Nissan QashQai Forums

Hi guys,

I've been trying various tyre pressures to get the 'optimum ride' out of my QQ Tekna with 19" wheels, the recommended pressures are 33 psi front and 30 psi rear (which I think pretty much gives the best results), however using the display screen I have to inflate the tyres by pretty much 2lbs psi lower in order for them to reach the desired pressure when the tyres get to their working temperature after a few miles.

I've always been led to believe that tyre pressures should always be checked from cold, however if I set them at 33 psi & 30 psi after a few miles they invariably end up as being 35-36 psi and 32-33 psi respectively?

Which in your opinion is the correct method, do I inflate them to 33 psi & 30 psi, or under-inflate them by a couple of pounds so that they will (after a few miles) match the target tyre pressures on the display screen?

When I first got mine I dropped then by 4psi because I don't carry anybody and its makes a better ride .....the harder the tyres the better mpg and yes I was always taught check when cold.

Baker69, please take a look at this attachment it might be of some help hopefully ! - Dave

The conditions in which you set your vehicle's tyre pressures are almost as important as the fact that you do set it. "Cold" as specified by the manufacturer assumes the ambient temperature to be about 70°F (21.1°C).

The rule of thumb is for every 10°F change in air temperature, tyre pressures will change about 3% (up with higher temperatures and down with lower). This means that light-duty, standard-pressure tyres (typically inflated to 30-50 psi) used in applications on cars, vans and light trucks will change by about 1 psi.

Additionally (as Baker69 notes), when running your tyres, the air pressure in all of them is likely to go up about 1 psi during every 5 minutes of use for the first 20 minutes of operation. Then the air pressure stabilises, typically gaining no more than 1 psi of additional pressure during the next 20 minutes. This is your hot tyre pressure. When the tyres cool down, they return to the pressure set at the original ambient temperature. If you've tried to "compensate" for the higher running pressure by underinflating them, then their pressure will be too low once they cool down.

Manufacturers know the tyre pressure will increase during use, but by how much is dependent on several variants (temperature, length of journey, etc), so your vehicle's recommended tyre pressure is its cold tyre inflation pressure. It should be checked in the morning before you drive more than a few miles, or before rising ambient temperatures or the sun's radiant heat affects it (fat chance in the UK though).

The upshot of all this is that the tyre pressure readout can be a bit misleading for people who don't realise the pressures displayed should be a little higher than the "recommended figure", unless they look at it as soon as the vehicle is under way. It's useful for seeing if a tyre is drastically under- or over-inflated, however.

Set cold, simple as that.

My car reported a low tyre pressure last Friday - the display showed the left front down 2psi. Curiously the rear two were also down 2psi but it only highlighted the front one. However I didn't get the first illustrated screen or the [Check Cold Tyre] message...

david sunderland wrote: ↑Fri Sep 22, 2017 12:53 pm When I first got mine I dropped then by 4psi because I don't carry anybody and its makes a better ride .....the harder the tyres the better mpg and yes I was always taught check when cold.

Hi David,

I've always understood that under-inflated tyres worsen fuel economy???

Thanks for the replies and information guys , very useful and informative.

I think the general consensus is to set the tyre pressures cold (to 33/30 in my case) and expect these to rise by anything up to 3 psi as the tyres warm up. As Hound said the ambient temperature affects it as well so now the temps dropping a bit I expect the variance to be a bit less and expect them to increase by no more than 2 psi per wheel.

For me I have found that 33/30 gives the best comfort on the 19's (given the right road surface), as the rear tyre pressures go up to 32-33 psi you can tell a slight difference. If I set them to 28-29 psi in order for them to increase to 30 psi when they get warm I find the ride too hard.

gloucester wrote: ↑Fri Sep 22, 2017 5:41 pm My car reported a low tyre pressure last Friday - the display showed the left front down 2psi. Curiously the rear two were also down 2psi but it only highlighted the front one. However I didn't get the first illustrated screen or the [Check Cold Tyre] message...

I had a tyre pressure warning as well recently, got out and it all looked ok and the same as the other side. However when I eventually did check using a real meter, it was indeed down by a couple of psi, so the system must work.

Baker69 wrote: ↑Mon Sep 25, 2017 12:51 pm

david sunderland wrote: ↑Fri Sep 22, 2017 12:53 pm When I first got mine I dropped then by 4psi because I don't carry anybody and its makes a better ride .....the harder the tyres the better mpg and yes I was always taught check when cold.

Hi David,

I've always understood that under-inflated tyres worsen fuel economy???

Yes its true .. But iam happy at ave 35 mpg on the runs I do.... maufac do over-inflate to give better mpg fig.....if I went anywhere I would set to correct psi but due to family reasons can't go anywhere but around doors or I would have got a diesel....david