Tyre Pressures
Having moved across from caravans to a mho, which we have only had for a couple of weeks, and done a couple of day trips, our initial impressions are, " its a real boneshaker'. Like riding on solid tyres.
I know our roads are not kept in the best of condition, but even so, this is an uncomfortable ride.
The mho is a 2015 Bessacarr Hi-Style 412, based on 2.3L FIat Ducato, and has done just over 6000 miles, so not a tired old workhorse.
The Fiat handbook say 80psi all round, which what the tyres are inflated to.
The tyres are Continental 225/75 R16 CP 116R , and on the tyre wall it says 69psi, which I assume in the maximum.
Having had a browse around some of the mho forums, an overly hard ride seems to be a commom complaint, when running the tyres at 80psi, and I have now experienced it.
It seems that some owners run at around 65psi, and enjoy a much more comfortable ride.
What do you guys do?
I'm inclined to drop them back to the tyre manufacture's specified limit (69psi) or just below.
Comments
-
I think 80 psi on the rear is common on a lot motorhomes but 80 psi on the front seems a bit OTT. Are the recommended PSI's to use not the on the door column of the cab?
David
0 -
Before you change anything I think you would have to weigh the motorhome to establish axle weights and from there you could work out more accurately what the pressures should be. Interesting you say the Fiat handbook, is there not a separate Swift handbook for the Bessacarr? Perhaps contacting Swift, either direct or via the Swift Talk forum might provide more information.
David
0 -
I would agree with DD's advice above about weighbridge and contacting continental who apparently are very helpful.
I didn't bother myself however. When I noticed that the recommended pressures were higher than Continentals advised max for my tyres, I dropped them all to below that figure. It wasn't very scientific, but on a trial basis, I adjusted the pressures on shorter journeys on the basis that if it felt right and looked right they shouldn't be far out. I have now used 60 psi front and 65 psi rear for over 2 years. The ride is ok and tyre wear is even across the width of the tyre.
I also noticed this year, with the hotter weather, that the pressures went up in the heat by 5-10 psi and needed adjusting.
0 -
The problem with later model MH's is the preset pressure monitors. Drop the pressures to a realistic level and you get nagged incessantly with dashboard warnings.
1 -
A couple of points :-
Accurately weighing each axle in touring trim and getting manufacturers advice is the best approach. In my direct experience Continental are very helpful and quick to provide pressure advice about their products but some other manufacturers apparently give a default answer of 80psi rear perhaps for legal reasons.
Tyre pressures are given for the tyre when cold so if the tyre when cold is inflated to the correct pressure adjusting (reducing) the pressure because the tyre is hot is not normally appropriate although of course if the tyre is hot (overheating) for another reason e.g. deflation from a slow puncture/valve problem that a different matter.
0 -
I have e-mailed Continental, giving them the details from the VIN Plate, which gives a max front axle weight of 1850kg, and 2000kg for the rear axle, making a max gross weight of 3850kg.
Of course the max permitted gross weight for the motorhome is 3500kg, so some 350kg lighter than the VIN Plate maximums.
Having had another look at the info on the tyre wall, I see that 5.5Bar is the absolute maximum cold tyre pressure for these tyres, which means that Fiat/ Bessacarr (Swift), recommend running them at the limit, which can't be good.
Certainly with 80psi in the front, the steering is far too light, and twitchy.
Driving on even the slightest HGV created ruts, the requires constant correction.
0 -
Earlier in the thread I posted :
I also noticed this year, with the hotter weather, that the pressures went up in the heat by 5-10 psi and needed adjusting.
Just in case anyone has misunderstood that comment, I was referring to the unusually high ambient temperatures we have had this year rather than the pressures increasing due to tyres getting warmer in use.
I checked the pressures when the temperature outside was about 15 deg C in the spring and they were spot on. Without moving the van at all, and in full sun with an ambient temperature of 28 deg C all four had all gone up by 5 to 10 psi just by sitting there in the hot sun. Recently, now the heatwave has gone, and again with no movement, the pressures have dropped again and I've just put a little more back in...
0 -
Our maximum recommended tyre pressures were 80 PSI over all four wheels. We always carry an "RAC Ring 900 tyre inflator" which allows for accurate pressure checking and rapid inflation/deflation when required.. Would not be without it.
K
0 -
This seems to be quite a common issue, I did quite a lot of digging in other forums and sites and found that many people drop the pressures by 10 - 20 psi as the manufacturer figure of 80psi is a "safe" figure, but the tyre manufacturers will sometimes give a lower figure if you supply them with the axle weights.
Personally I've reduced my fronts by about 15 and my rears by 10 and the ride is so much better.
There is of course one other thing to check, and that is the springs, make sure you're not running on the bump stops due to the spring being almost fully compressed, a common issue with Ducato's and the converter not up-rating them (More of a problem with A class to be fair). I up-rated my fronts and it's a different vehicle.
0 -
Ok, I have heard back from Contintental (very helpful as has been mentioned)
As suggested here, I have just had the vehicle weighed. Full water tank, and full tank of fuel. but no passenger, or driver.
The total weight of the vehicle is 2960kg.
The front axle weight: 1280kg
The rear axle weight: 1680kg (total weight minus front axle weight)
This means that without us, clothing, and food etc, in the van, we are 540kg under the 3500kg max.
Going by the chart (attached) from Continental, it would seem that Fiat/Bessacarr's 5.5Bar all round, is excessive, and unnecessary.
0 -
A roughcalculation, adding our combined body weight, brings the front axle weight to 1430kg.
Adding this to the weighbridge total weight, brings it up to 3110kg.
This leaves 390kg of remaining payload before reaching the 3500kg limit.
A guestimate would be that any of this extra 390kg will over, or behind the rear axle, and so adding this to the weighbridge given rear axle weight, takes it to 2070kg.
Continental's chart doesn't go down as low a 1430kg for front axle weight, but erring on the higher side for the rear axle, a weight of 2130 gives a recommended level of 65.3 for the rear tyres.
I am going to try 55psi for the fronts, although this is way above what the chart would indicate.
0 -
Now have 55psi front, and 65psi rear.
Visually, the tyres don't sit any differently on the ground, so certainly not looking under inflated.
Took the vehicle out for a short run, and didn't notice any additional body roll on cornering.
Need to try it at speed 65mph, to see if the steering still feels like driving on marbles, as someone described it. I suspect that it won't.
Need a more extensive run to confirm, but it does feel a more comfortable ride, and not like diving on solid tyres, as it did.
0 -
Dave, if your 3500kg MH is based on the 'light' chassis (more than likely) then you have an issue...
the front axle weight limit is 1850kg (no problem) but the rear is 2000kg and your guesstimate is 2070kg...not good.
ok, a couple of points.....some good, some not so good...
firstly, the extra weight of driver and passenger will not just be loaded to the front axle....it will be split around 70/30...so some effect in the rear axle.
similarly, any weight added to a garage (rear storage behind the rear axle) will add MORE than the nominal KG value, due to the fulcrum effect.
so, 390kg added to a garage may add approx 450-500kg to the rear axle but remove that same extra 60-110kg from the front axle...
any overall 'upgrade' of MTPLM to (say) 3650kg will NOT increase any axle limits, of which the rear will always be the Achilles' Heel...
i strongly suggest you do the whole operation again, as in DDs earlier post, and FULLY load the van with everything you intend to carry, including full fuel, full water, gas, driver, passenger, bedding, bikes, BBQ, chairs, tables, tools, electrical items, books, clothes etc, etc
this is the only way to get an exact weight of both axles.
good luck.
0 -
An interesting input BB input. Thanks for taking the time to put it together.
I can understand the fulcrum effect, but hadn't considered this.
If as you say, its something like 70/30% split, front to back, then I guess the it works both ways, back to front.
From the weighbridge results, I know that the front axle weight is 1280kg. Taking the 70/30% split into account, our combined body weight of 150kg, adds 105kg to the front axle, taking it up to 1385kg.
Whilst adding the remaining 30%, 45kg to the rear axle, taking this to 1725kg.
1385 + 1725 = 3110kg., which leaves 390kg, before reaching the 3500kg limit.
If all of this 390kg, was added the rear axle loading it would of course now take it to 2115kg, so over the 2000kg limit you refer to.
However, if we assume assume that only 70% of this 390kg is loaded onto the rear axle, and the remaining 30% applied to the front axle, then 273kg would be added to the rear axle loading, and 117kg added to the front axle.
So now we have a calculated front axle weight 1502kg, and a rear axle weight of 1998kg. Close to, but not exceeding 2000kg.
1502 + 2000 = 3502
Realistically, we are never going to load 390kg of clothing and food into the van, and so not going to get anywhere near to the full 3500kg.
The only thing missing from the van when it was weighed, was me and the wife, clothing and food.
Chairs, TV toiletries etc, etc, were all onboard. Fuel and water tanks both full. No rear garage, and we don't carry bikes.
When we do go off for more than a day trip,loaded with clothing and food, I'll say to the wife, "I've just got to go to a weighbridge on the way"
2 -
Added info.
Continental's chart, as posted earlier, states that for the tyres fitted to my vehicle, the pressure for the rear tyres, with a 2130kg axle load, is 65.3 psi
For the front, the chart only goes down to a front axle loading of 1730kg, and for that the tyre pressures are 43.5 psi, which. A tad far removed from Fiat's 80 psi.
As I said earlier, I am now running at 55 psi at the front, which from Continental's chart is for an axle axle loading of 2070kg.
0 -
"If all of this 390kg, was added the rear axle loading it would of course now take it to 2115kg, so over the 2000kg limit you refer to.
However, if we assume assume that only 70% of this 390kg is loaded onto the rear axle, and the remaining 30% applied to the front axle, then 273kg would be added to the rear axle loading, and 117kg added to the front axle."
Dave, firstly, my comment re 70/30 of passenger weight distribution was based on their seating position in relation to the two axles.
however, the fulcrum effect of any load placed behind a rear axle depends on the length of the overhang and the wheelbase.
a simple example....a van has a 4m wheelbase and a 2m overhang (not unusual with some of the latest AS and swift and AT and etc coachbuilts...) 100kg placed at the rear of the locker will exert 150kg loading onto the rear axle (and remove same from front axle).
it was your earlier comment suggesting that any remaining payload would be placed 'over or behind' the rear axle which led me to believe you had a garage or larger rear underbed locker...
...and, thus, your above comment re the effect of that hypothetical extra 390kg is not true.
unless it is placed between the axles (this may be what your comment was describing) it cannot have the effect you describe.
if it were all over the rear axle the spread would be 0/100 front/rear, but the real effect of putting (say) 390kg behind the rear axle would be as in my earlier post, approx 450kg rear and a reduction on the (already light) front axle...
looking at it another way, what it means is that any nominal spare capacity on the rear axle of (say) 200kg is not, in fact 200kg...
as illustrated above (albeit an extreme example) it might only take around 150kg placed in a rear locker to cause a force of 200kg on that axle......
now, from your figures, I don't think you will be overloaded, however, unless you know the overhang ratio etc, it's difficult to precisely predict how load position truly affects axle loadings.
i think you are doing the right thing, to get totally loaded up and then re-weigh...
despite the fact that I'm sure youll be fine, the numbers might still surprise you.
good luck.
EDIT: having just noticed it's a Bessacarr 412 (6m and no rear storage) it looks like all the available storage is under the lounge seating which will spread the weight fairly evenly.
i don't see a real problem, but weighing is still good practice as youve discovered.
0 -
Certainly an interesting discussion
For now, I am comfortable with the reduced pressures that I have set (55psi front, and 65psi rear), but I will, when the occasion arises, and are fully loaded, re-visit the weighbridge, and get it weighed with us onboard.
On driving the vehicle, I quickly knew that that things weren't right, as the ride was extremely hard, and the steering at speed, like driving on marbles. This is why my attention turned to tyre pressures.
It would appear that mho manufacturers, and Fiat, apply a 'blanket' 80psi all round, to allow for a maximum loading on the tyres, irrespective of axle loading, but in many cases this would equate to grossly over inflated tyres for the actual load carried. Especialy the fronts.
I have to wonder how many mho owners are driving around with 80psi all round, just because the 'book' says so, even though though the tyre manufactures say different.
Having sent my weighbridge results to Continental, I received another reply this morning which gave this info:
" ContiVanco Camper 225/75 R16 (CP*) 116 R tyres.
Front Axle: 1280 Kg - 3.0 bar/ 43.5 psi (maximum weight for pressure given = 1730 kg)
Rear Axle: (single fitment) 1680 Kg - 3.5 bar/ 50.8 psi (maximum weight for pressure given = 1740 kg)"
Of course, these weights were without passengers, clothing, and food, but even so, still far removed from 80psi.
80psi is for a real axle loading of 2500kg, and 70psi for a front axle loading of 2500kg. Of course these figures are for the tyres fitted to my vehicle.
My advice would be to consult the tyre manufacturer, and not assume that 80psi all round is correct. After all, it is the tyre that is carrying the weight, and who knows the tyre's capability better than the manufacturer of the tyre.
In the case of my tyres, 80psi is the absolute maximum pressure, and I would not be happy running them at the limit.
As I said BB, an interesting discussion, and one which I hope may have been of interest to others.
0 -
Dave, payloads (and associated axle weights) are always 'interesting' discussions.
opions vary, even within the industry...
eg....Continental will respond directly to a customer and will recommend appropriate pressures based on axle weights...
Michelin, on the other hand, seem only to do this for the front axle, recommending 80psi for the rears, irrespective of weights....the reason given is that there is a 'tyre body' (can't remember their name) that stipulates this and they won't go against this.....despite doing as Contindid for many years...
Thirdly, we have the converters, who seem to think that 80 all round will do the job....
despite some of their customers rejecting this and inflating to (say) Conti's recommendation, some converters won't help with getting TPMS updated in line with the change, merely saying 'it isn't possible' so customers either suffer a hard ride or a continual being in the cab...
re: payloads specifically, some are totally oblivious of even the MTPLM let alone individual axle weights, just loading a van, because it's a van and has plenty of space....
some recognise these limits, yet 'sail close to the wind' or bury their head in the sand....
some manufacturers (certainly, swift, AS, AT) are marketing vans at 8m on a 3500 chassis.....with huge overhangs, storage under rear beds etc.
some of these have 'payload' in MIRO of just. over 200kg....the rear axle must be close to busting the limit before anyone gets in it....
fortunately, there are also plenty of vans with decent payload at 3500 and plenty of owners who are aware of their vans technical properties and act accordingly.
happy vanning.
0 -
DD, yes, I thought Michelin used to respond as you said, too.
however, I picked up my comments from MMM possibly 6 mths ago...
i can't remember the name of the tyre 'body' whose "thoughts' Michelin now side with...
perhaps Google MMM Michelin pressures will,throw it up..
have to go, cinema awaits....
0 -
DD, I think it's Tyresafe that only give a 'calculated' pressure for the front and 80 for the rear...
ive just put my figures into their website calculator and got the fugures below...
firstly, here is Contis reply for my weights...
ContiVanco Camper 225/75 R16 (CP*) 116 R tyres.
Front Axle: 1600 Kg - 3.0 bar/ 43.5 psi (max weight for pressure given = 1730 kg)Rear Axle: 1820 Kg - 3.75 bar/ 54.3 psi (max weight for pressure given = 1840 kg)
here is the Tyresafe web response....along with their rear axle loading 'advice/rider'
Suggested cold tyre inflation pressure:
Front Axle : 44 psi / 3.06 bar
Rear Axle : 80 psi / 5.5 bar
Do not exceed the maximum cold inflation pressure marked on the tyre sidewalll
Advice :
Tyre valves must be suitable for the inflation pressures and for the wheels, and must be in good condition. Metallic or special high pressure valves are normally required with CP-type tyres. Seek the advice of a tyre specialist.
CP-type tyre construction enables the use of higher inflation pressures to provide resistance to the difficult conditions of use encountered on motorhomes. Therefore, when CP-type tyres are fitted on the rear axle in a single formation set the inflation pressures to 5.5 bar (80 psi) for all loads.
im sure it's this last para (rear axle only) that Michelin are now noting when giving out to customer requests....whereas they never used to...
its interesting that Coninental still give figures based on both axle weights.
what could Tyresafe know that Continental don't?
im more than happy with my figures from Continental.
PS, re the noise thread ...I won't mention the ear plugs to L
0 -
0
-
I dont know about anyone else ? But to me, having a Tyre pressure monitoring system that isnt settable by the driver is an anathema. So all vehicles running around with tyre pressures ALWAYS set for maximum loading and everyone onboard getting a very uncomfortable ride ?
Not me, IF i purchase such a vehicle, I would get the system replaced by a customer settable commercially available system, as they are a useful addition, and evidently can fail an MOT if its not working ?
But compulsory over inflated tyres ??? A step too far.
0 -
Ok, I now have my tyre pressures set, based on the tyre manufacturers recommendation, not Fiat/Swift-Bessacarr's excessive pressures.
Today, we loaded the mho with what we would carry for at least two weeks away. Clothing, fridge food, cupboard food, folding chairs, etc, and my photography gear (several Kgs worth)
Full tank of fuel, full tank of water, two full 6kg gas cylinders, and all the other 'bits & bob's', eg, toilet chemicals, and levelling ramps etc.
Me and the wife to remain in the vehicle (drivers seat, and front passenger seat) while being weighed.
Then off the weighbridge.
Plated weight; 3500kg
Actual weights:
Gross: 3140kg
Front Axle: 1380kg
Read axle: 1760kg
" ContiVanco Camper 225/75 R16 (CP*) 116 R tyres.
Manufacturer's load v tyre presssure
Front Axle: 1740kg - 3.0 bar/ 43.5 psi (1740kg is a low as the chart goes)
Rear Axle: (single fitment) 1840Kg - 37.5 bar/ 54.4 psi
With my fully loaded front axle weight of 1380kg, I have set my front tyres at 45psi
For the rear tyres, with my fully loaded axle weight of 1760kg, I have set the pressure at 60psi.
61.6 psi, would be a rear axle weigth 2035kg.
In both cases above the manufacture's recommended pressures, but a LONG way from Fiat/Swift-Besscarr's 80psi all round.
Physically , the tyres don't look any different in terms of inflation, but a big difference in ride comfort, and no more 'skittish' steering.
Even the rattles and creaks are reduced.
Job done!!
N.B: I should say that Continental Tyres customers service dept, were very helpful, and quick to respond to my e-mail.
0
