15 more PSI = 7% better MPG

[RedDevil]

Originally Posted by cbaber

I'm pumping my tires up to 60 PSI after work tonight. Thats a whopping 16 PSI over the tires indicated limit. (...) I'll continue to experiment with tire pressure in the real world, gathering my own data.

I'll watch that with interest. Think you can delete power steering, if you haven't done that already. Hope you do use top quality tires. Be careful not to overheat your pump.
(I'm at 48 PSI now... runs fine on that)

[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

[California98Civic]

I maintain 60 psi by checking during the warm hours of a day, at the end of my commute, when the tires are their warmest. I boost then as needed. The purpose it to try and keep the cold temp maybe 10 psi over the 44 max sidewall. Been doing that forever, following the PaleCivic of Palemelanesian (who ran his at 60psi for years too, without problems).

[qx4dude]

Originally Posted by cbaber

I'm pumping my tires up to 60 PSI after work tonight. Thats a whopping 16 PSI over the tires indicated limit. My car will certainly vibrate to pieces, my tires will blow out, I'll wreck due to decreased traction, my fuel economy will get worse, and the center of my tires will wear unevenly. You can follow the progress in my project thread and when your theories are confirmed, feel free to post, "I told you so". Until that time, I'll continue to experiment with tire pressure in the real world, gathering my own data.

The cavalier attitude about exceeding "max sidewall" pressure is astounding. Teams of engineers at major tire manufacturers have worked with teams of engineers at auto makers to determine the maximum safe tire pressure - but we know better because someone on the Internet pumped his tires 30 PSI over the design specification of the tire. Clearly, a few of us put saving a few bucks on fuel ahead of the risk to ourselves, our families, and others on road. This isn't only about risking a blowout, or premature tire wear, it's about the affect that over-inflation has to driving dynamics, and the car's reduced ability to maneuver (or stop) in an emergency situation.

I'll admit that I have raised pressure in my tires 6 PSI over the door sticker's recommended 36 PSI (which has improved FE), but I won't go anywhere near the stated maximum 51 PSI sidewall pressure. I'll put my trust in the engineering team that designed the tire over an anonymous Internet user's "research".

[California98Civic]

Originally Posted by qx4dude

The cavalier attitude about exceeding "max sidewall" pressure is astounding. Teams of engineers at major tire manufacturers have worked with teams of engineers at auto makers to determine the maximum safe tire pressure - but we know better because someone on the Internet pumped his tires 30 PSI over the design specification of the tire. Clearly, a few of us put saving a few bucks on fuel ahead of the risk to ourselves, our families, and others on road. This isn't only about risking a blowout, or premature tire wear, it's about the affect that over-inflation has to driving dynamics, and the car's reduced ability to maneuver (or stop) in an emergency situation.

I'll admit that I have raised pressure in my tires 6 PSI over the door sticker's recommended 36 PSI (which has improved FE), but I won't go anywhere near the stated maximum 51 PSI sidewall pressure. I'll put my trust in the engineering team that designed the tire over an anonymous Internet user's "research".

Your choice, but if you read and think about the knowledge people share here (something you clearly have not done yet in any serious way), you'll realize that the engineering of tires creates considerably more possibilities than suggested by these simple consumer guidelines you're espousing. Ironically, your argument here is the definition of cavalier, because it blithely dismisses the discussions as if everyone is just a hack and these anonymous "engineers" have published the full summation of their knowledge on your car door and tire sidewall. The limits and capacities of these tires are far greater than any stresses 60psi at slow speeds on paved roads puts on them. Our cars are mass produced for all possible extremes of conditions at once. The psi guidelines are a lowest common denominator kinda thing. The consumer information does not try to represent the absolute extreme capacities of the vehicles that the engineering has identified. So don't go near the stated sidewall if you choose, but that's not realistically a thoughtful choice about safety, though you clearly think it is. It's about your preferences, your applications, and the conditions in which you drive your car.

He'll keep an eye on his tires, as should you. Your softer tires face different blowout possibilities than his do at 60psi. He's better off in some conditions at 60psi than you are at 42. Hydroplaning for example.

Gotta go to work. I hope that's clear and useful. Have a good day.

[qx4dude]

Originally Posted by California98Civic

Your choice, but if you read and think about the knowledge people share here (something you clearly have not done yet in any serious way), you'll realize that the engineering of tires creates considerably more possibilities than suggested by these simple consumer guidelines you're espousing. Ironically, your argument here is the definition of cavalier, because it blithely dismisses the discussions as if everyone is just a hack and these anonymous "engineers" have published the full summation of their knowledge on your car door and tire sidewall. The limits and capacities of these tires are far greater than any stresses 60psi at slow speeds on paved roads puts on them. Our cars are mass produced for all possible extremes of conditions at once. The psi guidelines are a lowest common denominator kinda thing. The consumer information does not try to represent the absolute extreme capacities of the vehicles that the engineering has identified. So don't go near the stated sidewall if you choose, but that's not realistically a thoughtful choice about safety, though you clearly think it is. It's about your preferences, your applications, and the conditions in which you drive your car.

He'll keep an eye on his tires, as should you. Your softer tires face different blowout possibilities than his do at 60psi. He's better off in some conditions at 60psi than you are at 42. Hydroplaning for example.

Gotta go to work. I hope that's clear and useful. Have a good day.

The extra 6 PSI I have in my tires now make my front drive wheels spin with little effort. That didn't happen at 36 PSI. The reason FE is increased with higher PSI is because of the lower rolling resistance associated with a smaller contact patch - and thus less maneuverability and stopping power. If you want to transform your tires into hard plastic discs at 60, 80, or (heck, why stop there) 100 PSI - that's your prerogative.

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.

[Daox]

I'm pretty sure nobody here is blindly follow advice to over inflate tires. For that matter, anyone who mods their car at all in any way shape or form should know what they are doing. Its your own fault if you don't do your homework.

[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......

[wdb]

Originally Posted by ACEV

Or there is the other possibility that the tire and auto manufacturers are involved in a conspiracy to:
A. Use more fuel,
B. Reduce their individual and collective liability,
C. Confuse the buyer,
D. Sell more cars,
E. Sell more tires,
F. Sell more repair parts,
G. Make money on repair labor,
H. Or all of the above.

You forgot at least one:

I. Substitute tire sidewall for suspension complexity/cost in an effort to improve ride quality. See the early Ford Explorer, and bucketloads of other SUVs, for evidence.

Manufacturer recommended tire sizes and pressures have only the barest amount of connection to technical needs necessary to ensure reasonably safe operation (or sometimes less - again see early Ford Explorer). After that it's all about handling characteristics, ride quality, NVH, and, in no small part, fashion.

Door sticker, shmoor shticker. I'm going to stick with my own well considered and long used criteria for tire pressures, thankyouverymuch.

[RedDevil]

There's no way in the world that adding 6 PSI is going to make the difference between easily spinning wheels and not. The rubber is the same (it does not turn into plastic), the power and weight of the car is the same; just the contact patch size is slightly smaller.
Friction has a direct relationship with the force (weight) applied, not with the size of the contact patch, unless that is covered by some gelly fluid or so; and even then, higher pressure will probably help grip, not hurt it.

Road surface otoh can make a big difference of course, if he let it roll through some grease no doubt the wheels will spin.

I found I got better grip with higher pressure, but the troll either did not read that or chose to ignore it. Ah well. Can't have a site like this and expect none of such come around.