Tyre pressures

[ActiveCampers]

Funny thread to appear
My van, a MY20 MH2 Ducato, now the build was finished and weighed, and a debate "elsewhere", I decided to do some digging

I've called Continental who must be the most authoritative on this and had a really good chat with their technical guy about the vehicle and tyres - and both Fiat and the website calculator are well off (!)

My details

• Continental VanContact4Season
• 225/75/R16C 121/120 load
• Front axle weight (pre packing) 1560kg
• Read axle weight (pre packing) 1440kg
• Loaded, with water, bikes, and stuff, would expect
• Front axle: 1650kg
• Rear Axle: 1700kg

He has sent me a 3mb technical data book which I'm happy to share but need a to email to a mod to make available.

This shows the pressure should be 3bar (42.5psi) - which is good for 1725kg axle loading, so is the same for front and rear.

What is confusing, is he said Fiat give pressures to the maximum axle weight which on my van is 2000kg - and at that the pressure should be 3.75 bar (55psi). 5 bar, as recommended by fiat, is for axle of 2600kg which is far in excess of the vans rating. Even 4.5bar for the front is 600kg higher than the front axle rating.. He also said the pressure is based on weight - so why the tyresafe website has different pressure for F/R with the same load is odd.

Very odd.

So the final results

• Fiat: F 65psi R 73psi
• https://www.tyresafe.org/motorhome-tyre-pressure/ F: 51psi R 59psi
• Continental: 44psi F & R

Hmmm

 

[cronkle]

The problem with the tyresafe calculator is that whatever weight I put into it for the rear axle on my CP tyres it comes up as 5.5 bar and to justify that I would have to be overloading that axle by over a quarter of a tonne. They also do a separate chart/booklet for motorhomes that cover my CP rated 15" tyres https://www.tyresafe.org/motorhome-tyre-safety/load-and-inflation-tables/ and that gives more sensible pressures until you read the small print which states that CP tyres should always be set to 5.5 bar - contradictory or what? I now find it difficult to trust Tyresafe.

Continental, on the other hand give, as I think you have found, straight-forward advice and have a Tyre Data book http://blobs.continental-tires.com/...MmVhMGU4YzlkYzZlMTE0YzQwNjE1NTM2MTczNDU2OTU=~ with a lot of info in it.

 

[wildebus]

The problem with the tyresafe calculator is that whatever weight I put into it for the rear axle on my CP tyres it comes up as 5.5 bar and to justify that I would have to be overloading that axle by over a quarter of a tonne. They also do a separate chart/booklet for motorhomes that cover my CP rated 15" tyres https://www.tyresafe.org/motorhome-tyre-safety/load-and-inflation-tables/ and that gives more sensible pressures until you read the small print which states that CP tyres should always be set to 5.5 bar - contradictory or what? I now find it difficult to trust Tyresafe.

Continental, on the other hand give, as I think you have found, straight-forward advice and have a Tyre Data book http://blobs.continental-tires.com/...MmVhMGU4YzlkYzZlMTE0YzQwNjE1NTM2MTczNDU2OTU=~ with a lot of info in it.

I assume Tyresafe do not want to disagree with Michelins stated recommendations for CP tyres for liability reasons?

 

[cronkle]

I'm guessing you are right. I decided to not buy Michelins because they are inconsistant and quite insulting to those of us who want to comply with the law by assuming that all m'homes will be overloaded. I replace with Continentals when I have to because of their uncomplicated way of doing things.

 

[wildebus]

I'm guessing you are right. I decided to not buy Michelins because they are inconsistant and quite insulting to those of us who want to comply with the law by assuming that all m'homes will be overloaded. I replace with Continentals when I have to because of their uncomplicated way of doing things.

I fitted Michelins a few months ago. However I didn't fit the Camping Tyres but opted for the Agilis CrossClimate 225/70 R15 S (112).
Excellent tyres for all year round use (where I am, the temp is low enough for Winter Tyres for over half the year)

 

[maingate]

The problem with the tyresafe calculator is that whatever weight I put into it for the rear axle on my CP tyres it comes up as 5.5 bar and to justify that I would have to be overloading that axle by over a quarter of a tonne. They also do a separate chart/booklet for motorhomes that cover my CP rated 15" tyres https://www.tyresafe.org/motorhome-tyre-safety/load-and-inflation-tables/ and that gives more sensible pressures until you read the small print which states that CP tyres should always be set to 5.5 bar - contradictory or what? I now find it difficult to trust Tyresafe.

Continental, on the other hand give, as I think you have found, straight-forward advice and have a Tyre Data book http://blobs.continental-tires.com/...MmVhMGU4YzlkYzZlMTE0YzQwNjE1NTM2MTczNDU2OTU=~ with a lot of info in it.

The rear axle pressure on a 2 axle motorhome is always given as 5.5 Bar, sometimes 5 Bar on smaller motorhomes on the Tyresafe website. On a Tag axle van it gives the actual recommended pressure for all 3 of the inputted axle weights. There is an easy way round it to get the actual pressure you need.

Input your actual axle weights and find the pressures. Input again but this time put front load as rear and rear as front axle. You will then get the correct pressures for both axles. You will find in both cases that the rear axle figure is just tosh.

 

[Jenrai]

@ActiveCampers really good post, just what I was thinking about all of this confusion.

Just to clarify something:


As someone else has pointed out this says "fully Laden" so would that be the MAM which on my van is 3500kg or the 4900kg which the van could carry when it was shipped from Italy to the converter as just a commercial van?

 

[wildebus]

@ActiveCampers really good post, just what I was thinking about all of this confusion.

Just to clarify something:
View attachment 60094

As someone else has pointed out this says "fully Laden" so would that be the MAM which on my van is 3500kg or the 4900kg which the van could carry when it was shipped from Italy to the converter as just a commercial van?

where does the 4900kg number come from?

 

[number14]

I fitted Michelins a few months ago. However I didn't fit the Camping Tyres but opted for the Agilis CrossClimate 225/70 R15 S (112).
Excellent tyres for all year round use (where I am, the temp is low enough for Winter Tyres for over half the year)

I fitted 2 of these in May and will fitted another 2 in September ready for winter. I am sticking with the pressures marked on the door frame (renault master). IIRC 3.8F and 4.2R . It's late and I can't remember exactly but definitely way under 5.5b.
BTW love the chunky tread, the original vanco 200s look like slicks by comparison!

 

[wildebus]

I fitted 2 of these in May and will fitted another 2 in September ready for winter. I am sticking with the pressures marked on the door frame (renault master). IIRC 3.8F and 4.2R . It's late and I can't remember exactly but definitely way under 5.5b.
BTW love the chunky tread, the original vanco 200s look like slicks by comparison!

they do look a bit meaner than the average tyre without going to the extremes of the off-road jobbies

 

[Molly 3]

Why would a manufacturer put the wrong TP on the their motorhomes . I suppose the answer is they wouldn't,

 

[Jenrai]

where does the 4900kg number come from?

I was looking at the Relay load capacity, i think that should be 4400kg for 35 heavy L4H2

 

[Jenrai]

Why would a manufacturer put the wrong TP on the their motorhomes . I suppose the answer is they wouldn't,

As @ActiveCampers said the manufacturer is basing that on the fully laden load carrying capacity which in my case would be 4500kg, (2100kg front and 2400kg rear. As my van is plated at 3500kg MAM the tyre pressure stated is 1000kg in excess of what I can legaly load up the van to.

I am just trying to point out how confusing this all is, not saying anyone is wrong.

 

[wildebus]

I suppose the theoretical maximum might be the sum of the two axle ratings, but that would mean you would have to have a perfect weight distribution.
Was your van downplated to 3500KG at sometime as 2100 and 2400 are pretty good numbers and suggest (to me anyway) it has a much higher design weight
(I know some people get an uprate to 3850 on a Sevel (Ducato/Relay/Boxer) Light Chassis with a 1750 Front and a 2000 Rear, which again means a perfect distribution which will only happen by pure luck)

 

[Mr and Mrs Tupcox]

I have 2015 Peugeot boxer coach built .
Can I remove the tyre monitoring system
Our is set at 79psi nd want to drop rear tyres down to 65/70 psi but keeps seting dash board warming lights off.

 

[Molly 3]

I have 2015 Peugeot boxer coach built .
Can I remove the tyre monitoring system
Our is set at 79psi nd want to drop rear tyres down to 65/70 psi but keeps seting dash board warming lights off.

No instant mot fail , it can be reset to lower pressure by a dealer but they don't like doing it ,making some customers signe a disclaimer ,

 

[wildebus]

you could put all 4 valves inside a little wheel, inflate it to 80PSI or whatever it wants and the light will go out! totally pointless of course in terms of a TPMS system, which are a very good idea - WHEN they can be setup right, and it seems the Boxers one can't be

I would think a Peugeot dealer or even a standard garage could either change the pressure parameters or disable the system using the appropriate software connected to the EOBD port - which for PSA vehicles is Lexia 2000 I think (that is what I bought for my Citroens IIRC)

 

[mark61]

The plate showing max pressure @ max weight doesn't give anywhere near enough information, surely there is far more in the operators manual.

My manual shows pressures unladen & fully laden, front & rear axles over a range of tyres.
As an example, the largest difference between unladen and fully laden is 26PSI, obviously that will be rear axle for one of the higher GVW models.

 

[TR5]

Why would a manufacturer put the wrong TP on the their motorhomes . I suppose the answer is they wouldn't,

The manufacturer of the vehicle has no idea what their chassis cab is going to finish up as, and guided by Michelin who have no idea either, they just add the maximum tyre pressure to cover themselves.

Commercial vehicle tyres are designed for varying loads, and can be run over-pressure than the load predicts much more safely than running under-pressure, so they just put the maximum on.

 

[TR5]

This is such an emotive subject, and one that is discussed so regularly between all walks of motorhome users.

There seems to be two camps - those that believe that the pressures shown on the door pillar is 'gospel', and anyone who dares to argue with the vehicle manufacturers / converters figures are putting everyone else's lives at risk, and there are those that understand that the tyre pressures that should be used are relative to the load carried by that tyre.

Firstly, you DO NOT have to use CP tyres on a van - chassis/cab converted into a motorhome. There are plenty of 'C' (commercial van) tyres with reinforced sidewalls and 10 ply that match and indeed many exceed the load rating and speed rating of CP tyres.

If going to use 'C' tyres, look for 'reinforced walls' and '10 ply rating'. I would never advocate using the 'cheap' budget tyres in any situation.
I actually fit Michelin CrossClimate tyres - all seasons, with 'A' rating for stopping in the wet and snow. The grip with these is far superior to the Agilis CP tyre. These are excellent tyres, and generally as dear or dearer than the CP equivalent - but a much better tyre in my opinion.

I also have TPMS (after-market type) fitted to the tyre valves.

Commercial tyres are designed to take varying weights, and should always be set for the load carried, not the empty weight.

Many will argue that insurance companies will refuse claims if CP tyres are not fitted. I have always fitted 'C' tyres, always informed my insurers of such, and their replies have always been, as long as they are the same size, and match or exceed the recommended load rating, that's all they are interested in. I always log with the insurer that I have fitted different, as some 'may' regard this as a modification.

The load rating of the two tyres together on an axle must at least match, and preferably exceed by at least 10%, the maximum axle load they are fitted to.

It is easy to work out the tyre pressures by using a simple calculation, and if you can do percentages and/or use a calculator, then you are half way there.

*The tyre pressures required are a percentage of their gross load capacity, and relative to the load they are carrying, so firstly determine the load capacity of the tyres fitted - for instance 116 loading is 1250kg per tyre - so two tyres on an axle equals 2500kg maximum load capacity for those tyres on that axle (not necessarily the maximum axle load). Assuming the maximum pressure of that tyre is 80lbs psi - then weight the van (axles separately) when fully laden for a trip, including driver and passenger(s) - whatever you normally have on board.
If the weight on that axle is say 2000kg - then 2000/2500 is 4/5th's or 80% of the maximum tyre load. So use the 80% calculation to work out 80% of 80psi
80/.8 = 64psi. There is your recommended tyre pressure for those tyres on that axle.

Do exactly the same for all axles, and you will have much more accurate tyre pressure for the load on your tyres.

*This calculation is not suitable for tag axles or twin-wheel axles, and reference to the tyre manufacturer should be sought for further advice on these. The usual recommendation is to run each tyre at 2/3rd the pressure of what they would be if single-tyres - but please check first!