mythbusters tests tyre / tire pressure
 

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

http://ecomodder.com/forum/attachmen...1&d=1304427953

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

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test car: 2004-2007 Ford Taurus

test methodology:

" 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?

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.

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.

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.

From my own experience, the higher pressure allows the tires to wear more evenly, old thread here:
http://ecomodder.com/forum/showthrea...ear-10265.html

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!

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'

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.

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 :cool:


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.

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.

http://ecomodder.com/forum/attachmen...1&d=1304415644

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

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.

Mythbusters' methodology wasn't great...
 

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

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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:

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.

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.)

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

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!..."

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

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.

Funny thing is that it HAS to be on TV for some to believe it!

well i reckon everyone should, inflat their tyres to the recomended pressure or more if possible,

you just aren't an ecomodder without doing this.
im going to start my front grill block now :),

mythbusted :p

I upgraded to Toyo Proxes low roll resistance tires 3 years ago. Added a good tire pressure monitoring system. The tires are inflated to 45 PSI and for tires only rated to 45,000 miles wear I have not seen any abnormal wear. From a fuel consumption stand point I do a variety of things and have dropped my utilization from 11.4 gallons / week to 8.3 gallons. I have a 18 gallon tank. So I really only replace 12-13 gallons every 11-12 days. I keep all of my receipts so I can better track my utilization. My ride is a 1997 VW Passat VR6 rated at 19 mpg city. I avg 25-27 mpg in city driving.

Lots of tips here on Ecomodders and they work without going to extremes.

That's because if it's on TV it must be true. :rolleyes: Seriously the last set of michelin snow tires I had were rated at 50 PSI max. I set them from the stations 32 up to 50 and got a 3MPG increase just like that. It was on my wife's car and I didn't tell her what I was doing so for all intents it was a blind test. By looking at the MB data perhaps 45 would have been just as good. The thing you have to live with higher PSI is a harsher ride on small road imperfections.

Hi Tire Pressure
 

The high tire pressure will increase the stiffness of the ride increase the chance of the car to push a little more and it will most of all increase the wear on the center of the tire... Watch your tires closely the cost saved at the pump could be less then a new set of tires or a fender.....

You're supposed to spread those out so that you have one at the end of every sentence.

...ellipses are just a period with hiccups!

Running tire pressure at 45 psi or higher increases danger of loss of control, bouncing and the suspension is NOT tuned for it. It can affect stopping distance. Plus the tires will not last as long.

Last time I checked last fall, about the cheapest tires out there for a GEO for instance were around $50 each and rising. Saving $75 dollars over a year on fuel you would probably burn more than that off the overinflated tires.

Different story for engineered, lowered rolling resistance tires. You will save approximately as much in fuel as the extra cost of the tires. So it is a break even.

Enginator

It's good to see some MPG "myths" put to the test. Maybe more of the public will understand the importance of tire PSI.

Actually running your tires at their max PSI will make them last longer. This is because the tread wear is more consistent.

First thing I do is bump the tire pressure up to whatever it says on the sidewall after any service - they always lower it back down to the door sticker.

I've got a pickup truck, I really don't care if the ride is slightly more truck like at max PSI :)

Definitely gets better MPG - and there's no tire whine

I have been driving my Geo Metro convertible with 40psi in the tires at 70 degrees F. I made 2 recent trips of 730 miles each within 3 weeks taking the same roadways. The first trip netted me 44.1 mpg after setting the tires to 30psi front and rear. I switched back to 40psi and averaged 47.8mpg on the second trip. I held local speed limits on each trip which included stretches of 70mph. The load was myself, my dog, toolbox and overnight bag.

The ride is slightly rougher with the additional air in the tires but it is well worth the added mileage. The car is stock except for the XFI cam and timing gear changes, ATF in the transmission. Driving was with the top up and windows closed on both trips. The weather was similar both times.

I did some maintenance before the first trip and found one tire to be at 30psi, so rather than open the garage again for the compressor I just evened out the tire pressures with the thought of checking mileage changes. This was about as accurate a test as I have done in a long time. I also fill right up to the filler neck to be sure the usage is accurate.

This is a great thread about the 1st mod that everyone should do. I have always inflated to 100% of tire rated max. cold pressure. I believe that is the safest because: (1) low tire pressure builds up tire temperature due to hysteresis, when the rubber is hotter it is weaker, thus the Ford explorer situation (2) a leak will give a bit more time to catch it before it get dangerously low. (2) grip is close to optimum at high pressure, even if slightly reduced. stiffness is high which make the car handle stiff not sloppy. Sloppy handling like old US cars is dangerous.

A trick I use to reduce leakage a lot is grease the tire valve. A tiny dab of grease in the valve when adding air get pushed into the valve seat area. I have fixed many leaky valves this way. It works best on bikes since they loose pressure much fast for a given leak volume. Leaky valves are very common. Yokohama sells a tire that looses less air thru the rubber. I have gone many months without having to add 1psi.

jakobnev thanks for the 3rd grade education. I was just trying to get my message out that it is not safe to over inflate the tires.

As mentioned before the suspension is not designed to work with a tire that bounces a lot. A over inflated tire on a rough road will bounce. It is the shocks job to keep it from continuing in this motion. If the tire is bouncing it is not on the road. If it is not on the road you have no control of the car.

I have been racing cars for over 35 years now and suspension is what keeps the car on the road. Yes the tires do also but if the suspension is not working properly you can not maintain control in the extreme. And it is in the extreme that I want control. Most of the time everything is fine it is when the idiot pulls out that you want complete control. If your willing to give up control for $77 a year go for it.

Me I will keep my tires at a presure that give me the most control over my car and spend my energies else were. A well tuned engine, driving habbits, and just not driving around to see the sites.

I think a real test would be to really squeeze them and see how firm they are. See if she has them just right before you take them for a test drive. Visually it looks like the set is perfect in diameter but until I can get my tool on them to check them for sure will just have to assume there with in tolerance.

i run my Geo tires at 50 psi and they wear just fine. Tomorrow I'm installing a small lift to the suspension and raising it to clear my new 15" rims and tires so i can turn my 5 gear into a 6 th gear. I did this a few years back and it really helped on mileage but i actually never wrote the numbers down. This weekend I'm driving 1200 miles from Washington to Montana and back with two and three people on board so will see how it goes. I'll post my numbers. I'm hoping to really use the heck out of my kill switch on the down hill runs. I'll also measure the tire heights and post them as well. I have log book now on my first 10,000 miles on this restored and modified 94 metro.
FYI just bought a tracker 1994 4wd gets 28 mpg at 60 mph with just me in it. and over 300 miles it averaged 25.49 towing my geo metro behind it on a tow bar. it turns 3500 rpm at 60mph. it has 205 70 15 on it and tomorrow i'm switching it to 235 75 15 to lower the rpm and recheck the gas mileage. I'll post some reports. its the 1.6 8 valve motor if any one wants to know in a manual and the geo car is a 3cyl 5 speed.

One point to recall on tire pressure, the effects of heating. I run the tires on my electric Civic conversion at about 40 PSI front and 38 PSI rear. The sidewall rating is 44 PSI, factory sticker says 32 Front and 28(?) rear. The thing is the factory rating is for cold pressure and assumes you may be driving at high speed for hours, which would really heat up a tire and raise the pressure. Since my EV is an in town only commuter and seldom exceeds 45 mph, heat buildup and the resulting pressure rise simply never happens. For all intents and purposes my tires stay pretty cold most of the time which is not what the factory expected. Effectively at the factory settings they may be under inflated.

Isn't sidewall rating for cold pressure too?

Search the old posts before dragging all of this up again!

http://www.oocities.org/torisstarburst/deadhorse.gif

So I gave a quick question to throw in here.. If I were to get the Geo metro tires and inflate them to bout 50 psi then id see a decent increase in gas mileage in general? Ive considered this, along with some pretty sweet Moon hub caps:D HAHA
Thanks,
Wyatt

And with energy you used to be an ass, you could of provide simple answer which seem to be very clear to you, wear to your keyboard would been less, also usage of electricity etc.

So you did not achieve nothing else than being an ignorant person.