Uneven PSI in tyres

premiumz

Hi All,

We ran over a nail today and it punctured our driver side tyre. Luckily Quickfit had 1 tyre our size left in stock and said they could do it. It was 30 minutes before they closed, so I rushed down there.
It was the only tyre they had but it was a decent one at £305, Bridgestone
The problem is, when I got home I had a look at the tyre pressure as the mechanics don't seem to inflate tyres all the way so you need to do it yourself.
It was 40PSI. My other 3 tyres are 50PSI.
This has me concerned that this tyre will not have equal pressure on the road if the other tyres are slightly bigger?
Is this potentially dangerous?

premiumz

Mickey666 said:

What vehicle have you got?  50psi sounds very high for a car.

Audi Q7. We have Sorpion tyres and they're filled with foam apparently for noise reduction?

knightstyle

Read your handbook or the plate by the drivers door and inflate/deflate all the tyres to the correct pressure.
Note the pressure for a car with 5 passengers is higher than for the same car with just a driver.

premiumz

knightstyle said:

Read your handbook or the plate by the drivers door and inflate/deflate all the tyres to the correct pressure.
Note the pressure for a car with 5 passengers is higher than for the same car with just a driver.

Not sure if this was just a generic response? I said three of my 4 tyres are 50PSI and the new one was 40PSI. Meaning they will not be the same at full pressure.

unforeseen

What is the recommended tyre pressure for your vehicle as that is normally the pressure that a tyre fitter will set the new one to

Car_54

What do you mean "had a look at the tyre pressure"?

You need to check what the car maker specifies, either in the handbook or on a sticker (fuel flap or door jamb), not anything that may be stamped on the tyre.

BTW £305 sounds a lot. And wasn't the old one repairable?

lesalanos

Take your tyres back too if they get bigger between 40 & 50 psi
As the others have said find out what the pressure should be and adjust 1,3 or 4 accordingly 

premiumz

The pressures are meant to be 50PSI. My 3 tyres hover around 48-50PSI most of the time. But this new tyre can only inflate to a maximum of 40PSI meaning it will be quite a bit lower than the other three. Will this be dangerous?

AdrianC

premiumz said:

We ran over a nail today and it punctured our driver side tyre. Luckily Quickfit had 1 tyre our size left in stock and said they could do it. It was 30 minutes before they closed, so I rushed down there.
It was the only tyre they had but it was a decent one at £305, Bridgestone
The problem is, when I got home I had a look at the tyre pressure as the mechanics don't seem to inflate tyres all the way so you need to do it yourself.
It was 40PSI. My other 3 tyres are 50PSI.
This has me concerned that this tyre will not have equal pressure on the road if the other tyres are slightly bigger?
Is this potentially dangerous?

I assume you mean "the others are slightly harder", not bigger, and they're actually all the same size?
So set all four to the same pressure... Takes a minute. If you don't have a pump, go to the petrol station. I mean, you do check the pressures yourself regularly, right?

50psi is feasible for a Q7, at least the rear, assuming you're usually using it fully laden. But even then it's overinflated for the front.

TBH, it sounds like the tyre place are nearer right here, and at least one of your old ones is over-inflated.

(yours may differ slightly)

In case you're not sure what that's saying, the tyre sizes are in three basic groups.

Lightly laden, the three groups vary:
255/55 18 (unless V rated) and 265/50 19 should be 35 all round.
275/45 20 (Y rated) should be 39 F/35 R.
Anything else, including 255/55 18 V rated and 275/45 20 V rated M+S, should be 38 all round

Fully laden, all should be 44 F, 49 R.

The space-saver spare should be 51.

lesalanos

It's only likely to affect handling, tyre wear and fuel efficiency
Are the tyres the same size?  Same load ? 
Does the fitted tyre meet manufacturers recommendations?

premiumz

AdrianC said:

premiumz said:

We ran over a nail today and it punctured our driver side tyre. Luckily Quickfit had 1 tyre our size left in stock and said they could do it. It was 30 minutes before they closed, so I rushed down there.
It was the only tyre they had but it was a decent one at £305, Bridgestone
The problem is, when I got home I had a look at the tyre pressure as the mechanics don't seem to inflate tyres all the way so you need to do it yourself.
It was 40PSI. My other 3 tyres are 50PSI.
This has me concerned that this tyre will not have equal pressure on the road if the other tyres are slightly bigger?
Is this potentially dangerous?

I assume you mean "the others are slightly harder", not bigger, and they're actually all the same size?
So set all four to the same pressure... Takes a minute. If you don't have a pump, go to the petrol station. I mean, you do check the pressures yourself regularly, right?

50psi is feasible for a Q7, at least the rear, assuming you're usually using it fully laden. But even then it's overinflated for the front.

TBH, it sounds like the tyre place are nearer right here, and at least one of your old ones is over-inflated.

(yours may differ slightly)

In case you're not sure what that's saying, the tyre sizes are in three basic groups.

Lightly laden, the three groups vary:
255/55 18 (unless V rated) and 265/50 19 should be 35 all round.
275/45 20 (Y rated) should be 39 F/35 R.
Anything else, including 255/55 18 V rated and 275/45 20 V rated M+S, should be 38 all round

Fully laden, all should be 44 F, 49 R.

The space-saver spare should be 51.

We drive to France quite a bit. 4 of us and tons of luggage.
So although my three scorpion tyres have a maximum pressure of 50PSI and my new bridgestone tyre has a maximum pressure of 40PSI. I'm not meant to be inflating them to those numbers? Even if I inflated them to a lower PSI. Say, 44. The new tyre cannot go that high as it is 40 PSI maximum. So I would need to inflate that one all the way to 40 to get close to the other three and it still wouldn't be the same.