Tyre Pressure - Too High or Too Low? (1 Viewer)

[DBK]

I completely understand that but of the tens of thousands of new vehicles and new sets of tyres that hit the roads every month , my point was that very few would question the info already provided.

Indeed. I was driving through sleet today and about 20% of the cars I saw didn't have any lights on. Ignorance of how to do things properly isn't an excuse! I only learned how to determine my MH tyre pressures by reading about it here. Previously I had been driving around on 5.0 bar because that was what the handbook said. When I drove over a coin I could tell if it was heads or tails uppermost! Now umpteen thousand miles later at 3.25 bar all is peace and calm.

 

[Larrynwin]

Indeed. I was driving through sleet today and about 20% of the cars I saw didn't have any lights on. Ignorance of how to do things properly isn't an excuse! I only learned how to determine my MH tyre pressures by reading about it here. Previously I had been driving around on 5.0 bar because that was what the handbook said. When I drove over a coin I could tell if it was heads or tails uppermost! Now umpteen thousand miles later at 3.25 bar all is peace and calm.

Thank you !

 

[Jaws]

Thanks for the info. When I checked with Michelin, giving them the loaded weights (which were about 50kg under max for all axles) they advised me 70 front and 80 on both rears. 80 was bone rattling so I reduced the rears to 70, not much better though. Was the 55psi in the handbook? I will have a look at that. When you say 55 is that for front and rear?

It is in the Autotral handbook..
The fronts are 75 and the rears 55

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[Southampton]

It is in the Autotral handbook..
The fronts are 75 and the rears 55

Thanks Jaws found it. I will reduce the rears tomorrow.

 

[Southampton]

I always thought it was a harsh ride.

 

[Larrynwin]

It is in the Autotral handbook..
The fronts are 75 and the rears 55

Contrary to tyre manufacturer recommendation with correct info in handbook, makes sense

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[Brian and Jo]

The only way to get it absolutely right is to weigh each axle on a weigh bridge and call the tyre manufacturer and speak to technical Every body loads their Motorhome differently ,some well within the payload ,others on the edge .what is the right pressure for one will be wrong for another.
Brian & Jo

 

[sdc77]

Tyre manufacturers pressure recomendations , as far as I know , are not generally included with new vehicles or provided when replacement tyres are fitted.
This only leaves the vehicle manufacturers recommendations for pressures provided in the hand book and in the door pillar as I am sure most vehicle owners trust this .
I for one would not risk tyre damage/blowout by running pressures 10/15 psi above or below the vehicle manufacturers recommended pressure.

When contacting continental for my correct pressures they sent the following along with an extract from their pressure chart for my tyres ...
"Continental tyres would always recommend having the motor home weighed on a weigh-bridge at your heaviest travelling weight including liquids to achieve specific axle weights. It is extremely likely that the relevant information supplied with the chassis is documented for use as a commercial vehicle, therefore proposed before the conversion to a motor home."

And of course they are correct as the door pillar sticker was put there by Fiat.

If you run at the documented tyre manufacturers recommended pressures then you cannot be wrong.

 

[Chockswahay]

It's been discussed to death on here in the past.

I agree fully with @DBK

I telephoned Continental and spoke to one of their engineers. She was quite precise in what to do............. weigh front and rear axle at intended touring weight.......... pressurise tyres in accordance with Continental technical manual

Fiat's own figures on the door are excessive by a country mile

My fillings have lasted longer, the tyres have worn evenly and I managed over 30000 miles on the front pair

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[Larrynwin]

A visit to the weighbridge beckons .

 

[Robert Clark]

A visit to the weighbridge beckons .

I'm going tomorrow - £25

 

[peterc10]

Who is right, the dealer or the manufacturer?

Hi Robert.

I agree with others who say that the best source of info is Continental. They are very helpful. With my old Adria I phoned them with the axle weights and they gave me the figures. They also emailed me to confirm them and I kept a copy of the email in the van in case anybody queried the pressures.

Picked up the new motorhome and the ride was very harsh. It has the same tyres as yours. Went to a nearly weighbridge and got the axle loads, took it back to the dealer who phoned Continental and got the correct pressures for me and put them in. A much better ride. Once I have finished filling it all with the stuff I want I will get it weighed again in the normal trim (so with Angela, all the holiday stuff and full diesel and water and contact Continental myself.

Peter

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[peterc10]

I'm going tomorrow - £25

Where is that Robert? When I tried to find one locally I ended up Sevenoaks way - paid about £35 for two axles.

I got one for free (well £10 for the tea kitty) in Great Yarmouth, but the problem was it was not built into the ground so there was a ramp up, which distorts the figures if you are weighing with one axle on and one off. Could tell that because the total was higher than the aggregate of the two axles.

 

[Robert Clark]

Where is that Robert? When I tried to find one locally I ended up Sevenoaks way - paid about £35 for two axles.

I got one for free (well £10 for the tea kitty) in Great Yarmouth, but the problem was it was not built into the ground so there was a ramp up, which distorts the figures if you are weighing with one axle on and one off. Could tell that because the total was higher than the aggregate of the two axles.

Hi Peter
I'm going to Ripleys
They've got weighbridges in Hailsham, Hastings, Ashford and Newhaven

http://www.hripley.co.uk/public_weighbridges.html

 

[Larrynwin]

I guess from this that the chassis and mohome builders presume maximum axle weights when recommending tyre pressures.

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[peterc10]

I guess from this that the chassis and mohome builders presume maximum axle weights when recommending tyre pressures.

Not just that. They also assume commercial use (overloaded and rough ground) and commercial tyres rather than specific motorhome ones.

 

[TheCaller]

I guess from this that the chassis and mohome builders presume maximum axle weights when recommending tyre pressures.

Also remember that they may presume chassis design weight, which may be higher than the converted MAM - remember that converters often down plate to 3500kg to allow older drivers to use than without regular medicals.

My Globecar is plated at 3500kg, but the design weight of the Fiat Ducato LWB Maxi body that it is based on is something over 4 tonnes.

 

[Robert Clark]

When I got to the weighbridge at Hailsham today, they only charged £20, not £25 as quoted over the phone on Saturday

Its in a scrap yard, so its a bit grim and access is a bit tight with all the skip lorries coming and going, overflowing with scrap, but I came away with a proper printed certificate

Based on my Fully Loaded weight and the info provided by Continental on their technical data sheet for the tyre, the dealer is suggesting over inflating the front tyres by 0.5 bar, and under inflating the rear tyres by 0.5 bar.

The Carthago recommended pressure is 1.25 bar too high for the front and 0.5 bar too high for the rear.

I've emailed Continental just to double check the figures, and I've booked the van in to get the wheel alignment checked.

I did get the wheel balancing checked before our last trip as I was getting vibration though the steering wheel, and discovered that all the wheels were incorrectly balanced - what a difference that made!

As our nearest decent commercial tyre depot is a fair distance away, I invested in a good quality Tyre Inflator

Amazon product ASIN B000W08QZY
The lead on it reaches over 7m and the crocodile clips connect direct to the leisure batteries.

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[icantremember]

they only charged £20

You should have only used the bridge ... not bought it.