Loaded tire pressure

[Aaron_D]

Sure it does. Beyond the static inflation condition, equal additional deflection in a filled vs unfilled tire will cause a higher pressure in the filled tire. This prevents the filled tire flattening as much as the unfilled under equal load. For this reason you can run the filled tire softer in general, giving a good ride and still not too much squat under heavier loads.
larry

What you said is all correct except you won't see equal deflection. The deflection is based on the load vs. compressible volume. When you replace the air with a liquid your compressible volume decreases but normal force remains the same. When a load is applied the air will compress until the pressure rises until it can compensate to be able to have the correct normal force to counteract the applied load. Same load, lower air volume = less deflection.

 

[SPYDERLK]

Sure it does. Beyond the static inflation condition, equal additional deflection in a filled vs unfilled tire will cause a higher pressure in the filled tire. This prevents the filled tire flattening as much as the unfilled under equal load. For this reason you can run the filled tire softer in general, giving a good ride and still not too much squat under heavier loads.
larry

What you said is all correct except you won't see equal deflection. The deflection is based on the load vs. compressible volume. When you replace the air with a liquid your compressible volume decreases but normal force remains the same. When a load is applied the air will compress until the pressure rises until it can compensate to be able to have the correct normal force to counteract the applied load. Same load, lower air volume = less deflection.

Yes, that is the beauty of a filled tire. Pressure rises quickly with additional load so the tire doesnt mash down so much that it endangers the sidewalls. The pressure in an unfilled tire hardly rises at all as it flattens- the load [the product of pressure and contact area] being borne almost soley by increased contact area. In a filled tire pressure increases more significantly, so the area does not have to increase as much. That means it doesnt deflect as much. You can set up a filled tire softer without concern for heavier load conditions you may encounter that would flatten an unfilled tire to the point of damage.
larry

 

[Signa]

I don't know about everyone else, but I get on my tractor for a lot of reasons - the most primary being to NOT think about calculus or physical chemistry. I'm sure there's some sort of forum out there for such things!

 

[The Haymaker]

Yes, the static pressure will be the same, but under load, pressures will increase greatly, ending up in a harsh ride. I use someone elses theory of adding air until the full tread makes contact with the ground.

When working with the front suspension of a dirtbike, a very powerful tool is to change the oil level in the forks. You can greatly reduce bottoming without affecting compression or rebound damping simply by adding 10mm of oil to each tube. Reason being is that the increased volume of non-compressible oil cuts down the air space at the top of the fork. This creates a much more rapid pressure rise to slow or stop the compression of the fork before full travel is reached. Add too much oil, and the pressures will rise to the point of extreme harshness (sore wrists!) or actually blowing the seals out.

Same theory behind the bad things that happen when you add 4 quarts too much oil to a Ford Tempo motor. "But, the engine light was on, so I added oil." she said.

 

[SPYDERLK]

Yes, the static pressure will be the same, but under load, pressures will increase greatly, ending up in a harsh ride. I use someone elses theory of adding air until the full tread makes contact with the ground.

[When working with the front suspension of a dirtbike, a very powerful tool is to change the oil level in the forks. You can greatly reduce bottoming without affecting compression or rebound damping simply by adding 10mm of oil to each tube. Reason being is that the increased volume of non-compressible oil cuts down the air space at the top of the fork.]

Progressive springing w/o more spring coils. Extremely effective. I did it on roadbikes. Lets you run a lower rate spring with just a slightly higher preload. Gives a good ride with powerful anti bottoming characteristic. :thumbsup:
larry

 

[mustangsallysdad]

Wow... Hate to jump into this storm but... The compressibility of the ballast liquid has no affect on straying from your mfg recommended tire pressure. Yes liquids are not incompressible (nothing is) but due to their low compressibility they are often assumed to be so. Additionally the change in temperature changes the density vastly more than pressure and even if the density changed, the pressure is equal throughout.

In a standard automotive tire for every 10 degrees the pressure changes approximately 1 psi. As a tractor tire has way more volume, it should be more. Adding a liquid would reduce the volume of air changing the affect of density. As SPYDRLK stated, lowering the volume of air does slightly change the way your tire reacts to tire deflection by requiring the air to compress more per its volume making the ride more harsh. It doesn't change the internal pressures the tire see's though.

Keep the pressure the same. By that I mean that your pressures should reflect your usage and load at the time. There is no 1 perfect tire pressure. The mfg recommended pressure is the starting point (general one size fits all) but usage dictates the proper pressure for your need. Just don't exceed the max pressure rating on the tire.

I just found my car washing sponge crying uncontrollably in it's bucket...seems it was quite disheartened to find out that "nothing is compressable".

 

[sevilla]

I started this thread with a legitimate question, I believe. But the thread is getting out of control. More than the tire pressure perhaps we should talk about blood pressure!

 

[mustangsallysdad]

I started this thread with a legitimate question, I believe. But the thread is getting out of control. More than the tire pressure perhaps we should talk about blood pressure!

You think!!! LOL...In all seriousness...it is obviously a VERY subjective subject...go with what works for you...you'll find a sweet spot that encompasses all of the things you are looking for...everything is somewhat of a compromise. PSI, load handling, weight of implements, contact patch, bead rollover, sidewall deflection and ride quality will all relate to one another in some way. Try what YOU THINK is best for your situation and adjust up or down as you feel necessary. It comes with experience, really. As you can see, we all have our opinions (sometimes heated) and it boils down to personal preference or experience. You really got everybody goin' didn't ya??? Good luck, you'll figure out what's best for you.