If a tyre has the load markings "90/88" T after the tyre size surely it cannot have two load ratings of 560kg and also 600kg? Why the two figures with a slash in between them? I am aware of the speed rating T.
Load rating question?
- Thread starter Buckman
- Start date
They are used for vehicles like commercial vans that have two wheels on each end of the axle, and fir vehicles that have only a single wheel on each hub. I believe the lower is for twin wheel set up.
The marking is off a twin axle caravan with a MTPLM 2000kg. Seems at 88 it has a safety margin of "240kg? If the 90 is taken then adequate safety margin of 400kg.
Well even 240 kg is more than the advised 10% margin.
I had a van upgraded by Bailey and it’s MTPLM was 1400 kg and combined tyre load index 1420 kg. They said nothing about upgrading tyres.
Exactly right - so for caravanners only the first, higher figure is relevant - that's for single or twin axle caravans.
In the OP's example, regard them as 90T with a 600 kg rating - twin axles need a higher margin than single axles as the two axles may not be loaded evenly..
A load rating of 600kg makes me feel more comfortable. Highly unlikely we would ever get anywhere near 10% or 60kg of the safety margin. LOL!
Don’t forget though that the tyre itself will have a margin for load and speed built into it by the manufacturer. We don’t put extra high load margin tyres on our cars do we. Although some tyres sizes are offfered at standard or XL.
No, you have understood Otherclive's reply wrong. He was referring to twin wheels on one axle, not twin axles.
I've understood it just fine - the lower rating refers to twin wheels on one axle - but the extra margin is used with twin axle caravans.
Tyre rating explained two LI.
Australian but US and U.K. are the same. It comes down to safety margins.
Australian but US and U.K. are the same. It comes down to safety margins.
IMO, you can rest even easier in that there is also a hidden, far from insignificant margin.
In real life using a "T" speed rated tyre, i.e. 118 mph, twice the legal speed the caravan can go at on any road, massively increases the actual safety factor.
The loading credited is determined by the energy being pumped into the tyre by the flexing and various frictions and ambient involved, here carrying 600 kg at 118 mph.
So whilst they don't grant you a higher load carrying capacity if you don't go as fast as the rated speed 118 mph, or you use it in the typically lower ambient of the UK, the physical facts are the tyre must be way less "stressed" than it is specified to cope with.
To me an engineer, the facts of what our caravan's actually inflict on our tyres make it hard to understand the UK tyre retail trade body recommending to put yet another blanket 10% margin onto what the tyre makers have determined for a very much more arduous duty than we face? ( it certainly transfers to me their lack of confidence in their wares!)
I could better understand it if specifying it just for say "L" [75 mph] tyres, but not a blanket figure even here for 118 mph tyres working only at 60 mph and typically used mostly even slower.
My 1900 kg German van came shod with 109/107S, so 1030kgs at 112 mph, they risk just an 8.4% margin, but it was with Goodyear tyres.
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Thank you for an excellent explanation and it has certainly enlighten me and increased my limited knowledge base. Never thought about it regarding speed, stress etc. When it is time to change the tyres we will certainly be looking at mid range with the determining factor the load rating.
A bit like the 85% guide that’s really what the 10% is for caravan tyres, so Your 8.4% is in the ball park. When I upgraded a Bailey S5 Bordeaux to 1400 kg MTPLM. the OEM tyres combined load rating was 1420 kg. So when I decided to upgrade the tyres the dealer service manager told me that they would be so stiff that they would shake the fittings off the walls. I pointed out to him that the equivalent van in the next range up had the same tyres that I was planning to fit and it’s MTPLM was only 1460 kg. So did he really think that the 60 kg lower weight would make that difference. He then tried to tell me that my OEM tyres ran at 42psi whereas the plannned upgraded tyres ran at 55psi and that’s why they could damage the van. Don’t think he’d heard about adjustment of pressure for load when required.
Tyre pressure v LI is one example I’ve not checked this one but when I was doing some calcs I used one from US Tire Rack. But the results should be the same.............???
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So what do you set your tyre pressures at, to carry the real load or carry the 10% or whatever extra you have fitted?
Undoubtedly running at pressures to potentially carry some extra, but non existing loading, will be more punishing to the van than running at the right pressure.
I simply use the tyres and pressures Hymer state in the manual, but it is IMO very harsh.
Undoubtedly running at pressures to potentially carry some extra, but non existing loading, will be more punishing to the van than running at the right pressure.
I simply use the tyres and pressures Hymer state in the manual, but it is IMO very harsh.
So do I, as my current van is fitted with identical tyres to those supplied by Swift and I run at the pressure stated in the handbook. But 59 psi does make fir a harsh ride too.
I was referring to a previous Bailey where I upgraded the tyres after a payload upgrade. There are websites which give the linear formula for running tyres at a pressure matched more to their actual load rather than max load being assumed all of the time. No different to car although for caravans the extra load carried as payload is proportionally less than a car solo then fully loaded with five people and luggage.
Like JTQ, I cannot understand the caravan industries approach to tyre ratings. Its as if they don't trust what the tyre manufacturers stamp on their products. Or more likely they expect caravanners to overload their caravans!
We do know how difficult a caravan can be to tow compared to a garden trailer, and I wouldn't want to belittle the job the tyres have to do, but they don't have to withstand the power of an engine being delivered through them, and neither do they have to withstand the additional turning forces of the steering, so compared to a life fitted to a car they are not stressed as much. And they should not be running at such high top speeds. Even braking forces will be less dynamic than those on a car.
Caravan tyres do on average have to carry more weight than a car tyre, but that is why they have load ratings.
Just from a pure engineering perspective, Its inconceivable that a tyre manufacturer could get away with a product that cannot carry its rated load under normal conditions. Just as JTQ has suggested, the loads inflicted on a tyre when underway are massively different to the static weight load, so the tyres do have to be much tougher than you might imagine.
Where a tyre is perhaps more sensitive that is where some tyres have restrictive speed limits, such as farm tractor tyres.
It would be both foolish and illegal to fit a tyres with a lowercomined load margin than MAM of a vehicle or trailer, there should be no need to add and additional safety margin over and above what the tyre manufacturers have already designed into the tyre.
There is of course no practical downside to choosing tyres with larger load rating than necessary, apart from perhaps a less compliant ride, and there might be a cost difference.
We do know how difficult a caravan can be to tow compared to a garden trailer, and I wouldn't want to belittle the job the tyres have to do, but they don't have to withstand the power of an engine being delivered through them, and neither do they have to withstand the additional turning forces of the steering, so compared to a life fitted to a car they are not stressed as much. And they should not be running at such high top speeds. Even braking forces will be less dynamic than those on a car.
Caravan tyres do on average have to carry more weight than a car tyre, but that is why they have load ratings.
Just from a pure engineering perspective, Its inconceivable that a tyre manufacturer could get away with a product that cannot carry its rated load under normal conditions. Just as JTQ has suggested, the loads inflicted on a tyre when underway are massively different to the static weight load, so the tyres do have to be much tougher than you might imagine.
Where a tyre is perhaps more sensitive that is where some tyres have restrictive speed limits, such as farm tractor tyres.
It would be both foolish and illegal to fit a tyres with a lowercomined load margin than MAM of a vehicle or trailer, there should be no need to add and additional safety margin over and above what the tyre manufacturers have already designed into the tyre.
There is of course no practical downside to choosing tyres with larger load rating than necessary, apart from perhaps a less compliant ride, and there might be a cost difference.
The tyres not actually been in use rolling for extended periods, and the longer time span of their use due to wear being trivial could be factors, plus with sloppy caravan designs there could be quite asymmetric across the axle loading; these might be factors scaring the trade. It could also be they sell more expensive tyres than needed, or simply their lack of confidence in the integrity of compliance to spec across the very wide pricing range of similar claimed spec tyres.
Aging is certainly something that happens, I recall changing just one side tyre due to puncture wrecking it and was staggered by how that simple act altered its temperature rise related change in the running pressure, new tyre to old of the identical brand model etc.
Sorry, but my aging is denying me remembering with confidence which way it went!
The guess would be the new should have run hotter as the flexing would be greater than the hardened with age older tyre?
Aging is certainly something that happens, I recall changing just one side tyre due to puncture wrecking it and was staggered by how that simple act altered its temperature rise related change in the running pressure, new tyre to old of the identical brand model etc.
Sorry, but my aging is denying me remembering with confidence which way it went!
The guess would be the new should have run hotter as the flexing would be greater than the hardened with age older tyre?
The tyres not actually been in use rolling for extended periods, and the longer time span of their use due to wear being trivial, could be factors, plus with sloppy caravan designs there could be quite asymmetric across the axle loading; these might be factors scaring the trade. It could also be they sell more expensive tyres than needed, or simply their lack of confidence in the integrity of compliance to spec across the very wide pricing range of similar claimed spec tyres. I have personal experience of appallingly substandard tyres been fitted to a new caravan, all three tyres.
Aging is certainly something that happens, I recall changing just one side tyre due to puncture wrecking it and was staggered by how that simple act altered its temperature rise related change in the running pressure, new tyre to old of the identical brand model etc.
Sorry, but my aging is denying me remembering with confidence which way it went!
The guess would be the new should have run hotter as the flexing would be greater than the hardened with age older tyre?
Aging is certainly something that happens, I recall changing just one side tyre due to puncture wrecking it and was staggered by how that simple act altered its temperature rise related change in the running pressure, new tyre to old of the identical brand model etc.
Sorry, but my aging is denying me remembering with confidence which way it went!
The guess would be the new should have run hotter as the flexing would be greater than the hardened with age older tyre?
As I said, "sloppy design", almost certainly passed off by a "stylist" as opposed to a "designer" but then it is this industry where standards are IME very low, not aviation, marine etc.
I think Swift stated at one time that the maximum asymmetric load can be 20%.. i came across that when ferreting around wondering why my offside suspension had “ relaxed” leading to a new axle being required.
Bailey do sell new tyres for self fit🤔🤔. They quote specific tyres for each model but do not mention load ratings. I guess that’s in the hand book. Unlike Buckman my ta pressures are 29psi. My previous sa Pageant was 42 psi. The load ratings were not the same. I‘ve often wondered what technical discussions take place Bailey and Al-ko on both tyre and axle loadings?
Watch Bailey - and/or Prima Leisure. We took our van into the dealer for service and saw an identical van sitting there. Looked a bit odd so I squinted at the MTPLM label and the tyres. It should have had 185R14 104/102 at 58psi: it had 175/70R14 96 on it. I told the dealer who stopped the owner taking it away and they checked with Bailey. Seems Bailey's tyre specialist had specified the wrong tyres at some point and that was what they had in stock! New tyres fitted at Bailey's expense plus tyre stock disposed of.
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