Tyre Pressure

Hightower · 06 February 2009, 17:06

Got some new rubber on my Jeep today and when I picked it up I asked what pressure he'd blown the tyres to. 35 PSI Sir, he said. But the Car maker suggests 26 PSI is correct for this model, I replied.

Who is right?

I didn't see a suggested pressure on the sidewall of the tyres, so no clues there. My trailer tyres do have pressure info on the wall.....Isn't this strange not to have any on car tyres?

JSP · 06 February 2009, 19:07

They normally have the max PSI the tire can take marked on the tire wall. I'd go with what it says in your manual. Although when in doubt for normal use I always got told to do them to 30PSI until you found out for sure.

JSP · 06 February 2009, 19:40

Sorry should have said, CAR tires normally have the max PSI marked. Haven't got a clue about trailers!

Bigmuz7 · 06 February 2009, 19:58

I think Codders once said .. 'what looks right' and I have to agree with that in part , save for the conditions you are using the motor in, ie off roading, long distance etc and in those cases you inflate for those circumstances, IMO 35 is a little too high. All my 4wds are 28 -32 for road work including trailing. That said when towing, I'd sooner have a little too much pressure than too little, cos if they are too low, or imbalanced pressure wise .. thats when the trouble starts !!

jwalker · 06 February 2009, 20:17

Quote:

Originally Posted by Hightower

Got some new rubber on my Jeep today and when I picked it up I asked what pressure he'd blown the tyres to. 35 PSI Sir, he said. But the Car maker suggests 26 PSI is correct for this model, I replied.

Who is right?

The car manufacturer is correct.

Quote:

Isn't this strange not to have any on car tyres?

It's my understanding that pressure information on car tyres is only necessary for the American market. I'm not certain that is necessarily so for trailer tyres. Also it's not running pressure, it's maximum pressure.

Generally, tyre adhesion is improved as the inflation pressure increases. Obviously there is a limit and other characteristics also become more important.

chewy · 06 February 2009, 21:29

If you look under the fuel filler it sometimes tells you the tyre pressures, on my Jag it was under the centre arm rest.
They do vary for speeds/loads etc.

Hightower · 06 February 2009, 22:36

I know exactly what pressure the Manufacturer recommends, it's 26 PSI, there is a sticker inside the passenger door jam with all the info on. I usually inflate to 28 because I'd rather run a slightly over inflated tyre as opposed a more dangerous under inflated one.

I was speaking to a friend tonight and he said that there are pressures that tyre companies recommend (not maximum pressures) for particular brands or types of tyres that do conflict with car manufactures figures. Usually special types of rubber.

If an accident where to occur and the tyre pressure was to blame I guess the law would fall in favor of the car pressures?

chewy · 07 February 2009, 17:38

I think it'd be hard to prove as the pressure will change with the weather how fast you drive etc.

On the Jag I played with the pressures till it handled the best.

codprawn · 07 February 2009, 20:22

The car makers aren't always right. Land Rover suggest tyre pressures of 28/48 for the Defender 110. That may be fine when you are carrying 1 ton in the back but what about when running empty? Most of the weight is over the front - the back tends to be quite light with no load which is the way many people drive them!!!

I currently run my Discovery on 32 psi all round which seems about right for the 235/70 tyres.

BogMonster · 08 February 2009, 13:53

My 110 runs at about 25/28 front/rear on 265/75R16 and the tyres wear fairly evenly, on the Mudzilla 33x13.50-15 I run it as low as 20psi because they are crossplies and pretty solid!

BruceB · 22 February 2009, 21:31

There will be no recommended tyre pressure on a tyre as the same size tyre can be fitted to many different vehicles and the pressure is related to the axle loading.
All you may find is the maximum pressure but this should be considerably higher than the recommended pressure.
Go with the car manufacturers figure

Simon B · 02 March 2009, 13:05

On my Land Rover Forum a poster has indicated that you can achieve correct tyre pressure by taking the inflated height to the ratio of;

75-80% of the tyre wall height (for any given load)

i.e. 265x75R16 (Common Land Rover fitment
= 198.75mm wall height (max)
= Between 150mm - 160mm

It does require some measuring and pressure is variable.