Tyre pressure?

The Pontiac

Every time I get new tyres fitted they inflate them to 30psi, no matter what car or tyres I have.

I have 225/45/17 94Y XL tyres. The recommendation in the owner manual is minimum 35psi. I thought a specialist tyre centre would know this?

But I actually prefer the ride quality on 30 psi to 35 psi (might settle on 32 psi).

What's the problem going below the recommended pressure? Is there a danger of a blow-out or decreased breaking distance etc. ?

I know the car would handle better at 35 and the tyres would probably wear more evenly, but the ride is just too hard.

dh0011

if the tyre pressure is too low you can generate a wobbling force that can be of higher magnitude than the friction between the tyre and the road. i.e. the car can slide in a bend. That said a few pounds per inch may not be significant.

Another thing to consider is that the tyre may not be touching the road uniformly across it which could cause uneven wear

Henry Ford III

Reecommended tyre pressures vary car to car.

I have a car which needs 24psi in the rears and 28psi in the fronts.

Stella Virgo

the recomennded tyre presurre in normal car tyres is 32psi.

dh0011

Stella Virgo wrote: »

the recomennded tyre presurre in normal car tyres is 32psi.

depends on the car, tyres and what you are carrying.

The Pontiac

Henry Ford III wrote: »

Reecommended tyre pressures vary car to car.

I have a car which needs 24psi in the rears and 28psi in the fronts.

You would think the tyre centre would set the correct pressure to the particular car instead of always setting it to 30 though.

dh0011 wrote: »

depends on the car, tyres and what you are carrying.

Yeah my car is heavy enough, so the minimum is 35. Feels better at 30 though. Might try 32.

coylemj

If the tyre is over-inflated it will tend to wear excessively in the centre of the tread and if under-inflated, it will wear excessively on the outsides. In both cases there won't be optimum contact between the tread and the road which will mean poorer grip and longer braking distances. The recommended pressures should achieve even wear across the tread because you'll have maximum contact between the tyre and the road.

OP, you're saying that the ride is too firm at 35 psi but given that your tyres are low-profile (45), I think that's more the issue than the tyre pressure. If you want a softer ride, get yourself a car with bigger sidewalls i.e. higher profile tyres like 55 or 60.

richardsheil

The Pontiac wrote: »

You would think the tyre centre would set the correct pressure to the particular car instead of always setting it to 30 though.

Of course they don't set them to the particular car. They just bang 30 in everything. No attention to detail required by them. Every time I bought tyres for my wife's Ford Galaxy I told them what pressure was required (around 42 psi). Each time they would tell me that I was wrong and to put in 30. So I gave up eventually and just let them go ahead. Then drove to the next garage and set them to what the handbook stated.

coylemj

The only thing they care about in tyre centres is flogging rubber.

I brought my car to one of the well known chains once, the guy in charge of the place told me that one or more of my tyres was 'below the legal limit'. I asked him to quote the regulations so that I'd understand exactly how I was in breach of the them, he couldn't answer the question so I said to him 'well if you don't know the regulations, how can you stand there and tell me that I'm in breach of them?'

Needless to say he had no answer to that question either so I walked. He didn't even mention '1.6mm' (the legal minimum tread depth) so he was simply programmed to find a worn tyre and tell the owner that it was below the legal limit.

georgefalls

My Alfa Spider, which is small and light. Has 36 in the rear and 39 in the front, as per the hand book.
Every time its in a garage, I tell them the pressures and they never believe me.
I always inflate to those pressures, and I've never had a problem with uneven wear, or bad handling.

Go with what the manufacturer recommends. They do it for a good reason.

The Pontiac

The recommended tyre pressure is printed inside the glove box of my car (minimum 35 psi). Takes 10 seconds to look. Yet they always pump to 30psi. :rolleyes:

There's no 225/45/17 on 30. Lower profile means higher pressure than your average tyre. Yet it's always 30!

No a big deal I suppose, but how many people actually check after getting tyres fitted? It makes a big difference on tyre wear, fuel economy and maybe breaking distance or even a blow-out. 'Minimum' is stated by the manufacturers for a reason - depending on the weight of the car etc.