inconsistent info re tyre pressures

[andy72]

Just found the manual for my old 91 swift and was having a read through.
On the van wheelarch there is a small imprint in the plastic with tyre pressures, noting 33psi. which is what i have always set them at.

In the original sales reciept in the manual there is a note also saying 33 psi for tyres.

yet when i got to the back of the manual, in the printed specs bit it lists every van swift made around the time and the specs. For mine and the majority of vans it notes 42psi which is quite different from the 33psi currently.

I have been noticing a slight swaying when towing (maybe an inch either way) which i posted on and it was thought it was down to it being too light. I wonder if the tyres should be set at 42 rather than the 33?

any thoughts?

 

[Lutz]

Tyre pressure data is a bit meaningless without details of the tyre size to which they refer.

 

[RegandPat]

This may not help but I put 50 psi in my Swift Challenger 490sl as that was what was in the tyres when I got it.
Reg

 

[andy72]

Tyre pressure data is a bit meaningless without details of the tyre size to which they refer.

how is tyre size relative to tyre pressure?

they are 165 R 13 though.

 

[Gafferbill]

Andy72
………… to work out if the correct tyres are fitted to your caravan and what their inflation pressure should be you need the following information.

1. What is the maximum weight of the caravan…… this should be stamped on a plate near the bottom of your caravan door?
2. What is the size type and load index of the tyres you have fitted?

The following link takes you to a leaflet that explains how to read tyre information.

http://www.tyresafe.org/data/files/caravan%20leaflet.pdf

Once you have this information and then using the tables provided in the leaflet for your tyre type and the weight of your caravan (axle load if a single axle caravan) ……….you can look up the correct pressure.
So if your tyres are 165R x13 with a load index of 82 then the inflation pressure should be 33psi and it is recommended that they should not be fitted to a caravan weighing more than 855 kg with 950 kg as a less safe maximum.
If they are reinforced tyres of the same size, the pressure would be 42psi and your caravan could weigh up to 954kg.
If they were light commercial tyres of the same size the pressure would be 65psi and your caravan could weigh 1206kgs

Remember a previous owner may have fitted tyres with the wrong specification !

 

[andy72]

thanks for that, its actually given me a little concern. The previous owner was my dad and im pretty sure he wont have put commercial tyres on but rather standard tyres. The van is light weight at 850KG but with an additional 200kg payload which will put it over the weight limit. I need to go up to the storage place and check.

Looking at the tables it appears that most vans will need commercial tyres and not standard road tyres which will be way below the load limits. I wonder how manypeople actually know this?

 

[xtrailman]

Duplicate Post

 

[xtrailman]

Just found the manual for my old 91 swift and was having a read through.
On the van wheelarch there is a small imprint in the plastic with tyre pressures, noting 33psi. which is what i have always set them at.

In the original sales reciept in the manual there is a note also saying 33 psi for tyres.

yet when i got to the back of the manual, in the printed specs bit it lists every van swift made around the time and the specs. For mine and the majority of vans it notes 42psi which is quite different from the 33psi currently.

I have been noticing a slight swaying when towing (maybe an inch either way) which i posted on and it was thought it was down to it being too light. I wonder if the tyres should be set at 42 rather than the 33?

any thoughts?

Unless the tyres are not the same as the original, then i would go by the wheel arc sticker.
It was 42 psi for my 1992 swift challenger 440/4.
But my 1997 avondale was 33psi.
Pressures will vary from one model to another, even in the same range, due to the load, and tyre type fitted.
The tyres on the avondale always look low, but i wrote to avondale only to be given confirmation that 33psi was correct.

 

[Gafferbill]

........ pressures of 33psi (if correct) applied to caravan tyres invariably mean that the caravan is a twin axle or very lightweight!

I still have a 1995 Swift Challenger bought new and it came with reinforced tyres and recommended pressure of 42psi.
I have fitted light commercial tyres and the recommended pressure is 50psi

 

[JonnyG]

Having just read that link, thanks gafferbill. and fore sure i am not an expert where caravans are concerned, but let me say, that site is the most misleading bit of info i have read concerning "recommendations!
I have a burstner, and the Germans aren't too bad where safety is concerned, my tyres are original 195/70 R15Cindex linked 98 that means they are rated to 750kg each. my caravan has a max weight is 1500kg.According to that site they would not recommend the use of those tyres because of the index load! And yet as they are manufacturers of tyres, it is they that need to comply with the law!
Max index load mean just that, and not for short burst of time, the tyre can carry that weight safely ALL OF THE TIME!
Also those quoted tyre pressures seem to relate to the max index load, if you have tyres rated to 750kg X2 and your caravan is towed at 1200kg, then those figurers are too high
It would be more helpful if that site gave the formula for actually working out what you pressure should be in relation to your tyre index and actual van weight whilst towing.

 

[andy72]

ive re-read the owners manual and it states the tyres should be 165 R13 Reinforced radial at 42psi. That seems to tally with the advice so far. What i think i have fitted (i need to check) is just normal 165 /13 car tyres at 33psi which will cover the 850KG the van wieghs but not the 200 payload which puts it over the safe load of the tyres. Im hoping my dad did fit reinforced and they just need pumping up to 42 psi.

 

[JamesH]

I have a 91 Swift Corniche and the handbook gives 42psi as the pressure for all Corniche models. My wheel arch is also marked 42psi.
The handbook specifies 33psi for the Silhouette and all Conqueror models.

 

[Guest]

There is no formula, the one often refered to is useful in the absence of charts but far from accurate.

The correct tyre pressure depends on the pressure required to force the required volume of air into the available volume inside the tyre.
The volume of air for any given load is a constant, ie, a volume of 0.5 cubic metres of air is required to support 500kg, this amount then need to be forced inside the given tyre, the pressure arrived at is what it is!

As for Tyresafes therefore the tyre manufactures recomendations, my car can do a quoted 138mph, I would not expect it to last long if I did that every time I drove it? as it is I obviously drive it well withing those capablilities and I don't see any difference with tyres!

 

[colin-yorkshire1]

One would think than van manufacturers would fit the best tyres to suit their vans sadly this is not allways the case.
our bailey had the original tyres on when we got it :- 175 R 13 load rating (83) with a tyre pressure (on vin plate) of 33psi.
on taking delivery and on the way home with a empty van noticed how unstable it seemed, it wallowed about like a seal on dry land.
on arriving home I checked everything over just in case the dealer had missed anything but no all was as it should be however when pushing the van side to side was alarmed how much movement there was in the sidewall of the tyres after checking the pressures and confirming them correct asked the dealer for the tyre specification they were correct.also.

not being too happy with them as they were changed them for a pair of 175 R 13C load index (97) and inflated them to 42psi as recommended for the axle load of the van at maximum MTPLM The transformation was remarkable even with a full load. It was just not the same van in tow. allthough the new tyres were technically overrated for the van.
it did however cause one small problem on our first trip out with the new tyres when some of the top cupboards emptied out on to the floor "hum" but the fitting of after market shock absorbers cured this.
we have done a few thousand miles since the mod and in 4years had no more tyre related problems, they are due to be changed soon but will be going with the 175 R 13C's again.

 

[JonnyG]

Hi Gary, maybe that's the info that should be printed on the side wall then.
Interestingly my bus has 205x55x16 H 91. rated to 615kg each. front tyre max pressure is 44psi rears are 51 psi![as written on the tryes] assuming that because of their supposedly same size the volume should be near as dam it the same give or take plus minus 1.5% ? so why the big difference in max tyre pressures
As you can see the differing psi figurers fall well outside that spec.

Got the book out for my Mondeo 2.2 tdci it has the same tyres as my bus[Alhambra] normal psi should be 32 front 30 rear. fully loaded it should be 34 front and 40 rear, and for hi speed use above 100 mph it should be a few more psi in the front and rear.!
In other words it accounts roughly for all the different uses and weight the car could be carrying.
Those figurers given on that site take none of these differences into account,one would consider with their expertise this would be something they would shine at!And never the less as I said earlier my caravan has tyres rated to 750kg each which is the same max as my caravan can carry. so who do I believe?

With regards the comparison of running a car at its top speed, to carrying the max load on a set of tyres! one is merely a claim, the other is a legal requirement,and therefore the comparison is hardly a good one, but being as my Mondeo actually has a claimed top speed of 138mph too, which indecently equates to 3900rpm, well below the max safety revs for that model, if i did do the claimed but not legal max speed, I would not expect it to go bang as its revs are well within its safety margin, and that rule,as a course of legality applies more so to tyres, so why is it that site is giving the advice that they are! Reminds my of the 85% rule, sorry guideline !

 

[Guest]

Regards two tyres the same size with differing max pressures, two possibles, first different construction so different internal volumes, (all tyres of the same size must have the same external dimensions).
Second, as above all tyres of a particular size and construction must conform to the international standard for that tyre, ie, dimensions, load and max pressure as well as many more
A few years ago Matador reinforced tyres as fitted to caravans had 51psi on them and this falls outside the 42psi spec, irrespective of that max pressure being ok. At the time tyresafes tech guy looked into it but I don't know the outcome. All I knew at the time is it should not have been there, but as here, it only serves to confuse.
Things move on though and construction and materials improve and I'm even less sure today if ‘the standards' have been updated?
So funny you have the same 2.2lt car as mine, quick ain't they! my estate though sits on 18" rims and 245's at 36 and 33psi. I've just looked and the Michelins on the front say 50psi, Barnums on the back 51psi, so it would seem specs have changed for reinforced tyres as I would expect Michelin to conform?
Staying with cars for a moment, the tyres get a lot more hammer than caravan tyres, the difference is though they get it everyday, caravans on the otherhand sit doing nothing in one spot getting hard and it's this that does not leave them best able to cope and why Tyresafe recommend giving an extra margin, nothing more than that!
So like the 85% guideline which I also fully agree with, it's all to give you, the car and the van the best chance of getting there and back in the least stressed manner.
PS, and off topic, I don't think 3900rpm is not stressing the engine, I'm new to diesel's but it's not like a petrol engine which thrives on revs and it's well off the top end of it's torque curve?!

 

[colin-yorkshire1]

PS, and off topic, I don't think 3900rpm is not stressing the engine, I'm new to diesel's but it's not like a petrol engine which thrives on revs and it's well off the top end of it's torque curve?!

just because 3900rpm is over it's top end curve does not mean it is stressing the engine if the engine will rev to lets say 5000rpm
without red lining it is safe to rev to that level the manufacturer makes sure of that if it was not a rev limiter would be in place. as in fact most diesels have especialy turbos types.
I am sure some engineers on here could explain this but my understanding is there is a 30% safety marging built in to make them idiot proof, like remapping a manufacturer could build engines to the top spec but dont to keep within the 30% margin all remapping does is cut down on this safety margin to boost power.

 

[JonnyG]

Gary.
Its that site that left me some what confused, i mean it clearly states all markings in Red are specifically for the American market!
That would include the LOAD index! and max tyre pressure! If that statement is legally true, and given the severity of us fitting the right tyres with the right load capability, I find that strange.As I find the statement with regards not using tyres to no more than 90% or so of there max capability, when the ones fitted to mine are matched to 100% by a reputable caravan manufacturer!
One also has to assume that tyres are made in such a way as to be in sorts "over engineered" in comparison to their load index and indeed to some of the quoted Max psi figurers too.
I have always assumed the quoted standard psi figurers for cars, but they would equally apply to caravans took into account the weight they needed to carry, that's way the same tyre fitted to different cars manufactured by differing company have different quoted psi figurers. given say a VW passat could weigh 150kg more than say a Mondeo?
To me none of this is very clear, and it worries me that sites like that make it no more clearer...

 

[Lutz]

The maximum load (in pounds) that is marked on the tyre sidewall applies to the American market only. However, the load index rating, which is part of the size identification, is international and that specifies the maximum permissible load everywhere else, other than the USA.
The two values may be the same, but not necessarily so.

 

[andy72]

It seems a subject that initially seems clear but when you open the can and look inside, a whole bunch of worms jump out.

In a non sadistic way im glad im not the only one confused by all this as i had put it down to a newbie thing but aparantly its anything but. Changing the spec of tyres fitted to a brand new caravan as Colin had to do, is just plain scary.

Speaking with my dad, the former keeper, It turns out mine is fitted with LGV tyres (need to check the load rating) as recommended by the tyre fitter at the time but only inflated at 33 psi as that what the dealer stamped in the book. This could explain why my fuel consumption drops from 40 when solo to 15 when towing (audi A3 1.6 Petrol sportback) as although the car is quite underpowered, its dragging the van rather than towing it. It also explains why the van rolls around so much. when parked up on the hitch, you can rock it like a boat, seriously. My wife wont even stand in it when its hitched as its so wallowey.
Isnt it a scary thought that the dealer physically writes in the front of the book, given to the first owner back in 91 that the psi should be 33. Yet at the back of the book, on the table provided by the manufactuer it states 42psi. I wonder how many carvan are running around on either wrong or incorrectly filled tyres without even realising it.

 

[Gafferbill]

Andy72.....................in answer to your last sentence.

…….that is exactly why Tyresafe produced the leaflet and why I drew your attention to it.

 

[colin-yorkshire1]

It seems a subject that initially seems clear but when you open the can and look inside, a whole bunch of worms jump out.

In a non sadistic way im glad im not the only one confused by all this as i had put it down to a newbie thing but aparantly its anything but. Changing the spec of tyres fitted to a brand new caravan as Colin had to do, is just plain scary.

Speaking with my dad, the former keeper, It turns out mine is fitted with LGV tyres (need to check the load rating) as recommended by the tyre fitter at the time but only inflated at 33 psi as that what the dealer stamped in the book. This could explain why my fuel consumption drops from 40 when solo to 15 when towing (audi A3 1.6 Petrol sportback) as although the car is quite underpowered, its dragging the van rather than towing it. It also explains why the van rolls around so much. when parked up on the hitch, you can rock it like a boat, seriously. My wife wont even stand in it when its hitched as its so wallowey.
Isnt it a scary thought that the dealer physically writes in the front of the book, given to the first owner back in 91 that the psi should be 33. Yet at the back of the book, on the table provided by the manufactuer it states 42psi. I wonder how many carvan are running around on either wrong or incorrectly filled tyres without even realising it.

Yes Andy it is scary and even with all the towing history I had amassed it was not a step I took lightly but with experience you feel when something is not right,
the symptoms you describe seems identicle to my own however from your last post it seems your dad has changed the spec of the original tyres anyway, but has them under inflated. do check the load rating of the tyres and post the size and load index of them should be 91 or 92ish if this is correct 42psi seems about right. then check the side movement of the tyre walls I think you will find it better
colin