Tyre Pressure

[spike]

Just had four new Michelin Agilis Camp tyres fitted to my Motorhome, Fiat Ducato 1.9TD 2004/ Hymer 494. The original fitments were the Michelin Camping XC 215/70r 15c.

 

The fitters were no too sure as to the correct pressure and said they will adjust them for me if I got the information for them.

 

The information on the vehicle id plate shows:

3200kg max weight

4600 +trailer (which is not used)

1650kg front axle

1750kg rear axle

 

Michelin states that according to the id plate weights the rear should be 80psi and front 55psi, but I’m wondering if these measurements are the absolute maximum and lower pressures are the norm. We do not carry a lot of weight.

 

[Brian Kirby]

First step: take your van, fully laden including all passengers to your nearest weighbridge and get it weighed, including the weight on each axle. It is important that the van is weighed in its heaviest state with all reservoirs brim full. This is to guard against under-inflation relative to actual load.

 

Then, go here http://tinyurl.com/mxnzlqz and download the Motorhome Tyres and your Safety booklet. In it you will find the pressure for load tables for various tyres. Your Michelin Agilis Camping tyres are CP rated, so use that table, but be careful to match exactly the size, load and speed ratings for the tyres on your van to the table. Then, look for the column that most closely matches the loads you have from the weighbridge for your tyres, noting that the top row in each case is for front axles and the second row for rear axles, and then read up the column for the correct pressures. Where the match is inexact, use the next higher pressure. These will be the optimal pressures for the load on each axle, giving the ideal compromise between performance and comfort.

 

If you wish, you could then contact Michelin again and re-quote the pressures from the document against your axle loadings and ask them whether they agree with the result. They should, because they are members of the parent association that publishes the guide.

 

You may possibly find that the handling becomes a little imprecise at the pressures you get from the table, especially with taller vans. If so, you can safely increase the pressures selectively until you are happy with the way it handles, subject to not exceeding 80psi. If not, just use the pressures from the table.

 

80psi is the maximum safe pressure for the tyre, and is suitable for a rear axle load of 2,060kg - which in your case would be a fairly substantial overload! The Michelin recommended front pressure seems to relate to the maximum permissible front axle load of 1,650kg.

 

It should be possible to substantially reduce the rear pressures, and the front somewhat, depending on the actual axle loads for your van. However, it is important to check the actual loads on a weighbridge before departing from the motorhome manufacturer's recommended pressures, as under-inflation relative to actual load is dangerous, and can lead to overheating of the tyres and possible blow-out.

[Derek Uzzell]

Despite spike's motorhome's rear axle having a 1750kg limit, it's unlikely that Michelin will advise (for Agilis Camping tyres) a pressure other than 80psi.

 

If a fully-loaded motorhome's axle weights are established via a weighbridge, Michelin's current policy seems to be that they will advise on front tyre pressures based on the weighbridge measurements, but just quote a 'one-pressure-fits-all' 80psi for the rear tyres.

 

In principle, a pressure of around 60psi would be somewhere near for an axle-loading of 1750kg, but I'm doubtful that Michelin would confirm this.

 

As XC Camping and Agilis Camping are both 'camping-car' patterns, spike should be able to use pressures for the latter tyres similar to those he used for the former.

[Sundowner]

Thanks for the useful link Brian, I've printed it off for future reference!

[spike]

Thanks for the advice boys, will do as recommended.

 

[camocam1]

I have just put on 4 of the same tyres of a ducato based MH and ATS recommended 60psi on front rather that 80psi and 55psi on the rear says will get a better ride but slightly less mpg

So that's what I have, never checked to see what the book says just went with the tyre fitters

 

[spike]

Kwikfit said the rear was 55psi. When I pursued it they said they had no info for MH's but would alter it if I got the correct pressures. Presumably 55psi was for commercials

[Roryboys Dad]

Thanks for the link to the TyreSafe information Pdf - I have downloaded it.

I still can't work out from the chart of Motorhome (CP) tyres what my tyre pressures should be.

I have Michelin 225/65 R16 CP tyres fitted and the manual that came with the MH gives pressures as Front 3.8 bar (55lbs) and Rear Single as 4.4 bar (63lbs).

But I can't see anything that relates to those figures – 3.8 bar isn't even on the TyreSafe list – 4.0 bar is minimum.

Weighed recently fully laden at 1500 kg front and 1680 kg rear - again I can't seem to see a row of figures that relate to the weights on my MH.

 

My VIN plate -

Gross Vehicle weight – 3500

Gross Train weight - 5100

Max weight Axle 1 – 1850

Max weight Axle 2 - 2060

 

Or have I got the wrong end of the stick?

 

Any advice would be appreciated.

 

[Brian Kirby]

You don't say what make/model your van is, but the pressures in your manual appear to be correct for "white van" tyres and not for CP rated tyres, and are suitable for the maximum axle loads as on your VIN plate. I assume your tyres are in fact Michelin Agilis Camping tyres?

 

Looking at Continental's Vanco Camper (CP) pressures for the same size tyre and axle maxima would give 3.75 bar front and 5.0 bar rear.

 

Taking a standard (i.e. non CP, "white van") Vanco of the same size and for the same axle maxima, would give 3.75 bar front and 4.5 rear.

 

Using the Tyresafe tables for the above axle maxima, but applying the table for the "white van" tyre of the same size, would give about 3.8 bar front and 4.5 bar rear.

 

Again using Tyresafe's data for CP rated tyres of same size and axle maxima, would suggest a minimum 4.0 bar front (as you say, the table does not list front axle loads below 1952kg) and 5.0 bar rear.

 

So, as you can see, the main difference is the enhanced pressure in the CP rated tyres on the rear axle, for the same load, and both data sets broadly agree the pressure for load figures. However, the Continental data does list axle loads for their CP rated Vanco Camper tyre down to 1550kg front - for which they stipulate a pressure of 3.0 bar.

 

Using your actual axle loads, but applying the Continental CP data, would suggest that 4.0 bar rear and 3.0 bar front may be acceptable.

 

If you consult Michelin they may give you a pressure for load at the front, but as Derek says above, it seems they will only recommend the maximum permissible pressure of 5.5 bar for the rears. You could try asking them how they react to the Tyresafe data for your tyres that suggests you could reduce the rear pressures to 4.0 bar, and see how they jump. Or, you could go back to the manufacturer of your van and ask them whether the pressures they recommend are, in fact, for a CP rated tyre.

 

However, if you are satisfied that the ride and handling you experience at the van manufacturer's recommended pressures is acceptable, as both seem to be above what is recommended for the Conti Vanco camper at those axle loads.

 

Not conclusive, and you need some clarification, but the van makers pressures seem safe, and you at least have those in writing. Simple question: why change?

[Derek Uzzell]

spike - 2013-06-10 4:37 PM

 

Kwikfit said the rear was 55psi. When I pursued it they said they had no info for MH's but would alter it if I got the correct pressures. Presumably 55psi was for commercials

 

Logically, the greater the weight being placed on a tyre the higher the inflation-pressure shoud be.

 

So, if a motorhome's rear tyres are carrying more weight than the front tyres, the pressure used for the rear tyres should be higher than the pressure used for the front tyres. Adding, say, 10% more pressure to the front tyres than the 'static load' requires is sometimes recommended to better cope with cornering and/or braking weight-transfer loadings. However, if someone recommends that your motorhome's front-tyre pressures should be significantly higher than its rear-tyre pressures, you'd be wise to question the thinking behind that advice.

 

Motorhomes - certainly 'coachbuilt' motorhomes - when normally loaded usually carry a higher percentage of their weight on their rear tyres than on their fronts, and the tyre-pressures chosen should reflect that imbalance. This rule-of-thumb applies to vehicles with two axles: for vehicles with tandem rear axles, rear-tyre pressures lower than the front-tyre pressures may be OK.

[Lochburn]

Hi

I contacted Conti yesterday and asked for advise on my Continental 10 PLY 215/75/16 R "C" 116/114 - VancoCamper . and got following based on axle weights :

 

215/75 R 16C 116/114R

 

Front Axle @ 1480 kg = 3.00 bar / 43.5 psi

Rear Axle @ 1900 kg = 3.75 bar / 54.3 psi

 

Have been driving with slightly higher pressure as got slightly confused with info given on their web site :

 

QUOTE

 

As the CP standard acc. to ETRTO is only valid for 8 PR tires, the 10 PR size 215/75R16C marked only as a „C“ tire requires a front inflation with 5.25 bars and a recommended and permitted rear inflation with 6.0 bars. Despite its C marking this tire provides safety reserves like a CP tire.

UNQUOTE

 

 

Can anyone explain the difference in pressure since they both come from Continental?

 

 

 

 

 

[Roryboys Dad]

Brian – thank you for the informative, extensive and helpful replies.

I've been in touch with a Knaus representative and he agrees that the tyre pressures in my manual (3.8 bar/ 55 lbs Front and 4.4 bar/63 lbs Rear) are correct for the tyres I'm running on.

They are Michelin X Radial (XC Camping).

He suggests I stay at those pressures and increasing them will only lead to noticeable problems with the MH shaking and rattling.

I can't see any point in altering the pressures unless something, as yet unknown, gives me cause for concern.

Again thanks.

[Brian Kirby]

Lochburn - 2013-06-11 3:27 PM

 

Hi

I contacted Conti yesterday and asked for advise on my Continental 10 PLY 215/75/16 R "C" 116/114 - VancoCamper . and got following based on axle weights :

 

215/75 R 16C 116/114R

 

Front Axle @ 1480 kg = 3.00 bar / 43.5 psi

Rear Axle @ 1900 kg = 3.75 bar / 54.3 psi

 

Have been driving with slightly higher pressure as got slightly confused with info given on their web site :

 

QUOTE

 

As the CP standard acc. to ETRTO is only valid for 8 PR tires, the 10 PR size 215/75R16C marked only as a „C“ tire requires a front inflation with 5.25 bars and a recommended and permitted rear inflation with 6.0 bars. Despite its C marking this tire provides safety reserves like a CP tire.

UNQUOTE

 

Can anyone explain the difference in pressure since they both come from Continental?

I think only Continental can clarify that advice, as it is theirs. I suspect the word "requires" may be a mis-translation, and possibly should say "permits". That would agree with the maximum recommended pressures as in their technical data for van tyres booklet.

 

What I can say is that the pressures you have been advised to use are as those published in their technical data for van tyres.

[Brian Kirby]

Roryboys Dad - 2013-06-11 4:28 PM

 

Brian – thank you for the informative, extensive and helpful replies.

I've been in touch with a Knaus representative and he agrees that the tyre pressures in my manual (3.8 bar/ 55 lbs Front and 4.4 bar/63 lbs Rear) are correct for the tyres I'm running on.

They are Michelin X Radial (XC Camping).

He suggests I stay at those pressures and increasing them will only lead to noticeable problems with the MH shaking and rattling.

I can't see any point in altering the pressures unless something, as yet unknown, gives me cause for concern.

Again thanks.

Good, and you are welcome.

 

However, if your van is on XC campings, have you checked their ages? Opinions vary, but it is generally held that tyres should be replaced at between 5 and 10 years of age, with the most frequently quoted age for replacement being 7 years.

 

XC Campings have not been produced for a few years now, so it is possible yours are near to the end of their lives. This will apply equally to the spare, so changing them a pair at a time, rather than all five at once (assuming there is a spare) will induce less wallet trauma!

[Lochburn]

Thanks Brian

Have asked them to clarify, but have no reply as yet so will go for the tyre pressure given.

On the other hand on their Norwegian website they stipulate "recommended" and not "required" so you are right.. Thanks again.