tyre air pressure?

animaal

Apologies in advance for a stupid question

I'm going to be making a long drive with the family and luggage, so beforehand I'm going to check the air in the tyres.

In the car's handbook, it shows the correct air presure; it shows air pressure value for the car loaded with passenger and luggage, and a different value for the car with me alone.

What situations do these refer to? If I go alone to fill the tyres, do I go for the "driver alone" measurement, because that's what's in the car at the time I'm pumping the tyres? Or do I use the "fully loaded" measurement, because that's what's going to be in the car when we make the journey?

landmarkjohn

You will want to use the fully loaded option as this is going to be the majority of your driving.

animaal

Great, thanks. I've spent years filling it half way between the two suggested values, just in case.

landmarkjohn

animaal wrote: »

Great, thanks. I've spent years filling it half way between the two suggested values, just in case.

Well that wasn't a bad strategy if you spend some of the time fully loaded. I spend most of the time in the car on my own but tend to opt for middle to higher pressure in the range to try and maximise fuel efficiency although it compromises comfort slightly by making for a harder more crashy ride.

coylemj

landmarkjohn wrote: »

I spend most of the time in the car on my own but tend to opt for middle to higher pressure in the range to try and maximise fuel efficiency although it compromises comfort slightly by making for a harder more crashy ride.

It will also lead to more wear in the centre of the tread and there will be less of the tread in contact with the road which will extend your braking distances.

corkgsxr

coylemj wrote: »

It will also lead to more wear in the centre of the tread and there will be less of the tread in contact with the road which will extend your braking distances.

There isn't a specific psi that is the perfect traction/wear.

I ran a avensis diesel at 37,37 and had perfect flat wear after 20k miles.

There's a range your fine at. It's not like it's recommended at 33 and if your 35 your centres will wear out.

shedweller

coylemj wrote: »

It will also lead to more wear in the centre of the tread and there will be less of the tread in contact with the road which will extend your braking distances.

Wrt the centre wear, that is partly true.
As for the braking distances, i have looked for years for a definite answer to that but it remains elusive. I found no test results, no youtube videos, no nothing.
I once put 100k on a set of tyres and they went away to be scrapped with the car and had an even 4mm tread depth.
Braking wasnt an issue at all either. I could brake as hard as i wanted. Tyres spent their life at 38 or so psi.

CJhaughey

All tyres are different with regards to pressures, I tend to use the manufacturers spec as a guideline and adjust them to suit, if they feel rolly then put another couple of PSI in them, if they are crashy reduce the pressure a bit.
Not all tyre sidewalls and carcasses are the same stiffness and this makes a big difference with ride quality.

Joe 90

CJhaughey wrote: »

All tyres are different with regards to pressures, I tend to use the manufacturers spec as a guideline and adjust them to suit, if they feel rolly then put another couple of PSI in them, if they are crashy reduce the pressure a bit.
Not all tyre sidewalls and carcasses are the same stiffness and this makes a big difference with ride quality.

Yes, that is common sense.