Tire pressure question..

[rcy]

Weird question...but....if I inflate my tires with the vehicle off the ground, will the psi increase when the vehicle is lowered and the tire is being compressed by the weight of the vehicle?

I meant to test this today when I switched from winter rims/tires to summer, but I forgot. I could just jack up one corner of the vehicle to check this, but I'm sure someone here will have the answer.

 

[abycat]

Well how this, A tire guy puts the correct pressure into the tire after he seats the bead so then its off ground so to speak. It must change but what do YOU set your tires at (pressure wise)? The door sticker or close to your max? most people dont know the correct pressure for their situation. Im just curious what you personally go by.

 

[gathermewool]

Not much, since the area the pressure is acting on doesn't change. The tire may flex or change shape, but the overall surface area remains nearly constant.

 

[Donald]

The pressure should be set via the sticker on the door with the vehicle on the ground gas tank full, driver in his seat and mother in law in back seat. That assumes your tires are somewhat close to what came from the factory. Some vehicles have a pressure listing for 1/2 load and full load. Full load would be w/mother-in-law.

 

[eljefino]

The area inside the tire won't change more than under one percent, so you won't measure it with your pencil stick thing, be under a third of a pound. And yeah the side will bulge when the bottom gets compressed.

The only car I ever had that told me to run different pressures was my dodge spirit. Probably wanted softer ride at 32 PSI (lightly loaded) but had to pump up to 35 PSI because of nearing the tire's load range.

Manual also said (IIRC) to pump them all up to 35 if spending lots of time driving really fast.

 

[rcy]

Originally Posted By: abycat
Well how this, A tire guy puts the correct pressure into the tire after he seats the bead so then its off ground so to speak. It must change but what do YOU set your tires at (pressure wise)? The door sticker or close to your max? most people dont know the correct pressure for their situation. Im just curious what you personally go by.


I go by the vehicle manufacturer's recommendation - usually found on a placard or sticker somewhere in the vehicle (typically the door jamb, driver's side, though I have seen it in the glovebox or the centre armrest console.

 

[Garak]

Fuel tank door on the old Audi, of all places. It had the heavy load/light load specs, too.

The max on the tire is certainly not a good idea. The placard on the G says 33 pounds. The tires are rated to 51 pounds, and I'm NOT putting 51 pounds in a passenger car tire, unless I want it to ride like a grocery cart.

 

[wkcars]

Yes there will be a slight change in pressure, but not enough to matter or enough for most tire gauges to even measure the difference, you probably get more error from each time you measure the tire depending on how you work the tire pressure gauge on the valve stem than what the change in pressure is. This is assuming tires are in good condition and not deteriorated.

 

[Chevys_n_Hawgs]

Originally Posted By: Donald
The pressure should be set via the sticker on the door with the vehicle on the ground gas tank full, driver in his seat and mother in law in back seat. That assumes your tires are somewhat close to what came from the factory. Some vehicles have a pressure listing for 1/2 load and full load. Full load would be w/mother-in-law.


That's the funniest thing I've read on BITOG tonight! I pretty much second Donald's vote on what he said.

 

[CapriRacer]

Originally Posted By: rcy
Weird question...but....if I inflate my tires with the vehicle off the ground, will the psi increase when the vehicle is lowered and the tire is being compressed by the weight of the vehicle?

I meant to test this today when I switched from winter rims/tires to summer, but I forgot. I could just jack up one corner of the vehicle to check this, but I'm sure someone here will have the answer.


I've done this with a sensitive pressure gauage and got between 0.1 psi and 0.5 psi loaded to unloaded.

In other words - Don't worry about it.