I was thinking again (ya i know always a bad thing) does tire pressure increes when you put the weight of the car on it?
I was thinking again (ya i know always a bad thing) does tire pressure increes when you put the weight of the car on it?
A very tiny amount approching 0.
I've noticed a slight increase in the past. I've been meaning to test that theory on a greater scale since I amost always inflate tires while they are on a hoist.
The weight of car mostly just distorts the shape of the tire, not the volume, right? So it would stand to reason it wouldn't have any significant effect. That said, I've never measured this in anyway, so I could be completely wrong.
The distortion of the tire versus volume and the resistance to expansion are all factors. I am betting bias ply tires react different than radials and sidewall stiffness all play a part as well. I need to actually check this. With radials having so much steel in them I bet that you are getting distortion of the tire and no aprecable change in tire volume. Where as a bias ply tire can expand and contract with loading causing greater changes in pressure. Does this make cence?
I would suggest that very little stretching takes place (as in none), but the deformation can change the volume of the tire. Different shapes have different surface:volume ratios, and not stretching or compressing the tire just means the surface stays constant while the shape is changing due to deformation. The ratio and thus the volume may change with that deformation.
I haven't tested (it'd be an easy test, though!), but I think Toyman's answered it.
An "idealized" tire would simply deform until the surface area on the ground in square inches multiplied by the tire pressure in psi was equal to the weight on that tire. Carcass stiffness will reduce that amount of deformation. Which, I suppose, is how we can have different size contact patches by changing tire sizes.
I've tested this.
The answer is, it depends on the tire.
Race tires, or other stiff sidewall tires will not change at all (at least nothing that is measurable with typical instrumentation).
Cheapo squishy soft sidewall tires will increase as much as 2 psi.
The volume DOES change. Picture a flat flask type container. Fill it with water. Now stretch the sides away from each other. The container will increase in volume. The surface area of the outside does not change, but one shape is flat or concave, and the other is convex, therefore the volume is very different. Obviously, an extreme example.
Food for thought. http://www.bridgestonetrucktires.com/us_eng/real/magazines/98v3issue4
Food for thought from our favorite forum. http://grassrootsmotorsports.com/forum/grm/tire-pressure-hoist-vs-on-the-ground/3231/page1/
my 5 beer .02 worth thinking
just putting the car on the ground, being tread and sidewall are flexible to an extent, any loaded weight put on the tread contact patch should deform the sidewall out to an extent, not seeing a measurable pressure increase there
MG_Bryan wrote: Food for thought from our favorite forum. http://grassrootsmotorsports.com/forum/grm/tire-pressure-hoist-vs-on-the-ground/3231/page1/
Wow. Now THAT was a thread that spent WAAY too much energy on this!
SVreX wrote:MG_Bryan wrote: Food for thought from our favorite forum. http://grassrootsmotorsports.com/forum/grm/tire-pressure-hoist-vs-on-the-ground/3231/page1/Wow. Now THAT was a thread that spent WAAY too much energy on this!
Yeah, I think this topic has already been pretty thoroughly examined, but if someone wants to do more testing I'd be interested in their results.
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