Spare Car / Truck Tyre Pressure

[torrenova]

Following on from the tyre pressure thread I wanted to ask about the spare tyre ?

My logic, though perhaps flawed, says that a tyre under pressure, namely the weight of my truck, will read a higher internal pressure than the spare tyre which is not load supporting. This is given that they all had the same tyre pressure under zero load.

Am I missing something here ?

The end answer I am looking for is what pressure to put in the spare and if different why and if the same then explain away my flawed logic.

[JetsetBkk]

I keep it at the same pressure as the tyres on the pick-up - 30 psi.

I have never had to change a wheel yet - touch wood - but I keep a pressure gauge in the pick-up, so would check it after changing the wheel.

I think your logic is correct - the tyre would be at a slightly higher pressure when fitted to the vehicle because of the load, hence the need for a pressure gauge.

A bigger effect, I believe, is temperature. I don't check tyre pressures if the tyre is hot as the pressure would read high. I think you should check the pressure when the tyre is cold but, as most people check the pressure at a garage, how do they get there without the tyres getting hot?

Life's a b1tch and then you die.

[Lancashirelad]

Makes no difference whether loaded or not.

Spare should be kept at the higher of the 2 recommended pressures of the 2 axles. (front is usually higher).

However, i usually put about 5 psi more in the spare to allow for pressure loss over time as the spare tends not to get checked as often as it should.

[Thanyaburi Mac]

Makes no difference whether loaded or not.

Spare should be kept at the higher of the 2 recommended pressures of the 2 axles. (front is usually higher).

However, i usually put about 5 psi more in the spare to allow for pressure loss over time as the spare tends not to get checked as often as it should.

Had my van up on the hoist a couple days ago for an oil change, usually ask that it be raised so I can get underneath with a flashlight to check for problems, glad I did this time, see attached re missing nut.

I also checked the spare, it was down to 15 PSI. The mech asked when was the last time I'd had a flat, which was about 3-4 years back. He recommended at least 50 PSI for the spare to allow for leakage/seepage over time, did so.

I also carry one of those inexpensive air pressure pumps powered by the cigarette lighter outlet, handy, has saved my bacon on a couple of occasions.

Mac

[JetsetBkk]

Makes no difference whether loaded or not.

If you load up a pick-up, the pressure of the tyres on the rear axle will increase - hence balloons go 'pop' when you sit on them . So the logic from torrenova is that the spare should be at a lower pressure since it is completely unloaded. However, much more important is that the spare is hardly ever checked, so it should be set at a higher pressure to allow for leakage over time.

Spare should be kept at the higher of the 2 recommended pressures of the 2 axles. (front is usually higher)...

Front pressure may be higher for cars - where the weight of the engine/transmission/driver rests - but in pick-ups it's the rear tyres that are at a higher pressure when the pick-up is loaded - at double the pressure of the front tyres.

When unloaded, all tyres on my pick-up should be at 29 psi all round, measured when cold. When it's loaded, the rear tyres should be at 58 psi.

[BSJ]

Check the owners manual first. Personally I keep the spare at 5psi above recommended cos I only check it 2-3 times a year.

Carrying a plug in compressor is sensible. Or better still Fix-A-Flat in an aerosol can. The advantage of Fix-A-Flat is it will actually fix most flats temporarily! That will get you or your partner to a garage or tyre shop without having to fit the spare. Comes in mini, full size and SUV sizes. Not to be used on motorcycle tyres though... which is a pain.

[Lancashirelad]

Check the owners manual first. Personally I keep the spare at 5psi above recommended

I'd say that's about right. I think 50 is too much.

Carrying a plug in compressor is sensible. Or better still Fix-A-Flat in an aerosol can.

Yes, good idea, carry both. Though probably not a good idea to leave any kind of aerosol inside the passenger compartment when parked in the sun.

As for running the rears of a pickup at 58 loaded. If you forgot to let them down again immediately after unloading it would hop & skitter about all over the place, produce a most uncomfortable ride & be horrendous in the wet.

[JetsetBkk]

...As for running the rears of a pickup at 58 loaded. If you forgot to let them down again immediately after unloading it would hop & skitter about all over the place, produce a most uncomfortable ride & be horrendous in the wet.

Yes, and I can't believe people who use their pick-ups for carrying heavy loads actually bother to keep pumping them up and letting them down again. I realise now that when I did use my pick-up for moving house - so it was loaded up quite well - I never actually thought about the tyre pressures or did anything about them.

[torrenova]

I've moved some stuff in my pickup but I would never think about doubling the pressures. I think that sounds dam_n well dangerous. More air, yes, double - I'd guess no.

As for the spare, I will take on board that about keeping it higher pressured than normal as I can always check it if I have to use it anyway.

[Dave the Dude]

I've moved some stuff in my pickup but I would never think about doubling the pressures. I think that sounds dam_n well dangerous. More air, yes, double - I'd guess no.

As for the spare, I will take on board that about keeping it higher pressured than normal as I can always check it if I have to use it anyway.

Slightly Off-topic

When I questioned why my truck tyres were inflated to 50psi!!! I was told "you save petrol,It rolls easier"

<deleted> It just sends you to paradise instead, if emergency braking is required!

Since then, I always leave a pressure guage in the glovebox.

Dave

[JetsetBkk]

I've moved some stuff in my pickup but I would never think about doubling the pressures. I think that sounds dam_n well dangerous...

That's what it says in the pick-up's manual and on the sticker on the driver's door jamb.

But I don't do it either.

There must be all sorts of intermediate pressures that are required depending on how much the pick-up is loaded. You may as well just pump it up until the tyre looks right - i.e. sits flat on the road.