Tyre pressures - comfort v mpg?

Discussion in 'Tech/Mech General' started by peterc10, Mar 12, 2014.

  1. peterc10

    peterc10 Funster

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    In preparation for our trip away to France and Spain on Friday I have weighed our Adria Coral when fully loaded and ready to go and with both of us in it. We are well within the maximum - 3360kg v 3500kg max. And both of the axles are well under their maximums too. So good news - we will be able to bring plenty of wine back.

    I phoned our tyre manufacturer (Continental) and got their recommended tyre pressures for the axle weights we have, and they are well below what we have at present, as recommended by Adria. We have 6 bar throughout and Continental say 3.5 bar on the front and 4.75 bar on the rear, which they have confirmed in an email.

    I hope by changing to these I will get a better ride quality, which has always seemed hard and rattley to us. From other peoples' experiences is that likely and will it have an adverse effect on my mpg?

    Thanks for your help yet again.
     
  2. WillH

    WillH Funster

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    We too had high tyre pressures and found the ride very harsh. With the advice of a local tyre fitter at ATS I gradually reduced the pressures and have found a happy medium , much better ride and reasonable fuel economy.

    Rgds
    Bill
     
  3. Jim

    Jim Ringleader

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    If it was only fuel economy and comfort is important then I'd say yes run under. nice and comfy, it's only money, especially if you only do the average 6k a year.

    I do about 15k a year and like most motorhomes at the all up weight. I prefer to run at the recommended pressures, ensuring optimum road holding and braking. For comfort I sit on a nice memory foam cushion purchased from the fuel savings:Smile:
     
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  4. Yorick

    Yorick Funster

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    It's free, get plenty in :Smile:
     
  5. JeanLuc

    JeanLuc Funster

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    I would go with the Conti recommendation. I realise my van has a different set-up to yours (RWD Sprinter chassis - single rear tyres, not twin) but the Hymer (and Merc) recommended pressures for 225 70 R15 tyres are 3.5 bar front, 4.5 bar rear. I have Conti Vanco tyres and it runs well on them. Those pressures are for a MAM of 3,800 kg with a max rear axle load of 2,240 kg.

    6 bar seems very high anyway and at that pressure, I hope it was fitted with high pressure valves. The standard Schrader car-type valve is rated for a maximum inflation pressure of 4.5 bar.
     
  6. hdvrod

    hdvrod Read Only Funster

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    I too have merc sprinter and that's what I run.
     
  7. magicsurfbus

    magicsurfbus Funster

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    Likewise, I prefer rattle to screech any day of the week.
     
  8. chaser

    chaser Funster

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    This is a good one, I have always come on here and gone for lower pressures when this argument has come up before, but been round wales for a day or two so decided to put more in , don't understand bars but put 70 lb in front and 75 in back as opposed to recommended 79 all round , usually only have 60/65 in , couldn't find much difference comfort wise but haven't filled up yet but it's looking like an extra 5 mpg, and that's round the hills.:BigGrin:
     
  9. Jim

    Jim Ringleader

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    A ball park figure, but Michelin suggest that 10% under-inflation can add 6% to your fuel bill as well as reducing tyre life, handling, holding and braking. 6% of my fuels bill plus tyres is a considerable saving for me.
     
  10. peterc10

    peterc10 Funster

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    But the question is recommended by whom?

    Adria, who have just copied Fiat's figure, which is based upon the maximum axle loadings possible with the chassis (and which I am way under). Or the tyre makes who have given a recommendation based upon their tyres and the axle loading I actually have. I suspect the latter will be closer to "correct", whatever that may mean.
     
  11. Jim

    Jim Ringleader

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    The tyre manufacturer. The only way to know the correct pressure, is to load up and go to a weighbridge. Tell them you want both axles weighed, give these weights to the tyre manufacturer and they will give you the precise pressure to run on. I know it seems a pain to do, but it's only once and its good to know what you weigh anyway:thumb:
     
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  12. peterc10

    peterc10 Funster

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    In that case we are in total agreement! :thumb::thumb: As I said in my OP that is exactly what I have done and the tyre manufacturers have recommended the lower pressures.
     
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  13. old-mo

    old-mo Funster Extra Special Life Member

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    Comfort or safety... :RollEyes::Wink:

    I prefer to go along with what the manual states.... I should imagine they know when the manual is written what tyres/weights etc are on..:BigGrin:
     
  14. peterc10

    peterc10 Funster

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    When Fiat wrote it (and Adria have just copied them) they did not know what weights were on, because it was sold as a cab and chassis unit only. The handbook is for all forms of Ducato, including all the commercial uses it may be put to. And they certainly don't know what weights I am running it on at the moment!
     
  15. Scotties

    Scotties Funster Life Member

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    Not an exact science ...

    It's not an exact science. Weight, surface, speed, ambient temperatures, wheel position etc will make a big difference.

    On our last Spanish visit the incab monitors showed 25% plus pressure increase on rear wheels (low van skirts). Alarms on the system go off at + 10%. Believe me these systems are TMI so I've taken it off, Jim's flashers are probably all you need.

    Everyone must make their own decision but I definitely run slightly lower pressures in hot weather.:Cool:
     
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