CONTINENTAL REAR CP TYRE PRESSURES

In May 20 Continental told me:
 
ETRTO – the European Tyre & Rim Technical Organisation provides the following additional guidance related to Camper Van tyres:-  “The LI designation of CP-type tyres carries a single ‘load index’ indicating their normal use in single fitment.  In this case only, tyres on the rear axle have to be inflated to 550 kPa (5.5 bar), (to compensate for severe conditions of unequal load distribution, but with no further concession to increase the maximum load capacity)…”   As all tyre manufacturers must comply with this then you should be inflated your rear tyres to 5.5 bar.
 
I have recently learnt from Continental that they have decided to continue showing and recommending lower rear CP tyre pressures for lower rear axle masses in their Databook. 
 
Continental sponsor TyreSafe who recommend using the cold tyre pressure for an axle mass that is 10% higher providing it does not exceed the maximum pressure recommended by the tyre manufacturer.  This is reflected in their on-line calculator for front CP tyres but not for rear CP tyres which shows 5.5 bar for all rear axle masses.  If the Continental axle mass figure is divided by 1.1 it will give the axle mass figure for that pressure that is used by TyreSafe.  For example, if the Continental figure shows a cold rear tyre pressure of 5.5 bar for a rear axle mass of 2060 kg, the TyreSafe figure for 5.5 bar would be 1873 kg.  This means that if the rear axle mass is 1873 kg or more, the rear CP tyre pressure should still be 5.5 bar.  This calculation can be done for any of the axle mass figures in the Databook.  Although this could result in a degree of over-inflation, this is judged to be safer than any tyre being under-inflated.  Under-inflation can be caused by uneven loading across the axle, which is inevitable in a motorhome, load that is added or moved around after the axle masses have been measured, infrequent or inaccurate measurement of tyre pressures and falls in the ambient cold temperature.   

Well that's cleared that up!
5.5 bar is 80PSI, my tyres have a maximum pressure on the sidewall of 65PSI.
Al.

bikeralw wrote:Well that's cleared that up!
5.5 bar is 80PSI, my tyres have a maximum pressure on the sidewall of 65PSI.
Al.

Sounds like you have a C tyre.  My post is about CP tyres.

Interestingly, since I have had a cheapo, but accurate enough TPMS fitted, it always agrees with my tyre pressure gauge which itself agrees with the calibrated one at my local garage, not scientific, but near enough.

I always run my tyres at 60psi, and on a run of any length, the pressure rise, as seen by the TPMS evenly over all 4 to 65 or 66psi, the ambient temperature is 60psi, the running temp (all tyres increase in temp when under load and running) increases by about 6deg C. 

So a temp rise and working temps increased by rolling and drive loads, increases the pressure by circa 10%. As I have never used a different base pressure I cannot say that this is a linear change with temperature, but it certainly was in the aircraft I used to fly, indeed our turn-round times could be affected solely by tyre cooling time.

My point, eventually is, that if tyres are run at their max of 80psi, then it is likely that the pressure will rise to, perhaps 10% more as mine do, to 88psi, surely that cannot be acceptable if the max is 80?

I feel this will go on and on as usual, this is all I will contribute this time!!!!

IanH wrote:
I always run my tyres at 60psi, and on a run of any length, the pressure rise, as seen by the TPMS evenly over all 4 to 65 or 66psi, the ambient temperature is 60psi, the running temp (all tyres increase in temp when under load and running) increases by about 6deg C. 

So a temp rise and working temps increased by rolling and drive loads, increases the pressure by circa 10%. As I have never used a different base pressure I cannot say that this is a linear change with temperature, but it certainly was in the aircraft I used to fly, indeed our turn-round times could be affected solely by tyre cooling time.

My point, eventually is, that if tyres are run at their max of 80psi, then it is likely that the pressure will rise to, perhaps 10% more as mine do, to 88psi, surely that cannot be acceptable if the max is 80?

I feel this will go on and on as usual, this is all I will contribute this time!!!!

I see you have a 2013 PVC.  I think only C tyres were available in 2013 but they could have been replaced by CP tyres.  60 psi equates to about 4.1 bar.  If its a Continental 215/70 R15 CP tyre, 4.1 bar at the rear would equate to a loaded rear axle mass of about 1620 kg (810 kg per tyre) or 1470 kg if more cautious TyreSafe figures are used.   These masses are much lower than on any of the coachbuilts.  This can be  accounted for by your different layout and shorter rear overhang.  

All tyre pressures that are given are cold pressures before a journey starts and with the tyre not in the sun.  As you have found out the tyre pressure increases as the tyre warms up as it will do when it is driven.  This is quite normal and the tyre is designed for that.  The same applies with a rear CP tyre whose cold pressure is 5.5 bar.  As it is driven it will warm up and the pressure will go above 5.5 bar and there is nothing wrong with that.

...thanks for the above....so, ill carry on as ive always done with my Conti CP tyres....use the axle loads to determine required pressures....

bikeralw wrote:Well that's cleared that up!
5.5 bar is 80PSI, my tyres have a maximum pressure on the sidewall of 65PSI.
Al.

If you do a search  you will find that cp  tyres  are stamped at 65 psi  .but that is for American  Market  only .

Molly3 wrote:

bikeralw wrote:Well that's cleared that up!
5.5 bar is 80PSI, my tyres have a maximum pressure on the sidewall of 65PSI.
Al.

If you do a search  you will find that cp  tyres  are stamped at 65 psi  .but that is for American  Market  only .

Just been out and read the rest on a tyre. You're right, it goes on to say STANDARD FOR NORTH AMERICA AND AUSTRALIA.
Al.

bikeralw wrote:

Molly3 wrote:

bikeralw wrote:Well that's cleared that up!
5.5 bar is 80PSI, my tyres have a maximum pressure on the sidewall of 65PSI.
Al.

If you do a search  you will find that cp  tyres  are stamped at 65 psi  .but that is for American  Market  only .

Just been out and read the rest on a tyre. You're right, it goes on to say STANDARD FOR NORTH AMERICA AND AUSTRALIA.
Al.

As far as I am aware, if it's a CP tyre the North America reference will state 69 psi not 65 psi.  That is what is written on mine.

glyne lock wrote:just a tip anyone getting an mot you can see the axle weight on the brake test

Had my Mot this week but wasnt allowed to view due to Covid (only one person allowed in reception/ waiting room ) so didn't see brake test and not given a printout.

glyne lock wrote:

Paulmold wrote:

glyne lock wrote:just a tip anyone getting an mot you can see the axle weight on the brake test

Had my Mot this week but wasnt allowed to view due to Covid (only one person allowed in reception/ waiting room ) so didn't see brake test and not given a printout.

maybe  if anyone going for test now could ask for a print out or ask the tester to make a note of the readings for them .like you say Paul you don't get a print out  of brake test at a car test centre 

Exactly why I mentioned it. I have a free council weighbridge locally to use.

As I am now aged and relatively stupid , what’s the difference re a C tyre and a CP tyre. Thanks 

Cymro wrote:From Caravan Guard: "“CP” after the rim diameter code denotes a commercial vehicle tyre for service on motorhomes. “C” would denote a standard light commercial tyre. ** “CP” type tyres usually only have a single load index indicating their normal use as a single fitment. ... “C” type tyres usually have two load indices (e.g. 109/107)."


i.e. CP [ "Camping Pneu"] are designed for the typical pattern of use of a motorhome: usually heavily loaded (furniture and fittings and occupants and liquids etc ) and much of the time spent sitting on a drive or parking lot during the year.  Contracst with white van man: intensive daily use, not always heavily loaded.


Yer pays yer money and yer takes yer choice!


Cymro

Thanks Cymro, ours is a May 13 built Merc so presume C?.  Yes I know they are 7 years old   and I’ll be replacing soon if we’re allowed out much that is.

From tyremen.co.uk....

What are the differences between Motorhome Tyres and Normal Tyres?
Motorhome tyres or Camping tyres are those designed specifically for mobile homes. They have several important features which make them a necessity for campers:
 One of the most important qualities of Motorhome tyres is their ability to carry heavy loads. They have a much higher weight carrying capacity than  normal tyres and van tyres. Car tyres can typically take a load of up to 500kg with van tyres able to withstand 700kg. Even smaller motorhomes, weighing around 2700kg, can put loads of 675kg on each tyre. This will certainly burst normal car tyres at speed. Some motorhomes require tyres that can take a maximum load of over 1200kg on each tyre.


Due to the shear load, motorhome tyres need to withstand high pressure. A typical car tyre is limited to a maximum pressure of around 40 psi compared to a light commercial vehicle tyres which are inflated to around 65 psi. Specialist motorhome tyres can be inflated to 80psi.
 
Tyremen tip - Like all tyres, motorhome tyres need to be inflated correctly. Incorrect tyre pressures can have an adverse affect on handling, wear out more quickly, increase fuel consumption and cause blowouts which may lead to accidents. Always check your vehicle/chassis handbook and inflate your tyres to the correct pressure. Remember, the volume of pressurised air within the tyre determines the load the tyre can withstand. Reducing the tyre pressure reduces the load capacity of the tyre.



The tougher sidewalls on camping tyres bring two major advantages. Firstly, they're better at running at the high pressures motorhomes demand and secondly their rigidity gives the vehicle a more solid base, which prevents it from moving around and swaying.
 
You'll also see differences in tread compound. Tread compound is important for grip in poor weather conditions. It also makes your motorhome better at dealing with wet campsites, country lanes and heavy impact.


Can you use normal van tyres on your motorhome? and more importantly, should you?
It's perfectly legal to use van tyres for motorhomes on UK roads. However, the load rating must be high enough to carry the weight of the vehicle. Standard van tyres won't give you any of the benefits of camping tyres, as described above.
Camper tyres are 15% more expensive than standard van tyres. For obvious reasons, this is why many motorhome owners use standard van tyres instead.
However, the major benefits of safety, wear and tear and fuel savings more than make up the extra cost.

I have Continental C tyres Load rating 121, 10 ply, the Equivalent CP tyre is 115 rating 8 ply. At all inflation pressures the permissible load is greater for the C tyre than the CP tyre.

I'll stick with Conti All Season C, at pressures to suit my load usage.

Thanks Paul, very well said. 

May I ask, as my tyres are getting near to being replaced, although a new lock down may make me wait, what tyres have you got on your van?

Difficult question I know as they may just be your own choice, but after reading all the posts on the subject, there still seems confusion. 

My van is running on original Bridgestone Duravis light truck R630 215/70R15 C 109/107S which I would expect as when the van was made they didn't know is was up for conversion and AS did not change the tyres of course, may be they should have, but in their defence I expect all converters follow the same due to cost.
---------
Richard
 PS I run at 60psi allround.

rgermain wrote:Thanks Paul, very well said. 

May I ask, as my tyres are getting near to being replaced, although a new lock down may make me wait, what tyres have you got on your van?

Difficult question I know as they may just be your own choice, but after reading all the posts on the subject, there still seems confusion. 

My van is running on original Bridgestone Duravis light truck R630 215/70R15 C 109/107S which I would expect as when the van was made they didn't know is was up for conversion and AS did not change the tyres of course, may be they should have, but in their defence I expect all converters follow the same due to cost.
---------
Richard
 PS I run at 60psi allround.

My van is older than yours so I expect it also was supplied new with C tyres. When we bought it , new wheels had been fitted with CP tyres, dated 2015 so they will be replaced anytime between now and spring depending on when we are allowed out. Currently they are Michelin Agilis 225/70x15CP. There appears to be only 2 brands available in that size, Michelin and Continental. Maxxis make CP tyres but only in 215/70x15. I had Agilis on my Nuevo and was happy with their performance so I see no reason to change. 
As for pressures , I run at 60 front and 65 rear , obviously I am disregarding Michelin advice of running tests at 80 but find 60/65 gives a comfortable ride.

Yes thank you, we also had Agilis on our Topaz from new and I replaced with same after 7 years.

I also disregard pressures and run to give a comfortable ride. I see Agilis come in my size, not sure how effective the M&S is , you should see the tyres on my Grandsons Defender! A warden once told me, no wonder I had to tow you up the grass field with those pretend M/S tyres!, he had a sit on lawn mower
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Richard

rgermain wrote:Yes thank you, we also had Agilis on our Topaz from new and I replaced with same after 7 years.

I also disregard pressures and run to give a comfortable ride. I see Agilis come in my size, not sure how effective the M&S is , you should see the tyres on my Grandsons Defender! A warden once told me, no wonder I had to tow you up the grass field with those pretend M/S tyres!, he had a sit on lawn mower
----------
Richard

I got off very wet grass at Tewkesbury with an uphill slope with advice from a warden to keep straight as possible and taking it slow. We use a lot of THS which tend to be on grass  , never had a problem with this van or the Nuevo. In fact I've only been towed off once in 10+ years and that was at Peterborough show (anyone who was there will remember that show.)

I was at Smedmore house Kimmeridge, very windy, very wet, so I decided to park up at bottom of field to escape the wind, not a good choice as it flooded due to water running down hill. The other time with the Topaz, was in Normandy, after constant rain and leaving site each day, I made tracks in the grass which bogged us down, again towed out with a Mower.

I also took it straight and slow, but didn't work for me.
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Richard

Always check your vehicle/chassis handbook and inflate your tyres to the correct pressure.

Unfortunately the handbook will only state the pressures suitable for the base vehicle. I relied on the rating label on the door frame of 60/65psi on our Nuevo until I caught an earlier thread on CP tyres.