Incorrect Information re: Tire Pressure in Efficiency Mods

[NachtRitter]

autoteach, Weather Spotter -

Good inputs, & I appreciate the civil discussion on this topic (unlike stuff that's been going on in other threads!). As others, I'll choose to do what I want, but like to have good information to base my decisions on. From the information I've read here, I'll continue to inflate over the manufacturer's recommendations; I've not seen strong enough data to change my mind on that. I have no beef with others that would rather not "over-inflate".

[VegasDude]

Clev pretty much summed it up.

As far as the negatives: Over-inflated tires will cause extra noise and a harsher ride, that much is certain. Most of us hypermilers don't drive fast so that helps reduce those two problems a lot. Having no any real data myself, I would still agree over-inflation probably causes increased wear on suspension and increases the possibility of being damaged by road hazards. Again, we drive slowly (compared to most people), deliberately, and attentively, reducing these problems.

Lastly, over-inflated tires will make it easier to spin your tires on dry pavement. So while it's easier to do a burnout, your 0-60 and 1/4 mile times will increase. Also not really much of a problem for us non-racers and ricers.

[Clev]

Originally Posted by autoteach

Overinflation would be over the car's recommended value. It may be a good way of saving fuel, but it does pre-maturely wear tires (but I am sure that someone will say that it doesn't, as I said above this is a very tough argument.) It also causes suspension to wear prematurely as well as drivetrain, but once again someone will dispute that. I also believe (this is something that I know will be questioned, read previous post) that it does provide significant safety hazards under certain driving conditions. Argue away, like it has been in other posts and for the same reason that I told the OP that this may be the biggest waste of his time. I will keep my inflations within reason.

Feel free to continue to portray opinions as facts. The manufacturer uses many factors to determine their recommended pressures, and fuel economy and performance often take a backseat to comfort.

[autoteach]

Well, I am not sure which portion you are calling opinion that is not fact. I work on plenty of cars (check the username) and I have seen the difference in inflation of 4psi effect wear pattern either way. Or was it my opinion that it saves fuel a misrepresentation of facts or opinions. Is it the suspension and drivetrain wear? The tires are an active part of the vehicles suspension, stiffening that portion causes wear at others, that is not an opinion. And I qualified my safety concerns as opinion.

I am being civil, and what I said to the OP is exactly what is occurring here as well as what has occurred on the numerous threads on this topic. There is about as many people on each side of the fence, and those that have weighed in before and were dismissed, or realized the futility of the situation, are probably going to sit this one out. I dont blame them. I suppose I should have sat it out and just let the OP get the onslaught without the explanation. This topic becomes a hostile environment, and I believe it to be more so those that feel they have been cheated out of fuel economy by the manufacturers rather than those that believe otherwise. I wont reply to this thread again, and not because I want to get the last word in, but because there is no other reply necessary for the OP to see that there is no way that he will ever convince ~50% of this population that the other ~50% of the population is correct (and it goes both ways).

My words of advice, inflate your tires to the pressures that you see fit. If you drive an suv, 32psi should be a minimum despite what the manufacturer says (ford). Live with the consequences of your inflation, be it + or - MPG, handling, tire wear, noise, or component failures. Learn from that, and don't try to share what you have learned from it because those that believe otherwise already know your full of ****

[Clev]

Originally Posted by autoteach

Well, I am not sure which portion you are calling opinion that is not fact.

Just the part that stated that exceeding the manufacturers' recommendations causes poor tire wear. That is by no means universal. In fact, I see far more uneven edge wear in "properly" inflated tires than in "overinflated" tires, especially in larger cars.

[eco30BMW]

I really didn't realize this was such a touchy subject, or that argument had been going on elsewhere on the board. I'll keep it civil, but I do have a few responses.

Originally Posted by Daox

Maintaining momentum through turns is a good idea for saving gas. I see no reason to take that tip it down.

Agreed, my point is that people will take turns faster than they ought to if they believe they have more grip than they really do.

Originally Posted by Clev

Taking the above to its logical conclusion, inflating tires higher than placard makes the contact patch even a bit smaller, which would not increase stopping distances.

Oh, ok, so taking that to its logical conclusion, having NO rubber on the road would not increase stopping distance, correct? The resource you cited was written during the Firestone fiasco, where the concern was underinflation. It's clearly only comparing underinflated tires to ones inflated to the placard pressure. You're applying a trend across a boundary (the placard pressure) and it's invalid.

Originally Posted by Weather Spotter

Last winter I did some tests on my weekly drives home from school. Higher pressures increases my wet and snow traction by a good margin (over 15% better traction). I also tested stopping distance on wet and icy roads. I found that higher PSI was about the same to slightly better stopping distances.

I'd really like to hear how you arrived at that figure, because since opening this thread I have searched for a good study with a skidpad or drag strip and different tire pressures and found none.

Originally Posted by Weather Spotter

When I worked at a major auto maker I liked to put this topic up for discussion. The people who did track testing and noise testing came up with the same resign for the OEM specks on tire pressure: ride comfort and noise.

Had you asked the people who design the suspensions I'm sure you would have gotten a different response. The tires act as a spring, and are designed into the suspension that way. You're also messing with the dynamic geometry of the tire while cornering, and I'm sure there's suspension designers that would not be pleased with that.

Originally Posted by Vegas Dude

Lastly, over-inflated tires will make it easier to spin your tires on dry pavement. So while it's easier to do a burnout, your 0-60 and 1/4 mile times will increase. Also not really much of a problem for us non-racers and ricers.

But that's one more vote for less traction.

The bottom line is that EM is responsible for what it puts on the site as fact and there is no proof that increasing tire pressure past the placard spec will increase traction. Just take it down already. I don't understand why EM would feel the need to say anything about wet traction anyway, many people here seem to feel it's a question better left to performance driving forums.

[Weather Spotter]

How I came up with my better wet and snow traction numbers:
Disclaimer: this was not a very scientific test.

Last winter on some wet and snowy days I went out and from speed tried stopping, I did it both with OEM psi and at 44 PSI. The higher PSI allowed me to press harder on the breaks without skidding, thus allowing me to stop sooner. I also tested start up traction by using my scangauge to see what rpm I started to spin.The OEM psi had me spinning sooner by about 10% than when the tires were at 44psi.

I will give you that this test is not that great, but with it and my driving I noticed a difference. It may not be the same on all cars.

About the suspension people, I did not ask them. The ride quality is based on the shocks and the tires ability to dampen bumps. I will grant that when cornering I am slightly changing the angel of the suspension. On my car I think this is a good thing (my OEM ties wore badly from cornering). Once again I think each car is different, which is why there is so much debate on the effects.

traction is a function of surface area and down force. Higher tire pressure results in a smaller contact patch but more weight per unit of area. Once again it is a balance.

[vtec-e]

I put up 100,000km on my last set of tires on my civic. They are currently retired in the shed with about 4mm left on them and it is quite even across the tread.
Re: traction. I gave up searching for scientific data on traction at elevated pressures. Stopping distances in the wet too for that matter.
I will say this though: If the wheels bounce under braking or cornering due to being so hard, braking is seriously compromised. I've experienced it and it's not pretty. Thats not to say braking is compromised in all other situations. On the contrary, i "feel" it is better, as is the general consensus here too. But i have yet to find ANY scientific data on that, other than the stuff the NHTSA did, but only up to 32psi if i remember correctly. Which is suspicious and smells like a conspiracy......
I'd love an accelerometer or something to measure it properly but alas, they are a little pricey.
I'd like to also add that inflating to sidewall from new will most likely result in centre wear as it has also happened to me also. Inflate normally for the first 500 miles then sidewall 'em. Well, thats what i did and it worked. My yaris was sidewalled from when i got it and i figure there was maybe 10,000 miles on them. That was at the end of 2008. They have had many more miles put on them and there is no centre wear.
So if the OP could provide data that shows a loss of traction, in the wet, at sidewall that would be great.

ollie

[Ryland]

Originally Posted by autoteach

I have seen the difference in inflation of 4psi effect wear pattern either way. Or was it my opinion that it saves fuel a misrepresentation of facts or opinions. Is it the suspension and drivetrain wear? The tires are an active part of the vehicles suspension, stiffening that portion causes wear at others, that is not an opinion. And I qualified my safety concerns as opinion.

I tend to read owners manuals whenever I'm a passenger in someones car for a longer car ride, I've read alot of owners manuals and they tend to have this pattern that boils down to, If you have snow tires or are driving on the highway you should increase your tire pressure by 4psi to decrees tire wear, this is seems to be consistent among most of the owners manual I've read.
So in that aspect increasing your tire pressure by at least 4psi is fallowing the auto manufacturers recommendations.
There have also been a number of studies, like people have already posted links to, that boil down to say that going up to the designed pressure does help with traction and wear and no reviewed studies that have shown that you should lower your tire pressure.
If you have a study that says lower pressure for modern tires (not bias ply) is better then please tell us about it, if you worked on someone else's car and noticed that the tire wear was uneven then you need to give a detailed history of how many miles they put on those tires at what pressure under what conditions, high wear down the center could be because their tire pressure was to low, not to high, with radial tires the center of the tread has more support due to the how the tire is constructed so it doesn't cup and pull in like the older bias ply tires did when they were under inflated.

[Jyden]

On the wet:

Greater surface arear (broader tires or low infaltion) will reduce grip, as pressure pr sq inch are reduced.

Grip/traction are also very much down the the rubber compound. Soft rubber = more grip, and wears easy.

Higher inflation (providing good compund) will go through water better beacuse of pressure per sq inch are higher.

On the dry:
More surface arear = more grip - best is slicks. Boarder tire = more grip and traction, but also equals more rolling resistance.

Harder rubber compund = less wear and less grip

Higher pressure = less wear because the tires dosent flex as much, and therefore dosent build up as much heat.

Higher pressuer = more milage due to: lower rolling resistance, less flex, and a smaller contact arear.

Higher pressure migh lead to early wear out on the rubber bruches in the suspension on some cars, if they are not top quality, as the bruches are subjected to stronger forces.

Higher pressure = better cornering, as car dosent sway so much

Higher pressure = longer braking distances due to less contact surface, and on very uneven surfaces could lead to "jumping" which can further prolong brakingdistances as contact with the road are lost in the jumps.

I drive with 2.8 bar instead of the recommended 2 in my tires, and havent seen much negative effects, but if I go to 3 bar, the handling og the car goes bad op uneven surfaces, and braking distances are longer. Car also starts to Jump.