Hyperinflating tires

[PaleMelanesian]

Originally Posted by cookie96civic

I'm running them at 45, and the eoc difference is visibly noticable. Where i used to come to a stop, bump starting at 20 in 3rd I have to substantially brake harder towards the stop sign or start the eoc much earlier. One EOC that I do which used to last .8 miles, is now almost 1.2 miles, so I can start about 5 MPH slower without blowing the red light. With adding P&G to the mix and knocking some weight off the car, I have seen an incredible increase in MPG. Check my chart on the last 2 fill ups, roughly 4-5 MPG. I'm tired of typing.

Just last month, I informally tested 55 vs 60 psi. There's a certain long but gentle downhill on my commute, about 1/2 mile long. 55 psi would just maintain speed at 40mph, while 60 psi would gain about 5, to 45mph at the bottom.

[mohr84]

Originally Posted by tasdrouille

I would absolutely LOVE to see someone take an old wheel and pump the tire till it bursts. What I read in the past lead me to believe it would not burst below 150 psi.

Anyone got an old wheel in his backyard, a compressor with a pretty long hose, and some place to take cover? (That could turn into a redneck's "watch this" so play it safe)

Several Years ago my friends little brother pumped up a flat tire on his mother's mini-van. He did not know how to do it, so he just kept the compressor on for several minutes. My friend and I went out and saw that the tire was clearly over inflated. We took a pressure gauge to see what the pressure was. The pressure was so high that it shot the measuring stick out of the gauge about 10 feet. If I recall correctly, it was a 75psi gauge. I would guess that the pressure was over 100psi to destroy the gauge like that.

[CapriRacer]

Originally Posted by bikin' Ed

Years ago, when employed by a certain US tire maker headquartered in Akron, OH, I was told that passenger tires had to be able to withstand 15% mor load and 15% more pressure than what is posted on the sidewall. This was not the manufacturer's, but rather DOT"s testing requirement. Based on that info I have always pumped my tires to the max on the sidewall.

Sorry, but the DOT regulations specify a test that uses the load that is written on the sidewall (called the rated load) and its corresponding pressure (called the rated pressure), but the regulations only specify the tire has to MEET that rated load / rated pressure combination per the conditions of the test. It is common for tire manufacturers to have an internal acceptance level that is higher for the load (once the test starts, you don't change the pressure), but the regulations are moot on this point.

BTW, there is a disagreement between tire manufacturers concerning what the regulations say about what pressure should be imprinted on the sidewall of a tire. As a result, you will see different pressures for what are essentially the same tires. What is written on the sidewall of a tire is also based on a note in the tire standardizing load tables and is usually higher than the rated pressure (keeping in mind the disagreement mentioned above).

[moorecomp]

All,

While looking for hard evidence in regards to the question of over/hyper inflation of tires, I came across a technical report from the National Highway Traffic Safety Administration. Report number DOT809297 titled "An Evaluation of Existing Tire Pressure Monitoring Systems". Does'nt sound as if it would say much about overinflation, but they evaluated TPMS's based on direct pressure and also indirect systems. The indirect systems detect a low tire based on the decreased rolling radius (circumference) of a tire that has lower pressure. Twice in this report (Section 2 - Objectives - page 2, paragraph 1 and Section 3 - Systems Tested - page 27, paragraph 3) it was stated "It should be noted that though tire over-inflation leads to accelerated tire wear (in the center of the tread pattern), it is not known to be a significant safety issue." Later in the report, when talking about Wheel Speed Based systems, Section 9 - Discussion - page 102, "This can be attributed to the fact that the rolling radius of modern, standard- profile radial tires will only change about 1mm when the tire pressure drops from 2.1 to 1.4 bars (30 to 20 psi) (See Figure 9.1)." The figure 9.1 shows a straight line correlation between pressure and rolling radius, so it would correspond that a 1mm increase would be seen with a 10psi increase in pressure. 1 freaking mm increase in circumference! Any center tread wear would be hardly noticable! It's not like we are talking about would happen to a bias ply tire.

As far as the person who wants to know why race cars have wide tires, no one has mentioned that tires have different compounds. Racing tires are sticky. They have a higher coefficient of friction than street tires. Dragsters do a burn out to get them up to temp and make sure they are as sticky as they can be. The only problem with that is that sticky means soft and they wear much quicker. A narrow, soft tire would wear out very quickly, so to make them last as long as practical, they must have more material, a larger surface area to spread the load and heat. It is a balance between traction and durability. Think about different street tires and the wear ratings. Some tire are rated for 45000 miles, and some are rated for 65000 miles. The higher rated tires are a harder compound, and wear longer, but have to sacrifice traction. High performance street tires are not the best choice for us hypermilers, even if you overinflate them.

As for inflation pressures, car manufacturers and tire manufacturers have the same balancing act, comfort, durability, safety, performance, even asthetics. Is putting more air in a tire any different than removing weight from your car and running the tire at the "normal" pressure? Both reduce the rolling resistance. Running a tire 10% over the sidewall rating is a compromise that I choose, I don't load my vehicle to max, I know I "may" have sacrificed some resistance to road hazard damage or reduced handling. I drive them like I would if the road was wet all the time. I don't follow close and look ahead. I live in Northern Michigan and we have enough practice in the winter!

There is a big difference in simply putting air in a tire until it explodes, and putting a tire on a car, overinflating it and loading at or beyond its rated capacity, and then running until it explodes. I see it as long as we stay well below the load rating, we can safely run elevated pressures. Tires that are overinflated generate less heat due to sidewall flex, and heat is the number one killer of tires.

Lastly, from the report - "Alerting a driver to the condition of overinflation may also be beneficial. Overinflation causes excessive wear to the center of the tread pattern and shorter tire life. This condition is not known to be dangerous; however, avoiding overinflation and ensuring expected tire life would increase consumer satisfaction. Since overinflation is not known to present the same danger that underinflation does, a different visual display should be used to indicate overinflation."

[whitevette]

Originally Posted by PaleMelanesian

Just last month, I informally tested 55 vs 60 psi. There's a certain long but gentle downhill on my commute, about 1/2 mile long. 55 psi would just maintain speed at 40mph, while 60 psi would gain about 5, to 45mph at the bottom.

Excellent road test! As long as one pays attention to head/tailwinds and conducts these tests in the dry ( no wet, no damp!) the results should impress any disbeliever. Wait! Is gravity constant in your test area? LOL!

[trikkonceptz]

He may have done his road tests here;

The Mystery Spot Official Website

[RH77]

OK...

Still anyone with excessive wear or blowouts as a result of overinflation? Plenty of real-time, rolling data out there.

I'll be checking-in periodically with the same question. So far, no problems here at 50 psi / 3.45 Bar / 2586 mmHg.

As far as handling, handling is closer to 50/50 under/oversteer in wet weather. That's a plus IMO.

RH77

[MetroMPG]

Only Cd's leaking valve stems that I'm aware of...

[trikkonceptz]

Ha I love being topical .. Scratch your head at this one. While at lunch today I walk past an Expedition and it had it's front tires turned out. Wha caught my attention was that the center tread was worn almost smooth, but you could tell their was tread there at one time, yet the tire looked flat.

So what did I do, I ran back to my car and grabbed my mechanical gauge and measured their tire pressure. Figuring, if this is what everyone is talking about let me use an innocent by stander to prove a point. Well DS tire PSI = 22, PS PSI = 20, both tires were worn in the center third of the wheel.

So WTF? I doubt this truck spent its life @ 70 psi then reduced pressure to even out the wear .. LOL

[PaleMelanesian]

Originally Posted by PaleMelanesian

Just last month, I informally tested 55 vs 60 psi. There's a certain long but gentle downhill on my commute, about 1/2 mile long. 55 psi would just maintain speed at 40mph, while 60 psi would gain about 5, to 45mph at the bottom.

Originally Posted by whitevette

Excellent road test! As long as one pays attention to head/tailwinds and conducts these tests in the dry ( no wet, no damp!) the results should impress any disbeliever. Wait! Is gravity constant in your test area? LOL!

LOL! Dry both times, wooded back roads so wind is not a factor. Temperatures were about the same both times, mid-70's. They were two different days, but on my same commute, both with a cold start 2 miles earlier. Very much apples-to-apples, but not scientifically controlled.

I noticed the bit about only maintaining 40mph, so I checked my tires and found they were down to 55. I inflated to 60 and recorded the 45mph terminal speed the next morning.