I understand that a specific pressure is needed to achieve the rated Load Index - but I don't see how the rating can exceed the Load Index with the pressure exceeding the maximum permitted - surely Maximums are just that, a maximum?
So am I, this points to the industry's lack of conviction in the validity of their "load index" in camper type applications.
Much like the industries extra 10% margin on their own load index rating for caravan applications.
Not that they are alone in not trusting their standards, neither do I trust them, in particular with budget branded tyres.
That based on direct experience with all three tyres supplied on a new caravan, that at three years and one not even used!
They can't, you're right. Its the same argument as to why bother having even a C though? Standard 'car' tyres have one load/pressure set, C tyres behave/are rated to a different set of pressures/loads , CP tyres are rated to a different set of loads & pressures again.
The use of "C" for commercial vehicle tyres (and "XL" for Extra Load tyres) goes back before the advent of Load Index and in reality are superfluous since the introduction of Load Index - I'd suggest that "CP" is just a marketing exercise, but then I'm cynical!
Our twin axle Lunar had standard car tyres and the tyres were within the load rating. Different story with our current caravan due to load rating.This article opens some interesting pointers, eg CP marked tyres, pressures and cracking.
Caravan, Motorhome & Campervan Tyres | National
National stocks motorhome, campervan and caravan tyres from all the major brands. Home fitting service available. Check the full stock today.www.national.co.uk
On the whole I have always used Maxiss Trailermaxx tyres which are allegedly specifically for caravan / trailer use.
Looking back on the posts here I wonder if those buying caravan tyres really give much thought to the specific application.
Here’s a good description by Goodyear of how tyres of the same size can have significantly different load ratings. Hence why it is vital to only fit the caravan with tyres of the correct load index. It’s Goodyear North America and Uses pounds and tires, but the principle is well explained.
www.goodyear.com
What are C-Type Tires? | Goodyear Tires
Are you driving a cargo van? If so, you may be driving on the wrong type of tires. C-Type tires are made for carrying heavy loads in cargo vans. Learn more how the C-Type tire could be the better option for you.
www.goodyear.com
I believe it's the US tire industry that invents all these meaningless* codes - unlike tyres sold in Europe which comply with ETRTO standards.Here’s a good description by Goodyear of how tyres of the same size can have significantly different load ratings. Hence why it is vital to only fit the caravan with tyres of the correct load index. It’s Goodyear North America and Uses pounds and tires, but the principle is well explained.
What are C-Type Tires? | Goodyear Tires
Are you driving a cargo van? If so, you may be driving on the wrong type of tires. C-Type tires are made for carrying heavy loads in cargo vans. Learn more how the C-Type tire could be the better option for you.
* meaningless in the sense that there's no defined standard so any tire maker can claim whatever they want - eg M+S has no standard but the European 3PMSF has.
I only put tge link in as it is useful in describing what C means in regards to tyres, I didn’t expect it to elicit an anti American response. As I said the principles are the same whether buying a tyre in Britain, Europe or North America, although spelling and units differ.
The principles aren't the same - tyres sold in Europe must have Load Index, which is absolute in my view - in North America buyers have to rely on coded marketing descriptions, eg LT=Light Truck, C=Commercial, XL=Extra Load - the situation is clouded as most tyre manufacturers use both methods to enable their tyres to be sold in both markets.
Crikey Clive never mind Uncle Sam I‘m still relearning U.K.🤪🤪.Here’s a good description by Goodyear of how tyres of the same size can have significantly different load ratings. Hence why it is vital to only fit the caravan with tyres of the correct load index. It’s Goodyear North America and Uses pounds and tires, but the principle is well explained.
What are C-Type Tires? | Goodyear Tires
Are you driving a cargo van? If so, you may be driving on the wrong type of tires. C-Type tires are made for carrying heavy loads in cargo vans. Learn more how the C-Type tire could be the better option for you.
Never in my 45 years of towing have I heard of the CP thing. But good practice always said use tyres specifically designed and built for caravan/ trailers.
I understand your views but you are reading too much into my link. All it was intended to demonstrate is that for the same size tyre it can have different load indices. And that principle holds good in Europe as well as NA.
I’ve fitted Hankook Vantra LT C rated tyres to caravans. They aren’t trailer specific but the LI was more than adequate for the duty .
I’ve also fitted GT Radial and Kenda trailer specific tyres with the FRT marking on the side wall.
I have never come across CP tyres and find it a bit difficult to understand the logic. Surely pressure affects load carrying ability on all tyres.
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Yes it does, but the CP moniker is just a way of telling us that this tyre has features that allow it to run higher pressures than standard c tyres.
Some recommendations are for a 20% margin now, which I guess is difficult to get to on a regular C tyre even on a caravan, with some motorhomes on well over 2 tonne per axle on what looks like a fairly standard tyre from 10' away they're going to need to be different than the regular C tyres.
Some recommendations are for a 20% margin now, which I guess is difficult to get to on a regular C tyre even on a caravan, with some motorhomes on well over 2 tonne per axle on what looks like a fairly standard tyre from 10' away they're going to need to be different than the regular C tyres.
Or do they just need higher Load Index tyres?
It seems to me that we simply don't need both Load Index and C/CP - since Load Index is mandatory and precise it's time to ignore C/CP - in my opinion.
Yes but you could say that about anything where certain styles of things are grouped together and also have a definite numeric value attached to them. Where the value of the C or CP lies is that if you buy a C/CP tyre in the right size you know it will have the minimum load index required for your vehicle at the right pressure as long as your caravan company didn't go out of their way to find one with a couple of points higher, and I don't know of any examples where this has happened. You don't therefore need to know what the load index is or should be. I'm not advocating people don't check it, but it's reassuring I guess.
It's a solution to a problem that didn't exist, at least didn't exist in Europe - Load Index works just fine, easy to find the maximum kg load and compare that with the plated maximum axle weight - the C/CP system requires the tyre size to be correct but that's often difficult to determine other than using the existing size fitted.
I must admit that when we change tyres as long as the load index is within spec that is all that counts as all this C stuff has confused me.
What about pressure? You also need the right PSI. Running lower PSIs will result in squirm or maybe just 'different' handling as your suspension would be set to work with rock hard tyres. Worked example, what pressure should this tyre be run at? As you can see its got a good high load rating for a 195r14c.
KENDA Tyre 195 R 14C,108/106 N, TL, KR101 MasterTrail 3G, M+S
When I had a Pajero SWB for off roading I changed the standard 30 inch tyres for BFG M/T 33 inch which weren’t an OEM size. but still rated for 15 inch wheels. Spent time calculating what pressure to run them at for A road and M way use based on loaded weight, then did a practical test of driving for 30 minutes on M way at 60 mph and then checking pressures to see if I’d obtained a 4-5 psi increase. Mind you with those tyres and suspension lift it wasn’t the sharpest of drives.
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Can't possibly state the pressure unless you know the recommendation for the vehicle it's fitted to as standard - or - do a basic calculation based on the plated axle load, the tyre maximum load and tyre maximum pressure.
However, the basic calculation can give a low reading - the calculated figure for my 1495 kg MTPLM caravan with 185 R14C 102 tyres is 45 psi while Lunar specify 65 psi, the maximum for the tyre - having tried them at 45 psi, they wear noticeably on the shoulders, so I reverted to 65 psi.
That 4-5 psi "rule" is very useful - it seems to be commonly used in Australia but rarely in the rest of the world - you're the first person I've come across who's even heard of it.
SKB has explained something I never knew nor have I seen regarding C/CP. I have been ignorant of this fact for 45 years. The reality is all my caravan tyres have been correctly chosen and fit for purpose. There has been discussion on the high pressures used on SAs. It seems to me the tyre maker designs the tyre for a range of pressures. So long as you are within that “ cold” pressure no problem.
There have been previous posts mentioning it, I think Hutch may be aware of it, as he’s a well traveled bloke.
I've used it to adjust the pressures on my Touareg - the VW figure for part load is 2.3 bar front & rear - the fronts go up to 2.5 bar in use so a 0.2 bar increase (3 psi) which suggests dropping the cold pressure but I won't go below the manufacturer's recommendation - on the other hand the rears go up a lot more in use so I now run them at 2.5 bar cold and they increase by 0.2 bar, the same as the fronts.
That wasn't where I was going - the tyres are a real world example of where CP labelling would be useful for me. I considered buying these tyres as my single axle Hymer has a high max load and so running the stock tyres won't get you a 10% margin, these offer much higher loads... but at much higher PSI. If I run them at the caravan's recommended PSI in order to retain the handling, I wouldn't actually increase the load, so the whole excercise would be pointless. However I had to go find the max PSI (not easy with Kenda) in order to then know what I would get at 65.
If it had been labelled CP rather than C, I wouldn't have bothered as I would already known the answer.
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