mythbusters tests tyre / tire pressure

[jakobnev]

Impressive gains up to 40psi. I wonder how the graph shifts when you go to a LRR-tyre, does it just move down, or does it move sideways too, giving you less or more gains with different pressures.

[user removed]

Perfectly even tread wear and 5% loss of tread depth after 24,000 miles. That's at 44 PSI, the rated max pressure. Measured to the thousandth inch with a dial caliper.

Same for another set of new tires (both sets bought new) on a different car.

Running my Altima factory tires at the same pressure.

Tires last a lot longer (less heat buildup and stress on the sidewalls).
Lower cost per mile due to longer tire life.
Significant increase in fuel mileage.

After 60k miles of running higher pressures I will never go back, and I drove over 600k using manufacturers recommended pressures over the last 45 years. Worked in the auto repair industry from 18 until 50 and ran my own shop the last 15 years.

regards
Mech

[metroschultz]

Originally Posted by euromodder

I very much doubt the overinflated tyre will fail on this side of 100psi .

I worked at the "Corner Gas Station" for many years.
I saw (literally) hundreds of passenger tires inflated at or very near 100psi.
These were older gentlemen who grew up with bias ply tires.
They were adding air to attempt to get rid of the characteristic side wall bulge of radial tires.
I would set the tires to car manufacturer spec, and next oil change they would have the tires right back up to 100.
To the best of my knowledge, none of these tires ever blew out.
Again, these are just my observations.

[MetroMPG]

See also: http://ecomodder.com/forum/showthrea...ures-2721.html

---

It would be nice to document their methodology (always good to be able to critique - to point out both the flaws & the good points).

So far, here's what I was able to note:

test car: 2004-2007 Ford Taurus

test methodology:

1. Lay out a driving course that simulates normal city driving with a series of stops, turns, etc.
2. Bypass the car’s gas tank and fit it with a fuel cell that can be removed and weighed in order to measure precisely the amount of gas used during each test.
3. Make sure tires are inflated to the recommended pressure of 35 psi for the control test.
4. Drive the course and calculate the gas mileage.
5. Repeat step 3 with tires extremely under-inflated (10 psi) and extremely over-inflated (60 psi).
6. Repeat step 3 with tires slightly under-inflated (30 psi — 15% lower than recommended pressure) and slightly over-inflated (40 psi — 15% higher than recommended pressure).
7. Analyze the results.

(source: TV Review: Mythbusters 8.23 – “MiniMyth Madness” | Fandomania )

So obviously the biggest flaw in their testing was the attempt to duplicate the exact same "real world", variable speed, stop & go type driving for each run. Impossible to do!

Even though it was on a closed course (removes variable of other traffic), and they attempted to time the stops & acceleration to ensure consistency, it's still silly. For best data, they need to remove the driver from the equation. Of course, footage of a car on a dyno would be boring TV (for the average non-Ecomodder viewer ), but would be the most accurate. A TV compromise: Grant should build a programmable "driver robot" for future tests!

On the plus side is their fuel measurement technique - much better than a ScanGauge! (or equivalent)

Could also question the data based on ambient conditions (depending on how long the tests took, changes in temperature as the day progresses could significantly affect results).

Could also wonder about how warmed up the car was before the first run & whether they allowed it to cool significantly at any point between runs (union lunch break between tests??)

And they never repeated the control at the end of the test, so we have no hint of how much inherent variability there is in their numbers.

[MetroMPG]

PS: pounsfos - hope you don't mind I added "tire" to your thread title. Want Google searchers using both spellings to find this discussion. (Assuming Google doesn't automatically use both - they're clever sometimes.)

[bwilson4web]

Higher pressures:

• increases weight capacity - allows smaller tires to carry a heavier load.
• improves rain and braking - found in an EPA report, the brakes worked better and it handled water on the roads better.

It is such as good idea that I've been looking at adjustable resistance, race shocks. Without the sidewall flex, the shocks need to be 'lightened' to reduce road noise and improve comfort.

Bob Wilson

[ChazInMT]

I had my tyres inflated to 38psi on my EX and the tosser at Costco where I had the tires balanced put a note on my service record that I had the tires overinflated by 8 psi. Guess that'll void my warranty huh?

[gone-ot]

Originally Posted by ChazInMT

I had my tyres inflated to 38psi on my EX and the tosser at Costco where I had the tires balanced put a note on my service record that I had the tires overinflated by 8 psi. Guess that'll void my warranty huh?

...you can simply "counter" that statement by answering: "...that's just pressure rise due to heat build-up from driving!..."

[ChazInMT]

I had thought of that. It was a warm day.

[jtbo]

Originally Posted by MetroMPG

PS: pounsfos - hope you don't mind I added "tire" to your thread title. Want Google searchers using both spellings to find this discussion. (Assuming Google doesn't automatically use both - they're clever sometimes.)

Google seem to use both, I have tested with tire and tyre when searching data from tire sizes and seem not to matter how I type and I type it both ways without thinking as my english is horrible mix of US and UK english learned from web, so sorry about that.

I have put my tyres to 44psi, that is max pressure from tire sidewall, my tires are winter tires not meant to be used on hot summer, but they seem to cope that ok. For several winters and summers I have been on these same tires, currently having around 50 000 miles on them, which is about double what best summer tires manage here on our rough tarmac. Tire companies refuse to sell high mileage US tires here, so it is not unheard that tires will last only 15 000 miles, actually anything lasting over 20 000 miles is considered very good here.

I can still drive this summer with these tires, until I need new ones, I think that lot of it is from increased pressure, but I have not much data to back this up, only the fact that my mileage is about double of what others have managed with similar tires.