I'm sorry to bring this subject up yet again but wanted to run it by you experts.
My single axle Swift Cornice 17B (2002) caravan tyres are 175R14 C 99/98R so light truck/commercial. I think I've seen that the max pressure is 65psi cold for them but am I correct with this?
My van MTPLM is 1550kg and I think the max load per tyre is 775kg so 1550kg total. MIRO is 1273kg.
When I use the Tyresafe guide it shows 65psi but says: "Tyre loads exceed the maximum recommended load*, but are still within the maximum permissible load". Is this safe for me to tow?
Also, when I started to inflate my tyres it seemed to take ages to get from 50 to 60psi. I gave up at about 56psi as was worried that I was over-inflating. Any advice would be greatly appreciated.
While legal and probably safe to tow, I would not recommend those tyres for that van. I would suggest a tyre with a 100 load index to be safe. Having a tyre that is loaded so close to it's maximum load makes any sort of damage to the tyre much more likely to result in failure, as do high temperatures. With such a high load on those tyres I would inflate them to the max pressure marked on the tyre.
Your tyres are rated to carry your caravan weight OK. My caravan quotes 65psi but I have never gone above 62 psi as I find higher pressure tends to make it bouncy.
Sorry, but I would change the tyres: all three, but it is your decision.
Your present tyres, if rated at 98, (or 750 Kgs/tyre), are at the maximum load, hence the high tyre pressure, with no extra safety.
Your van has an MTPLM of 1,550 Kgs, and it is advisable to add 10% as a safety factor, so that brings it to 1,705 Kgs. Divide by 2 gives a load per tye of 852.5 kgs/tyre.
I would go with a minimum loading of 102 i.e. 850 Kgs per tyre.
This would reduce the tyre pressure to 59.26 psi, but it is your choice.
There is another factor which the OP's original calculations overlook, which is weight distribution across the axle! My van, as I'm sure is common to many vans is inherently heavier one side than the other (no doubt due to kitchen, shower and door all being on same side), by 10's of Kgs, so the total weight distribution is NOT a simple 50:50 split! That would likely push one tyre to being overloaded, rather than just up to it's limit!
The thought of a tyre both up to it's weight and pressure limit is not a comfortable one for me! I certainly wouldn't be running it under recommended pressure as the extra heat generated by sidewall flexing would encourage failure more than the high pressure would. I'd also diligently replace them regularly, probably more frequently than the industry recommended every 5 years.
The suggestion of going for a higher load rating may not be an option, a quick check (a more thorough check may prove more fruitful) suggests that the highest load rating on offer for that tyre size is 99 (775Kg)!
All things considered, I think I'd personally only be happy towing a near empty van close to it's MIRO, rather than it's MTPLM, unless I could find higher load rated tyres.
I've little doubt, the bureaucratic needs would be satisfied by the 99 load rating and 65psi, but I just don't like pushing safety to the limits.
Oh blimey Monty, I was borderline travelling slowly to Norfolk but I'll have to seriously think about it now. I don't think we have a very high amount of stuff in the van that would add much weight to the 1273 MIRO to be honest so it may "only" be more like 1373 but I'd have to weigh everything!
Quote: Originally posted by keeper1405 on 21/7/2021
Sorry Monty, do you recommend running tyres at 65psi then rather than 60 - 62ish?
Cheers
I'd go with the manufacturers (tyre and/or caravan manufacturer) recommended pressure, which is based on loading of tyre. 1 or 2 psi is probably neither here or there as typical variation from cool to hot conditions anyway.
If you are worried go for 185/75 R14 C 102/100R TL, this gives you the increased load rating.
Personally I would not worry unduly for two reasons, the speed rating of your current tyres is far higher than your towing speeds so lateral forces etc will be within the performance envelope of the tyre.
The issue with inflating above 50psi taking ages is due to your pump. A lot of pumps are only rated up to 50psi and just leak after that so you can pump all day but not get any inflation.
If you look on the original brochure data for the caravan the present tyres you have fitted are the Swift specified size and loading when new, and pressure should be 62 psi.
Thanks very much Phishing & Birdman. I would have to check whether the 185/75 tyres would fit under my arches but thanks and also for inflation advice.
Yes 62psi sounds good to me. I ran this by the guy who did a full service to my caravan a few months ago. He said 65psi would be too high as tyres can increase by 10psi when travelling. He suggested 50-55psi!! I'm think I'm going to stick to 62 though...
Just a note that I weighed all my contents which come to APPROX 65Kg making my total weight of MIRO (1273) + contents = 1338Kg
I guess it must be down to the heavier weights of modern caravans, but the manufacturer's recommended pressure for my caravan tyres (175 X 13) is only 36psi. 65psi sounds so really high to me, similar to what I used to put in bus tyres, and they were huge in comparison!
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Topic: Tyre Pressure (yes I know...)!
via mobile 21/7/2021 at 3:08pm
