Re: CONTINENTAL REAR CP TYRE PRESSURES

by Paulmold Fri Oct 16, 2020 11:16 am

Unless you belong to a forum such as this, the fact that your motorhome is fitted with CP tyres would mean nothing to you and you would probably inflate to the pressures on your door pillar. How are novice motorhomers meant to know any different?

by Caraman Fri Oct 16, 2020 11:44 am

Paulmold wrote:Unless you belong to a forum such as this, the fact that your motorhome is fitted with CP tyres would mean nothing to you and you would probably inflate to the pressures on your door pillar. How are novice motorhomers meant to know any different?

I think the advice for anyone is use the pressures recommended by the tyre manufacturer for a given axle mass. The plated figures as you know are the pressures for when the vehicle is fully loaded which is stated on the tyre pressure label and in the handbook. ColinCamper's tyre pressure label is clearly for a C Tyre which set a front tyre pressure of 4.1 bar for an axle mass of 1850 kg and a rear tyre pressure of 4.5 bar for an axle mass of 2000 kg. Both figures are slightly above the ETRTOs recommendations for these axle masses which allows for some uneven loading across the axle. If the actual axle masses when fully loaded are significantly less that 1850/2000 kg which they definitely will be at the front on a Nuevo, lower pressures should be used. When ColinCamper's Nuevo was produced I don't think CP tyres had been invented so no reference would be made to them. The problem arises when a Nuevo has had its C tyres replaced with CP tyres or vice a versa. If CP tyres are inflated to C tyre pressures they will be dangerously under-inflated and if C tyres are inflated to CP pressures they will be dangerously over-inflated.

by Paulmold Fri Oct 16, 2020 12:14 pm

Your last 4 lines are precisely what I'm talking about. My Nuevo (2006) was fitted with CP tyres when we bought it in 2013 so unless I'd read such forums as this, I would not even know that CP tyres weren't around when the Nuevo was made. I repeat, how are novice motorhomers meant to know any different?

by Caraman Fri Oct 16, 2020 12:29 pm

Paulmold wrote:I repeat, how are novice motorhomers meant to know any different?

Paul - I suspect this is a rhetorical question but the answer is better education from the NCC, national clubs, motorhome magazines, dealers and of course the converter when they write their handbooks. This is what it states in Swift's handbooks which is as good as it gets:

"Tyre Pressures The motorhome tyre pressures noted in the Technical book are the pressures stated by Fiat for your vehicle calculated in a fully laden condition. If you are not running fully laden, reduced pressures could be used but please seek clarification from the Tyre manufacture.”

If clarification is sought from the Tyre Manufacturer they will want to know if its a C or CP tyre. I doubt that many motorhome dealers will provide sensible advice. Several I spoke to earlier this year didn't know the difference between a C and CP tyre but that's salesmen for you.

by Paulmold Fri Oct 16, 2020 5:11 pm

The ignorance of the difference by salesmen is what bothers me and of course the private sale. You could be following a new motorhomer down a motorway at 70mph whose tyres are dangerously under or over-inflated through no fault of his own.

by ColinCamper Sat Oct 17, 2020 4:29 pm

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 [You must be registered and logged in to see this link.].

After trawling through the databook, Looks like page 87 is the correct one for 215/70 15inch rims, 8 ply, load factor 109.

by Caraman Sat Oct 17, 2020 5:12 pm

ColinCamper wrote: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 [You must be registered and logged in to see this link.].

After trawling through the databook, Looks like page 87 is the correct one for 215/70 15inch rims, 8 ply, load factor 109.

Yes - it shows both the C and CP versions with different pressures for each. The front and rear pressures for the C are the same. The rear pressures for the CP are higher than the front. These pressures do not take into account uneven loading across the axle which will result in one tyre being under-inflated for its load which is unsafe. So higher pressures should be used hence the TyreSafe model.

by anders4 Fri Oct 23, 2020 7:20 pm

I have a Nuevo ES and have always run my tyres at the recommended pressures stated on the van (59/65psi), but have been continually worried that they look under inflated even when the van is running very light. I have Continental Vanco2 tyres fitted and recently noticed in small writing on a tyre that they can be inflated up to 80psi due to their construction. A few weeks ago I had a round trip of 500 miles and inflated the tyres to: front 75 and rear 80, to keep the differential as stated on the vehicle label. They look a lot better and apart from feeling potholes more through the steering wheel, I got better mpg.

by Cymro Fri Oct 23, 2020 7:26 pm

Anders4: what pressures does the Continental table recommend for your type of tyre, and for your tyre size and for your axle weights?

I'd be surprised if they're as high as 75:80, though I admit I'm not familiar with Vanco2 tyres. Hope you've got a good dentist!

Cymro

by Caraman Fri Oct 23, 2020 7:53 pm

anders4 wrote:I have a Nuevo ES and have always run my tyres at the recommended pressures stated on the van (59/65psi), but have been continually worried that they look under inflated even when the van is running very light. I have Continental Vanco2 tyres fitted and recently noticed in small writing on a tyre that they can be inflated up to 80psi due to their construction. A few weeks ago I had a round trip of 500 miles and inflated the tyres to: front 75 and rear 80, to keep the differential as stated on the vehicle label. They look a lot better and apart from feeling potholes more through the steering wheel, I got better mpg.

I recommend you contact Continental Tyres through their on-line contact form to find out what tyre pressures you should be using. For this you will need to know your tyre size and type and axle masses (which must not exceed your Nuevo's MPTLMs) for when your Nuevo is fully loaded for normal use. The pressures on your Nuevo's tyre pressure label are those recommended for a light Commercial C tyre when each axle is at is MPTLM. I would have thought that a Vanco2 tyre is a C tyre with a maximum permitted pressure of 4.5 bar (65 psi) but the maximum permitted pressure you quote of 80 psi (5.5 bar) on the tyre wall is for a Camper (CP) tyre.

[You must be registered and logged in to see this link.]

by jadatis Fri Oct 23, 2020 8:12 pm

The Continental group gives often 2 pressures on their C-tyres, and CP- tyres.
1 direct after the loadindex/speedcode combination ( fi 109Q 65psi) .
This is called the reference-pressure, and is the cold pressure for wich the maximum load is calculated for, for the reference speed of mostly 160kmph/99mph.

On the other side they give the "maximum inflation pressure" of 10 psi higher.
On CP they also give the 2 pressures.

In earlyer days higher then reference pressure was allowed, nowadays not anymore.
But on the Continental group tyres still allowed.
CP tyres max infl pressure almost always 80 psi , so if refpres is 65 psi even 15 psi higher.

To my opinion CP are not that different from C-tyres, and are put in the market to cover the overloading on most motorhomes rear tyres, without having to upgrade the rimm's maximum load.

Better would be to upgrade the tyres and rimms to the real load on most loaded tyre( also the valves) , so you dont have to use the higher then reference-pressure-trick , as is used on CP-tyres.

Someone here mentioned already his 10 plyrated tyres 121 loadindex, against the 8 pr CP LI 115.
Question is if he also upgraded the rimms to maxload 121.
Risk if not, is a slow leaking rimm, courced by crackes , because rimm is to weak constructed, for the real loads.

by Knick-Knack Fri Oct 23, 2020 8:22 pm

I am somtimes wrong, but:

1 The whole tyre pressure issue is a pile of poo. An important pile of poo, but poo nevertheless.

2 Vehicles for conversion arrive with a tyre pressure label (which might say 59 & 65psi). AS do their conversion, and fix a new label over the top (which might say 72 & 79psi) - or they might forget to.

3 Different conversions will have different axle weights, but I suspect that all of the new AS labels are the same.

4 The lower tyres pressures as per Continental tend to look under-inflated, will give a smoother ride (and therefore fewer bits falling off!) but will give less mpg.

5 Tyres inflated at the AS "new label" pressures will not be under-inflated, will give a rougher ride, but better mpg.

6 I reject the significance of uneven loading across an axle. This will undoubtedly occur, but if my wife and I give Big Daddy a lift in our car I don't feel the need to specially calculate and set the perfect tyre pressures. I suspect that, on our Nuevo, any difference in loading across an axle will not be critical.

For me, the Continental pressures (for my weighbridge axle weights) are too low, and the AS new-label pressures are too high. I have set mine mid-way between the two, and that's good enough for me.

Happy motorhoming!

by Caraman Fri Oct 23, 2020 8:53 pm

Knick-Knack wrote:I am somtimes wrong, but:

1 The whole tyre pressure issue is a pile of poo. An important pile of poo, but poo nevertheless.

2 Vehicles for conversion arrive with a tyre pressure label (which might say 59 & 65psi). AS do their conversion, and fix a new label over the top (which might say 72 & 79psi) - or they might forget to.

3 Different conversions will have different axle weights, but I suspect that all of the new AS labels are the same.

4 The lower tyres pressures as per Continental tend to look under-inflated, will give a smoother ride (and therefore fewer bits falling off!) but will give less mpg.

5 Tyres inflated at the AS "new label" pressures will not be under-inflated, will give a rougher ride, but better mpg.

6 I reject the significance of uneven loading across an axle. This will undoubtedly occur, but if my wife and I give Big Daddy a lift in our car I don't feel the need to specially calculate and set the perfect tyre pressures. I suspect that, on our Nuevo, any difference in loading across an axle will not be critical.

For me, the Continental pressures (for my weighbridge axle weights) are too low, and the AS new-label pressures are too high. I have set mine mid-way between the two, and that's good enough for me.

Happy motorhoming!

The tyre pressure label on Auto-Sleepers' motorhomes is the same as the one fitted by the base vehicle manufacturer on the unconverted vehicle, which is for when the unconverted vehicle's axles are loaded to their MPTLM. Even though when the motorhome is fully loaded an axle mass is less than its MTPLM, Auto-Sleepers do not change the tyre pressure label which they can do as part of the Stage 2 type approval. This is because unlike for example Bailey, Auto-Sleepers do not road test their motorhomes to determine their optimum tyre pressures.

The tyre pressures shown in Continental's Databook assume even loading across the axle. As you point out the loading across the axle will never be even. One tyre will always have a higher load than the other. For this reason the pressures used for the axle should be set around the tyre with the higher load which will be higher than the pressures shown in Continental's Databook. This is partly why TyreSafe who are sponsored by Continental recommend using the tyre pressure for an axle mass that is 10% higher.

by Knick-Knack Fri Oct 23, 2020 9:05 pm

Carama! wrote:The tyre pressure label on Auto-Sleepers' motorhomes is the same as the one fitted by the base vehicle manufacturer on the unconverted vehicle, which is for when the unconverted vehicle's axles are loaded to their MPTLM. Even though when the motorhome is fully loaded an axle mass is less than its MTPLM, Auto-Sleepers do not change the tyre pressure label which they can do as part of the Stage 2 type approval. This is because unlike for example Bailey, Auto-Sleepers do not road test their motorhomes to determine their optimum tyre pressures.

Well my Nuevo has two labels, one stuck on top of the other. The pressures (just discernable) on the one underneath are different from (and significantly less than) those on the top label.

by gassygassy Fri Oct 23, 2020 10:38 pm

Has anyone here been stopped by the Tyre Police and had their pressures measured? I am a bit surprised having read all through it that for example a 2010 coachbuilt of 3500kg will have apparently inferior C tyres whereas the same weight 2020 model will have apparently superior CP tyres with higher pressures. Does anyone know of any blow-outs on 3500kg motorhomes with C tyres? Other than because the tyres were 20 years old and 0.5mm tread, of course.
I did see, right in front of my very eyes, a lorry tyre blow. I was waiting at the front of traffic at red lights at a T junction. I was in the straight-on road and a presumably heavily laden HGV pulled out from the side road and turned right, i.e. going in the same direction as I was. As he turned the corner, extra load was put on his front nearside tyre and it burst. Quite a pop obviously, but it did make me realise that tyre stress changes i.e. increases when you corner because extra load is put on the outside tyre.
My personal take on what tyre pressure to use would be to look in the motorhome owner's handbook and do what that says. The label on the door pillar could be the vehicle manufacturer who doesn't know what use the chassis will be put to.
Ultimately, if you were stopped by Plod, what would they expect your pressures to be? If you were in an accident they would take your tyre pressures, they always do I believe.
. . . . . . now I have got to go and read my owner's hand book studying

by Caraman Fri Oct 23, 2020 10:39 pm

Knick-Knack wrote:
Carama! wrote:The tyre pressure label on Auto-Sleepers' motorhomes is the same as the one fitted by the base vehicle manufacturer on the unconverted vehicle, which is for when the unconverted vehicle's axles are loaded to their MPTLM. Even though when the motorhome is fully loaded an axle mass is less than its MTPLM, Auto-Sleepers do not change the tyre pressure label which they can do as part of the Stage 2 type approval. This is because unlike for example Bailey, Auto-Sleepers do not road test their motorhomes to determine their optimum tyre pressures.

Well my Nuevo has two labels, one stuck on top of the other. The pressures (just discernable) on the one underneath are different from (and significantly less than) those on the top label.

Does the top label have anything written on it in Italian or French as mine does or anything that indicates it was put there by Auto-Sleepers?

by PLOUGHLIN Fri Oct 23, 2020 11:03 pm

jadatis wrote:.

Someone here mentioned already his 10 plyrated tyres 121 loadindex, against the 8 pr CP LI 115.
Question is if he also upgraded the rimms to maxload 121.
Risk if not, is a slow leaking rimm, courced by crackes , because rimm is to weak constructed, for the real loads.

That would be me, probably. The 10 ply rated tyres 121 load index mentioned are what was supplied and as specified when AS ordered the base chassis from Mercedes with uprated max vehicle weight, suspension equipment and Mercedes OEM Alloy wheels.

I have no worry about the adequacy of the rim/tyre combination.

by glyne lock Fri Oct 23, 2020 11:51 pm

gassygassy wrote:Has anyone here been stopped by the Tyre Police and had their pressures measured? I am a bit surprised having read all through it that for example a 2010 coachbuilt of 3500kg will have apparently inferior C tyres whereas the same weight 2020 model will have apparently superior CP tyres with higher pressures. Does anyone know of any blow-outs on 3500kg motorhomes with C tyres? Other than because the tyres were 20 years old and 0.5mm tread, of course.
I did see, right in front of my very eyes, a lorry tyre blow. I was waiting at the front of traffic at red lights at a T junction. I was in the straight-on road and a presumably heavily laden HGV pulled out from the side road and turned right, i.e. going in the same direction as I was. As he turned the corner, extra load was put on his front nearside tyre and it burst. Quite a pop obviously, but it did make me realise that tyre stress changes i.e. increases when you corner because extra load is put on the outside tyre.
My personal take on what tyre pressure to use would be to look in the motorhome owner's handbook and do what that says. The label on the door pillar could be the vehicle manufacturer who doesn't know what use the chassis will be put to.
Ultimately, if you were stopped by Plod, what would they expect your pressures to be? If you were in an accident they would take your tyre pressures, they always do I believe.
. . . . . . now I have got to go and read my owner's hand book

that might take a long time to find in your owners hand book read

by glyne lock Sat Oct 24, 2020 12:30 am

jadatis wrote:

To my opinion CP are not that different from C-tyres,

1 the tread pattern .years ago maybe a big difference but now you can get with the same load index same max pressure and as ploughlin has said can now get a c tyre with a higher load load index than a cp tyre . a lot of what people have posted on this topic is old school and things have moved on .so yes 1 reason cp tyres came on the market for the higher load required by motor homes years ago but is no longer the case

by Caraman Sat Oct 24, 2020 7:41 am

glyne lock wrote:
jadatis wrote:

To my opinion CP are not that different from C-tyres,
1 the tread pattern .years ago maybe a big difference but now you can get with the same load index same max pressure and as ploughlin has said can now get a c tyre with a higher load load index than a cp tyre . a lot of what people have posted on this topic is old school and things have moved on .so yes 1 reason cp tyres came on the market for the higher load required by motor homes years ago but is no longer the case

I think Glyne is right. C tyres can have the same load index as CP tyres and therefore have the same maximum load - 1030 kg in my tyre's case. As I understand it, more expensive CP tyres are stronger to better cope with high loads all the time and being parked up in one place for long periods. A commercial vehicle with a cheaper C tyre might carry a high load some of the time but not all of the time and would be in fairly constant use. CP tyres are also supposed to suffer less damage from sun/UV exposure and their design requires them to have a higher pressure e.g a C tyre loaded to its maximum of 1030 kg would have a pressure of 4.5 bar but the equivalent CP tyre would have a pressure of 4.75 bar or 5.5 bar if its at the rear.

The stronger CP tyre might cope better with the dynamic forces gassygassy refers to which may be higher on a motorhome than a standard van due to a higher CoG and long rear overhang.

by gassygassy Sat Oct 24, 2020 9:16 am

glyne lock wrote:
that might take a long time to find in your owners hand book

. . . . .specially if it was a Haynes Manual hugegrins

I think they shove you around at least four different pages before you find tyre pressures.
I'll go and look now. If it says 'refer to door pillar' I'll just have to have a grilled bacon sarny.

by Skizzydo Sat Oct 24, 2020 12:02 pm

Well that’s truly muddied the waters, if I put 80 psi in the tyres I would bounce all over the road , almost undriveable methinks. Having spent sometime look at various tyre tables etc I am even more confused, it’s bad enough on the Mercedes with a soft suspension. I put 50 front 60 rear and it seems happy at that . Usually the pressure rises by 6 psi, except when we were driving in an ambient temp of 30c plus, when the psi went up by 12 psi. Totally confused

by MarkD Sat Oct 24, 2020 12:33 pm

I fear that most of this will be beyond the many motorhomers who routinely overload their vehicles.
Every day I see Van's way down at the back especially those with large overhangs and enormous 'garages'.
So many of these are played at 3500 kg gross and their real payload after putting 2 passengers in is minimal.
Some people even downplayed large motorhomes to get round the C1 licence restrictions.
Mine was and when I weighed it empty it was 3.6T because of extras like a towbar (50kg when I took it off) 4m swing (50kg?) rooftop aircon (50kg).
I even the front axle was overloaded with the 2 of us and 40kg dog!
Even the 3850kg original plate was no good - I had to put up rated front springs and air assist on Alko rear axle (£2.6k) to get a decent legal payload.
Also had to go up a tyre size to get 118 LI on the rear tyres which required handbrake cable to be pulled away.
A bit of a nightmare really but you don't want to get pulled in and have to leave 200kg of stuff on roadside before you continue

by Caraman Sat Oct 24, 2020 12:48 pm

Skizzydo wrote:Well that’s truly muddied the waters, if I put 80 psi in the tyres I would bounce all over the road , almost undriveable methinks. Having spent sometime look at various tyre tables etc I am even more confused, it’s bad enough on the Mercedes with a soft suspension. I put 50 front 60 rear and it seems happy at that . Usually the pressure rises by 6 psi, except when we were driving in an ambient temp of 30c plus, when the psi went up by 12 psi. Totally confused

Another forum member reported that M-B gives tyre pressure direction in its handbook or on the tyre pressure label for motorhomes. Is this the case and if so what pressures do M-B recommend for the CP tyre?

Don't worry about the hot tyre pressures i.e. when the vehicle is being driven. All that is important is the cold tyre pressure before a journey starts which can only be measured using a tyre pressure gauge.

by MarkD Sat Oct 24, 2020 3:06 pm

You need to reformat the Conti Handbook to get loads and tyres on same page.
This is interesting as CP tyres on rear axle need higher pressures for a given load than front and 10 PR need more pressure than 8 PR before ultimately having greater capacity.
I did this by 'printing' from page 2 as pdf and then saving to my device.
Unfortunately I can't see how to upload a document here - if someone shows or points how I will.