Tyre pressure and worn suspension bushes

[Tighchris]

Just had first MoT on my 3 yr old Fiat Ducato PVC. Had an advisory for cracked suspension bushes at front of rear springs.

I run the tyres at the Fiat recommended pressure of 79.5 psi all round and have checked on Tyresafe website that all Camper tyres on rear axle should be run at 80 psi. I have Michelin CP tyres. I weighed the van when I first bought it and all is within the axle limits and also within the 3500kg total limit. Looked underneath and the single rear springs are both flat and up against the suspension assist bellows but I have read on various posts on Fun that this is not a problem. Anyway, the Hymer handbook suggests the tyres should be run closer to 50 psi but I have tended to trust Tyresafe and the info on the door pillar from Fiat. The ride is appalling and I hope that people might advise me about whether it is the high tyre pressure that has brought on the premature failure of the bushes. Fiat not saying yet and although I have a 5 yr warranty I guess they won’t cover the bushes. Most of the 20000 miles on the van have been on motorway. Should I go with Fiat, Hymer and/or Tyresafe? Does high tyre pressure mean more wear on the bushes? It certainly shakes the internal fittings around and on the van as well!

Anyway, you can probably see that I don’t really understand how these things might be linked so hoping to benefit from your wisdom.

thanks

 

[Scotch mist]

They look perished to me , don’t think it’s anything to do with tyre pressure BUT I run a fleet if 3500kg vans & 50-55 psi was used , imo 80psi is far to hard , it would knock the fillings out your teeth , I run my 4500kg van at 60-65 psi

 

[Tighchris]

Thanks for your knowledge. I literally feel each time that I drive that 80 psi is too much. I think I will try the lower Hymer pressure and see what Fiat say about the bush failure. Thanks again. Chris

 

[Lenny HB]

Why not change the tyres Michelin CP are awful got rid of mine after 3½ years changed to Toyo Observe Van, the ride is so much smoother, far more grip and fairly cheap.

 

[Pausim]

Fortunately for me Carthago provide more sensible pressures.

^{_{Subscribers  do not see these advertisements}}

 

[Tighchris]

Thanks Lenny, will definitely look to change the type of tyres soon. I see the Toyo ones are Winter and I need the three peaks symbol to regularly visit my grandchildren in Germany. I think the German exemption on non- three peaks marked tyres ends soon anyway. Pausim, exactly the same size and type of tyres as mine. I just don't understand how the recommended pressures can be so far apart. Seeing this chart has given me confidence to try the reduced pressure for a few weeks. Even if the excessive (!) pressure hasn't caused the suspension bushes to fail I really could do with a more comfortable ride. Also, now I think about it all the Hymer warranty work needed on the van has been due to things shaking loose including plumbing, electrics and fittings.

 

[Just smiffy]

I had a hymer 4250kg and ran 55psi on the front and 65psi on the rears, a much smoother ride…

 

[TerryL]

Surprised to see that the normally excellent and accurate Tyresafe website is recommending such high pressures. However if you ask Michelin they will say 80psi all round. Also the numbers on the door pillar are Fiat Commercial which really don't have any relevance to a coachbuilt or A-class motorhome, but maybe does for a PVC.

But yes, IMO that's far too high. I run on Continental winter tyres and Conti gave me pressures of 56psi front and 65psi rear on an uprated to 3850kg Fiat "Light" chassis. Your settings would, for me, be undriveable!

So it't difficult to say what you should do, bearing in mind that if you are stopped with "low" tyre pressures how are you going to prove that they are correct? I carry Conti's email with me.

If your tyres need changing then now is the opportunity to sort it out - not going to jump on the recommendation bandwagon here, just say that I'm more then happy with the Contis.

As regards your suspension, flat springs up against the spring assisters (they're not bump stops no matter what some garages will say) would indicate the vehicle has been run overweight but you seem to have discounted that. I agree the bushes appear to be degraded rather than worn out so maybe there's something else causing it - wrong bushes fitted in manufacture maybe? Whatever, you should get them changed then keep an eye on them.

Finally fitting rear air-assistance will not only sort out the flat springs, but make a marked improvement to the handling and ride - subject of course to those tyre pressures.

 

[Tighchris]

Thanks Terry. Really interesting about the flat springs. They are right up against the spring assisters when the van is empty so not probably good when it is full, an extra 450 kg! Starting to look at air assistance now. Just for the comfort and handling and then as I need winter tyres I cam change and run them at lower pressures.

 

[pappajohn]

I'm with scotch mist.... Rubber is perishing.
I used to run my 3850kg Kontiki at 64psi rear and 52psi front.
No excessive wear, no rolling and no heat.
In my opinion 80psi is too high for any van.
My 7500kg RV had twin rear wheels and 65psi with 65psi in the rear airbags

^{_{Subscribers  do not see these advertisements}}

 

[Marmite]

I have recently reduced my pressures from the 5.5 Bar all round to 4.0 Bar PSI Front and 65 PSI Rear. These are higher than the Dethleffs quoted pressures (Manual and confirmed with Dethleffs) which I thought maybe a bit low, but gives me some leeway. Much nicer ride and even hamdles better. Plated at 3499Kg

 

[wd1506]

When looking at the Michelin Agilis tyres on my Moho it says 80 psi is the maximum psi that the tyre should be inflated to. So if you are running them at 80psi they are on the limit and have a bigger chance of failing. This is just my opinion based only on trying to stay safe out there. So just for the record I run all four tyres at 65psi.

 

[Lenny HB]

When looking at the Michelin Agilis tyres on my Moho it says 80 psi is the maximum psi that the tyre should be inflated to. So if you are running them at 80psi they are on the limit and have a bigger chance of failing. This is just my opinion based only on trying to stay safe out there. So just for the record I run all four tyres at 65psi.

The max psi on tyres only applies to the American market.

 

[jezport]

I think you would have a more pleasant ride at max 70 on the front and 75 rear.

 

[tonyidle]

The giveaway on the bushes isn't the perishing but the fact that the pivot bolt is miles off the centre of the spring eye indicating a collapsed / badly worn bush. Nothing to do with tyre pressures but the bushes need replacing.

^{_{Subscribers  do not see these advertisements}}

 

[BILL 875]

Re Bushes is it not the modern wisdom to use a plastic type bush, I got that from somewhere cant remember where.

 

[Tighchris]

Thanks Tony. I didn’t have the expertise to understand how bad they are. I will try and get an earlier appointment at the Fiat dealer. they said the earliest was the middle of June and then only to inspect the bushes and order the parts if needed meaning a further visit. I will need to go elsewhere I think.
Bill, I am going to be asking them about why the bushes have failed so early in the vehicle’s life. Hope I can get the work done under the five year warranty - probably the reason that the dealer isn’t too keen to do the work.