Take a look at this youtube video which shows in effect, that at higher tyre pressures the footprint of your tyre is very small thus effecting road grip.
For all of you you think high tyre pressures are safe
- Thread starter Otter Spotter
- Start date
Thus the reason Unimogs have a 4 buttons above the drivers head to deflate tyres down to a very low psi if in a soft spot, get back on firm ground and press 4 buttons to re-inflate. No idea how it works on a turning wheel tho but it does!
Offset by the weight of the vehicle. If you're pushing a tonne on to the tyre, it needs to be higher pressure.
Too much deformation is bad for road driving because it generates too much heat. And if it's too flat, it'll affect fuel economy.
My van is pretty light and I've got fairly heavily rated tyres. Apparently I can run 45psi on the front according to Continental. They look really flat at that pressure, so I run 50psi.
Too much deformation is bad for road driving because it generates too much heat. And if it's too flat, it'll affect fuel economy.
My van is pretty light and I've got fairly heavily rated tyres. Apparently I can run 45psi on the front according to Continental. They look really flat at that pressure, so I run 50psi.
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I've not looked at the video but surely the tyre footprint will depend on the tyre pressure but also the weight it's carrying. Increasing the tyre pressure will reduce the footprint increasing the load will increase the footprint. For every amount of load there will be an optimum pressure. Similarly for every type of tyre use there will be an optimum as in the unimog example you might want a squidgy tyre with a big footprint on mud but not going around a corner fast on a smooth surface. Thinking a really high tyre pressure is a good idea outside the msnufacturers recommend range is probably a bad idea but so would be running way lower than their recommendations
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It's not that they are too high - just incorrect. Too high - less grip and uneven wear. Too low pressures will result in high temperatures and too much wear which could cause a blow out. There will be a correct pressure - not too high, not too low. If Michelin and Burstner (or any other manufacturer) state 80psi is the best pressure then I'd go with that. Of course you may need more or less depending in the load within your motorhome.
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I run at 5 bar even though 5.5 is recommended. It runs well at that pressure. This is well within the manufacturers maximum ( Continental Vanco) If I had to I would increase to 5.5 like running with a heavy load but it hasn’t felt necessary.
Phil upmetyres
Phil upmetyres
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When I have been running for some time on motorways when we have a coffee break I go round to check the tyre temperatures, just by hand. Warm - OK, hot - problem. I see HGV drivers doing the same.
Also saves me making the coffee.
Also saves me making the coffee.
Good thinking that manAlso saves me making the coffee.
Do any of you reduce tyre pressure during hot weather, I generally run on 5.5 bar but on checking them on a hot day pressure had gone up. Google this and think advice was to lower them on such days, is this right?
If so then inference is that continual checking to adapt to conditions should be the norm?
If so then inference is that continual checking to adapt to conditions should be the norm?
Or get a TPMS thingy
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1 Bar = 14.5psi.
5.5 bar is effectively 80 psi 
When racing we used to check temperatures on three points, in the centre and near each edge as the car came in to the pits to see where the contact points were working hardest.
If the edges were hotter that would suggest under inflated but if the centre was hotter it was over. The ideal was obviously equal contact across the surface of the tyre.
If the edges were hotter that would suggest under inflated but if the centre was hotter it was over. The ideal was obviously equal contact across the surface of the tyre.
dawsey
Free Member
define ‘hot’?Good thinking that man
I do the same and mine are always too hot to touch as are the wheels. Roughly 30-35 deg above ambient is to be expected after a long motorway run. If ambient is 35 that is 70, too hot to touch.
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Run at 1 psi for max grip seems to be the logic 
pappajohn
LIFE MEMBER
Yeah, but you tend to get roll on corners.Run at 1 psi for max grip seems to be the logic
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But surely if you're on the wheel rims roll will be reducedYeah, but you tend to get roll on corners.
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No - tyre pressures are always a compromise so better to have a constant pressure than let them down and blow them up on a daily basis.
As already mentioned, on a long drive I also walk around them and feel the temperature of each tyre, you’ll know if you have a problem before it becomes a problem if you know what I mean.
dawsey
Free Member
So much debate on this subject. So many ‘experts’.
There are only two ‘real’ experts who you should take advice from regarding your tyre pressures. The organisations whose reputations, businesses and legal positions depend entirely on giving you correct advice, advise developed by their employees, qualified specialist engineers - people who really do what they are taking about. I know this, as I am one.
These organisations are the Motorhome manufacturers and the tyre manufacturers.
Read your manual. It will tell you the optimum pressure for your tyre. Yes it will go up when it’s a hot day. They know that, they allow for it. It’s why they all tell you to measure it only when cold.
The most important thing to understand is that there’s always a load ‘range’ for any given tyre. Thus a tyre manufacturer will always print on its tyre the maximum pressure and absolute maximum static load. A tyre manufacturer can not provide much more information on pressure vs load range as they do not know the application.
This is where the motor home OEMs come in. Their engineers will look at other factors like typical loads and speeds and dynamic loading, which is seriously affected by high centre of gravity, uneven load distribution, overload and overhang. Motorhomes are unique in that they can suffer from all four of these issues which all increase peak dynamic loads.
It is the reason that almost all motorhome manufactures and all specialist organisations will advise running the rear tyres at the maximum pressure (usually 80psi) all the time. Most go further and advise the use of the XC camping tyre that has a stronger construction and stiffer sidewall, as this type of van tyre is designed to better resist the extreme dynamic loading forces produced by a heavily loaded motorhome when cornering and improve handling by deforming less under extreme load. It could easily be the difference between a serious crash or not in an emergency manoeuvre.
The slight compromise is a harsher ride, especially at the rear, and especially with an older van with a poor chassis/suspension set up. This is the price of safety. The solution to the crashy ride is to add air or semi-air suspension.
There are only two ‘real’ experts who you should take advice from regarding your tyre pressures. The organisations whose reputations, businesses and legal positions depend entirely on giving you correct advice, advise developed by their employees, qualified specialist engineers - people who really do what they are taking about. I know this, as I am one.
These organisations are the Motorhome manufacturers and the tyre manufacturers.
Read your manual. It will tell you the optimum pressure for your tyre. Yes it will go up when it’s a hot day. They know that, they allow for it. It’s why they all tell you to measure it only when cold.
The most important thing to understand is that there’s always a load ‘range’ for any given tyre. Thus a tyre manufacturer will always print on its tyre the maximum pressure and absolute maximum static load. A tyre manufacturer can not provide much more information on pressure vs load range as they do not know the application.
This is where the motor home OEMs come in. Their engineers will look at other factors like typical loads and speeds and dynamic loading, which is seriously affected by high centre of gravity, uneven load distribution, overload and overhang. Motorhomes are unique in that they can suffer from all four of these issues which all increase peak dynamic loads.
It is the reason that almost all motorhome manufactures and all specialist organisations will advise running the rear tyres at the maximum pressure (usually 80psi) all the time. Most go further and advise the use of the XC camping tyre that has a stronger construction and stiffer sidewall, as this type of van tyre is designed to better resist the extreme dynamic loading forces produced by a heavily loaded motorhome when cornering and improve handling by deforming less under extreme load. It could easily be the difference between a serious crash or not in an emergency manoeuvre.
The slight compromise is a harsher ride, especially at the rear, and especially with an older van with a poor chassis/suspension set up. This is the price of safety. The solution to the crashy ride is to add air or semi-air suspension.
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If the stiffer sidewalls of camper tyres provided better support, why do they also need such high pressures?
I suspect it's the reverse. The stiffer sidewalls are for longevity when parked. But their lack of deformation means they need lots of support from the air, hence the high pressure.
Camper tyres drive like rubber from 20 years ago. They have terrible grip. I'd prefer van tyres, which are revised much more frequently.
dawsey
Free Member
Nothing to do with longevity when parked. Someone, somewhere, made that up and it’s become an urban myth.
The required pressure is due to the load. The stiffer sidewalls, as explained, are to help resist deformation during cornering and improve stability. I don’t know how to explain it in terms any more simple.
If you don’t want to believe me that’s fine, but do your own research, read technical papers, visit specialist websites and the tyre and Motorhome manufacturer websites before typing uninformed ‘opinion’ or you risk misinforming others.
Yes the ride is compromised.
Yes absolutely spot on my thinking entirely. Couldn't have put it better.
Certainly refers to long term parking there.
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OP
OP
So you would trust what Motorhome manufactures say when many of them cannot fit equipment inside the van correctly, I would be very surprised if they employ any tyre specialists! Most don’t even employ constructors they are assemblers
I would say there is only one expert - the tyre manufacturers. The motorhome manufacturers just play safe with a one pressure suits all attitude. For example our first motorhome was a small Elddis with a rear lounge. The rear axle was quite lightly loaded and in fact was carrying less load than the front axle. Our second motorhome was also an Elddis but had a large rear overhang resulting in a heavily loaded rear axle. Elddis quoted the same tyre pressures for both motorhomes. A quick visit to a weigh bridge and an email to Continental resulted in the correct tyre pressures, which in both cases were less than what Elddis had specified.
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Articulated valve stems Seen them but hard to describe,,BUSBY
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