Tyre Pressures

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Dashnine
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Tyre Pressures

Post by Dashnine » Sat Jul 27, 2019 3:06 pm

Having just returned from a max load camping trip, the tyres had to be pumped up to 40psi Front, 50psi Rear. These seem to be really high pressures (50psi was the max tyre pressure printed on the sidewalk of my last DS Contis) compared to the Normal load pressures of 37psi Front, 32psi Rear.

However, the ‘Normal’ pressures are for “Comfort setting (up to 3 occupants and 1 luggage item)” which then seems low, more than three people and a bit of shopping and you have to pump the tyres up.

Can you could pick pressures somewhere in between if you regularly drive 4 up for example, but them the TPMS system will moan at you. There just seems a huge extreme between the two settings. Thoughts?
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Re: Tyre Pressures

Post by Pauld » Sat Jul 27, 2019 5:43 pm

I tow a coachman 575 VIP caravan 1600kg + and I just leave mine set to normal load, saying that the car only has two adults up front two medium sized dogs on the back seat and the full of clothes/food etc. can't say I've ever had any problems the DS is pretty robust


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Re: Tyre Pressures

Post by roadster » Sun Jul 28, 2019 9:09 am

Have you actually had any warnings when running pressures which are not close to target settings ( high or low ones)? One of my tyres was several psi low on delivery but it didn't trigger any alert. I suspect the permissible range is a bit wider than it would be for an ordinary car given that off-roaders might want to drop tyre pressures to suit conditions. Perhaps warnings are only triggered if the is a sudden drop in pressure on one corner only.
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Re: Tyre Pressures

Post by Dashnine » Sun Jul 28, 2019 9:22 am

roadster wrote:
Sun Jul 28, 2019 9:09 am
Have you actually had any warnings when running pressures which are not close to target settings ( high or low ones)? One of my tyres was several psi low on delivery but it didn't trigger any alert. I suspect the permissible range is a bit wider than it would be for an ordinary car given that off-roaders might want to drop tyre pressures to suit conditions. Perhaps warnings are only triggered if the is a sudden drop in pressure on one corner only.
Yes when setting the high pressures I set the load setting first and you get a warning diagram with the low pressure corners highlighted. As I remember the highlighting disappeared at about 3psi from the correct pressure. No warning of high pressure when resetting to low load however.
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Re: Tyre Pressures

Post by EYR » Sun Jul 28, 2019 10:14 am

Right or wrong, but my thoughts from another thread.

"The only place to get my figures from is the V5C and the GVW for the seven seater is as stated at 2640kg, the Mass in Service for my seven seater states 1954kg and that figure includes the driver, so that leaves just under 700kg payload.
So going by the above figures minus the driver it comes out at 410kg with approx 275kg to play with, so no I would not inflate to heavy load but choose a halfway figure.

LR recommend my towing a caravan to inflate to heavy load but there is only two of us, an 80kg towball (OK its rear of the axle but still way within limit) weight, plus 60kg on the back seat, that is no more than 4 people in the car so I inflate a 'little' (36psi all round on 18" tyres) to a midpoint between light and heavy. Even with 36psi all round it does not complain in the light load setting when towing.

No definitive answer really and in my circumstances the Caravan Club and LR disagree, but it doesn't take much to disagree with LR anyway :roll: "


Just returned from a 10 week European tour with the caravan, 3500 miles with an in between pressure and no warning from the TPS system that was set at low. No hiccups and stability spot on.
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Re: Tyre Pressures

Post by Dashnine » Sun Aug 18, 2019 11:49 am

Pumping up the tyres again as we’re three up with luggage and with bikes on the tow bar. Still find it somewhat alarming that normal load setting is 50psi on the rear (40 on the front), which is the max inflation pressure for the Conti tyres.

Accepting there’s a safety margin, and that the tyres gain a few psi when in use, but is it such a great idea to have the normal setting (the ‘comfort’ setting is 37/32) right at the max tyre pressure?

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Re: Tyre Pressures

Post by roadster » Mon Aug 19, 2019 9:29 am

I suspect that higher recommended pressures on low profile tyres are aimed at preventing rim or sidewall damage if you hit a rock or a kerb. It is standard practice to offer larger wheels only with lower profile tyres in order to keep the rolling radius about the same and therefore match gearing and related emissions figures without mechanical changes or re-homologation.
For some strange reason bigger wheels with low profile tyres are seen as an "up-market" feature that manufacturers insist on putting on top-spec models. Having had a sidewall destroyed by hitting a protruding concrete lump at 70 mph on a low profile set-up (45%) I know how vulnerable they can be and I was very lucky that the wheel was not damaged too.
Because the tyre is also wider the static deflection under extra load shouldn't be any greater but even if the extra deflection is the same there is far less margin when hitting something solid.
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