Tire Pressure

[garman]

Yea seems to vary based on wheel size, tire and or model.
Seems all the 18" Wheels with the 255 tires found on models like the Lariats call for 30 PSI.

Sounds like the 17" the OP has is calling for 35 psi.

I want to say the Raptors 17" 285s call for 38psi not 100% on that off the top of my head.

For the record all my tires are set at 35 psi, now

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[purdyd]

Yea seems to vary based on wheel size, tire and or model.
Seems all the 18" Wheels with the 255 tires found on models like the Lariats call for 30 PSI.

Sounds like the 17" the OP has is calling for 35 psi.

I want to say the Raptors 17" 285s call for 38psi not 100% on that off the top of my head.

I just don’t understand why the pressure is so different on the door between the 17” and 18” Tires.

the tires aren’t really that different in size, have essentially the same load rating, same tire construction.

the chart from Australia makes more sense to me.

 

[cc1999]

I just don’t understand why the pressure is so different on the door between the 17” and 18” Tires.

the tires aren’t really that different in size, have essentially the same load rating, same tire construction.

the chart from Australia makes more sense to me.

All I can speculate on, is that cast aluminum or steel can support mor weight then a rubber sidewall.
‘I could see how more sidewall could potentially need a bit more air to compensate in terms of load carrying capacity compared to a smaller sidewall and larger wheel.

 

[cc1999]

For the record all my tires are set at 35 psi, now

Since we can get 30-50 degree temp swings here this time of year I have our Lariats set at 32-34 psi.

I have my Raptors set at 36-38 psi.

I want to say you can potentially see up to a 2 psi pressure swing for every 10 degrees of ambient temp variance. A 38 psi tire at 80 degrees outside could fall low enough to trip the tpms light in the dash on 20 degree day. So I set them at 34 on 50-60 degree day to try and compensate to keep them in safe range regardless of the temp swings we get this time of year.

 

[purdyd]

All I can speculate on, is that cast aluminum or steel can support mor weight then a rubber sidewall.
‘I could see how more sidewall could potentially need a bit more air to compensate in terms of load carrying capacity compared to a smaller sidewall and larger wheel.

well 6.5“ sidewall versus 7”

that doesn’t seem to me like it should be 8psi difference to. Me

i believe sl tires are rated at 36 psi and the 255/70 r17 actually has a higher max load

and then there is the chart from the ford Australia where the pressure for the two tire sizes is the same

 

[Jason B]

I just don’t understand why the pressure is so different on the door between the 17” and 18” Tires.

the tires aren’t really that different in size, have essentially the same load rating, same tire construction.

the chart from Australia makes more sense to me.

Might have something to do with the volume of the tire.
That's why road racing bicycle tires can be up to 80 - 100 PSI.

 

[purdyd]

Might have something to do with the volume of the tire.
That's why road racing bicycle tires can be up to 80 - 100 PSI.

since they are the same width, the volume difference is the ratio of the side wall dimension

7/6.5 * 30psi = 32.3 Psi. That is a lot less than is on the doors for the 17” wheels

but once again there is the chart from Australia that shows recommended pressure is the same

and

the 255/70 r17 has a load rating of 112 at 36 psi
The 255/65 r18 has a load rating of 111 at 36 psi

so you could actually push a little less air in the r17 tire to have the same load carrying capability.

https://www.discounttire.com/learn/load-range-load-index

 

[stemplar]

I want to say you can potentially see up to a 2 psi pressure swing for every degrees of ambient temp variance.

Umm, no. More like 1-2psi per TEN degree (F) swing, assuming regular air in the tires. Nitrogen-filled tires are more temp-stable.

 

[purdyd]

Umm, no. More like 1-2psi per TEN degree (F) swing, assuming regular air in the tires. Nitrogen-filled tires are more temp-stable.

I can tell which side of my vehicle is facing the sun by the tire pressure.

id be curious what the internal temp is in that condition

i understand that the tire temp can be displayed by using forscan

 

[cc1999]

Umm, no. More like 1-2psi per TEN degree (F) swing, assuming regular air in the tires. Nitrogen-filled tires are more temp-stable.

Umm, yes. Is there really a difference between me saying up to 2 psi and your saying 1-2 psi? LOL

 

[stemplar]

Umm, yes. Is there really a difference between me saying up to 2 psi and your saying 1-2 psi? LOL

…per what? There’s a difference between “per psi” and “per TEN psi”

 

[cc1999]

…per what? There’s a difference between “per psi” and “per TEN psi”

Fixed it was meant to read up to 2 psi per 10 degrees of temp swing.

 

[Jason B]

since they are the same width, the volume difference is the ratio of the side wall dimension

7/6.5 * 30psi = 32.3 Psi. That is a lot less than is on the doors for the 17” wheels

but once again there is the chart from Australia that shows recommended pressure is the same

and

the 255/70 r17 has a load rating of 112 at 36 psi
The 255/65 r18 has a load rating of 111 at 36 psi

so you could actually push a little less air in the r17 tire to have the same load carrying capability.

https://www.discounttire.com/learn/load-range-load-index

What's it say on your doors? My 2024 XLT FX4 with 255/70-R17" wheels says 30 PSI.
The Ford Pass App says "Optimal cold tire pressure is 30 PSI"

 

[purdyd]

Mine says 30 psi 255/65 r18 too. Being the same makes sense to me

but I’ve seen much higher pressure for the 255/70 r17

https://www.ranger6g.com/forum/threads/tire-pressure-question.13791/

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