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Old 05-02-2011, 10:31 PM   #1 (permalink)
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mythbusters tests tyre / tire pressure

It's about time guys, Mythbusters has finally tested the myth of over inflated and under inflated tyres!!!



heres the link ad the results

MythBusters: Tire Pressure Test : Video : Discovery Channel
TV Review: Mythbusters 8.23 – “MiniMyth Madness” | Fandomania


Control, 35psi (manufacturer recomendation)
tyres at 10psi = 3.7% increase in consumption
tyres at 30psi = 1.2% increase in consumption
tyres at 40psi = 6.2% decrease in consumption
tyres at 60psi = 7.6% decrease in consumption

im amazed that even at 5PSI over recomended pressure there was a 6% increase!!!

They even said that over 1 year you would save roughly $77(us), that may not sound like much but that $77 more in my pocket for spending 2mins pumping up tyres

---

test car: 2004-2007 Ford Taurus

test methodology:

Quote:
  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 )

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Last edited by MetroMPG; 04-15-2012 at 10:19 AM.. Reason: Added methodology info
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Old 05-02-2011, 11:25 PM   #2 (permalink)
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Quote:
Originally Posted by pounsfos View Post
It's about time guys, Mythbusters has finally tested the myth of over inflated and under inflated tyres!!!

heres the link ad the results

MythBusters: Tire Pressure Test : Video : Discovery Channel
TV Review: Mythbusters 8.23 – “MiniMyth Madness” | Fandomania


Control, 35psi (manufacturer recomendation)
tyres at 10psi = 3.7% increase in consumption
tyres at 30psi = 1.2% increase in consumption
tyres at 40psi = 6.2% decrease in consumption
tyres at 60psi = 7.6% decrease in consumption

im amazed that even at 5PSI over recomended pressure there was a 6% increase!!!

They even said that over 1 year you would save roughly $77(us), that may not sound like much but that $77 more in my pocket for spending 2mins pumping up tyres
" However, although the car got even better gas mileage when the tires were over-inflated, this is not a good idea for safety reasons and because it causes the tires to wear unevenly."

But did the do any testing to prove this statement?
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Old 05-03-2011, 12:21 AM   #3 (permalink)
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isn't that idea a fact? when over-inflated only the middle of the tire will have contact with the road and that part will wear out faster than the outside; it will wear unevenly.
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Old 05-03-2011, 12:58 AM   #4 (permalink)
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I ran my OEM tires for about 48,000 miles at between 40 - 44 psi and they wore perfectly even and I got more miles out of them then most people I have talked to at yourcobalt.com and cobaltuniverse.net

I believe the tire lifts the front and back of it's tread patch more then it's left and right sides.
There are still safety issues with a reduced contact patch and braking though.


I see a test coming up.
Jack up the front of a car, put some washable paint on the bottom of the tire then lower it onto a piece of paper.

Try that at 15 psi, 30 psi, 45 psi and measure the difference in contact patches.
Would be a solid way to see what changes.

I'm working 12 days strait without a day off and about 55 hours a week so no chance I'll have time to try this anytime soon but if somone else wants to give it a go they are more then welcome.
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Old 05-03-2011, 01:02 AM   #5 (permalink)
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Quote:
Originally Posted by capnbass91 View Post
isn't that idea a fact? when over-inflated only the middle of the tire will have contact with the road and that part will wear out faster than the outside; it will wear unevenly.
If you have bias ply tires, yes they will wear down the center, I haven't seen bias ply tires sold in the US in the last 20 years or more tho.
This is not scientific but there are plenty of people like my self who for years have run their tires at 45 to 50psi (I have tire pressure valve caps that change to red when the tire pressure drops to 45psi) and my tires wear dead even, my old civic vx belongs to a friend of mine now and is still running 50psi on a set of tires I bought new over 50,000 miles ago and my current tires I've personally put 20,000 miles on, are near the end of their life with the same pressure and dead even wear as well, I tend to be cheap so I don't like spending money on tires, but I also buy decent tires with a 44 psi rating or 51psi rating, so my pressure is not really beyond what the tire is designed for and I recommend that others pay attention as well to what your tire is rated for and not go above that unless you are willing to take that risk on your own.
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Old 05-03-2011, 01:34 AM   #6 (permalink)
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From my own experience, the higher pressure allows the tires to wear more evenly, old thread here:
Measured my tire wear (20,000+ miles at elevated pressure - 44 PSI)
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Old 05-03-2011, 01:38 AM   #7 (permalink)
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Quote:
Originally Posted by nemo View Post
it causes the tires to wear unevenly."

But did the do any testing to prove this statement?
I guess not! Nor even looked at the tyres to see them bulging in the centre (or not!) It's easier to simply recycle the old 'received wisdom' which, as stated, is no longer true. Radial tyre treads don't deform in that way, instead the sidewalls stiffen up with higher pressures. That is what reduces rolling resistance!
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Old 05-03-2011, 03:40 AM   #8 (permalink)
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Relax, its just a TV show. The subject was whether or not over inflating tires improved FE which they proved beyond a shadow of a doubt and they also provided some data in the process. As a TV show they have to watch their legal liability in case some yahoo blows a tires and decides to sue to producers because 'the mythbusters said its ok'
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Old 05-03-2011, 04:09 AM   #9 (permalink)
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Quote:
Originally Posted by capnbass91 View Post
isn't that idea a fact? when over-inflated only the middle of the tire will have contact with the road and that part will wear out faster than the outside; it will wear unevenly.
Depends on what you'd call overinflated.
Higher than recommended for the car.
OR
Higher than max. rated tyre pressure. (That's overinflated to me.)


At max. rated tyre pressure, the bulging ain't happening on my tyres.

Actually, on my car the max. rated pressure has finally evened out the tyre wear !
Despite being properly aligned, the tyres used to wear harder on the shoulders. Well, not anymore.

So the higher inflation is definitely lifting the center part of the thread.

Going beyond max. rated pressure, I'd expect to start seeing more wear on the center part of the tyre.
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Old 05-03-2011, 04:27 AM   #10 (permalink)
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Quote:
Originally Posted by nemo View Post
" However, although the car got even better gas mileage when the tires were over-inflated, this is not a good idea for safety reasons and because it causes the tires to wear unevenly."

But did the do any testing to prove this statement?
If they did, they didn't show it in this show or any other that I've seen.

My take is that it is the usual US legal BS to avoid liability - thereby sustaining the myths they're pretending to be busting.

Maybe we, as part of the ecomodder / hypermiling community, should ask them to test when tyres really blow out, to settle the issue once and for all.

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


Test conditions :
- decently handling, non-hybrid car.
- fuel use and course times to be monitored
- good quality, new tyres rated for say 45psi.
- no re-use of the underinflated tyres for any of the other tests !
- demanding handling and/or harshness course to get the heat in the tyres.
- say 30 psi under and over the car's recommended pressure.

Test ends when a tyre blows or comes off the rim.

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