Plastic "TYRE SAVERS"

[Lutz]

Lutz.........you have in the past posted that you could only find one make of tyre that had the performance required by your caravan as to the weight loading.
Would you accept that single axle caravan tyres operate at around 90% of their load range (if inflated correctly)?
Would you accept that cars tyres operate at around 50% of their load range (if inflated correctly)?
Would you accept that single axle caravan tyres work harder than car tyres because of this?

Yes, Semperit is the only manufacturer that produces a tyre in the size and load rating that I need for my caravan.
I really don't see where you get that figure of 50% from that you claim car tyres operate at.
Our towcar has a maximum rear axle load of 1350kg and it's fitted with tyres with a 100 load index, equal to 800kg. This works out at 84% per tyre. My wife's car has a maximum rear axle load of 745kg and tyres with a 75 load index (= 387kg) which is 96%. That compares quite closely with the caravan, MTPLM of 1800kg, tyres with a 106 load index (= 950kg), thus arriving at a calculated figure of 94%.
So, where does the 50% figure come from?

ps: I can only find a very vague reference in the link that you have provided to long periods of storage being a potential cause of tyre failure. As I read it, they imply that it may result in pressure loss, i.e. underinflation, over time. They don't specifically mention flat spots. What they do correctly point out is that underinflation and UV deterioration due to environmental exposure are detrimental to the life of the tyre. They've forgotten to mention ozone. These 3 factors and possibly undiscovered physical impact damage are by far the most important criteria in tyre ageing.

 

[Dustydog]

Two things.

On long term storage is it wrong to pump the tyres up to their maximum stated pressure helping to support the static load?

If a suspension system cannot support the vehicle weight for the expected life expectancy then the design must have been flawed in the first place!

The original Issigonis mini used rubber suspension.

 

[RogerL]

Would you accept that single axle caravan tyres operate at around 90% of their load range (if inflated correctly)?
Would you accept that cars tyres operate at around 50% of their load range (if inflated correctly)?
Would you accept that single axle caravan tyres work harder than car tyres because of this?

The tyre isn't really doing any work when it's stationary - the load is transferred through the tread and is then born by the air pressure in the tyre - the effect of the air pressure on the sidewalls is all around the tyre and considerable less when static than when moving - in any case the effect of the air pressure on the sidewalls would be the same if you removed the wheel and stored it in the garage!

 

[Gafferbill]

So, where does the 50% figure come from?

......the actual load the tyre is carrying when used in every day use as opposed to the maximum plated load of axle.
Agreed your figures would be correct if your cars were fully loaded all the time..... most cars are used nowhere near their actual maximum axle loads.

The
tyre isn't really doing any work when it's stationary

........relative to the road the point of contact of the tyre with the road is always stationary whether the vehicle is moving or not.
The tyre is always doing work supporting the weight of the vehicle and this load acts vertically from the axle centre through the wheel and tyre to the road.
Hence the flexing of the side wall at this point of contact with the road.

When the vehicle is moving and the tyre is rotating this work is distributed evenly though out the tyre side wall structure .......the tyre is doing what it was designed to do.
It is not designed to not move for months on end whilst supporting a load near its maximum design recommended capability.

All these links provide advice recommending removing weight from single axle caravan tyres or turning them occasionally during long periods of storage.
I have given them before.........are all these organisations wrong?

http://www.tyresafe.org/images/campaigns/caravan_tyre_safety_leaflet.pdf
http://www.caravanclub.co.uk/media/1022844/caravan-tyres-and-wheels-mo.pdf
Camping and Caravan club
http://www.caravanguard.co.uk/news/check-your-caravans-tyres-2893/

 

[Lutz]

So, where does the 50% figure come from?

......the actual load the tyre is carrying when used in every day use as opposed to the maximum plated load of axle.
Agreed your figures would be correct if your cars were fully loaded all the time..... most cars are used nowhere near their actual maximum axle loads.

But the caravan isn't stored at anything like its MTPLM, either, but probably closer to its MIRO, which in my case is 400kg less and about the same as the car's payload. Therefore the percentage will be lower, but remain roughly the same for car and caravan when based on actual weight in service instead of max. plated weight.
Besides, leaving static conditions aside for a minute, the dynamic loads on the car's tyres are probably higher than those on the caravan. On the whole, I know that I certainly accelerate and often brake harder and go round corners quicker when driving solo than when towing the caravan.
No harm would be done by following the advice that your sources publish but I suspect that it was simply a case of someone thinking it would be a good idea and all the others jumped on the bandwagon without further critical examination, rather like the 85% weight ratio recommendation that nobody knows how it came to be 85% and not some other figure and yet various sources publish the same advice..

 

[colin-yorkshire1]

we seem to be talking about two separate things here resting the suspension and saving the tyres, although resting the suspension with the wheels off the ground would conceivably assit both.
this is what I do and have not heard any evidence to suggest it is a waste of time, so I will continue to do it, past experience leads me to believe this is the correct way.
Lutz I did not say that out of shape tyres caused the suspension to colapse. age and conditions did that although the tyres would not help matters, it could have been a contributing factor. it is a bit like the question do you need to balance trailer wheels some say no while others would say yes when asked why one of the reasons given would be long term damage to the suspension, if out of balance wheels could cause problems what would out of shape ones do as these must by defenition be out of balance, surely the best way is not to let them get out of shape (flat spot ) in the first place, prevention is better than any cure.
on the subject of wether dealers check the vehicle wheels on a PDI is quite enlightening, surely trying to suggest that a dealer who has had a vehicle stood in one place for months and the does not check the wheels before the customer takes it away is a little absurd. "sorry"
your comment in the last post, would seem to contradict my own findings in that rather than there being less weight in the van during storage mine has a lot more, as during the winter it becomes a convienient dry holding shed

everything that is in the van stays in the van summer and winter (except clothes) but during storage it also contains all the items usually carried in the car as well, together with the stuff we dont take away like both awnings annex ect, so not only it is nearer the MTPLM it is probably well over it,but then this does not matter as it sits on axel stands,
regarding "Sir Dustydog's" comments "

If a suspension system cannot support the vehicle weight for the
expected life expectancy then the design must have been flawed in the
first place!

it would be hard to define life expectancy considering all the variables involved, ammout of weight length of time care and mantinance ammount of abuse ect, seening as how most trailers use indespension units something must be right but there is no doubt that a say a boat trailer that is regulary dunked in sea water then left for 4 months with a near maximun capacity sat on it will invariably not last as long as say a camping trailer, that is kept dry and stored empty, the very fact that manufactures like Alko recommend resting the suspension when not in use must mean something, surely.
The original Issigonis mini used rubber suspension" yes it did but theres a whole load of difference between a solid rubber doughnut weighing 2kg and the thin 8in long rubber strips used in indespension units, I also seem to remember that one of the faults regulary suffered by minis was collapsed suspension, not the dough nut but just about everything else connected to it,
edit.
ps, it may also be worthwhile to point out that competion minis used a beam axel and coil overs instead of subframes and rubber doughnuts.

 

[Lutz]

Lutz I did not say that out of shape tyres caused the suspension to colapse. age and conditions did that although the tyres would not help matters, it could have been a contributing factor. it is a bit like the question do you need to balance trailer wheels some say no while others would say yes when asked why one of the reasons given would be long term damage to the suspension, if out of balance wheels could cause problems what would out of shape ones do as these must by defenition be out of balance, surely the best way is not to let them get out of shape (flat spot ) in the first place, prevention is better than any cure.
on the subject of wether dealers check the vehicle wheels on a PDI is quite enlightening, surely trying to suggest that a dealer who has had a vehicle stood in one place for months and the does not check the wheels before the customer takes it away is a little absurd. "sorry"
your comment in the last post, would seem to contradict my own findings in that rather than there being less weight in the van during storage mine has a lot more, as during the winter it becomes a convienient dry holding shed

everything that is in the van stays in the van summer and winter (except clothes) but during storage it also contains all the items usually carried in the car as well, together with the stuff we dont take away like both awnings annex ect, so not only it is nearer the MTPLM it is probably well over it,but then this does not matter as it sits on axel stands,

Neither out-of round tyres nor unbalanced tyres should have the slightest effect on the durability of the suspension. (Ensuring that the tyres are properly balanced is for a totally different reason). I have towed my caravan for several hundred miles on gravel roads where the loads on the suspension were a lot greater than what any imperfection in the tyre can contribute, and the suspension didn't suffer as a result.
I would suggest that the dealers' check of wheel and tyre equipment during the course of PDI is limited to ensuring that the tyres are properly inflated. A dealer once sold me a used car with tyres that didn't have an appropriate speed rating and he didn't pick the fault up during his own warranty check although he willingly reshod the car with a new set of tyres at his own cost after I pointed it out.
Yes, I did mention that my caravan isn't stored at full MTPLM, but really the difference between actual weight and max. is hardly going to be much more than about 20%. In view of the fact that the margin of safety on tyres must be well in excess of that figure in order to cope with much higher dynamic forces encountered in service, the tyre will hardly notice a variation of only 20%.

 

[colin-yorkshire1]

hi Lutz,
On this aspect i think we may have to agree to disagree

and move on, obviously lifes experience changes the way individuals see things, and from that one forms ones own oppinions and practices.
It would seem that your experience is well different from mine, in so much as to have views at opposite ends of the spectrum.
I could demonstrate the reason for this but there is little point as it would not change anything, it is sufficient to say that the best practice is the one that suits oneself,
all I will say on the subject is that my van is now 7years old and when it comes out of hibernation in the spring it will be on its 3rd set of tyres, and the car is parked outside sat on a set of winter boots. just in case.
colin

 

[Gafferbill]

I have yet to experience a tyre blow out with a single axle caravan.......unlike some

If the OP is still following his post perhaps he could let us know what he has decided to do!

Update that might be of interest..............

I also have a 750kgs general purpose trailer that is stored at home standing on its tyres which are on gravel.
Every 3-4 weeks I lift the trailer by hand to rotate the wheels for reasons already mentioned.
Each tyre only supports 115kgs (max load 440kgs) when the trailer is unladen so I do not bother to put the trailer on axle stands.
This weekend I discovered one of the tyres was flat which puzzled me as the trailer has not moved for 6 months.
On trying to inflate the tyre I discovered that the rubber of the tyre valve was cracked and perished and leaking.
The valve on the other wheel was the same (although not leaking), as was the valve on the spare that has spent most of its time in a dark garage loft.
I admit to the wheels,tyres and valves being 9 years old..........the tyres still look as new and are not cracking or deformed in any way.

I am glad I discovered the state of these valves while the trailer was not in use ........ I have never experienced a problem with tyre valves before.

 

[philspot1]

Back to the original question: I have a pair of tyresavers, but for a particular purpose. My van is stored close to a garden wall on the right, nose in towards a garage door, with a hitchpost 3" in front of it. I first manoevered the van (with mover) to get the slightly diagonal angle required to avoid the battery box door fouling the garden wall when opened, (took several trial runs), but wondered how to make it easy to return exactly to this position after every trip. Once it was satisfactorily hitched on, I jacked the van up and slid the tyresavers under, then marked their position, removed the van, drilled and plugged the drive. Now the tyresavers are screwed into position, I just have to raise the jockey wheel high and motormove forwards so that both wheels climb into their cradles, then lower the jockey and the hitch clicks into place, ready for the hitchlock. If the mover hesitates at the climb over the lip (I have now added a "mini-ramp" in front of each to avoid this), I can always swing van L or R, so doing one wheel at a time - and it's still spot on!!

 

[brian_c]

Well what a reaction! I never imagined my post could generate such a vast amount of intrest.
Thank you everyone who has taken the time to post replies and comments.
The food for thought regarding all the points made and advice is quite overwhelming I must first admit to being rather layed back with my tyres. I do check them before each trip for signs of damage correct pressure etc. Also I inflate my car tyres to the recommended full load pressure before towing then reduce them after arrival at site.
I don't now intend to get the Tyre savers I am going to follow one of the pieces of advice with regard to increasing my Van Tyres just short of the design rating during the two / three months when the van is inactive. January is the anniversary of the annual service and being midway between my vans usual lay up period at least it will be moved if only a short distance so the wheels will get a bit of a turning but perhaps pot luck where they rest when returning to the side of the house. I am in the future going to look into axle supports, to try and follow the advice regarding resting the suspension coupled with this perhaps I will remove the wheels to the garage and follow the published advice re-their storage.
Again I would like to thank everyone for your valued contributions to my post.
Best Regards Brian