15 more PSI = 7% better MPG

[qx4dude]

Originally Posted by mcrews

"Are you prepared to accept liability for suggesting that people over-inflate their tires beyond design specs? It's important to let others know who to sue if / when their over-inflated tires are found to be the cause of an accident."

Reminds me of several 'hypothetical posts' over the last week.
Posters make these broad sweeping general post and expect us to roll over...

Like the guy saying that ecomodding wears out a car faster......
Funny, always seems to be some newbie who hasn't read or searched, has no idea about 99% of what this forum says.

or the guy wanting pictures of how we attach belly pans.....

must be a slow week......

The question about accepting liability required a yes or no answer.

The maximum sidewall pressure stated on the tire isn't a "hypothetical", it's a fact. The tire manufacturer's designers / engineers put a maximum rating on the tire to keep drivers safe - and to protect themselves from liability from blowouts or accidents should people choose to ignore it.

Michelin won't accept that liability, they clearly state it in their owner's manual:

"FAILURE TO OBSERVE ANY OF THE RECOMMENDED PRECAUTIONS
CONTAINED IN THIS OWNER’S MANUAL CAN LEAD TO ERRATIC
VEHICLE BEHAVIOR AND/OR TIRE DAMAGE, POSSIBLY RESULTING
IN AN ACCIDENT."

http://www.michelin.ca/mediabin/Appr...2011-09-01.pdf

[roosterk0031]

Lawyer's, that number is at least 100% below safe pressures, I work with engineers, the safety allowance is crazy with structural engineers with way less unknowns that tires. After 50 psi gains are so small (IMO) go to 50 and forget it(unless you car really drive bad at that PSI). I have close to 50 in all my cars and my 15, 20 and 48 yo girls are just fine with it.

[RedDevil]

Come to think of it, did I ever see a tire failure from overinflating?
Simply and true; NO.
UNDERinflating is the cause of death for many tires. People check their oil but forget about the tires when loading their family and weeks worth of luggage in their cars to visit the sunny South. The overloaded and underpressured tires overheat and delaminate and burst.

I am aware of what I do. I regularly kill the stereo, roll down the windows and listen; tires, brakes, exhaust, anything out of the ordinary? I wanna know, so I check.

Not just on my car, but my wives, parents, in-laws car; anyones. They are unaware. I see one of their tire sides bulge out, check it and yup, 7 PSI below door sticker so WAY low. They did not notice.

When a tire blows at anything below 200 PSI there must be something wrong with it. The carcass is cut or whatever. But what stresses the carcass is not the pressure but the repeated flexing. the higher the pressure, the less the carcass deforms at each rotation, and if the tire already was damaged, the slower that damage will increase.

Tire companies sell tires. They know what makes a tire last long and what not. Low pressure sells more tires. It also kills people. What a shame then to blame the experienced and investigating people who raise their tire pressure, even though they find only benefits from doing so?

[cbaber]

Originally Posted by qx4dude

The question about accepting liability required a yes or no answer.

The maximum sidewall pressure stated on the tire isn't a "hypothetical", it's a fact. The tire manufacturer's designers / engineers put a maximum rating on the tire to keep drivers safe - and to protect themselves from liability from blowouts or accidents should people choose to ignore it.

I've never tried to convince anyone that they should over inflate their tires. This thread is to showcase the results I experienced. This is my own data, theories, ideas, and modifications. You and everyone else are free to interpret it as you like. If you find it credible and wish to replicate the results you have to assume it is at your own risk. I'm not going to be like a car commercial and add a disclaimer to every post. If you can read my posts you should be smart enough to realize that what you do to your own car is your business, and only you are liable.

What I am doing is not scientific, and I have never claimed so. Nothing you or anyone else has posted is scientific evidence of the opposite opinion, either. All I am doing is exploring different tire pressures to see the effects. If I notice anything I would consider dangerous I'll report back and return the pressure to normal. I can only give you my real world experiences and you can take that as you like. But for you to argue that my real world experiences are incorrect and unsafe is just unfair. The reason I continue to explore the effects of higher tire pressure is because I haven't seen any evidence that higher pressures have the effects you seem to believe. Furthermore, many of the top forum contributors and ecomodders have shared similar experiences to mine. You have a dedicated group of people giving you real world accounts, and yet you choose to believe what a tire company wrote on its website. Tire companies want to sell tires. They want to limit liability. They are biased when it comes to determining what their tires are capable of. Many of the other posted sources simply talk about the issues, and fail to provide any proof or data.

[qx4dude]

Originally Posted by RedDevil

Come to think of it, did I ever see a tire failure from overinflating?
Simply and true; NO.
UNDERinflating is the cause of death for many tires. People check their oil but forget about the tires when loading their family and weeks worth of luggage in their cars to visit the sunny South. The overloaded and underpressured tires overheat and delaminate and burst.

I am aware of what I do. I regularly kill the stereo, roll down the windows and listen; tires, brakes, exhaust, anything out of the ordinary? I wanna know, so I check.

Not just on my car, but my wives, parents, in-laws car; anyones. They are unaware. I see one of their tire sides bulge out, check it and yup, 7 PSI below door sticker so WAY low. They did not notice.

When a tire blows at anything below 200 PSI there must be something wrong with it. The carcass is cut or whatever. But what stresses the carcass is not the pressure but the repeated flexing. the higher the pressure, the less the carcass deforms at each rotation, and if the tire already was damaged, the slower that damage will increase.

Tire companies sell tires. They know what makes a tire last long and what not. Low pressure sells more tires. It also kills people. What a shame then to blame the experienced and investigating people who raise their tire pressure, even though they find only benefits from doing so?

I absolutely agree with the reasons you've given that an under-inflated tire is dangerous. For that reason, and to increase FE, I increased pressure by 6 PSI over the door sticker.

Hey, it's a free country. If you want to inflate your tires to 200, or modify your car to run with bicycle rims & tires - fill your boots. I'm sure someone on the Internet says it's perfectly safe to do so.

[Frank Lee]

How many times have we had this debate already?

niky said it best: YMMV.

Some claim exceeding sidewall max doesn't result in wearing the centers fast; that could very well be. But I've had it happen so it could very well NOT be too.

I laugh at those who think +4 psi is fraught with risk. Geesh, get a grip.

Burst pressure on tires in good shape is around 200 psi.

Bulges and cord or belt issues can happen regardless of pressure.

The OEMs are in a tight spot with psi recs; if enough customers whine about a slight jiggle in the ride then all sorts of things that require effort and expense happen, so they rec lower pressures than those of us who prioritize low r.r. over no jiggling.

Raising psi vs lowering r.r. is not a linear relationship thus the first smaller increases in psi give the most r.r. and fe results; after that the returns diminish. You will NOT get another 7 or 9% fe with an additional 15 psi on top of the first 15 psi increase.

Regarding psi I paint with a rather broad brush; seems to me in most applications there is a zone between manufacturer rec (often around 32psi) +5psi, and lower than 50 psi, where tire pressure happiness will be found... so basically 37-47psi.

I fine tune that by driving on a dry dusty road then on a paved road then looking at how much of the tread at the shoulders is still dusty; I want it to look even so the lightly loaded rear tires on a fwd car end up about 5 psi lower than the fronts.

Then there is the resolution of the whole psi thing; gauges vary wildly AND pressures do too depending on temps and loads and trip lengths and whatnot so does it make sense to get hung up over one or two or even three psi? Whatever the gauge says, it's probably more important simply to have fairly equal pressures on each tire on each axle, just so each tire is doing it's share.

[ECONORAM]

Originally Posted by cbaber

Power steering delete is planned. I'm also in the process of deleting my alternator. I'm selling an old MG Midget parts car tomorrow and will be using those funds to finally purchase a deep cycle battery to complete that project. I'll have to wait at least 3 weeks before I can start turning off the alternator though, since I want to get at least 3 tanks in running 60 PSI to compare it with my 45.4 MPG average at 45 PSI.

After the 60 PSI testing summer will pretty much have ended and temperatures will start dropping. A/C will no longer be used, which could effect the results. I'll have to wait until next summer to really see the results. I have been lucky to have very consistent weather over the months of July and August, so I consider the 7% gain from tire pressure to be accurate. It's actually a conservative number because my actual number is 4 MPG improvement after running 4 more tanks since this thread was started.

3 tank average at 30 PSI = 41.4 MPG
5 tank average at 45 PSi = 45.4 MPG

(4 / 41.4) x 100 = 9.6 % gain

Thanks for the graph. I find the near 10% FE gain quite interesting; did not expect to see that.

[niky]

Originally Posted by qx4dude

Hey, it's a free country. If you want to inflate your tires to 200, or modify your car to run with bicycle rims & tires - fill your boots. I'm sure someone on the Internet says it's perfectly safe to do so.

Actually... nobody does. Most hypermilers and even hard-use drivers like cops and stunt drivers*** settle around 50-60 psi.

As Frank says, burst pressure is high. For a crappy (read: Chinese) car tire, it's around 100 psi. For good ones, higher. I wouldn't quite say 200... maybe 150 or so. For truck tires, it's somewhere around 300 psi (and sidewall sticker is between 60-90 psi). Bike tires use around 90-100 psi.

"50 psi" is not some magic barrier. It's determined by a number of factors. As said before, it's typically where the tire stops gaining usable load capacity, which means there's no mundane, everyday reason to exceed it.

-----

***Most people don't realize how low everyday pressures really are.


(I'm the guy with the GoPro on his face. Assigned data logger.)

And even if you have low profile tires...


(yes, that one made me nervous... as the GC has failed the moose test due to blow-outs)

As long as you're not lifting the edges of the tread, you can go higher. Harder (up to a point) is safer. Less sidewall deformation. Less heat. Less wear on the tires. Better steering response. Less chance of it de-beading if you have to suddenly avoid a moose. Braking distances may increase (contrawise, they will definitely increase below 35 psi), but that is highly dependent on a number of factors.

----

The pics are from handling tests earlier this year. We did acceleration and braking, too. While I was datalogging most runs, I did get to drive every fourth run...

[qx4dude]

Originally Posted by cbaber

I've never tried to convince anyone that they should over inflate their tires. This thread is to showcase the results I experienced. This is my own data, theories, ideas, and modifications. You and everyone else are free to interpret it as you like. If you find it credible and wish to replicate the results you have to assume it is at your own risk. I'm not going to be like a car commercial and add a disclaimer to every post. If you can read my posts you should be smart enough to realize that what you do to your own car is your business, and only you are liable.

What I am doing is not scientific, and I have never claimed so. Nothing you or anyone else has posted is scientific evidence of the opposite opinion, either. All I am doing is exploring different tire pressures to see the effects. If I notice anything I would consider dangerous I'll report back and return the pressure to normal. I can only give you my real world experiences and you can take that as you like. But for you to argue that my real world experiences are incorrect and unsafe is just unfair. The reason I continue to explore the effects of higher tire pressure is because I haven't seen any evidence that higher pressures have the effects you seem to believe. Furthermore, many of the top forum contributors and ecomodders have shared similar experiences to mine. You have a dedicated group of people giving you real world accounts, and yet you choose to believe what a tire company wrote on its website. Tire companies want to sell tires. They want to limit liability. They are biased when it comes to determining what their tires are capable of. Many of the other posted sources simply talk about the issues, and fail to provide any proof or data.

I choose to believe sources (in your words) that do provide proof and data - instead of simply talking about the issues. I re-read this post, and haven't seen anyone reference an external source regarding what over-inflation percentage is "safe". All sorts of baseless numbers are getting thrown around here. Tire companies won't share trade secrets, but they do offer specifications, and even provide test data their products. They list "hard" specs, derived from laboratory and "real world" analysis; not opinions.

I'm sure your intentions are honorable, and you've done everyone a service by sharing data regarding more inflation = more MPG. That said, I'd submit that it's somewhat reckless (perhaps even libelous) for forum members to advocate exceeding tire manufacturer's specifications without first recommending that the reader take the time to inspect their own tires (like the poster above) before arbitrarily over-inflating their tires. This may sound like common sense, but we do live in a litigious society so it's important to protect ourselves, and each other.

[Frank Lee]

I will laugh just as hard at any litigation as I do at freaking out over 4 more psi. It just ain't gonna happen.