Tyre pressures

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carmha

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Can anyone tell us where/how we can check the tyre pressures on our new campervan, and top up with air? Garages around us don't seem to have sufficiently powerful equipment.
 
We have a Globecar Roadscout R. It's just possible my partner may be remembering the exact pressures incorrectly (I don't have the handbook here), but the question still stands, as to where we can get the pressures checked and the tyres topped up.
 
I put 70psi about 5 bar in the rear and 50 or so in the front of mine, I have no issues with Sainsburys locally it goes a lot higher.
 
carmha said:
We have a Globecar Roadscout R. It's just possible my partner may be remembering the exact pressures incorrectly (I don't have the handbook here), but the question still stands, as to where we can get the pressures checked and the tyres topped up.
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I cannot see how we can help with the 'where' because we don't know where you are.

You say that you cannot find an air pump with a high enough pressure (a common problem), so why not buy your own tyre inflator. Google using 'Ring 12 volt tyre inflater', they make a range of them.
 
I top up the tyres on our Campscout at Sainsbury's, can't remember what the notice says is maximum, but we go over that with no problems, but then ours is in 60's psi, not 70's.
 
carmha said:
Garages around us don't seem to have sufficiently powerful equipment.
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I expect they have but are restricting the pressure to the public air line. We did this after someone burst their tyre by over inflating it and tried to blamed us. So ask in the garage to see if they will do it for you
 
hairydog said:
The way to determine the correct tyre pressures is straightforward, but not simple. First, load it up to the max you will be carrying (including fuel, water, people etc), then get it weighed, getting the axle weights separately. Write them down. The detail matters.
Next, look at your tyres. Each tyre will have a load index figure (something like 97/99 or 110/112) and a maximum inflation pressure (maybe 65psi, possibly more).

You then have to look up the max load for your tyres' load index. If there are two numbers (as in my example) use the highest number, unless it is a twin wheel axle. That will give you the maximum safe load for that tyre at the stated maximum pressure.

The calculation is then simply a matter of taking half the axle weight (from the weighbridge), dividing that by the maximum tyre load (from the index lookup), then multiplying the result by the maximum inflation pressure.

The result is the pressure you should run your tyres at. No less - that would be unsafe. Chances are that it will be the sort of pressure a garage airline will handle without problems.

A couple of psi more are OK, but overpressure more than that and you will get uneven tyre wear, bad handling, a harsh ride and risk bursting the tyres if you catch a kerb. Never underinflate.
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Never heard an explanation like that before, someone seems to be in the know thanks.
 
carmha said:
Can anyone tell us where/how we can check the tyre pressures on our new campervan, and top up with air? Garages around us don't seem to have sufficiently powerful equipment.
Click to expand...

Couple of weeks ago my Tyre Pressure Monitor warned of low pressure in left rear tyre. It was 5 bar instead of 5.5.
We were just pilling into Morrisons for a shop so I went to their airline. Set the desired pressure to 5.5 inserted £1 coin and watched as the pressure went down to 4.7 bar. Thinking I'd done something wrong I repeated the process, but the same happened. Went into the kiosk and asked what the max bar for the pump. Was told it doesn't work in bar only PSI and to try that. Selected 80 psi, inserted another £1 and it cut off at 69 psi. Spotted a Halfords Service centre across the road so I walked over and asked if their air line would do 5.5 bar. "No problem" the man said, "We'll be about 2 hours and it will cost £10" !

We had theatre tickets that evening and were running a little late so I decided to drive to the next petrol station. About 1/2 mile further on and I saw a type depot. Pulled in and explained the situation. The guy pulled out his airline and inflated the tyre, all in less than a minute. He even refused a tip, saying he liked helping people.
 
I'm never sure why Motorhomes are run at the tyres maximum, usually 80psi, which gives a harsh ride and on many roads could dislodge your false teeth with the hard tyres and no 'give'.

As said earlier you need to know the front and rear axle weights (around £5 to use a local weighbridge) and the size and type of tyres you have before adjusting your tyre pressures.

Any guesswork will mean your tyres probably won't last as long and may wear unevenly.

With the tyres I have fitted - Continental (225/70 R 15C 112/110) - on my Pilote on a Ducato base and with front axle 1560kg and rear axle 1940kg, confirmed fully laden by a weighbridge, the recommended pressures are 47psi front and 61psi rear.

Sainsbury, Tesco and other Supermarkets all have machines to give air, all mine do, and using them is a doddle.

The first thing when buying a Motorhome, besides showing it off to the neighbours, is to get it weighed and sort out those pressures – for your safeties sake.

:dog: :dog: :dog: :dog:
 
My CI clearly stated 5.5 bar all round a lot of garages seem to struggle ( I also kidded the machine into thinking the tyre was flat so compressor wasn't cutting in and out.

As Maingate said a ring or similar 12 v pump does the job but can get warm and make sure you don't flatten your battery leave the engine running.

I also used a dedicated pressure gauge to garages and cheap compressors often poorly calibrated,

Channa
 
hairydog said:
Why do you have your tyres at that pressure?
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If it’s like my Swift probably because the owners manual says so.
I did the wieghbridge / axle weight calculations and reduced the pressures considerably which gave a much better ride. I also have a ring compressor so never bother with garage forecourt air compressors.
 
hairydog said:
The way to determine the correct tyre pressures is straightforward, but not simple. First, load it up to the max you will be carrying (including fuel, water, people etc), then get it weighed, getting the axle weights separately. Write them down. The detail matters.
Next, look at your tyres. Each tyre will have a load index figure (something like 97/99 or 110/112) and a maximum inflation pressure (maybe 65psi, possibly more).

You then have to look up the max load for your tyres' load index. If there are two numbers (as in my example) use the highest number, unless it is a twin wheel axle. That will give you the maximum safe load for that tyre at the stated maximum pressure.

The calculation is then simply a matter of taking half the axle weight (from the weighbridge), dividing that by the maximum tyre load (from the index lookup), then multiplying the result by the maximum inflation pressure.

The result is the pressure you should run your tyres at. No less - that would be unsafe. Chances are that it will be the sort of pressure a garage airline will handle without problems.

A couple of psi more are OK, but overpressure more than that and you will get uneven tyre wear, bad handling, a harsh ride and risk bursting the tyres if you catch a kerb. Never underinflate.

[later] For completeness, if you have twin wheels on the rear axle, you should use the lower of the two load ratings and divide the axle weight by four (not two) to get the tyre load.
Click to expand...


this ought to be in an app so that you can type in the requisite numbers and have the answer auto calculated.

(yes I know it's a relatively easy bit of maths, but, well, you know.... ;) )


calc is (if I'm reading this right):
((axle-weight/2) / max-load ) * max-pressure

according to what I've just read, the max-load index is an agreed standard across all tyres - is that right?
 
hairydog said:
Strictly speaking, it's
((axle-weight/wheels on axle) / max-load ) * max-pressure

Yes, the max-load index is an agreed standard across all tyres
Click to expand...


Looks easy enough to code up into an app - hey @Admin - has anyone suggested putting this little calculation into the WildCamping App??
 
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