tire pressure arument, help

[djrocketodd]

What do you guys think, assuming you are running stock size on a car, should the tires be filled with the psi that is printed in the doorsill, or close to the psi that is printed on the sidewall?

[gpomp]

doesn't matter what size tires you always use the one on doorsill

[infected]

Doorsill.

[TomcoPDR]

Doorsill

[GTS Jeff]

Chalk your tires and adjust pressure until all the tread is used but none of the sidewall is being scrubbed.

[97'Scort]

Doorsill. I had my tires put on at the Tire Warehouse, turns out they put 35 psi in the tire off the car (doorsill), which translated into about 50 psi ON the car. No wonder the stupid thing took every bump like the rubber was solid. Fixed now

[GTS Jeff]

Originally posted by 97'Scort
Doorsill. I had my tires put on at the Tire Warehouse, turns out they put 35 psi in the tire off the car (doorsill), which translated into about 50 psi ON the car. No wonder the stupid thing took every bump like the rubber was solid. Fixed now

Where did the 15 PSI come from?

[rahim]

Originally posted by GTS Jeff
Where did the 15 PSI come from?

the weight of the car

[djrocketodd]

So why does everyone say the doorsill, at that psi all tires that i have seen look flat and get the rubbing on the sidewall, especially aftermarket rubber, like on my teg. The doorsill calls for like 35 and the nexen rubber say 50, at 35 they are basically flat and trashed the sidewall...?? anyone else have these issues?

even my g/f's optra's tires have scrubbing on the sidewall and look flat from 32 psi, but the rubber says max 44?

[gpomp]

Originally posted by rahim


the weight of the car

the weight of the car has nothing to do with it. the volume of the tire never changes so the pressure inside always stays the same. the shape may change but the volume does not.

Originally posted by djrocketodd
So why does everyone say the doorsill, at that psi all tires that i have seen look flat and get the rubbing on the sidewall, especially aftermarket rubber, like on my teg. The doorsill calls for like 35 and the nexen rubber say 50, at 35 they are basically flat and trashed the sidewall...?? anyone else have these issues?

even my g/f's optra's tires have scrubbing on the sidewall and look flat from 32 psi, but the rubber says max 44?

maybe your gauge is broken.

[TomcoPDR]

Originally posted by djrocketodd


even my g/f's optra's tires have scrubbing on the sidewall and look flat from 32 psi, but the rubber says max 44?

Yea, fill ur gf's Optra tires with 44psi we're all wrong.

Seriously, it might be different with aftermarket or when you change the tire size (and profile of tires in return)...

If I'm reading OP correctly, he/she was just trying to find out how to fill original tire PSI as a maintenance measure. And most of our answer are from the vehicle's door sticker. The Max. psi on the tire is only a warning of what the tire shouldn't be exceeded on, which might or might not blow up in your face.

[gpomp]

Originally posted by TomcoPDR
Seriously, it might be different with aftermarket or when you change the tire size (and profile of tires in return)...

it doesn't matter what tire it is or what size the tire is, you should always fill it to the doorsill specs.

[TomcoPDR]

Originally posted by gpomp
it doesn't matter what tire it is or what size the tire is, you should always fill it to the doorsill specs.

never heard of anyone running at 50 psi on a passenger car

[whiskas]

Originally posted by TomcoPDR


never heard of anyone running at 50 psi on a passenger car

I run 48psi on my azenis, but only on the track. Use whatever it says on your doorsill for the street.

[TomcoPDR]

Originally posted by whiskas


I run 48psi on my azenis, but only on the track. Use whatever it says on your doorsill for the street.

Edit: As per answering to OP, I got the impression we're talking about regular street driving use. (he/she was saying something about filling STOCK tires)

Don't wanna make the impression I'm don't know much.

[gpomp]

well i run my radials at 12 psi for drag racing but that doesn't mean the op should, lol.

[GTS Jeff]

Originally posted by rahim


the weight of the car

Uhh no.

[hjr]

the rating on the tire is the MAX pressure for the tire, not the recommended pressure

[SilverRex]

hmm I also notice a change in PSI number before and after car is driven with. So its best to measure after a car has not been driven over night.

As far as the doorsill goes, that is what I do, my acura calls for 32 psi in the front and 31 in the rear I believe. however I do notice the tires look kinda flat (like it doesnt have enough PSI or something), im assuming this is normal?

[97'Scort]

Originally posted by gpomp
the weight of the car has nothing to do with it. the volume of the tire never changes so the pressure inside always stays the same. the shape may change but the volume does not.

Alright, let's look at some basic pressure calcs for a second here:

Pressure = force/area

pressure = B x (V1/v2) where B= bulk modulus (constant), V1 is the initial volume and V2 is the final volume.

However, by looking at a tire on a car and the same tire OFF a car, it is easy to conclude that the weight of the car has compressed the tire at the bottom. Now, the tire DOES expand, but it doesn't expand the same amount as the air ( or whatever gas you've put in). Therefore, the final volume is smaller than the initial volume, which would result in a pressure increase.

It might help to think of it this way: if you lean on a balloon, why does it eventually pop? The air inside is compressing, but the balloon doesn't want to expand at the same rate the air does at any point along its expansion curve. Once the increase in pressure is too much, the balloon breaks.

The moral of the story is to pump the tire to the doorsill pressure off the car, and once installed, adjust accordingly.