Off on a big journey tomorrow, en masse. Setting off really early, so I want to get the car prepared to hit the motorway. Question is, how to check the tyre pressures. Obviously what I *should* do is load the car and drive directly to the nearest garage to do it at 5am with the tyres cold and the car at its travelling weight. What I want to do is pop round the garage now and do it, with the car empty. If I set the unladen pressures, will the pressure then be right when it's loaded, or is checking it when loaded the only way to be sure?
My basic physics says the pressure will go up as a result of loading, and so the loaded values provided by the manufacturer reflects a rough approximation of what's needed to maintain the correct tyre profile. But does this involve adding or removing air? I'm guessing it's load-dependent and there's no single answer, but it would be nice to know either way.
TIA
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The pressure in the handbook is for cold tyres, and allows for an increase when moving. Thats why it says always measure on cold tyres. The handbook may also give a higher reading for fully laden/high speeds but this is still checked on cold tyres.
Why not nip to the garage tonight and check them so there are no worries in the morning?
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Ah yes, but does it make a difference to measuring the tyre pressure if the car is fully laden or not at the time the measurement is taken? I haven't got a clue - but would have thought the reading would be increased if the car was laden.
I always check my tyre pressures cold, and with the car unladen, using the higher recommended pressure if I know I'm going to be carrying a load.
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On the basis that I have to drive to a petrol station to set the pressures and hence the tyres are not cold, I always set them slightly higher than they need to be, then next morning use a good quality gauge to set them properly, just letting air out.
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Whether the car is laden or no makes no difference - set the pressures to the manufacturer or tyre maker's recommendations and whilst the tyres are cold.
It's more important to get the front/back pressures ratio right (if there is a difference between them) than to be absolutely spot on - in fact very few people use or have access to an accurate tyre guage.
Don't forget to return the pressures to normal use settings after your trip (again whilst the tyres are cold!).
I normally leave my tyre pressures at three to four pounds over the recommendation - it aids fuel consumption, means they don't have to be adjusted for motorway use and tyre wear doesn't seem to be materially affected.
Have a good time...:-)
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What\'s for you won\'t pass you by
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Your vehicle handbook will give higher tyre pressures for when fully laden or travelling at a consistently high speed. Alternatively there may be a sticker in the door opening or under the bonnet somewhere. Buy one of the pencil type pressure gauges and a cheap pump and do it at home when the tyres are cold and before you load up.
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You should check the tyres when they are cold. Even a short trip to a nearby garage will warm them up and make the reading inaccurate (not to mention the unknown accuracy of the forecourt guage - reports in the past have been critical of this). The best time to check your pressures is in the morning when the car has stood overnight.
Check the tyres with the car unladen. The pressures given in the handbook for laden running take this into account.
This is going to sound very condescending though it isn't meant to, but I find it amazing there are still people who won't invest the price of a round of beers into a simple tyre pressure guage and basic foot pump that with care will last a decade or more and contribute to improved road safety for everyone. Then again, perhaps this is why NHTSA have found that improper tyre pressure is contributing significantly to road deaths in the USA and have made it a legal requirement for all new cars to have pressure monitoring systems fitted!!!
tinyurl.com/9lzv3
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Taking NHTSAs figures and applying them to the UK suggests that around 40 deaths per year can be attributed to underinflated tyres!!!
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(not to mention the unknown accuracy of the forecourt guage - reports in the past have been critical of this).
I was going to mention that. On a recent trip to Scotland, I had the car fully laden, which required a small pressure increase in the tyres to about 30 (ish) psi. The pump at the garage could seemingly only muster a maximum pressure of 25psi (which is what they were already at). Back at my grans? house (literally 2 minutes up the road) I checked them with a pencil gauge, which showed the pressures to be in excess of 33psi.
Always re-check them with a reliable gauge after using a garage pump.
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It's worth investing in a good pressure gauge, such as the ones recommended by HJ:
www.international-tool.co.uk/
I would also recommend £30 quid's worth of compressor, as advertised in the national press and mail-order catalogues. They work off the cigarette lighter and are very compact. Their gauges may not be 100% accurate, although I check mine regularly against the International Tool gauge and it's never far out. Alternatively, what's wrong with a good old footpump? I gave up with forecourt airpumps years ago as they were never reliable and then they had the nerve to start charging for their use.
On the advice of an independent mechanic, I always treat the pressures on the inside of the fuel filler cap as being definitive; they sometimes differ from those in the handbook.
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