Tyre pressure stupidity

[davepoth]

I thought I should share.

I was waiting behind a RAV4 in the petrol station to check my tyre pressures at Sainsbury's and the lady in front was taking a very long time; Around 1 minute of pumping for each tyre.

When she drove off I pulled up to the air pump, and she had just inflated the tyres on her car to 2.9 Bar (42PSI) rather than 29PSI.

Cool Story etc...

[Rob197]

I get alot of beemers at work set to things like 26psi instead of 2.6bar for an example. Its in the door, how can you fail?!

[Motorrad]

People are idiots. Be amazed she's aware of the concept of tyre pressures and that there is an ideal value one sets them to.

Maybe she was off for a spot of top ending or tracking the RAV4 and has found these higher pressures to be ideal when giving it some stick?

[fjord]

I got in a vehicle at work a few months ago.

Someone had been doing blue light runs in it all day. I thought the tyre looked a bit low so went to the garage. 15psi was in the o/s/r tyre.

So, buffoonery stretches across the board when it comes to basic car knowledge and maintanence.

[405dogvan]

Makes the steering lighter innit!?

The guy I used to deliver pizzas for used to insist on pumping the (scrapyard second-hand, usually) tyres on the vans up to something bonkers - made for 'interesting' handling (tho given they ALL had slow punctures - it wasn't interesting for long).

That job was 40% pizza delivery, 30% car maintenance and 30% dish washing tbh

[RocketScience]

Perhaps she was on her way to a car limits track session?

[Andyjc86]

I serviced a car recently, where all the pressures were 63 psi. After i corrected them (let some air out!) I asked the customer why he chose 63. His answer was because that's what it states on the tyre.

I quickly pointed out the proceeding sentence of 'do not inflate above' that he had missed.

[petrolsniffer]

Even those who do it for a living get it wrong

I had four new tyres on my puma It handled awful after and was very skittish around corners.

All the tyres were over inflated by atleast 6 to 8 psi so 36-38psi.

[22rgt B Squadron]

Used to look after a taxi workshop a few years ago and one of the new Russian drivers pulled in for a new headlamp bulb. Just happened to glance at his tyres as they looked as if they were bulging off the rims. On checking they all had over 70psi! Asked about the pressures and he replied we all do that at home, saves fuel!

[22rgt B Squadron]

Used to look after a taxi workshop a few years ago and one of the new Russian drivers pulled in for a new headlamp bulb. Just happened to glance at his tyres as they looked as if they were bulging off the rims. On checking they all had over 70psi! Asked about the pressures and he replied we all do that at home, saves fuel!

[AgentZ]

petrolsniffer said:

Even those who do it for a living get it wrong

I had four new tyres on my puma It handled awful after and was very skittish around corners.

All the tyres were over inflated by atleast 6 to 8 psi so 36-38psi.

Agreed. I was traveling in my dad's 2 week old Fiesta last week and felt the ride was a bit hard in the back. I checked the pressures the next day to find they had 37psi all round....Obviously not adjusted at PDI.

My Fiesta ST Weirdly had the correct rear pressure (26psi) but under inflated (30psi rather than 36psi) fronts!

[SV8Predator]

davepoth said:

she had just inflated the tyres on her car to 2.9 Bar (42PSI) rather than 29PSI.

Where does the 29psi figure come in to this?

Please don't tell me you went on to the internet and checked tyre pressures for a RAV 4?

That's even more sad than feeling you had to "share" this shock-horror story on PH.

[RDB]

She might have read the maximum pressure value on the sidewall of the tyres and thought that was the pressure she was meant to use.

I knew a woman who did that to the tyres on her Freelander. I got the handbook out of the car and showed her the correct pressure, but she wouldn't reduce them because she said it used too much petrol when the pressure was lower

[mnkiboy]

AgentZ said:

Agreed. I was traveling in my dad's 2 week old Fiesta last week and felt the ride was a bit hard in the back. I checked the pressures the next day to find they had 37psi all round....Obviously not adjusted at PDI.

My Fiesta ST Weirdly had the correct rear pressure (26psi) but under inflated (30psi rather than 36psi) fronts!

Are they really the correct pressures that Ford specify for the ST? I've never known a car to have such a difference in pressures between front and rear - 36 front and 26 rear?

[405dogvan]

Is this the best place to ask whether the recommended pressures are hot or cold then?

My awful grasp of physics says pressure drops as temp rises but then tyres probably expand and - erm - I've no idea which is the one they mean (but I know the diff between stone-cold and hot is 2-3 psi at least)

[McSam]

mnkiboy said:

Are they really the correct pressures that Ford specify for the ST? I've never known a car to have such a difference in pressures between front and rear - 36 front and 26 rear?

It's not so surprising, the Fiesta is already reasonably nose-heavy, but throw in a much heavier engine and give much more power to the front tyres.. I agree it's a big difference but not unreasonable if you look at the corner weights.

I would presume the four-up plus luggage recommendation is more like 40/34.



405 - pressure rises as temperature rises. The pressure is the result of air molecules within the tyre moving around, and the hotter they are, the more energy they have, so the more moving around they do.

[KM666]

My Mum did that, but the other way round to what OP saw. 20psi because the sticker on the door read 2.0bar. Worst bit is she used to be a teacher.

Re SV8Predator 29psi is a fairly common advised psi. Its not that hard to make the leap between 2.9bar being confused with 29psi.

Edited by KM666 on Thursday 5th September 21:57

[Huff]

405dogvan said:

Is this the best place to ask whether the recommended pressures are hot or cold then?

My awful grasp of physics says pressure drops as temp rises but then tyres probably expand and - erm - I've no idea which is the one they mean (but I know the diff between stone-cold and hot is 2-3 psi at least)

Manufacturers always recommended 'cold' pressure settings. Say within 5-10miles of cold start if visitng a filling station pump; 2-3psi is not something to worry about so long as side to side on the axle /tyre size is closer & within the recommended setting range (ideal gas law: pV=nRT; so with an essentially-constant-volume tyre, the pressure rises as carcass temp rises, in kelvin. Your roughly s10% pressure rise is about right )

E.g - pressure settings for my old E34 540 for the wheels fitted range from 2.4/2.7bar F:R for 2-up, normal use through to 3.2/3.2 4-up or any loading, sustained high speed. Quite a range to play in! It's certainly wide enough to have a useful/noticable effect on turn-in and ride comfort (within which I settled long ago on 3bar allround for use profile and handling balance)

Edited by Huff on Thursday 5th September 22:10

[All that jazz]

mrcoffee said:

While working at a petrol station I noticed a guy come and re-inflate one tyre every evening for a long, long time.

Always wondered why he didn't just get a new tyre. it was 50p for the air every time too! Would have asked if he'd ever come inside.

He probably spent half the cost of a budget tyre.

It's not forced to be the tyre. I had to pump up the tyre on my Golf on a near daily basis because the alloy wheel was corroded on the inside where the valve is mounted and it used to leak.

[NH1]

Without being a brainiack and getting the handbook out every tyre I have ever pumped up has took 30 psi.