Tyre pressure

The effect of warm tyres on pressure is miniscule to the point of being non-existent for normal road purposes. If you're concerned about it, put a couple of PSI extra in, then adjust them when cold by letting them down to the pressure you want.

Steve

Certainly when warm the pressures should be no less than the recommended. 44 seems high to me. I usually run about 30-32 ish all round and adjust depending on tyre wear etc. The tyre pressure should be in the handbook or perhaps on the door jam.

Eh?

Chris

It's generally accepted that tyre pressures in the UK should be within 10% of the maker's advised pressure in order for the vehicle to remain legal.

The effect of the sun at certain times of year can make more than 10% difference...

Chris

I didn't understand why the back tyres had to be more inflated

I've never heard that before, my 306's manufacturer plate just says

One of my old cars the handbook had the rears lower than the front unloaded and higher than the front loaded.

Manufacturer states my pressure should be 33 front and 27 rear, so you are wrong ;-P

Mike P

So if the sun comes out and raises your pressures by 10%, your previously legal tyre pressures become illegal? I don't think so somehow.

Steve

In theory, yes.

I was just making the point that tyre temperature does indeed make a significant difference to the pressure.

Chris

My fiesta recommends something along the lines of:

unloaded: 31 front / 28 rear fully loaded/high speed: 35 front / 42 rear

Presumably because unloaded there's no weight at all in the back, but fully loaded there could be 3 people + luggage.

Accepted by whom? They're either legal or they're not. The maker as in the tyre maker or the car maker? If the recommended level is 34 and I've got mine at 30 is my car illegal?

That makes sense, but it doesn't make sense to have rear higher all the time on all cars. I can understand it if the rear is heavier on a particular car, but not as the other guy said "Back should always be (quite a bit) higher than the front, as they're dumb, with no steer, on most cars."

And is that 34 degrees when completely cold, or when driving? If when driving, do you have to adjust them when you move from a 30mph road to a motorway as the temp will increase at 70+mph increasing pressure? What happens about the tyres cooling whilst you fill with cold air?

;)

The message from Chris Whelan contains these words:

Accepted by whom?

Not me.

Steve

Me :-)

The requirement to have tyres inflated to the correct pressure is here:

s41A(b) Road Traffic Act 1988, Road Vehicles (Construction and Use) Regulations 1986, reg 27, as amended

There is no tolerance allowed for within the regulations! Strictly speaking, any deviation is an offence.

My reference to a 10% tolerance is information I got from a friendly traffic cop. This is the value where they would consider reporting for prosecution.

Chris

The law requires you to have your tyres inflated to the correct pressure as stated by the vehicle manufacturer. The manufacturer quotes a cold pressure. As long as the pressure is correct *when cool*, they are legal.

Chris