Tyre pressure safe limits

building_with_lego

My tyres should be at 31psi and the last time I checked them, around a week ago, one was at 29.5, the rest at 30 when tested cold.

My as-yet-unanswered question is this: is 1.5psi under dangerous? Am I going to notice any performance/handling/fuel consumption issues yet? Is it ok to leave them a week until I fill up and get air?


To reassure, I have since re-inflated before a motorway journey; I'm just very curious as to how pernicketty I need to be about keeping the tyres *AT* 31psi, or how much leeway I have in terms of pumping them up. Any ideas?

Silver-Surfer_2

Nothing to worry about, how accurate was/is the gauge.

keith1950

The accuracy of the equipment at the average filling station is such that + OR - 5% won't make much difference meaning anywhere between 29-33 will be ok. I have always set mine to 33 whatever the manufacturer might say.

building_with_lego

I was using a Halford's digital gauge, then used the supermarket compressor to pump up. The gauge read the same as the compressor once they were pumped up.

It sounds as though I don't need to panic at 29psi then?

force_ten

some tyre manufacturers say 5-7 PSI under inflated is dangerous and could affect the cars handling

I would say run at a mid point as the norm so if the unladen/laden range on your car is between 30 psi unladen and 38 laden then run somewhere between the two like 34 PSI and then a few pounds loss of PSI will still keep you above the lower PSI range

forgotmyname

Dangerous no, using more fuel very slightly. Less grip possibly.

Going to cause uneven wear more likely. You need to check them more often not leave it a week knowing the pressure is slightly low already.

Richard53

A couple of pounds here or there won't matter much, but it's best to stick to what the manufacturer recommends unless you have a good reason not to.


Check your tyres every week, using the same gauge every time. Do it cold, i.e. the car hasn't run anywhere for an hour or two. Top up to recommended pressure if necessary. Rubber is porous and slight losses are inevitable, but if you are losing more than a pound a week from any tyre, you have a slow puncture which you need to get fixed.


Where an under-inflated tyre becomes dangerous (rather than just wearing unevenly and possibly causing soggy handling) is on a long journey in hot weather. An under-inflated tyre will flex a lot more and build up heat internally. Combine that with a 30C day and 100 miles of motorway and the tyre could easily fail completely due to the heat. The last time I did North to South in France in the summer, the police were at every motorway toll area offering free pressure checks and inflation if needed. They obviously see under-inflation as a significant cause of accidents there.

facade

Get yourself a cheap footpump, or one of those £5 electric pumps from B&M or somewhere.
Then you can top up the odd Lb or two weekly.
As long as you always use the same gauge to check them (don't use the gauge on the cheap pump)

vikingaero

building_with_lego wrote: »

My tyres should be at 31psi and the last time I checked them, around a week ago, one was at 29.5, the rest at 30 when tested cold.

My as-yet-unanswered question is this: is 1.5psi under dangerous? Am I going to notice any performance/handling/fuel consumption issues yet? Is it ok to leave them a week until I fill up and get air?


To reassure, I have since re-inflated before a motorway journey; I'm just very curious as to how pernicketty I need to be about keeping the tyres *AT* 31psi, or how much leeway I have in terms of pumping them up. Any ideas?

Any underinflation is going to worsen fuel consumption - by a very small amount if the tyre is only 1.5 psi under.

As you have noted most manufacturers will recommend checking tyre pressures when the tyres are cold. But what is the definition of cold? Ambient, below 5C or at 0C? There are one or two manufacturers basing tyre pressures at 0 degrees C.

In the real world I would inflate tyres to +1 or +2 over recommended to take into account current ambient temperatures. Buy a decent tyre pressure gauge and a foot pump and you won't have to worry.