Tyre Pressures

[Yogi-Bear]

Does anyone actually pump their tyres up to the recommended pressures when fully loaded? The chart in the filler cap suggests 2.7 bar (39PSI) for the front and 3.2 bar (46PSI) at the rear. The tyres themselves say max 51PSI, so those values are within the tyres capabilities, but they seem rather very high to me, especially the rears…

[kodiaqsportline]

I wouldn't be able to stop myself thinking of Mr Creosote if I were to put more than 40psi in to car tyres.

 

I haven't a clue how car manufacturers work it out, but airlines will use approx 85kg for the average male when working out weights. So unless you're carrying around 600kg worth of people, I'm not sure I'd bother about max weight.  ( good luck carrying two 85kg adult males in the rear most seats for any length of time. )

 

I'll add a few psi if we're going on a long journey with a car full of holiday gear but otherwise I don't bother changing pressures.

 

 

[J.R.]

1 hour ago, Yogi-Bear said:

but they seem rather very high to me, especially the rears…

 

Based on what?

 

When laden its the rears that carry the bulk of the extra load, I kept mine at the higher limit for most of the 45K that the tyres have already done because of my frequent laden and overladen journeys, the ride is more uncomfortable when unladen.

 

My reward has been that the tyres are all equally worn and all worn equally so I will get at least another 10K miles out of them probably more before they reach the legal limit, thats also because of my wheel rotation, I measure the wear gradient and will adjust the tyre pressures accordingly, the manufacturers ones are pretty much dead right.

[Yogi-Bear]

39 minutes ago, J.R. said:

Based on what?

Based on never having a car that specified anything near that high before (except my first Kodiaq, obv!).

 

It’ll be 4 plus a couple of suitcases this time… not fully loaded, so think I’ll go for somewhere between the unloaded and loaded values.

[skomaz]

5 hours ago, Yogi-Bear said:

Does anyone actually pump their tyres up to the recommended pressures when fully loaded? The chart in the filler cap suggests 2.7 bar (39PSI) for the front and 3.2 bar (46PSI) at the rear. The tyres themselves say max 51PSI, so those values are within the tyres capabilities, but they seem rather very high to me, especially the rears…

 

I'll stick my hand up to that - yes I do - I generally run the Eco (2.7 bar I think) pressures on a daily basis but up them to the loaded ones (3.0 at the rear from memory) when we're doing long fully loaded runs (eg holiday run to Belfast  and back or a run to and from Lancaster to Uni with my daughter - both fully laden).  There is a noticeable difference when laden as the back of the car is more stable, presumably due to less tyre squish)

[AGFalco]

Laws RTA 1988 sect 42 & CUR reg 32
Tyres. Tyres MUST be correctly inflated to the vehicle manufacturer’s specification for the load being carried.

 

Thanks. AG Falco

[Yogi-Bear]

The vehicle manufacturer tells me tyre pressures for two people with no luggage, and fully loaded. There is no specification for something in between.

[Warrior193]

19 minutes ago, Yogi-Bear said:

The vehicle manufacturer tells me tyre pressures for two people with no luggage, and fully loaded. There is no specification for something in between.

Depending on your estimated load, simply extrapolate a suitable pressure somewhere between the two sets of figures.

[silver1011]

I ran the higher recommended pressures when towing our caravan once, and forgot to reduce the pressures afterwards. The car was rock solid, I felt every lump and bump. I couldn’t wait to take some air out and restore the softer ride.

[J.R.]

1 hour ago, AGFalco said:

Laws RTA 1988 sect 42 & CUR reg 32
Tyres. Tyres MUST be correctly inflated to the vehicle manufacturer’s specification for the load being carried.

 

Thanks. AG Falco

 

Where did you find the quoted text which you claim is law as it is absolutely not within RTA 1988 sect 42 or CUR reg 32.

 

No offences are listed under section 42, it says that a failure to comply with a regulation in section 41 is an offence.

 

No regulations under section 41 regarding tyre pressures being inflated to spec for the load being carried, it does say "

The Secretary of State may make regulations generally as to the use of motor vehicles and trailers on roads, their construction and equipment and the conditions under which they may be so used.

Subsections (2) to (4) below do not affect the generality of this subsection.

(2)In particular, the regulations may make provision with respect to any of the following matters—

(a)the width, height and length of motor vehicles and trailers and the load carried by them, the diameter of wheels, and the width, nature and condition of tyres, of motor vehicles and trailers.

 

Construction and use regulations are not laws, regulation 32 is specifications for vehicle glazing.

 

 

 

 

[kodiaqsportline]

I'm just loving that law.

 

Say you drive with 2 people on board, then pick up another two on your journey, then pick up another two further on.  You all go off to your destination and on the way back, drop them off again.  I'm I supposed to carry a portable pump with me and adjust the tyres accordingly each time someone gets in/out the car?

 

If there is such a law then obviously it's impractical for our private cars.

 

 

 

 

Edited 28 July, 2023 by kodiaqsportline

[J.R.]

AGFalco should post that on a taxi drivers forum for maximum effect!

[J.R.]

39 minutes ago, kodiaqsportline said:

I'm I supposed to carry a portable pump with me and adjust the tyres accordingly each time someone gets in/out the car?

 

Pump not needed when passengers disembark 😄

 

I have always carried a footpump in my vehicles since forever, I do now have tiny 12V pump which will probably self destruct after a couple of uses, it fits in my DIY underseat storage bin so if I need it for my one leaking rim/beadseal I dont have to remove the load carried to get under the boot variofloor for the footpump.

[Warrior193]

As part of being an old Scout, I always carry a portable 12V power pack and a corded air compressor in my wagon, great for the many times I pick up a slow puncture from the seemingly countless nails and screws on the road - also useful for removing any possible risk of damage when being a good neighbour giving someone a jump start.

[AGFalco]

20 hours ago, J.R. said:

Where did you find the quoted text

https://www.gov.uk/guidance/the-highway-code/annex-6-vehicle-maintenance-safety-and-security

Then Vehicle Maintenance.

 

 

21 hours ago, J.R. said:

No offences are listed under section 42

Looking again, this relates to what is above not below. My Bad.

 

Thanks. AG Falco

[J.R.]

I would have made the same error myself. 👍

[DaveMiller]

Yes, I would use the recommended higher pressures if *fully* loaded.

 

The figures aren’t unusually high, nowadays.  My E-class Mercedes requires 39 psi all round for just me in it, and my van runs at recommended 75 psi.

 

 

 

[Carlston]

On 27/07/2023 at 12:23, Yogi-Bear said:

Does anyone actually pump their tyres up to the recommended pressures when fully loaded? The chart in the filler cap suggests 2.7 bar (39PSI) for the front and 3.2 bar (46PSI) at the rear. The tyres themselves say max 51PSI, so those values are within the tyres capabilities, but they seem rather very high to me, especially the rears…

 

There should be a weight plate fixed to the B-pillar that you should be able to see when the driver's door is open. Take a photo of that to see the maximum axle weights, as it's easier to see the details on a computer screen.

 

If you've got 235/45R20 tyres, 2.2Bar (32psi) in all four tyres can support over 2,000kg.

 

Pumping them up to 2.7Bar (39psi) front and 3.2(46psi) rear can support over 2,600kg, (ie. over 1,200kg on the front axle, and over 1,400kg on the rear axle).

 

If you're not carrying much weight in the back perhaps try 35psi front and 32psi rear. This can support over 1,000kg on the front axle and about 1,100kg on the rear axle, for a total weight of over 2,100kg.

 

Excessive tyre pressures is sometimes used to improve handling. However, I expect this is more to do with driving flat out around a smooth racetrack, and not day to day driving on the UK's bumpy and potholed filled roads.

 

Edited 31 July, 2023 by Carlston

[mdk1]

Had mine pumped up whilst on Holiday as we had a fair bit loaded.

Found the car steering felt really light, much better with them back down to normal.

managed a to drive from the south of France overnight to home, 770 miles in 11,47mins driving time and only stopped a couple of times.

avaraged 39mpg on that journey so can’t complain about the 1.5 engine.