tyre pressure confusion

[dream machine]

advice please

I have an AutoSleeper Rambler 2000X reg (similiar to the Trophy / Symphony models)

which is a Peugeot Boxer petrol. I don't load it particulary heavy and have been sticking to the tyre pressures stated on the SILVER LABEL on the drivers door frame which states 44 psi both Front & Rear

 

The metal plate under the bonnet states laden weight 3700 kg Front axle 1650 Kg Rear axle 1750 KG ....................... the Reg document states 'Revenue weight 2800 Kg' the tyres fitted are 195/70 R15C light truck.

 

I don't carry particulary heavy loads / items just the usual combination of clothes / equipment etc .However I often feel it leans a lot on cornering & perhaps I'm not inflating the tyres hard enough so I did some further checks.

 

 

On http://www.tyresafe.org/images/tyre-safety-guide/motorhome-leaflet.pdf

 

For my tyres 195/70R15C + those axle loads (nearest listed) their chart states - Front pressure 57psi Rear pressure 62psi !

 

when I log in my Reg details on their pressure checker it only shows this

 

Tyre size:205/70R15 Front tyres: 3.8 BAR / 55 PSI Rear tyres: 4.1 BAR / 59 PSI which is stating a slightly larger tyre size

 

can you offer any advice as to what you think I should use in the way of guidance as there is a large disparity between these & now I'm totally confused

[jadatis]

Ideal situation to use spreadsheets I made.

https://skydrive.live.com/?cid=a526e0eee092e6dc#cid=A526E0EEE092E6DC&id=A526E0EEE092E6DC%21128

This link leads to my public map, with second from the bottom "Pressurecalculationwithtemp"spreadsheet.

Click on the I in a cirlcle at the end of the line, then in the right bar info appears about it.

Click there on download and after downloading, open it in Excell or compatible programm to use it.

The browser cant handle some things I used in it so dont open it in the browser.

 

This spreadsheet can be used in your situation because you dont drive faster then 160km/99m/h.

I introduced in this spreadsheet the Load or Gripp-%. this is the percentage what the real weight on the tyre is of the weight, you calculate the pressure for. Under 85% things go bumping, over 100% tyre-damage begins at higher speed.

 

If you cant work it out , give me the maximum load or loadindex, and the referencepressure, as it is called. On the sidewall like this "maximum load ( single) xxxx kg (LBS)AT YYY kPa ( psi). The rest you mentioned already.

 

Yust for the used system for calculating, to wich country am I writing now, England or Australia?

Edit: already saw Wales so in Europe, where the list are made wiht the reasonably save power in the universal formula, but it can be better for C tyres.

 

[Derek Uzzell]

dream machine - 2011-09-14 4:59 PM

 

advice please

I have an AutoSleeper Rambler 2000X reg (similiar to the Trophy / Symphony models)

which is a Peugeot Boxer petrol. I don't load it particulary heavy and have been sticking to the tyre pressures stated on the SILVER LABEL on the drivers door frame which states 44 psi both Front & Rear

 

The metal plate under the bonnet states laden weight 3700 kg Front axle 1650 Kg Rear axle 1750 KG ....................... the Reg document states 'Revenue weight 2800 Kg' the tyres fitted are 195/70 R15C light truck.

 

I don't carry particulary heavy loads / items just the usual combination of clothes / equipment etc .However I often feel it leans a lot on cornering & perhaps I'm not inflating the tyres hard enough so I did some further checks.

 

 

On http://www.tyresafe.org/images/tyre-safety-guide/motorhome-leaflet.pdf

 

For my tyres 195/70R15C + those axle loads (nearest listed) their chart states - Front pressure 57psi Rear pressure 62psi !

 

when I log in my Reg details on their pressure checker it only shows this

 

Tyre size:205/70R15 Front tyres: 3.8 BAR / 55 PSI Rear tyres: 4.1 BAR / 59 PSI which is stating a slightly larger tyre size

 

can you offer any advice as to what you think I should use in the way of guidance as there is a large disparity between these & now I'm totally confused

 

You say that:

 

"The metal plate under the bonnet states LADEN WEIGHT 3700 kg Front axle 1650 Kg Rear axle 1750 KG..."

 

I'm sure that's wrong as a) the total of a vehicle's front + rear maximum axle loadings (1650kg + 1750kg = 3400kg in your case) will normally well exceed a vehicle's maximum overall weight (You quote 3700kg) and b) 3700kg would be a helluva maximum overall weight for a smallish panel-van-based motorhome.

 

I'm guessing that your Rambler's maximum overall weight is either 2700kg or 3200kg, which would tally (at least to o some degree) with the 2800kg 'Revenue weight' and with the 195/70 R15 tyre size.

 

For a Boxer 270 or 320 van, my 2004 Michelin technical handbook quotes the former as using 195/70 R15 97S reinforced car-tyres with recommended inflation pressures of 44psi(front) and 44psi(rear), while the latter used 195/70 R15C 104R 'white van' tyres with with recommended inflation pressures of 62psi(front) and 65psi(rear).

 

Can you re-check and quote the weight limits figures given on your Rambler's VIN-plate, please? There should be a list of 4 figures:

 

1: The vehicle's maximum overall weight

2: The vehicle's maximum train weight (ie. the maximum weight of vehicle + trailer)

3: The front-axle maximum weight

4: The rear-axle maximum weight

 

Can you also say EXACTLY which tyres are fitted by quoting the information on the tyres' sidewalls? For example - Michelin AGILIS 195/70 R15C 104R or Continental VANCO-2 195/70 R15C 104R.

 

As it seems that your Rambler may have started life with reinforced car-tyres and now has heavier duty 'white van' tyres, it's essential to know its current tyres' load-carrying capability which can be established by the tyres' load/speed index (eg. the "104R" marking on the two examples I gave).

 

Until you have confirmed exactly which tyres your Rambler has, and their load-carrying capability, it's a waste of time (and potentially dangerous) trying to advise on what pressures you might best use.

[jadatis]

Filled in with the data given.because a C tire with the same dimensions, always has the same loadindex.

Exception could be if the referencepressure is lower then 65 psi.

Filled it in in Kilo's , though the sheet shows LBS. But the calculation is OK .

For Load% of 100% , wich is not save , it shows 59psi front and 63psi back.

But I would calculate with front 95% wich gives 62psi front and back 90% gives 72 psi, wich is higher then the pressure that is put on the sidewall of 65psi but that is no problem, this is not the maximum pressure of these tires, and covers possible overloading and shifted loading R/L. Also covers pressureloss in time and misreadings of pressure.

With this pressure you have reserve and comfort and gripp enaugh.

It is always better to do a 4 point measuring of the RV, but then you still have to be ware of misreadings, even a calibrated schale has its deveation.Could be that if , the real loads are much lower, that even with this pressures things go bouncing, and/or your front tires goes slipping in difficuld situations, but you only know this for shure by weighing.Savety first.

But check for savety the data on the tyre and the RV.

 

[Derek Uzzell]

jadatis - 2011-09-19 10:28 AM

 

Filled in with the data given.because a C tire with the same dimensions, always has the same loadindex...

 

This statement is incorrect.

 

For example, Michelin produced 195/70 R15C tyres in "Agilis 61" (6-ply rating) and "Agilis 81" (8-ply rating) versions, with the former having a Load Index of 100 (800kg) and the latter a Load Index of 104 (900kg). Unsurprisingly, the pressure-to-load graph of the Agilis 61 tyre differs from the Agilis 81's, with the former having a maximum recommended inflation pressure of 54psi and the latter a maximum recommended inflation pressure of 65psi.

 

If your advice (as I understand it) would be to use 72psi for the rear tyres and the motorhome in question happens to have Agilis 61 tyres, then you'd be recommending over-inflation by some 18psi. I don't accept the argument that, because tyres are built with a 'safety margin', it's "no problem" inflating them beyond the sidewall pressure-marking. Any reputable tyre manufacturer will advise that the sidewall pressure-marking is not there for entertainment and, if the owner of a vehicle believes it is necessary to inflate tyres beyond that marked pressure, then the vehicle is either overloaded or the tyres are unsuitable for that vehicle.

 

Athough Dream Machine's Rambler's 3700kg '"laden weight" figure is undoubtedly wrong, it's likely that the 1650kg(F) and 1750kg® data are right. The latter figures indicate that 6-ply rated tyres with a 100 Load Index would be unsuitable for this vehicle, but that doesn't mean that it doesn't have them!! That's why it's vital for Dream Machine to provide details of his tyres' load index.

 

Assuming that DM's Rambler has tyres with a 104 Load Index, then 44psi front and rear pressures would be appropriate for static axle-loadings of around 1350kg (front and rear), but there's no way of knowing if such loadings reflect reality without weighing the Rambler in its fully-loaded state. As 195/70 R15C 104R tyres can safely be inflated to around 65psi, there would be plenty of scope for increasing the current 44psi to see if this would usefully reduce lean while cornering. But, until it's known what tyres DM's motorhome has (to set a benchmark) and then what its axle-loadings are (via a weighbridge), I can't see how anyone can 'calculate' what inflation pressures would be most appropriate.

 

I'd guess that 44psi is probably too low and (because I'm familiar with the Rambler) that 50psi(F) and 55psi® might be 'about right'. That assumes that the tyres have a 104 Load Index and that the vehicle is relatively lightly loaded, but it's very definitely a 'guess' and not a 'calculation'.

[Robinhood]

The attached extract from the Continental technical data manual (for similar profile tyres as those in question) illustrates a number of the points that Derek makes. (including the different characteristics by load index for the same profile tyre, and the pressure profile by loading).

 

Whilst I would hesitate to fully recommend the use of the data for other manufacturers' tyres, it does provide a good guideline for tyres of the same profile, ply, load index and speed rating.

 

As has been stated many times before, there is no better starting point than having your axle weights in full running order determined by visiting a weighbridge.

 

[jadatis]

Derek Uzzell - 2011-09-20 10:31 AM

 

jadatis - 2011-09-19 10:28 AM

 

Filled in with the data given.because a C tire with the same dimensions, always has the same loadindex...

 

This statement is incorrect.

 

For example, Michelin produced 195/70 R15C tyres in "Agilis 61" (6-ply rating) and "Agilis 81" (8-ply rating) versions, with the former having a Load Index of 100 (800kg) and the latter a Load Index of 104 (900kg). Unsurprisingly, the pressure-to-load graph of the Agilis 61 tyre differs from the Agilis 81's, with the former having a maximum recommended inflation pressure of 54psi and the latter a maximum recommended inflation pressure of 65psi.

 

If your advice (as I understand it) would be to use 72psi for the rear tyres and the motorhome in question happens to have Agilis 61 tyres, then you'd be recommending over-inflation by some 18psi. I don't accept the argument that, because tyres are built with a 'safety margin', it's "no problem" inflating them beyond the sidewall pressure-marking. Any reputable tyre manufacturer will advise that the sidewall pressure-marking is not there for entertainment and, if the owner of a vehicle believes it is necessary to inflate tyres beyond that marked pressure, then the vehicle is either overloaded or the tyres are unsuitable for that vehicle.

 

Athough Dream Machine's Rambler's 3700kg '"laden weight" figure is undoubtedly wrong, it's likely that the 1650kg(F) and 1750kg® data are right. The latter figures indicate that 6-ply rated tyres with a 100 Load Index would be unsuitable for this vehicle, but that doesn't mean that it doesn't have them!! That's why it's vital for Dream Machine to provide details of his tyres' load index.

 

Assuming '.

 

But I also wrote the exeption that if the reference-pressure was lower, and thats the case with the 61 tires.

For the 65 psi tires the 71 psi is no problem , but I agree that for the 54 psi tire it is to much.

Also have found list of semperit , in wich for lower speed, a system of more load to carry at higher pressure then the referencepresssure. Has been used in the past for caravans,so with 10% more pressure it might bare 10% more load. Normal car tires ( SL/P-tires) also only give maximum pressure, the referencepressure is lower, mostly 2.5 bar/36psi in Europe, max is 3 or 3.5 bar mostly.

 

Once asked Michelin about the Agillis Camping tire wich has only maximum pressure of 80 psi printed on the sidewall, The list I got from them before, placed them in the same pressurelist as the Agillis 81 and ice/snow, with reference pressure of 69 or 65 psi . There also the 80 psi is adviced ,as they called it, to cover peakloads, and they also have their maximum load at referencepresssure of 65 /69 depending on the sises. Then the advice is also higher then the referencepressure.

In the list it even says that when standing still, the tire may bare 2 times as much weight with 1,4 times as much pressure!!

It is possible that you dont overload your axle, but by shifted weight R/L one tire has more weight on it.

What the law says is not important then, laws of nature punish with tire-damage and blowing tires.

Then you can say , the tires may not have that, but with higher pressure, within sertain limits , no tire-damage appears, so you are save.

 

[Derek Uzzell]

Let’s go back to Square One…

 

Ian Cushing (dream machine) has been a motorcaravanner for about 4 years and a caravanner for over 30 years before that.

 

Ian owns an 11-years-old Auto-Sleepers petrol-engined Rambler that he says has (unspecified make and ‘pattern’) 195/70 R15C “light truck” tyres. His Rambler carries a tyre-pressure recommendation label on the driver’s door-frame that advises front-tyre and rear-tyre inflation pressures of 44psi and Ian has been following that advice (presumably) for the last 4 years.

 

Ian has provided weight-data for his Rambler of 3700kg ‘laden weight’, 1650kg front-axle maximum and 1750kg rear-axle maximum.

 

A contemporary Which Motorcaravan (WM) magazine indicated that, in 2000, Auto-Sleepers was marketing 2 panel-van conversion models (Harmony and Rambler) on a Peugeot Boxer 270S (short wheelbase) chassis and 2 models (Symbol and Symphony) on the 270M (medium wheelbase) chassis. For all 4 models, the standard motor was a 2-litre petrol unit.

 

WM gave a Rambler’s dimensions as 4.88m (length), 2.11m (width) and 2.76m (height). These data tally with current on-line adverts for similar age Ramblers.

 

WM quoted a Rambler’s ‘overall weight’ as 3200kg. I haven’t been able to confirm that figure, but the 3400kg total of the 1650kg + 1750kg axle-weights Ian provided suggests that it’s correct.

 

WM quoted a Rambler’s Mass-In-Running-Order as 2295kg – that’s a potential payload of 905kg. In Year 2000 Auto-Sleepers never made ‘essential habitation allowances’ for water, gas, passengers, luggage, etc. but a Rambler’s water-tank, gas-locker, refrigerator and storage-locker sizes will inevitably be small. In short, Ian’s Rambler is small, light in unladen form and, because of its restricted size and significant potential payload, unlikely to be loaded anywhere near its overall or axle-load maxima. In fact, Ian confirms that he does not “carry particulary heavy loads/items just the usual combination of clothes/equipment etc.”

 

Now, as I said earlier, my Michelin handbook quotes a 195/70 R15 97S (4-ply rated) reinforced car-tyre as one of the standard tyre-choice options for a Boxer 270 short-wheelbase panel van and advises 44psi pressure for the front and rear tyres. This tallies with the driver’s door-frame label on Ian’s Rambler.

 

However, a 97 Load Index equates to a maximum axle-load of 1460kg (2 x 730kg), which is way below the 1650kg/1750kg axle weights Ian gave. Alternative 195/70 R15C tyres available in Year 2000 would have been 6-ply rated (Load Index 100 – maximum axle-load of 1600kg) or 8-ply rated (Load Index 104 – maximum axle-load of 1800kg).

 

Sadly I can’t crystal-ball gaze, but (assuming that the 1650kg/1750kg data are correct) it would appear that, whatever tyres were originally fitted to Ian’s Rambler, it SHOULD have had (and SHOULD have now) tyres with a 104 Load Index. According to Michelin’s handbook, such tyres were one of the standard options for the Peugeot Boxer 320 swb van and the inflation pressures Michelin recommended were 62psi(front axle) and 65psi(rear axle). Assuming that a Boxer 320 chassis-model indicates a 3200kg ‘maximum laden weight’, then 62psi(F) and 65psi® would be about right for 1650kg(F) and 1750kg® maximum axle-loads.

 

So what we’ve got is a small, light motorhome with overall and axle maximum weight limits that are likely to exceed considerably the weights achieved by Ian’s Rambler during normal fully-laden usage. The 190/70 R15C tyres should have a Load Index of at least 104 to handle the largest maximum axle-load (1750kg) and it’s to be hoped that’s indeed the case.

 

I suspect (because I’m pretty sure this has been explored before on this forum in the distant past) that Auto-Sleepers did advice inflation-pressures in the 60+psi range for these small Peugeot-based models, as I vaguely recall forum members complaining that this resulted in a very harsh uncomfortable ride. The forum advice (then as now) was to have the fully-loaded motorhome weighed and then to contact the tyre manufacturer about what inflation-pressures would be safe but might provide a softer ride. There’s a A-S Symbol-related 2005 thread on:

 

http://www.outandaboutlive.co.uk/forums/forums/thread-view.asp?tid=2660&posts=6

 

but I’m certain there was earlier, more extensive discussion about this regarding the whole Harmony/Rambler/Symbol/Symphony group.

 

Ian’s situation is somewhat different, as the 44psi pressures he’s been using (and that may be contributing to excessive cornering-lean) could (possibly SHOULD) be increased to provide a firmer (but still acceptable) ride and reduce body-roll. But the question is “How much increase?”

 

Jadatis’s advice seems to be to choose inflation-pressures that are close to those that would be appropriate to 1650kg/1750kg axle-loads. You don’t need a complex spread-sheet or a rocket-science degree to do this – you just glance at the standardised inflation-pressure/load relationship for a 195/70 R15C 104 tyre (see Robinhood’s relevant listing), read off a couple of figures and, provided that Ian’s Rambler’s axle-loadings are approaching 1650kg(F) and 1750kg®, those pressures should be ‘correct’ and ‘safe’. But this approach completely ignores the technical specification of Ian’s motorhome and the fact that it’s been driven for several years with 44psi pressures with no catastrophic consequences.

 

Assuming that Ian’s Rambler’s 195/70 R15C tyres have a 104 Load Index, Ian can just follow Jadatis’s recommendation of 58psi(F) and 63psi® as these pressures are appropriate for static axle-loadings of respectively 1650kg or 1750kg. This should certainly help to combat cornering-lean, but it’s a fair bet that the high pressures will compromise the vehicle’s ride quality. If that proves to be the case, then weighing the vehicle and consulting the tyre manufacturer about judiciously lowering the pressures would be the logical way forward.

 

(Personally, I would have gone to the fountainhead and contacted the Auto-Sleepers company about this. If that proved unproductive, I’d have sought advice from the Auto-Sleeper Owners’ Club. As things stand, it’s still unknown what tyres Ian’s Rambler has and the vehicle’s stated ‘laden weight’ remains very questionable.)

[jadatis]

Then it is now up to the topic-starter to look at the tires and weigh the MH . Then we can stop speculating.

 

I totally agree with Dereck Uzhel, except that I would not ask the tire-maker, but calculate it with spreadsheet, because then you know that it is calculated with the newest European power.

 

The data that robinhood gave, i have checked, and it is the save calculation that they used. so the 0.8 power and not the 0.7 power in the formula that is still used in America.

 

Goal of the formula is to keep the same deflection at lower loads, then at maximumload and referencepressure .

 

If the load of TS apear realy that much lower when 4 point weighed. The lowest weight on the axle can be made 85% of the weight to calculate with , and see if the highest weight stays under 100% .

Then you still have a comfortable ride and enaugh gripp, but a good reserve.

 

If it apears that TS has 44psi on the 103LI 65psi tires, they cover a axle load of 1280 kg when devided.

Because tire damage would begin at the maximum speed of the tire then or if lower 160km/99m/h, and he will probably dont drive faster then 100km/h, even with a bit higher load , the tires are save, so that might explane, why he did not have problems with it, because his loads are realy that low.

 

So topicstarter give more data, especially the pressure that is printed on the sidewall, and do both axles have the same tires, and try to get the MH weighed at least per axle, but better 4 points.

 

 

[Robinhood]

Derek,

 

my archives show that the Rambler (and other A/S van conversions at the time) were built on the 270 series (2800kg MAM) base as standard.

 

(from personal experience, I know A/S would build on uprated base vehicles, as I had a previous model Symphony built on a non-standard base).

 

Given the quoted max axle weights, your assertion about the requirement for 104 rated tyres is correct, though it would be interesting to know the MAM for the base vehicle.

 

(My memory is that, around the change to the Peugeot Boxer, Autosleeper did some odd things with the 270 base, potentially uprating them to a higher MAM, and there was quite a bit of confusion over tyre ratings at the time - including a number being shipped with the wrong tyre - but my memory isn't what it was!! :-( )

[jadatis]

Then it is now up to the topic-starter to look at the tires and weigh the MH . Then we can stop speculating.

 

I totally agree with Dereck Uzhel, except that I would not ask the tire-maker, but calculate it with spreadsheet, because then you know that it is calculated with the newest European power.

 

The data that robinhood gave, i have checked, and it is the save calculation that they used. so the 0.8 power and not the 0.7 power in the formula that is still used in America.

 

Goal of the formula is to keep the same deflection at lower loads, then at maximumload and referencepressure .

 

If the load of TS apear realy that much lower when 4 point weighed. The lowest weight on the axle can be made 85% of the weight to calculate with , and see if the highest weight stays under 100% .

Then you still have a comfortable ride and enaugh gripp, but a good reserve.

 

If it apears that TS has 44psi on the 103LI 65psi tires, they cover a axle load of 1280 kg when devided.

Because tire damage would begin at the maximum speed of the tire then or if lower 160km/99m/h, and he will probably dont drive faster then 100km/h, even with a bit higher load , the tires are save, so that might explane, why he did not have problems with it, because his loads are realy that low.

 

So topicstarter give more data, especially the pressure that is printed on the sidewall, and do both axles have the same tires, and try to get the MH weighed at least per axle, but better 4 points.

 

 

[jadatis]

I asume the moderator will remove my double post.

Because internet was verry slow , pressed it twice I think.

Cant remove it myself.

Then he or she can remove this post too.

 

[Derek Uzzell]

Robinhood - 2011-09-21 10:54 AM

 

Derek,

 

my archives show that the Rambler (and other A/S van conversions at the time) were built on the 270 series (2800kg MAM) base as standard.

 

(from personal experience, I know A/S would build on uprated base vehicles, as I had a previous model Symphony built on a non-standard base).

 

Given the quoted max axle weights, your assertion about the requirement for 104 rated tyres is correct, though it would be interesting to know the MAM for the base vehicle.

 

(My memory is that, around the change to the Peugeot Boxer, Autosleeper did some odd things with the 270 base, potentially uprating them to a higher MAM, and there was quite a bit of confusion over tyre ratings at the time - including a number being shipped with the wrong tyre - but my memory isn't what it was!! :-( )

 

I would guess that Ian's Rambler's VIN-plate carries the following data:

 

1: 2800kg (Maximum overall weight)

2: 3700kg (Maximum train weight)

3: 1650kg (Front-axle maximum weight)

4: 1750kg (Rear-axle maximum weight)

 

My own (limited) archives indicate that the Peugeot Boxer 270S chassis and the equivalent Fiat Ducato 10S chassis both had a 2800kg MAM, with the Boxer 320S and Ducato 14S having a MAM of 3200kg. There seems to some indication that A-S may have built the Symbol/Symphony on the 320S as well as the 270S chassis, but Ian's statement that his registration document says "Revenue weight 2800 Kg" strongly suggests that his Rambler has the standard 270S 2800kg-MAM chassis. Ian's 3700kg 'laden weight' datum was clearly wrong and, although I've always suspected that it related to the vehicle's Train Weight, there was the small possibility that it was a misreading (or mistyping) of the 3200kg MAM that would be appropriate for a 320S chassis.

 

Fedd-back from Ian would settle any argument about his Rambler's VIN-plate data and the tyres fitted to the vehicle. As things stand, I've got reservations about the Which Motorcaravan information I quoted earlier and I'm very wary of the 44psi recommendation for the Boxer 270s (and Ducato 10S) chassis given in Michelin's handbook.

 

If it's assumed that 195/70 R15 97S 4-ply rated reinforced car-tyres WERE actually fitted to these chassis, then Michelin's own pressure-to-load figures for that size/type of tyre indicate that 44psi would be appropriate for a static axle-loading of no more that 1070kg. Double that figure to 2140kg (for both axles) and you'd still be 660kg down on the 2800kg MAM of a 270S chassis. According to Michelin's handbook the 195/70 R15 97S tyre had a design-maximum inflation-pressure of 65psi when it could support a static axle-loading of 1460kg. However, that's still well down on Ian's 1650kg front-axle datum, never mind the 1750kg rear. Nevertheless, Ian's Rambler does carry a SILVER LABEL indicating that 44psi all-round should be used!!

 

Whether it's possible to identify the tyres that Ian's Rambler started life with is anybody's guess (perhaps the original spare tyre remains unused?), but it's more likely that, after 11 years, all the original tyres have been replaced. We do know that the vehicle now has 190/70 R15C "light truck" tyres, but it's quite possible that these are not all the same make/pattern and could have a Load Index of 100 or 104.

 

A 44psi pressure for a 190/70 R15C tyre with a 100 or 104 Load Index would be appropriate for a static axle-loading of some 1300kg to 1350kg, so it seems possible that a lightly loaded Rambler MIGHT just be able to be run safely at 44ps F&R with either 100 or 104 Load Index tyres. In fact, that's what Ian has been doing. However, I would not be comfortable using that pressure myself unless I had weighed the vehicle and established its fully-laden axle-loadings. Even if I had confirmed that 44psi were safe, as Ian has commented that his Rambler leans noticeably when cornering, I'd want to increase that pressure to address that handling characteristic.

 

My Michelin handbook does not provide pressure recommendations for Boxer 270S chassis fitted 190/70 R15C tyres with a 104 Load Index, but 59psi(F) and 65psi® are advised for an equivalent Ducato 10S 'van' with those tyres. This equates (roughly) to the pressures appropriate for, respectively, 1650kg and 1750kg static axle-loadings, but (as I suggested earlier) it's doubtful that a petrol-engined Rambler's full-laden axle-loadings would approach either of those maxima. Hence my suggestion that Ian opt for 50psi(F) and 55psi® until he can confirm his motorhome's fully-laden weights via a weighbridge. 55psi should be 'safe' enough whether Ian's Rambler's tyres have a 100 or 104 Load Index and upping the pressures by 6psi(F) and 11psi® should give a clue as to whether the cornering lean can be usefully reduced by tyre-pressure adjustment.

 

[Derek Uzzell]

jadatis - 2011-09-21 10:57 AM

 

...except that I would not ask the tire-maker, but calculate it with spreadsheet, because then you know that it is calculated with the newest European power...

 

What you need to appreciate is how little understanding motorcaravanners (as a breed) have about motorhome tyre technicalities.

 

If I had bought Ian's Rambler, back in 2009, the first thing I would have done regarding tyre pressures is check any documentation it came with (eg the Auto-Sleepers and/or Peugeot Owners' handbooks) to see what they said. I would also have looked for anything on the vehicle itself that might provide tyre-pressure advice and the 44psi, front and rear, door-frame Silver Label recommendation would have alarmed me as I would have immediately judged the advice to be questionable.

 

I would then have checked the weight maxima data on the vehicle's VIN-plate and what tyres the vehicle was fitted with. After that, I'd have made a value-judgement based on the above information and my own technical documentation as to what pressures would make sense. If those calculations produced a result radically at odds with the Auto-Sleepers or Peugeot recommendations, then I'd have weighed the fully-laden vehicle and sought advice from the tyre manufacturer(s) based on the axle-loadings obtained.

 

There are two reasons why it's normally advised on this UK forum (and on others) that motorcaravanners contact the tyre manufacturers.

 

The first is for "credibility" - if Michelin, Continental, Pirelli, etc. is asked for advice about tyre pressures, it's reasonable to assume that the information provided will be as trustworthy as possible. Asking me, or using your spreadsheet, offers no similar level of credibility.

 

The second is "legality". I don't know what Dutch motorcaravanners' attitude to motoring law is, but many UK motorhome owners have a serious concern about being "legal". If a motorhome's documentation (or a label on the vehicle) advises the tyre pressures that should be used and the motorhome owner is trying to decide whether he/she should employ different pressures (as is the case here), then it makes sense to have something permanent (like a letter or a printed e-mail) from an expert source to support why the revised pressures have been chosen. The 'logic' behind this thinking is that, should the vehicle be involved in an accident, or be inspected at a official road-side check, and it's discovered that 'non-standard' tyre pressures are being used, having taken advice from an expert source should provide an acceptable defence. And, if an expert source is a requirement, the tyre manufacturer should be as good as any.

[jadatis]

I am already planning to review my spreadsheets, and make them multi-lingual at the same time.

Then I will give a warning to always use the highest pressures between that of the spreadsheet and what the tyre-makers advice is, and not to go over the maximum pressure, and what the difference is between Maximum and reference-pressure.

The language part is just today ready , so now first I will work on my caravan/trailer tirepresure calculator, after that this spreadsheet.

 

You could also do both , and calculate, and ask the tire-maker for something on paper or mail.

If you then stay between tyre-maker advice and maximum pressure, then the insurance can never make problems about that.

 

But where is Dream Machine, the topic-starter, shal we send him a personal message, mayby he swiched off his mailnotification of new posts here.

[dream machine]

Sorry I have not been back on here to respond to all your replies ............ I've been hit by a double whammy !

1 - I've gone down with a nasty bug that has laid me up & shows no sign of going away despite double dose of Antibiotics

2 - the Out & About Forum has been near on impossible to use recently (consistently slower than a snail + error messages / blank pages) making me give up trying to access it most days.

 

Oi. Modurator what's going on with the Forum lately - it's become so slow & almost unusable

:-(

 

 

Thanks all for your attempts to resolve my query - as I'm laid up I'm not able to get to the Vehicle at present let alone get it to a weighbridge ............. however (from memory) I can confirm the following

 

1 - the tyres are 195/70 R15C 'light truck' with a load rating of 104 ...... and state on the sidewall MAX pressure 65PSI

 

2 - the original Peugeot Boxer owners manual states that the 195/70R size IS CORRECT for the SHORT WHEELBASE model & that bokk states pressures should be 44PSI for front & rear

 

3 - I can't remember what make is fitted (but it's not a BIG name ie. Michelin / Pirelli etc.) but they're same make all round

 

4 - I did previously try emailing Autosleepers but never had a reply back

 

5 - the only extra fitted is wind out awning NO bikes / extra awning etc.

 

6 - we usually travel with minimal fresh water + empty waste tank ....but usually a pretty full fridge + lightweight clothes etc.

 

7 - My Wife & I weigh together approx 21 stone ....just occasionally we might carry 2 extra passengers but that's rare.

 

 

 

YIPPEE TODAY THE FORUM IS WORKING REASONABLE & HAS ALLOWED ME TO POST :-D

[Derek Uzzell]

Thanks for the reply.

 

If you look at the Continental Tyres listing provided earlier by Robinhood, you’ll see that, for a 195/70 R15C 104R tyre, an inflation-pressure of 44psi would be appropriate for a static axle-loading of 1300kg. As jadatis has explained, tyres with the same dimensions and load/speed specification will have much the same pressure-to-load characteristics. So, whatever make of tyre your Rambler currently has, inflating those tyres to 44psi will be appropriate as long as neither of your motorhome’s axle-loadings exceeds 1300kg.

 

Taking your Rambler’s 2800kg (?) maximum laden weight and halving it produces notional axle-loadings of 1400kg front and rear. To support a 1400kg axle-loading would require your tyres to be inflated to around 48psi.

 

Assuming that the Which Motorcaravan figure of 2295kg was correct for a Rambler’s Mass-In-Running-Order, that would leave a payload of 505kg to cover passengers, luggage, etc. It’s probable that the 2295kg figure included allowances for the 75kg weight of a ‘standard’ driver and the weight of a full tank of fuel, but for nothing else.

 

Your worst case scenario would involve adding in the weight of your wife and the occasional 2 extra passengers (let’s say 3 x 75kg), the weight of full gas bottles (let’s say 20kg), the weight of the awning (another 20kg?) and, say, 20kg for fresh water. Also the weight of the luggage, food, etc. - let’s allow 2 x 10kg for you and your wife’s personal effects, plus 10kg for each metre (or part-metre) of your Rambler’s length (5 x 10kg) for other ‘stuff’. Adding those figures produces a total of 355kg and, if we add this to the 2295kg, we get 2650kg. Halving that figure produces notional axle-loadings of 1325kg front and rear, which would require an inflation-pressure of about 45psi.

 

OK, this is very much finger-in-the-wind arithmetic, but it looks like 44psi might be acceptable for your Rambler given the specification of tyres it has and the way you use the vehicle. If you do weigh your Rambler fully-laden and (as seems reasonably likely) the axle-weights turn out to be around 1300kg front and rear, then seeking tyre-pressure advice from the tyre manufacturer should just confirm the 44psi figure. What I’m saying is that, even if you do weigh your Rambler fully-laden (and it would be a good idea to do so), I suspect that it won’t necessarily produce any real surprises that would DEMAND that you alter your present 44psi pressures.

 

Returning to your original inquiry about using higher tyre-pressures to combat cornering lean, as long as 44psi is actually appropriate for the vehicle’s fully-laden axle-loadings and, hence, ‘safe’, you are really on your own.

 

Low tyre-pressures will produce soggy handling but aren’t the only potential culprit. If your Rambler is softly sprung by design (or the springs have become a bit tired), then it’s going to tend to lean on corners irrespective of how high the tyre-pressures are. Though, plainly, if the tyre-pressures are also on the low side, that will aggravate the lean.

 

You’ve confirmed that your Rambler’s tyres have a design maximum of 65psi shown on their sidewalls. You could experiment by driving your motorhome several times round a corner (say, a local roundabout) where you can regularly (and safely!) provoke sufficient lean to make you feel uncomfortable. Do this initially with the tyres at 44psi. Then repeat the exercise with all the tyres inflated to 60psi. If there’s a noticeable reduction in cornering lean at the higher pressure, then it’s going to be worthwhile upping your present 44psi. If the vehicle still leans badly with a 60psi pressure, then it’s the suspension that’s the main problem not the tyre-pressures.

 

Even if you can reduce the cornering lean by using a significantly higher tyre-pressure, as I said earlier, you may well find that this affects the ride quality to an unacceptable degree. In any case, although it’s definitely dangerous to run tyres at an unsuitably low pressure, it’s not a good idea to run them inflated to an unnecessarily high pressure as this can adversely affect braking, grip and tyre-wear. It’s really suck-it-and-see and, if you don’t want to try flinging your Rambler through roundabouts, go for a compromise 50psi(F) and 55psi® and see what that does.

 

I notice that the ASOC forum (unsurprisingly) requires ASOC membership to participate. If you are not an ASOC member, you might try registering as a guest on the MotorHomeFacts website

 

http://www.motorhomefacts.com/

 

as this has a dedicated Auto-Sleepers forum section. On-line adverts suggest that there are plenty of Ramblers around of a similar age/specification to yours and (because the MHF website has a large forum size) you might be able get some useful feedback from MHF forum participants who are Rambler owners regarding what tyre-pressures they employ.

[Robinhood]

...as I set out above, from memory I recall that there was some (reasonably contemporaneous) debate about tyres and pressures on these Autosleepers Peugeot conversions. I believe it hit the MMM letters pages (amongst others), but I'm not about to go back and search through (and anyway, my memory would have associated it with coachbuilt rather than van conversions :-S ).

 

I have a niggling feeling that a number of units were built (by design) on 270 (2800kg MAM) chassis, with some uprating of components to provide a higher MAM rating akin to the 320 base. (Whether modified by Peugeot or Autosleepers is unclear to me). There was then a resulting flurry of correspondence about tyres and tyre pressures, and I seem to remember a number of instances of people coming to the conclusion that they had under-rated tyres fitted.

 

My views are reinforced by the following post from Motorhomefacts:

 

http://www.motorhomefacts.com/ftopic-57060-10-days0-orderasc-.html

 

...where somewhat down the page "Homenaway" posts about his 2000 Symbol, based (confirmed) on a 270M van, but with a 3250kg MAM. This implies some sort of factory uprating to me (and would, IMO, render any standard recommended pressures for the 270 invalid).

 

He is on similar tyres to the OP. What is also useful, is that he quotes the recommended tyre pressures from the manual (and his door pillar - which is different). He also quotes the pressures that he uses.

 

IMO, the handbook figures quoted in the post for the 320 van (59/65) are broadly appropriate for the OP's quoted maximum axle weights. In real terms, however, it is unlikely that either axle will be near to the maximum quoted, if the quoted MAM of 2800kg is not exceeded.

 

Personally, I think I'd bite the bullet, and head for a weighbridge in fully loaded mode, but (and it all remains conjecture until this is done), the values "Homenaway" says he uses in the post (51 all round) would appear better, with some margin for uneven loading, to me than 44 (but that's just an opinion B-) ).

 

(I have little doubt that - as per Derek's original post, the 44psi refers to reinforced car tyres, not the commercial tyres that are fitted - since 44psi in the latter would not be sufficient for the maximum load on either axle. Hence, it would not be sensible to use it as a (uninformed, without a weighbridge visit) guideline for the tyres you have fitted. I doubt very much whether the vehicle was actually originally shipped with tyres relevant to those pressures, given my memories and the referenced post above).

 

[jadatis]

Filled in an other spreadsheet of mine, where you can use diferent furmula's and diferent tires.

It is to make your own list, the same way the tire-maker does, but also other way.

 

Filled in your 104/65 tires with 3 kinds of calculation, in wich my calculation, I think, comes the closest to the ever to be constructed ideal formula. Because it gives lower loads for a sertain pressure, then the conventional way, it is never unsaver then the conventional one. But you will see how small the differences are.

You can change the spreadsheet. and it also works in a browser, with some limitations( no remarks ).

Try to atach a picture and the file to this message.

Then if you ever weighed, you can pick the right pressure out of this list.

Dreammachineexample.xls

[Derek Uzzell]

I would have thought it’s simpler just to use the ‘standardised’ axle-weight/inflation-pressures as provided in Robinhood’s earlier listing taken from Continental’s technical data manual. For a 195/70 R15C tyre with a 104 Load Index these are:

 

1300kg - 3.00bar/44psi

1385kg - 3.25bar/47psi

1470kg - 3.50bar/51psi

1555kg - 3.75bar/54psi

1640kg - 4.00bar/58psi

1720kg - 4.25bar/62psi

1800kg - 4.50bar/65psi

 

It will be evident from the above listing that, from 1300kg to 1800kg, for every 80kg (or so) increase in axle-loading above 1300kg the inflation-pressure needs to be increased from the initial 3.0bar/44psi by 0.25bar (3psi to 4psi). So, if an axle-loading is (say) 1400kg, then around 49psi would be appropriate.

 

A motorhome is not a racing car where a relatively small tyre-pressure alteration can affect on-track performance, so there’s little point in getting uptight about the odd pound-per-square-inch.

 

If you insisted on exactitude, then you’d need to include ambient temperature in the equation at the inflation and pressure-checking stages and, if the intention is to use tyre-pressures as a means to optimise a motorhome’s handling (which Ian has asked about), then the tyre manufacturers’ standardised axle-weight/inflation-pressure figures may well need to be ignored.

 

My own procedure for my Hobby was:

 

1. Ensure my tyre-pressure gauges were accurate.

2. Weigh the vehicle to establish its axle-weights.

3. Allow for any predictable axle-weight increases (eg 100 bottles of wine!)

4. Contact the tyre manufacturer for advice (because I was in a position to do so).

5. Drive the vehicle experimentally at the recommended pressures.

 

My motorhome stands unused for several months during the winter, during which period the tyres are inflated to 4.5bar. When I bring the vehicle back into service in March I reduce those pressures to 3.4bar(F) and 4.0bar®, which seem to provide adequate handling (for a motorhome), a good-enough ride and no signs of unusual tyre wear. The Hobby’s tyres lose pressure very slowly, so I don’t need to fiddle about ‘topping up’ those pressures. When we are travelling abroad in the vehicle (we don’t tour in the UK) I regularly check its tyre pressures (at least weekly and/or when I plan to drive a long distance), just to be certain that the pressures are what I expect. When I do this I’m not interested if readings are a tad higher or lower than 3.4/4.0 as long as the increase/decrease is roughly the same for all the tyres.

[jadatis]

Then here a new list to compare with the list Derek got from the tyre-makers list.

Then you see it is the same calculation, with some rounding of to the nearest 5 kg.

But I already sayd , that "then you see how small the differences are.

And those lists are not always so easy to come by.

And if you ask the tyre-maker, there is change that the maximum of the tyre is given as protocol.

Now you can draw your own plan. But make shure you read the data right from tyres and car.