Best tyre pressures - your experiences

[AndyP1957]

Puma 1.0 ecoboost 2020

Tyres 215/50 R17/98W

 

Curious to what experiences and values other drivers use for their tyres.

When I purchased new my tyres were 30 30  28 28

In the handbook and door plate for 1-3 people   it reads  35 35 30 30

 

When the car was serviced they said that was too high, so recently have been checking on tyre websites online and there seems to be so many variances as to what psi to use

Currently I have settled on   32 32   28 28   psi

 

 

 

[unofix]

Well I used to think it was all about road holding and how the vehicle handles but recently I've been educated by Corey who says the correct pressure is all about how a tyre looks 🤣🤣

 

[Eric Bloodaxe]

Well, call me boring, but it occurs to me that the vehicle manufacturer ought to know the best tyre pressures for the vehicle they have designed and manufactured, so I would (and do) go by what it says on the door plate/in the handbook.

Why your servicing garage (especially if a Ford dealer) would advise otherwise, I don't know.

 

[iantt]

I thought the plate said 2.3 and 2.1 bar so 33 and 30 psi? , Ah that's 18 in. 

So 2.4 bar and 2.1 for 17 in 

 

 

[AndyP1957]

Its the fact that the Handbook contradicts the plate, and searching for tyres on various supplier websites often get another figure again - then the dealer put something different into the tyre at the outset

You would think someone would know 

Bewildering is an understatement

[Eric Bloodaxe]

32 minutes ago, AndyP1957 said:

Its the fact that the Handbook contradicts the plate

? According to your initial post they both said the same:

On 11/18/2022 at 10:33 AM, AndyP1957 said:

In the handbook and door plate for 1-3 people   it reads  35 35 30 30

 

[StephenFord]

On 11/18/2022 at 5:27 PM, iantt said:

I thought the plate said 2.3 and 2.1 bar so 33 and 30 psi? , Ah that's 18 in. 

So 2.4 bar and 2.1 for 17 in 

Now, I was always taught that the size of wheel is a red herring, the pressure remains the same if it were a factory 16", or upsized to 17" or even 18". Have I been wrong all these years?

[iantt]

19 minutes ago, StephenFord said:

Now, I was always taught that the size of wheel is a red herring, the pressure remains the same if it were a factory 16", or upsized to 17" or even 18". Have I been wrong all these years?

Yes, you've been wrong all these years.🤣🤣🤣, 

[Tizer]

34 minutes ago, StephenFord said:

Now, I was always taught that the size of wheel is a red herring, the pressure remains the same if it were a factory 16", or upsized to 17" or even 18". Have I been wrong all these years?

Not true. For my exact model and specification of car, the two different Tyre sizes have completely different pressures. 38-38 for the 195-65-16 and 33-33 for the 205-60-16, quite a difference.

[StephenFord]

6 minutes ago, Tizer said:

Not true. For my exact model and specification of car, the two different Tyre sizes have completely different pressures. 38-38 for the 195-65-16 and 33-33 for the 205-60-16, quite a difference.

I need this explained to me, pressure is a constant, whether it is an 18" rim, or a 16" rim - all other things being equal, why would it need to change because of the volume size changing inside the tire? 

[Tizer]

1 minute ago, StephenFord said:

I need this explained to me, pressure is a constant, whether it is an 18" rim, or a 16" rim- all other things being equal. 

I'm not sure what you mean. Both the figures I quoted are for 16-inch wheels on the same spec of car, The 17-inch ones are the same as the second 16 inch one and the 18-inch one is different from all the rest.

The models with 17 and 18-inch wheels may weigh a different amount and may be faster than my one.

[alanfp]

This is only a "quick and dirty" answer, but it might help...

Pressure is measured in psi 

or Newtons per square metre

Either way, it's force per unit area, so if the area (like the footprint on the tarmac) is different , and the vehicle weighs the same, then the pressure would be different. 

 

 

[AndyP1957]

On 11/25/2022 at 6:10 PM, Eric Bloodaxe said:

? According to your initial post they both said the same:

 

sorry typo - the fact that the Dealers service department contradicted the book and plate

[Vendee]

On 11/25/2022 at 7:54 PM, StephenFord said:

I need this explained to me, pressure is a constant, whether it is an 18" rim, or a 16" rim - all other things being equal, why would it need to change because of the volume size changing inside the tire? 

All other things are not equal. Tyre width and aspect ratio are different. Contact patch will be different. Rotational speed may be different.

[StephenFord]

11 hours ago, Vendee said:

All other things are not equal. Tyre width and aspect ratio are different. Contact patch will be different. Rotational speed may be different.

Yes, but the PRESSURE should remain the same LOL

[unofix]

18 minutes ago, StephenFord said:

Yes, but the PRESSURE should remain the same LOL

You are indeed correct, 32psi in a 16" tyre will still be 32psi in a 18" tyre. I think that the issue here as i see it, is that with a larger tyre which typically has smaller side walls, it can be necessary to run the tyres with a reduced pressure, eg. 30psi to improve ride comfort and to allow the wider tread to make more contact with the road.

A tyre with a smaller side wall and a wider tread will tend to want to run more on just the centre of the tread pattern (like an egg) if the pressure is maintained the same as a tyre with high sidewalls and a narrow tread. Not sure if any of that has helped but that's my two cents for what it's worth 🤣

[Tizer]

26 minutes ago, unofix said:

You are indeed correct, 32psi in a 16" tyre will still be 32psi in a 18" tyre. I think that the issue here as i see it, is that with a larger tyre which typically has smaller side walls, it can be necessary to run the tyres with a reduced pressure, eg. 30psi to improve ride comfort and to allow the wider tread to make more contact with the road.

A tyre with a smaller side wall and a wider tread will tend to want to run more on just the centre of the tread pattern (like an egg) if the pressure is maintained the same as a tyre with high sidewalls and a narrow tread. Not sure if any of that has helped but that's my two cents for what it's worth 🤣

I'm not an expert but I think there is more to it than that.

My Tyres are 195 65 16 and the recommended pressure is 38psi. They are also Load Rated at 92 and Speed Rated at V.

If I ran them at 33psi, which is the recommended pressure for the alternative size for my car (205 60 16) then I would imagine that because the Sidewall on mine is massive it would flex too much and flap about like a Flounder.

Incidentally, the Tyre size on mine does not give a very comfortable ride and I imagine that is because the massive sidewall needs to be so much stronger to make it comply with the quite high Load and Speed rating compared to a Tyre with a small sidewall with the same rating. 

[Vendee]

On 12/4/2022 at 10:33 AM, StephenFord said:

Yes, but the PRESSURE should remain the same LOL

No, as others have alluded to, the factors which decide the correct pressure have changed. You seem to expect every tyre size, width, aspect ratio on every car to be running on a single universal pressure. That's just not the case.

[unofix]

I think it is safe to accept that this subject was brought to a conclusion on Sunday.