[willjames]

Just wondered what pressures you are getting in this hot weather?

My RFT 19's are usually 2.2 front and 2.5 rear when cold, however tonight (after car been in the direct sun all day) I got 2.5 front and 2.8 rears!

Got me thinking what pressures would they be limit tested to

[ronime]

Maximum working pressure for a given load is normally stated on the sidewall.

51psi for a maximum load of 630kg in the case of my 18" Bridgestones.

Upto 2500kg ish load on a car with a kerb weight of less than 1700kg. Plenty of margin there for a driver who likes his pies.

[robbiep]

Didn't fifth gear attach a tyre to a compressor a few years ago, to see at what point it blew up ?
I seem to recall the alloy failed first, at a ridiculous pressure of 20 bar (300psi) or so.

[King of the Hill]

Originally Posted by willjames

Just wondered what pressures you are getting in this hot weather?

My RFT 19's are usually 2.2 front and 2.5 rear when cold, however tonight (after car been in the direct sun all day) I got 2.5 front and 2.8 rears!

Got me thinking what pressures would they be limit tested to

Could be mistaken and hope to remember to look, bit I think it's meant to be 2.6 and 3.2 or something?

[willjames]

Originally Posted by King of the Hill

Could be mistaken and hope to remember to look, bit I think it's meant to be 2.6 and 3.2 or something?

I think it depends on what your carrying. My pressures are correct because I'm mostly in the car on my own.

[....,,,,..,,..]

Originally Posted by willjames

I think it depends on what your carrying. My pressures are correct because I'm mostly in the car on my own.

Yep the door card offers a choice of pressures depending on how many bodies you are carrying.

[creepy coupe]

More to the point. When should you set the pressures?

[Scottiedog]

Originally Posted by creepy coupe

More to the point. When should you set the pressures?

When the tyres are cold so first thing in the morning before you've driven it and before the sun has been on them.

[creepy coupe]

Originally Posted by Scottiedog

When the tyres are cold so first thing in the morning before you've driven it and before the sun has been on them.

That's my point really. If you do that in the winter. The running temps will be different to summer.

I left home this morning at 7am and the outside temp was 20°. I suppose the right answer is at the beginning of every day.

[gatsojon]

Originally Posted by creepy coupe

More to the point. When should you set the pressures?

Unless BMW quote an alternative, I'd use NTP - Normal Temperature and Pressure: -

Temperature: air at 20oC
Pressure: 1 atm 101.325 kPa, 14.7 psia
Air Density: 1.204 kg/m3

So a warmish UK day would be fine.

Mine went up from 2.2 bar at 14oC to 2.5 bar at 39oC yesterday.

[HighlandPete]

Originally Posted by creepy coupe

That's my point really. If you do that in the winter. The running temps will be different to summer.

I left home this morning at 7am and the outside temp was 20°. I suppose the right answer is at the beginning of every day.

We do need to adjust tyre pressures for seasonal changes in ambient temperature. More than just seasonal, if there are swings of temperature during a season. Worth remembering... the rule of thumb is 0.1bar for every 10°C change in ambient temperature. Ambient drops 10°C, we will be 0.1bar low, unless we add more air.

We are really using the recommended cold setting pressure, (tyre air temperature, the same as the ambient temperature), to get to the optimum working pressure, once the tyres warm up. Quite normal (and expected) to see 0.2 - 0.3bar increase in pressure, once the tyres are warmed up,

Winter time it can be more difficult to get to the optimum working pressure, particularly on short runs and/or wet conditions. I find I need to add a bit more to the setting pressure, to get the ideal working pressures.

[creepy coupe]

Originally Posted by HighlandPete

We do need to adjust tyre pressures for seasonal changes in ambient temperature. More than just seasonal, if there are swings of temperature during a season. Worth remembering... the rule of thumb is 0.1bar for every 10°C change in ambient temperature. Ambient drops 10°C, we will be 0.1bar low, unless we add more air.

We are really using the recommended cold setting pressure, (tyre air temperature, the same as the ambient temperature), to get to the optimum working pressure, once the tyres warm up. Quite normal (and expected) to see 0.2 - 0.3bar increase in pressure, once the tyres are warmed up,

Winter time it can be more difficult to get to the optimum working pressure, particularly on short runs and/or wet conditions. I find I need to add a bit more to the setting pressure, to get the ideal working pressures.

Yes. I found winter tends to vary much more. And need more regular checks.

[HighlandPete]

Originally Posted by creepy coupe

Yes. I found winter tends to vary much more. And need more regular checks.

Totally agree.

Besides the driving characteristics, keeping in the optimum pressure zone helps prevent odd tyre wear.

[creepy coupe]

Originally Posted by HighlandPete

Totally agree.

Besides the driving characteristics, keeping in the optimum pressure zone helps prevent odd tyre wear.

It only came to my attention since getting the Mini and messing around with pressure. 5° ambient gave a significantly different reading to 0°. + 5° made very little difference. God i'm a sado

[Rich9600]

Set your tyres when cold but be mindful of your driving conditions.

I've had 3 different 3 series cars each with runflats. Over the past 8 years, and 8 winters I've observed that runflats seem more susceptible to temperature variations than any go-flats I've had on previous cars have been.

The present car has the live tyre pressure monitoring and my inner geek has observed the differences in pressure and consequently ride quality as the temperature changes. A few miles of driving at 5C will add about 0.2 Bar, as will a 10C air temperature change.

My in-car monitoring system under-reads by 0.1Bar against my pressure gauge... But, if it under-reads by 0.2 Bar my ride quality suffers, the run flat sidewalls start getting involved over the bumps... So, about a 5C starting temperature drop gives a bumpy ride... But, a few miles on and the ride comfort improves as the heat builds and the pressure rises.

To the original question. Taking 5C giving about 0.1Bar (observation not calculation) pressure change, then you need about a 25C change to get 0.5Bar... So, if you're running 5C uk winter pressures and manage a 30C day you may get a 0.5Bar increase which would raise you up to about the high load/speed setting. When running higher pressures, the tyres own temperature buildup will be reduced as contact point and flex are reduced.

So, UK summer ambient temperature swings will affect ride quality and handling. But, in my opinion, are not going to cause a risk to properly inflated tyres.

[Scottiedog]

Originally Posted by creepy coupe

That's my point really. If you do that in the winter. The running temps will be different to summer.

I left home this morning at 7am and the outside temp was 20°. I suppose the right answer is at the beginning of every day.

Appreciate your train of thought and as others have said I check mine once a month and with each seasonal temp variation.

[HighlandPete]

Originally Posted by Rich9600

So, UK summer ambient temperature swings will affect ride quality and handling. But, in my opinion, are not going to cause a risk to properly inflated tyres.

Agree. The concerns about the spikes in temperature from sitting in the sun are not going to be much of an issue. As soon as we drive, we will be back to ambient temperature cooling, with normal heat up from use.

As long as we don't set the pressure in that direct sunshine with the tyres heated up, we will be in the working range.

[....,,,,..,,..]

Try driving some place like Qatar when the temperatures get utterly ridiculous lol.

Now that's where you get hot tyres


It's amazing the number of people that do not have a weekly / monthly tyre check regime.

As a Hearse driver my tyre pressures tend to vary a lot depending on number of bodies, crap being carried and journey length (and speed).

Mine are currently set to the high bit on door card as have been driving around 4 adults and a dog.

Will drop them to door card lower setting tomorrow as car due MOT and other stuff (brake fluid, end of warranty, sat Navy screen fault).