Boxster 3.4 tyre pressures…

[TTmonkey]

Ok, it’s a hot day out there….

Just wondered what tyre pressure should be at the end of a normal drive?

My pressures start at 2.1 bar in summer when car is cold, and run about 2.5 Barr when the car is up to temperatures.

Today a bit warmer.., 2.6 bar…. Note, this is after a totally normal drive keeping to speed limits on normal roads.
What pressure does everyone normally see…?

[Philvrs]

Thats just physics and temperature to pressure relationship, everyone will see the same if they check.

You could drop a couple of psi when cold, and possibly gain a couple of tenths on your trip to the supermarket. Don’t forget to put it up again once the weather cools.

[ATM]

Philvrs said:

Thats just physics and temperature to pressure relationship, everyone will see the same if they check.

You could drop a couple of psi when cold, and possibly gain a couple of tenths on your trip to the supermarket. Don’t forget to put it up again once the weather cools.

I think Phil is referring to Boyles Law. We all did Physics A-Level right?

https://en.wikipedia.org/wiki/Boyle%27s_law

[Orangecurry]

volume = temperature / pressure (without looking...)

Nope - forgot Boyle's constant - demonstrates why I didn't excel at A-level chemistry.

Edited by Orangecurry on Thursday 15th June 08:24

[TTmonkey]

I’m quite aware that the tyre pressure increases with heat, but I just wanted to check that the increase seen is in line with norm.

I dropped a few lbs out of all four tyres, the car is going to Italy tomorrow and will only get warmer during a long drive into warmer climates.

I’m desperately hoping for a major change in the weather in the U.K. now, no one likes going away when there’s an actual summer happening in the U.K…..

[alscar]

Those increased pressures don’t seem out of the norm particularly.
But I’m curious why have you taken some air now out ?
They will have cooled overnight back to where they were originally ie the 2.1 bar only now they will be less ?
Unless I’m missing something.

[996Targa]

I think that recommended tyre pressures are for 20c. Set them cold e.g. first thing, and before the sun has got at them as you can get a difference side to side which you don't want. I ignore increases during normal use.

Our 986 on 17" inch wheels has pressures of 29 front and 36 rear. Does your 987 run different pressures front to rear? As you have tpms is there a lower comfort setting.

We have only had the one Boxtser (for over 20 years) but our 911's have also had higher rear pressures than front although to be expected.

Enjoy your holiday.

[996Targa]

Sorry, that's 29 and 36 psi, about 2 and 2.4 bar.

[ATM]

996Targa said:

Sorry, that's 29 and 36 psi, about 2 and 2.4 bar.

Rear pressures on the 986 are a bit high in my opinion. The 981 book pressures are the same front and back.

[Orangecurry]

alscar said:

Those increased pressures don’t seem out of the norm particularly.
But I’m curious why have you taken some air now out ?
They will have cooled overnight back to where they were originally ie the 2.1 bar only now they will be less ?
Unless I’m missing something.

In winter/cold ambient temperatures, you have to increase the volume of air to maintain the pressure.

Opposite in summer/warm - the OP is driving south so he'll need to drop the volume beforehand to get the correct pressure under operating conditions.

[SV_WDC]

Probably worth checking the PSI/bar pressures against the door card & potentially dropping a PSI or two out of them when cold.

Driving with a higher than recommended pressure can cause uneven wear on the tyres

[alscar]

Orangecurry said:

In winter/cold ambient temperatures, you have to increase the volume of air to maintain the pressure.

Opposite in summer/warm - the OP is driving south so he'll need to drop the volume beforehand to get the correct pressure under operating conditions.

Thanks for that.
I’ve always checked our cars tyres every 3 weeks and yes in winter have often needed more in but from cold in summer if higher than recommended normal I’ve always left it untouched.
But UK only so I guess that’s the difference even with the current “ heat wave “ here.

[TTmonkey]

Orangecurry said:

In winter/cold ambient temperatures, you have to increase the volume of air to maintain the pressure.

Opposite in summer/warm - the OP is driving south so he'll need to drop the volume beforehand to get the correct pressure under operating conditions.

Yeah this. Many miles ahead in hot weather. Setting off in the morning route is Dijon-chamonix-Milan-Bologna-rhimini-san Marino-portofino-Nice-Grenoble-Troyes and back to Calais.

[ATM]

TTmonkey said:

Yeah this. Many miles ahead in hot weather. Setting off in the morning route is Dijon-chamonix-Milan-Bologna-rhimini-san Marino-portofino-Nice-Grenoble-Troyes and back to Calais.

I thought the 981 was 2.1 for sporty and less - 1.9 maybe - for the comfort setting?

If so just err on the side of comfort and you will be fine.