ADUK Archive

I have been told never to check/inflate tyre pressures on a slope, even a slight slope, because of the difference in load on the upper and lower tyres. Yet I seem to recall that a specialist tyre supplier may inflate a tyre before it is even put on the car. What is the right approach?

Tried it myself - on flat & then slope - hardly worth mentioning the diff.

I have never heard of that. Although whenever I check and fill my tryes I always mke sure I am on a flat surface and that my tyres are cold (i.e not after a long journey).

To our physics friends / racing experts : Is it true that overinflating them assists acceleration but compromises handling?

ROG: If you're on an icy road, would that be a limited slip diff?

Sorry, I'm leaving now I must learn to behave myself

There's no difference at all, the measured volume inside the tyre stays the same regardless of load. The rubber doesn't change in amount, if you held it perfectly square there'd be x cubic inches, if you change the shape, it's still x cubic inches.
You don't check them when they're hot because the pressure increases with temperature, and IIRC the rubber expands by a marginal amount.

Hope this makes sense.

Even a short journey can increase the tyre pressures quite a bit. I drove from university to my local station....~5-6 miles and my tyre pressures had shot up quite a bit when I checked them.

I've also never heard of tyre pressures being different on a slope.

I also repeat the advice to check pressures when cold, i.e. before driving even for a short distance. To the local car wash and back is just 3 km and makes 2psi difference.

I've also found that the fleet cars I maintain have to be checked in the early morning, certainly before midday as the difference between the shaded and sunlit side is 4psi by that time!

manilva15b wrote:
I've also found that the fleet cars I maintain have to be checked in the early morning, certainly before midday as the difference between the shaded and sunlit side is 4psi by that time!

If only we had so much sun

Sorry, I'm a bit late to jump in on this conversation.

But do you not feel it is benificial to check and adjust your tyres for the temperature they will be run at.

I appreciate you don't want to check them at molten temps but at standard operating temps seems more sense. I do mainly long distance so I tend to check them during that long distance so I know what pressure they are at while I'm driving.

That way I can adjust accordingly. If you track day your car you are supposed to lower your psi a few notches as they will be much warmer on track than everyday driving. So why do it when cold unless you are allowing for the rise in psi.

Manufacturers usually quote temperatures at cold - a standard ambient temperature, whatever that may be.

It shouldn't be hard to check tyre pressures before you set off. Once you've been moving a while then how do you know the temps are the same as last time you checked?

hardboiled wrote:Manufacturers usually quote temperatures at cold - a standard ambient temperature, whatever that may be.

It shouldn't be hard to check tyre pressures before you set off. Once you've been moving a while then how do you know the temps are the same as last time you checked?

Thermometer?

I'm only *half* joking, you know...

Cheers & God bless
Sam "SammyTheSnake" Penny

Yeah, you could get one of those infra-red beam ones, where you pull the trigger and it reads the temperature. Also good, if you put a hi vis jacket on, and take a reading of the temperature of your neighbour's car, then show it to him and convince him it's a speed gun...