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Subject Topic: Correct tyre pressures Post Reply Post New Topic
28/2/2020 at 9:19pm
 Location: Newtownards
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I have read previous posts about calculating the correct tyre pressures and I understand all that. What I need help in understanding is that for my Elddis Affinity 550 (1500 upgrade) the makers plate states a tyre pressure of 63psi but by calculation and using an online calculator the result is 54psi. Which is the correct one to use.  The tyres are rated load factor 104 max psi 65 and van mtplm 1500.



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29/2/2020 at 1:02am
 Location: Lichfield
 Outfit: Coachman Amara 450
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You haven't stated what the MTPLM was before the upgrade to 1500 kgs. However, if you have upgraded the the caravan payload with the existing tyres then the tyres may not be adequate to accommodate the extra weight so that's most likely to be the problem.


via mobile 29/2/2020 at 1:47am
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What size tyre are you using exactly?


29/2/2020 at 9:56am
 Location: Newtownards
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185R14C factory fitted by Elddis the same tyre is specified for the lower weight of 1465kg.
The weight plate for the 1465 kg specifies 61psi.
The weight plate for the 1500kg specifies 63 psi.



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29/2/2020 at 10:25am
 Location: London
 Outfit: Lunar Cosmos 524
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I would urge EXTREME caution in selecting the tyre pressure you use, especially one lower than the manufactures recommended!

When I picked my new to me s/h van up from a dealership, it handled like an absolute pig on the way home, despite having a damped coupling and ATC (which was kicking in and doing its stuff), it snaked at almost every undulation in the road (ATC stopping it getting too bad!) at speeds way below the 60mph limit. I really doubted that I had made a wise purchase!

Before writing off my new van as a bad lot, I thought I would do some basic checks like tyre pressure and nose weight (I had assumed dealer had done these correctly for me! - I was wrong!), tyre pressures were actually around 10psi below manufacturers figure (59psi), nose weight was a little over but not hugely. Pumped tyres up to recommended pressure and went for a test drive, well the difference was unbelievable dramatic, like an entirely different van! Having now covered thousands of miles over coming up 3 years I've never experienced another 'wobble', been rock solid at all sorts of speeds, roads and conditions.

There is no doubt tyre pressures can be absolutely critical to a safe and enjoyable towing experience.


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via mobile 29/2/2020 at 11:13am
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The reason I asked earlier was you said load index was 104? 185R14C are 102, max pressure 65psi at 850kg or 1700kg load per pair of tyres
Directly from this tyres pressure chart then, (as originally supplied by Tyresafe), correct pressure for 1469kg is 54psi and 1532kg is 57psi.

(As for the 'calculation' I dismissed that years ago as only suitable for getting close without going under. Reason being, air pressure doesn't carry load, volume of air carries load and the resulting pressure is arrived at by squeezing the required volume into the available space within the tyre.
Where then the error comes in calculating from two maximums is, as pressure increases, increase in load per psi added reduces due to back pressure trying to get back out!, so a graph of the results would be curved, (parabolic curve), and simply calculating from two maximums, must assume it's straight).


29/2/2020 at 2:00pm
 Location: Newtownards
 Outfit: Jaguar FPace
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My tyres are stamped 104/102 and the small print on the tyre wall states:-
“Single 900kg max at 65psi; and
Dual 850 kg max at 65psi”.

So these must be light commercial tyres that can be fitted to a rear axle in a pair.

However, I agree with Monty and I did the two sets of calculations. I have been towing last year at 60psi and all is good but thought the van was a little bit bouncy on some roads.

Thanks for the feedback.

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A. B.


via mobile 29/2/2020 at 4:00pm
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The one I quoted is light commercial, 185R14C-ommercial, the old 8plys as we once knew them.

I've got two other with 104 index but not 14inch, ones 195/70R15C, the other 195/65R16C carries 900kg but at 69psi
The 104/102 stated is for twin wheel setup
with two tyres on each side of one axel, 104 singular or 102 twin.
So if yours is 185R14C 104 then it's a tyre I don't have a chart for, I would then strongly suggest you call the manufacturer and get their opinion.


29/2/2020 at 5:17pm
 Location: Newtownards
 Outfit: Jaguar FPace
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Thanks I’ll do that. This the first time I can remember, that I have had a new van delivered with dual rated tyres, however using my Tyrepal monitor running at 60 psi shows both pressure and temp increases within accepted limits over an 80 mile run but I am fussy about safety to myself and other road users.

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A. B.


29/2/2020 at 9:42pm
 Location: Merseyside
 Outfit: Coachman 575
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Its a cost and weight thing for the manufacturers. Stronger tyres are heavier and cost more so they go with the best weight cost ratio they can get. They could reduce the pressures for their lighter vans but its far easier to just have on safe pressure for tyre wheel combo but this does make some lighter vans a bit bouncy.
The other advantage is 'flat spotting' if you use lower pressures when in storage the tyres take a set that results in a bumpy ride for the first 20 miles or so and shakes the van.

When due I will replace mine with 107 or 110 rated tyres and then run them at lower but still way over the required calculated pressures. Totally agree with post above, you can get a choppy ride if below recommended pressures.


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via mobile 01/3/2020 at 12:41pm
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Frankly I'm totally against adding extra pressure, except on horsebox tyres but thats to do with centre of gravity being 5ft of the ground!
Caravans need the easiest ride possible, not least due to all the vibration sensitive electronics they contain. That then also makes wheel balance essential, something else, still, not done out the factory, albeit they do finally fit tyres fit for purpose, but then go stick 10% extra pressure in!!!
And here's a safety warning, apart from the reduced tyre contact area with the road, when an over inflated tyre hits a bump, it and the relatively crude suspension absorb the impact. So reducing the tyres ability cannot help at all, this further reducing the contact with the ground as the suspension recoils and the van goes momentarily lighter than otherwise it might.


01/3/2020 at 2:21pm
 Location: Newtownards
 Outfit: Jaguar FPace
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The tyres are Ovation, and I have not been able to find any charts on line for the tyre.
Just so that I am clear are you recommending that in the absence of a specific chart for this tyre I should inflate to between 54-57psi rather than the higher pressure of 63psi Elddis have on the weight plate.

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A. B.



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