I think I remember reading that a gallon of gas weighs about 6lbs. So, that means when a 4th gen is on empty and is filled up, it gains over 100 excess lbs in the rear.

Would that be enough of a weight gain to justify putting more air in the tires to offset the extra weight?

The reason I mentioned it is that my car seemed to ride a bit bumpier after the fillup.

 

If the tires are slightly low, they should actually ride smoothere because they squish more when you hit a bump unless you are actually hitting the rim in an extreme case. 100 pounds will not make a substantial diferance on the tires since that is only about 3% of the total car weight. The extra wieght could be bottoming out tired shocks more frequently though so you may want to look into replacing them.

 

Your choice. Some people get alignments with full tank and ballast in the driver's seat. It's up to you on nitty-gritty details.

Jae

 

so by your logic, you'd be constantly adjusting the air pressure depending on how much gas is in your tank? There might be a 100lb difference from completely empty to completely full, but you're not driving around very often in those conditions. If you want to follow that logic even further you better start adjusting your tire pressure each time you have a passenger in your car. Then adjust again when you have 2 passengers. Then adjust your tire pressure again when your by yourself. Doesn't make much sense now, does it?

 

give it a try man, sounds true to me.

 

Why would you want to add extra air? Air pressure in the tires remains the same regardless of the amount of weight they are supporting.

 

According to Boyles Law, air pressure increases inversely proportional to volume.

Adding extra weight to the amount that tires have to support would cause them to deform more, which would, in turn, reduce the volume of air inside them.

Think, "Squeezing a balloon."

Even if air pressure and volume remained unchanged as weight was added while the car was parked, it wouldn't when the car is driven, because, thanks to heat given off from air molecules, the temperature inside the tire rises with both the amount of driving one does and the load that the tires have to carry.

NOW, why do you think that every tire manufacturer advises drivers to add extra air pressure if they plan on driving with a full load of passengers or cargo?

Simple: the extra air pressure reduces the temperature inside the tires because the volume of the tires increases. So, if both air pressure and
volume increase, then there has to be a concomitant drop in molecular friction.

 

Everything you said is abolutely correct. However, 100lbs is minascule in the big picture. If you want to change your tire pressure every 1/8 tank, have at it.

 

You could leave your tire pressure the same and stop at the fuel station everyday.... Again

 

hahahaha funniest post all day!

 

tire pressure changes with temperature, not weight

 

Tire pressure changes with temperature and or weight.... Physics.

 

To quote the over thinker^, Think of squeezing a balloon. When you squeeze it you decrease the volume and increase the pressure, even to the point that it pops. If the pressure did not increase, it would not pop.

 

Measure tire pressure when a wheel is removed from the car and when it is supporting the cars weight. The pressure will remain the same. I've done this many times.

 

Incorrect assumption. This is what invalidates your argument. Volume does not change. The shape of the tire is what changes. The same flexibility that allows the part of the tire in contact with the road to "sag" allows the rest of the tire to expand to maintain the same volume. Please do the test I mentioned in the previous post.


As for the balloon comparison, it's not the reduced volume/increased pressure that causes it to burst. It's the fact that when you squeeze it and the balloon expands at certain points to maintain the same overall volume, the balloon becomes too thin to contain the pressure at those points and ruptures. Pressure remains the same the whole time. A tire just happens to be strong enough to be able to change shape without rupturing like a balloon would.

 

Maybe you need to check your rear suspension.

 

The added pressure is needed to reduce the tendency of the tire to sag where it meets the road so the bead isn't broken and/or to increase lateral stability in the sidewall.


BTW, asking this question doesn't help your cause. If pressure increased with added weight this problem would take care of itself, right? The fact that you have to add air means that air pressure remains the same regardless of weight.

This makes no sense. Sure there's more volume, but there's also more air to match. For molecular friction to be reduced, volume and air pressure need to go in opposite directions. If air pressure rises protionately as volume goes up, then density has to go up as well. Higher pressure (regardless of volume) = higher density = higher friction.

 

Thank you. We finally agree on something.

 

the volume is the same no matter what.
i think the balloon analogy is the best for abstract thought.

 

wow you learn something new everyday however i dont understand rocket science so i didnt learn today....lol j/k good theory though. i expected to read this and laugh but it accually made me think