any size and type of tyre and the weights it is designed to carry. Coachman rec psi of 65 for my van when in actual fact that pressure is for a weight of 1700kg when my all up weight is 1465 kg and with the type and spec of tyre fitted the CORRECT pressure is 54psi. So check your van weight, size and type of tyre you should have a weight carrying margin of at least 10% over the 2 axles.

 

Jt

Interesting, the all up weight for my Lunar Solaris is 1450kg & the recommended tyre pressure is 54psi which sounds about right.

What's going on with the manufacturers of new caravans, have they discovered something new or have they got it wrong?

Link to comment
Share on other sites

As an aside but still connected to the subject of tyre pressures, I used to own a coachbuilt Fiat Ducato based Granduca Motorhome.

The recommended tyre pressures were 84psi which I always thought were pretty high.

I contacted Michelin to ask there advice giving the motorhome details with axle weights etc.

Michelin came back with a figure of 65psi which made the motorhome much more driver friendly.

It does make you wonder :(

Link to comment
Share on other sites

Once you do find the correct P S I it would be a good idea to buy yourself a digital pressure guage about £10 from Halfords when I bought mine. goes up to 100 P. S. I. Regards Peter.

Link to comment
Share on other sites

It is all very well for the manufacturers to specify these high pressures but what do we use to maintain the pressure. I am sure that my worthy foot pump is going to struggle and the guage will at best be unreliable.

Link to comment
Share on other sites

Interesting, the all up weight for my Lunar Solaris is 1450kg & the recommended tyre pressure is 54psi which sounds about right.

What's going on with the manufacturers of new caravans, have they discovered something new or have they got it wrong?

 

Good question. ...My view is that when people ask for a weight plate upgrade it is the makers way of saying its alright to tow at the higher pressure and weight. Its NOT in my opinion if that encroaches on your safety margin. You should run the correct pressure for the tyre on your van and the weight its is expected to carry safely. Try and maintain a 10%margin at all times.

I would encourage ALL owners to check and dont just accept your manufacturer knows best when in reality they wont even use the same tyre maker 2 years running. They will ALWAYS buy the cheapest available to them.

 

Jt

Coachman Pastiche

Link to comment
Share on other sites

As an aside but still connected to the subject of tyre pressures, I used to own a coachbuilt Fiat Ducato based Granduca Motorhome.

The recommended tyre pressures were 84psi which I always thought were pretty high.

I contacted Michelin to ask there advice giving the motorhome details with axle weights etc.

Michelin came back with a figure of 65psi which made the motorhome much more driver friendly.

It does make you wonder :(

 

I 100% agree with you Springtime.

 

I wonder what the technical departments at the tyre manufacturers would suggest as being the correct tyre pressures for the tyres fitted to caravans.

 

Who does actually come up with the tyre pressures for caravans, does anyone know ?

Link to comment
Share on other sites

It is all very well for the manufacturers to specify these high pressures but what do we use to maintain the pressure. I am sure that my worthy foot pump is going to struggle and the guage will at best be unreliable.

Good point. I have a large SIP air compressor which is used to drive various air tools.

It can pump over 100psi if required and has a garage type gauge / fitting for pumping up tyres.

All of my previous motor homes requires high tyre pressures especially the RV which needed 85psi on all 6 tyres.

It's not possible to do this using a foot pump so I appreciate the problems that other caravanners may have inflating their tyres.

Link to comment
Share on other sites

 

I wonder what the technical departments at the tyre manufacturers would suggest as being the correct tyre pressures for the tyres fitted to caravans.

 

Almost certainly the pressure suitable for the load being carried. Most caravans will operate very close to the MPTLM so the load and, therefore the pressure, is easy to determine.

 

Who does actually come up with the tyre pressures for caravans, does anyone know ?

 

In theory, the caravan and tyre manufacturers should discuss appropriate tyres and pressures as do vehicle manufacturers. .

More probably, in practice, the caravan manufacturer will work to the tyre manufacturer's load and inflation tables.

Link to comment
Share on other sites

Pressures are higher now due to the heavier loads that the new caravans being built to . If checking tyre pressures the weight of the caravan and the tyre size needs to be refered to as a different tyre can be fitted by the manufacturers or previous owner and not just whats quote for a specific caravan in the handbbok .

 

Caravan manufacturers like Car manufacturers will fit tyres that are in stock and available at the right price .

 

 

Dave

Link to comment
Share on other sites

Pressures also vary according to the tyre type and construction. The original Trailermaxx tyres (195/70 R14) on our Bailey Pageant were 42 psi; the replacement 185/75 C14 run at 50 - 52 (the former recommended by Bailey; the latter from Tyresafe). I use the higher pressure for long trips although I suspect a couple of psi makes little difference one way or the other.

Link to comment
Share on other sites

Pressures are higher now due to the heavier loads that the new caravans being built to .

 

Dave

So how does that work out when the maximum laden weight on my Lunar is 1450kg and the recommended tyre pressure is 54psi and the max laden weight on JTS's Coachman is 1465kg (virtually the same) and the recommended tyre pressure is 65psi.

Link to comment
Share on other sites

When doing my apprenticeship we had a safety film showing a tyre being inflated until it ruptured. It was done in the middle of an airfield, failed at approx 2 1/2 times its rating and it took nearly a minute for the rim to land.

 

The tyre is designed to distort so as to produce its correct footprint to support its load. It should be almost a rectangle with a slight curve on the leading and trailing edges to match the curvature of the tread face and the sides due to the sidewall bulge. This bulge moves around the wall as the tyre rotates and it is this flexing action which creates heat and is why it is much worse with low pressures leading to failure.

Link to comment
Share on other sites

So how does that work out when the maximum laden weight on my Lunar is 1450kg and the recommended tyre pressure is 54psi and the max laden weight on JTS's Coachman is 1465kg (virtually the same) and the recommended tyre pressure is 65psi.

Are they exactly the same tyres?

Brian

Link to comment
Share on other sites

Are they exactly the same tyres?

Brian

I don't buy that one.

Mine are currently Nexens but inflated to the handbook recommendations.

I would find it very difficult to believe that if you replace your caravan tyres with a different make but the same ratings then the pressures could be different.

If that was the case, the same would go for car tyres.

Link to comment
Share on other sites

Archived

This topic is now archived and is closed to further replies.

×
×
  • Create New...