Tyre pressure

Do you mean the vehicle maker?

If so, every handbook I have ever seen gives a precise value for tyre pressures under given conditions of load and speed.

Chris

I have to agree, the vehicle manufacturer states precise values for loading conditions and so any deviation could be considered to be making the car un-roadworthy.

The golf would have higher front end pressures as the idea is to maintain the best contact patch on the road and the correct amount of sidewall flex, with the golf being heavier at the front (front engine, front wheel drive), maintaining the contact patch size and sidewall flex would require increased pressure.

That said i run slightly higher than specified tyre pressures as i have

Its all rubbish though because your tester gauge is usually + or - 5% error anyway! You cant be expected to use fully calibrated equipment at every inflation.

Back to the question......... I wouldn't be without apump at home. Imagine going out inthe morning and realising you have a slow puncture - it gives you the opportunity to pump it up to get you to a tyre place safely. I have a double barrel pump and make checking my tyres part of my two weekly car wash routine

Equal pressures left - right is particularly important.

John

Of course I mean the vehicle maker. And every handbook I have seen gives not a precise value for tyre pressures, but a range of tyre pressures for various conditions, which can obviously change several times during the journey, or the journeys of a day. And as we have seen, the variation in them is more than 10%. It is also feasible that the optimum pressure for a make of tyre on a given car will not be the best possible option for a different make of tyre on the same car.

But realistically, and at risk of getting back to the original question, quite a wide range of pressures is acceptable for the vast majority of cars.

Steve

My 2002 VW Bora has the tyre pressures (in bar) on a label in the inside of the fuel filler cap.

I repeat, every handbook I have seen gives a precise value *under given conditions*.

If those conditions change, in theory so should the tyre pressures. Clearly that won't happen in the real world.

Acceptable to you, maybe not the law!

Chris

So my car is either "fully loaded" or "unloaded"?

It's a range. The extreme ends of the range are stated, for in between conditions I have to either pick either pressure, or one in between.

The law may require the tyre to be inflated to the manufacturer's recommended pressure, with no tolerence. However, the manufacturer's recommended pressures clearly have a tolerence, so I think you'll find it's quite legal.

I suspect if the car is 10% under the minimum recommended pressure, the police would be interested, and not otherwise.

Not quite "minuscule" but small enough (a couple of psi, between hot weather and cold) that not many people will notice the difference in the car handling.

For a personal air compressor, this survey is interesting:

Interesting, maybe. But those prices are way OTT.

I bought one from Wilkinsons for 8 quid a couple of weeks ago.

Door frame is where Citroen put the pressures. Try going to the Dunlop or Michelin sites, they have tyre pressures on them.

Yep, I'm sure you're right. Unless they can invent a camera that can check your tyre pressures... :-)

Chris

Over pressure is as dangerous, if not more so, than under!

Take mine from 34 to 38 and its like a skating rink, take it to 30 and it just wallows a bit.

Infrared photography, but I don't know the resolution.

Not so sure even infrared could spot it, it could tell temp for sure, and if you could use it to determin density maybe it could but not through a tyre.

Also that site is full of rubbish. Recommended 8K mile tyre rotation - a) Tyre rotation just covers unever wear and prevents fixing of problems b) Its not recommended for all vehicles c) My oil changes are every 3K miles but most peoples are every 12K so their rule of thumb of rotate-with-oil-change doesnt work.

Interesting also that the examples shown are of a tyre underinflated by 33%.

Steve

When you start getting to high speeds, the tyre pressure makes quite a large difference, not only to comfort but to safety. Most cars are front-wheel drive, and one steers with the front wheels. It's important these grip the road as much as possible, and really you're after 100% friction, which you'll never get of course.

The back wheels never do anything, apart from rotate and brake, and even if just one or two more PSI from your wee pump is recommended due to the physics involved in turning. I unfortunately had to investigate all this crap at my time at university; and the reason you will find many cars just say 35(etc) on all four wheels is usually down to simplicity, and the fact some cars are purposely heavy at the back, so by default more load on the tyres. Peugeot use slightly heavier metals at the back, to compensate for the fact there's no heavy object (engine) in it. Mind you, if your 23 stone heffer of a cousin is in it, it might not be required.

Not legal to drive with damaged tyres of course. ..and it's generally accepted that tyre fitters will use any dubious reason to sell you a new set of tyres.

If my recommended pressure was 32 and I found them at 28 I wouldn't be rushing of in a worry to get them inspected.

The message from "Lin Chung" contains these words:

I notice there's nothing there on overinflation. I run mine a few PSI over the recommended because without they wear too rapidly on the shoulders. The handling is adequate, as is the grip - certainly better than some cars I've had over the years were as standard.