BIFFO Posted March 10, 2012 Share Posted March 10, 2012 To answer an earlier question ...my van was registered in 2010........but came off the production line in 2008. It has 11000 miles and is used regulary. When last serviced the tyres were at 60 psi all round. I found that 60 was a bit harsh up front so lowered it to 55. I find the ride more comfortable and it doesn't seem to be affecting tyre wear , at least according to my dealer who was asked to check the tyres as I am heading to Portsmouth for Santader later on . Am coming back via Roscoff to Rosslare . So......am covering a bit of ground and of course am well aware that my tyres should be up to scratch. All I am saying and as stated ...this subject has been covered now for ten years and we are no nearer to a definate answer to the question.." what pressure for what tyre and what van of what weight " .? . We are most of us been driving for many years and have gained some insight into what is practical and what is just not done. We assess the problem and use our knowledge to make a decision . At least that's what I hope to do and hopefully I'll keep motoring as I have for the last 25 years of motor homing. In that time I've had one puncture. I have probably Insured a load of them now :D :D B-) Link to comment Share on other sites More sharing options...
Robinhood Posted March 10, 2012 Share Posted March 10, 2012 bgrobbins@hotmail.co - 2012-03-10 11:19 AM All I am saying and as stated ...this subject has been covered now for ten years and we are no nearer to a definate answer to the question.." what pressure for what tyre and what van of what weight " .? . I find that rather an odd statement given the repeated advice on this forum, and indeed on this thread. :-S Vehicles, tyres and axle loadings vary to such an extent that a single recommendation for tyre pressures is not relevant. Once again, (how many more times) the only safe method is to ascertain your actual axle loads, and request the appropriate pressures for your particular tyres from their manufacturer. It's quite straightforward, really! :-S A less safe way would be to obtain specific data for the tyre yourself, and then determine the appropriate pressures from that for your (actual) axle loads. (though this would, of course depend on your ability to accurately interpret the data). An even less safe way would be to guess the axle loads, and use one of the above two methods to ascertain pressures. (even using axle loads at the legal maximum for your vehicle would be suspect). ....and then, the final way would be to guess your axle loadings (or simply just not worry about them), and then guess the appropriate pressures for them. Brian Kirby is fond of his "Dirty Harry" moments, so I think I'll follow his example; "....you've got to ask yourself one question: Do I feel lucky? Well, do ya, punk?" With only four bits of rubber between nearly four tons and the road, I think I'd rather feel safe than lucky. Link to comment Share on other sites More sharing options...
BIFFO Posted March 10, 2012 Share Posted March 10, 2012 Fair enough robin hood........check axle weights.......check tyre manufacturer.....ring same .......follow their recommendations job done. Can I pose the question .........how many of us actually do this....or .....how many of us simply follow our gut instinct. Over many years of driving countless miles I have never had to replace a set of tyres because of under / over inflation, have always seemed to get the milage out of a set of tyres. So....the debate goes on . :'( Link to comment Share on other sites More sharing options...
Robinhood Posted March 10, 2012 Share Posted March 10, 2012 bgrobbins@hotmail.co - 2012-03-10 3:19 PM Fair enough robin hood........check axle weights.......check tyre manufacturer.....ring same .......follow their recommendations job done. Can I pose the question .........how many of us actually do this....or .....how many of us simply follow our gut instinct. Over many years of driving countless miles I have never had to replace a set of tyres because of under / over inflation, have always seemed to get the milage out of a set of tyres. ..........you oviously are feeling lucky then! ;-) bgrobbins@hotmail.co - 2012-03-10 3:19 PM So....the debate goes on . :'( Not with me it doesn't! You posed a question; it has been answered appropriately by numerous people on this forum; you choose to ignore the advice and use your judgement (aka guesswork) - fine (but I'd be very surprised if your tyre manufacturer, when advised of the exact circumstances, didn't advise somewhat higher pressures). The question isn't simply about mileage from tyre, it's about safety as well! The attitude is akin to that of the man who jumped off the top floor of the Empire State Building, and could be heard on passing every floor exclaiming "so far so good". :-S (And BTW, I have had 9 motorhomes over the years, and on each of the coachbuilts (5) except my current I have taken exactly the route I suggested (as the recommended pressures on the door jamb have been, as many people have found, too high). On my current 'van, the door jamb figures match exactly the manufacturer's data (Continental) for my tyres at the vehicle's maximum legally allowed axle loads. As, after weighing all-up, I can run close to the MAM of the vehicle, I choose to run at these pressures, in order to have some leeway on loading. There is judgement involved in this as well, but it is underpinned by an awful lot of solid data). Good Luck! Link to comment Share on other sites More sharing options...
Brian Kirby Posted March 10, 2012 Share Posted March 10, 2012 bgrobbins@hotmail.co - 2012-03-10 11:19 AM....................All I am saying and as stated ...this subject has been covered now for ten years and we are no nearer to a definate answer to the question.." what pressure for what tyre and what van of what weight " .? . We are most of us been driving for many years and have gained some insight into what is practical and what is just not done. We assess the problem and use our knowledge to make a decision . At least that's what I hope to do and hopefully I'll keep motoring as I have for the last 25 years of motor homing. In that time I've had one puncture. I have probably Insured a load of them now :D :D B-) You have three choices. You use the pressures as quoted by the vehicle manufacturer. You do as recommended above, and weigh your vehicle fully laden, noting the load on each axle separately. You guess. You need to know four things about your van. 1 The legally permissible load on each of your axles - see your VIN plate - and 2 the actual load on each axle, with the vehicle fully laden. 3 The legally permissible all up weight for your vehicle (MAM) - see your VIN plate - and 4 its actual, fully laden, weight. If the actual weight on each axle is below the legal limit, and the actual laden weight is below the MAM, your van is legal anywhere. If it is not, and you are check weighed you will have to dump load, probably there and then, and you may be fined. Generally, you will not be allowed to continue until your actual weights are within the legal limits. You need to know three things about its tyres and their pressures. First, that the ideal tyre pressure can only be established if you know what load the tyres are actually supporting. There is an ideal relationship between the tyre load, and its inflation pressure. This is established by the tyre manufacturer in testing the tyre. It varies depending on the tyre section, diameter, and speed and load ratings. It is not "one size fits all". Second, that the vehicle manufacturer's recommended tyre pressures are set to ensure you do not run the tyres under-inflated. They are therefore appropriate to the maximum permissible load for each axle. This will inevitably result in slight over-inflation, resulting in a rather harsh ride, but it is the safest option if the actual axle loads are unknown. Tyres over-inflated to this extent will wear a little faster in the centre of the tread band, and may lose some traction and braking performance, but they will not break up or suffer explosive deflation (sudden blow-out). Third, you need to understand that tyres that are run at pressures below the ideal, and so under-inflated, are liable to exhibit poor directional stability, poor braking performance, poor traction, and most dangerously, to run hot. Overheated tyres soften, exacerbating the poor braking and traction performance, but are also prone to break up or suffer explosive deflation. Under-inflation is a matter of degree, the more the tyre pressure is below its optimum pressure, the greater the risks. Your problem is that because you have no idea of your axle loads, you have no idea whether your tyres are at the optimal pressure for the axle load, or are over, or under, inflated. In effect, you are playing Russian Roulette. You have two remedies. First, go back to Hymer's recommended pressures, and put up with the harsh ride. That is the fail-safe. Second, take the fully laden van to a weighbridge and weigh it, noting the load on each axle. For this, you must have all tanks and reservoirs full, except waste water and toilet cassette which should be empty. You should have absolutely everything and everyone, including yourself, in the van when it is weighed - otherwise it is not fully laden, is it? :-) Then, you contact the tyre manufacturer with the actual, laden, axle loads, and ask them for their recommended tyre pressures for those loads. What you will then get are the optimum tyre pressures for the axle loads, which should give the best combination of directional stability, braking performance, traction, comfort, and wear. It is not difficult, and only a small amount of effort is required, and yes, most sensible people do indeed do just that. Or, you can just carry on guessing, as you seem to prefer! Over! :-D Link to comment Share on other sites More sharing options...
Brian Kirby Posted March 10, 2012 Share Posted March 10, 2012 kelly58 - 2012-03-09 8:48 PM I have just got in , so here is more details last year fully laden with 2 bikes half tank of fuel about 50 ltrs and the same of water it weighed in at 30kgs under 3300kgs I must admit I did not weigh each axle , so I asked SVTec to do an upgrade to 3500kgs the weight plate stipulates Front Axle 1750kgs and the Rear Axle 1900kgs , which when fully loaded I will check , but it will not be for a few weeks yet . I know if I fitted Airrides this would give more carry weight to the Rear Axle. I thought just to be on the safe side the uplift of gross weight would be beneficial if and when I had a full fuel load on board , I have no intention of adding a Solar Panel or a 2nd Leisure Battery ,so my normal gross carry weight should remain constant , My main concern was what would be the correct tyre pressures to A be legal and B a comfey ride . If that makes sense. But Kelly, laden with only half a tank of fuel and (presumably) half a tank of water, is not fully laden! Plus, you don't say if you were on board at the time, or in the weighbridge office. :-) 1750kg front, and 1900kg rear, are the standard Ducato 33 axle loads, they do not stem from anything SV Tech did. I would add that it is not necessarily the case that adding Air-Rides will bring any benefit to maximum rear axle load. One version of the Air-Ride may, but it has to be certified, others do not. To reiterate, your van must be weighed in its absolute heaviest condition, with everything, and everyone on board, with all reservoirs full (not guessed: full) and with waste tanks, including toilet cassette empty. Only then can you know what load your tyres must support, and so set the appropriate pressures. Once armed with the facts, you can then explore what to do with your tyre pressures. You have a van that, on the OEM figures, gives some latitude, but precious little. Your van has a fair rear overhang, and an end kitchen. Such vans tend to overload the rear axle before they reach their MAM: yours may not, but it is impossible, from what you say, to tell. If you were/are already overloaded at the rear, your remedy is to redistribute load forward within the van, or to see if it is economical to have the rear axle re-rated. Your existing tyres can support an axle load, at maximum pressure, of 2,060kg (that is to say, 1,030kg per tyre). Your axle can support a load of 1,900kg. You could possibly up-rate the rear axle by 100kg, but I'm guessing not more. This is because I doubt that anyone would push the axle limit any closer to the tyre limit, because of the possibility that the load on the axle is eccentric, with one tyre more heavily loaded than the other. (There must also be some allowance for sway loading, and I've no idea how this is normally provided for.) What I'm saying is that (at a guess) if you could push the rear axle load higher than 2,000kg you would probably have to up-rate the tyres but, for your 215/70 R15 size, my Conti data says they don't do one. Someone else may. This would obviously add to the cost. Then, changing the rear tyres would present a further problem if you carry a spare, because it would be unusable on the rear. So, because it is all so finely balanced, with the possibility that your rear axle is already overloaded, and the resulting difficulties that would create in catering for a higher load, I think you just have to bite the bullet and load it fully, and get the laden axle weights, before it is safe for anyone to say whether you can reduce the tyre pressures, or whether you need to find higher rated tyres from a different manufacturer to cater of your actual loads. Sorry. Link to comment Share on other sites More sharing options...
kelly58 Posted March 10, 2012 Author Share Posted March 10, 2012 When weighed the motorhome I was in the driving seat , to-day I have spoken to the manager at Bush Tyres where we have the lorry tyres serviced , he said pop in with the motorhome and he will do a thourough check and then ring Continental with the data and let them advise as to pressures for tyre / type and loadings as motorhomes are not the run of the mill when it come's to settings , because of the different designs of motorhomes via different manufacturers. I will keep you posted when I get the report. Link to comment Share on other sites More sharing options...
Brian Kirby Posted March 10, 2012 Share Posted March 10, 2012 kelly58 - 2012-03-10 5:51 PM...................to-day I have spoken to the manager at Bush Tyres where we have the lorry tyres serviced , he said pop in with the motorhome and he will do a thorough check and then ring Continental with the data and let them advise as to pressures for tyre / type and loadings as motorhomes are not the run of the mill when it come's to settings , because of the different designs of motorhomes via different manufacturers. I will keep you posted when I get the report. But how will he know your, actual, fully laden, axle loads to be able to consult Conti? Does he have a weighbridge, and will you take the van fully laden so that it can first be weighed? Why is this so hard? :-D Link to comment Share on other sites More sharing options...
Brian Kirby Posted March 10, 2012 Share Posted March 10, 2012 Robinhood - 2012-03-09 3:07 PM..................My Conti Tech Data I've been using is now a little out of date (and doesn't cover CP (Camping) tyres). I've been looking for an up-to-date set, and, though I can't find one in English, the latest German data is readily downloadable from that country's site. It is most useful if you can come to terms with having to mentally align two pages to read across the data............................. Try this link, it should get you the 2011/12 Technical databook in English. http://tinyurl.com/7crtn2e But, even though the 15" wheel tyre pressure table now includes a row for the 215/70 R15 CP tyre, it doesn't change the answer! :-D Link to comment Share on other sites More sharing options...
Robinhood Posted March 10, 2012 Share Posted March 10, 2012 Brian Kirby - 2012-03-10 6:56 PM Robinhood - 2012-03-09 3:07 PM..................My Conti Tech Data I've been using is now a little out of date (and doesn't cover CP (Camping) tyres). I've been looking for an up-to-date set, and, though I can't find one in English, the latest German data is readily downloadable from that country's site. It is most useful if you can come to terms with having to mentally align two pages to read across the data............................. Try this link, it should get you the 2011/12 Technical databook in English. http://tinyurl.com/7crtn2e But, even though the 15" wheel tyre pressure table now includes a row for the 215/70 R15 CP tyre, it doesn't change the answer! :-D ....why, thank you kind sir! (My technical German is just about good enough to use the German version, but it is easier in English). ;-) Link to comment Share on other sites More sharing options...
Brian Kirby Posted March 10, 2012 Share Posted March 10, 2012 Robinhood - 2012-03-10 7:05 PM........................(My technical German is just about good enough to use the German version, but it is easier in English). ;-) Well mine isn't, and I couldn't find anything in French, so I was driven by sheer desperation! You're welcome. :-) Link to comment Share on other sites More sharing options...
Keithl Posted March 10, 2012 Share Posted March 10, 2012 Thanks for the link Brian, very useful info. And that leads me to another point as I have seen varying ages quoted for tyres to be replaced. From page 12 of the 'Tyre Tips' brochure I have copied the following... All tyres (including spare tyres) that were manufactured more than ten years ago should be replaced with new tyres, even if they appear to be usable from their external appearance and if the tread depth may have not reached the minimum wear out depth. So this gives me a while longer until I need to change my tyres :-D Keith. Link to comment Share on other sites More sharing options...
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