The manufacturer - the tire manufacturer or the vehicle manufacturer?

I'll run 37# or sometimes 40# on my truck. Spec may be 34#.

Higher pressure = less rolling resistance and shorter stopping distances.

My Wrangler Duratracs on my Jeep jk are rated up to 80 psi or so. I keep them at about 42. I think Jeep recommended about 37 psi on the original tires.

Usually 35-37 if the door sticker says something like 32 and I'm still within the tire rating.

quote:

Originally posted by HuskySig:
I generally take the pressure on the B-pillar and double it.

Joking, right? On any car I've ever owned, that would put the tire pressure above the max rating from the tire manufacturer. For example, my F-350 says 80 psi for the rear and that also is the max pressure on the fire's sidewall. Following your rule, you'd run 160 psi? My compressor stops at 150 psi.

With the truck, I adjust the pressure for the load. Loaded it's 80 in the rear. Unloaded, 60 gives a decent ride and most of the tire is hitting the ground. They wear evenly this way when rotated with the fronts which will have the edges rounded off. I run 65 in the front. With a diesel, there's a lot of weight on the front all the time. With my tires, 60 gives 6000 lbs of load, 65 gives 6400 lbs of load, and 80 gives 7200 lbs of load. Last time I ran across the scales loaded, I was at 5200 front and 6400 rear.

On my cars, I start with the sticker on the door jamb, adjust for even contact across the width of the tread, and adjust for handling from there. On the Focus ST, that means less pressure than the 42 Ford calls for in the rear. On the Odyssey, it's a few more lbs over what Honda says.

The rating on the door is based on a number of factors and applies to the OEM tires specifically. Switch tires and it provides guidance only. As long as you don't run pressures lower than what's required to carry the load, adjust away.

I start at the recommended pressure, take a spirited drive to get the tires up to temperature, then use a laser pyrometer to measure the temperatures across the tread:
Hotter in the center> reduce pressure
Hotter on the edges>increase pressure
significantly hotter on inner or outer edge>adjust toe or camber.

quote:

Originally posted by Woodman:
The manufacturer - the tire manufacturer or the vehicle manufacturer?

I'll run 37# or sometimes 40# on my truck. Spec may be 34#.

Higher pressure = less rolling resistance and shorter stopping distances.

Shorter stopping distances with higher pressure? I think it might be relative. On your truck, the manufacturer's recommendation maybe a little underinflated to give a better ride. Increasing pressure from there may well reduce stopping distances. On my truck, the only time I break the rears loose is unloaded with Ford's 80 psi recommendation. When I lower the pressure, they don't break loose and I would bet my stopping distances would be shorter.

Depends.

On the street I keep within the range of at to roughly 10% over the recommended maximum of the tire, measured cold. Generally that rating is close to what the car manufacturer says is what works best with their chassis, but since I often don't stick with the tire that they supposedly designed the car around (discontinued, OEM rubber generally sucks, etc.) and go with what supposedly fits my driving style instead.

Elsewhere with fun time activities--like track days or autocross runs that I never seem to have any free time (or money) to do like I used to--in simplest terms I often staggered the pressure from front to rear, and sometimes from side to side, depending on which car I'm using and how many left turns vs rights a particular circuit/course is configured with. It also depends on how much camber the car is set up with for the day and the weather and temperature conditions. On dry days I like using Bridgestone track/street tires like the RE-71R but often will buy less expensive, harder compound Nittos or Hankooks just because of how quickly a few hot laps will wear down the rubber into nothing.

Characteristics like how much induced understeer, camber settings, tread hardness, ambient temp, etc., all play into how much air goes into each tire. None of which really extends the wear of the tire much. Track rubber goes away way too fast for my wallet, which in truth is one big reason why I don't do track days as much as I once did. Running cars hard gets EXPENSIVE. And living off of a gun shop salary doesn't usually afford such activities, certainly not like my old profession did.

I replaced the P rated oem tires on my last 2 pickups with light truck tires having a D load rating with 65psi being max load pressure. I adjust for temperature seasonally. I rarely have a lot of weight in the bed but do increase pressure accordingly when I do. For normal driving I inflate to 40-42 psi cold. I've gotten about 60,000 miles per set of tires. Mileage has been acceptable, handling and ride have been good.

I believe the tire pressure recommended by the vehicle manufacturer these days would be weighted more toward improved fuel economy to help meet federal MPG standards like motor oils are (0W-20 in my Tundra, for instance). It would be tempered, of course, by liability concerns, given some of the lawsuits in the past.

I'm a little surprised there are so many folks here who just "wing it". I had thought there would be a little more testing and analysis, i.e. the chalk test, from you guys. I think there is also a pretty fair amount of misinformation so far. Interesting stuff.

quote:

Originally posted by Nismo:
For you guys that run near max pressure, do you compensate for the rise of pressure when the tire/air heats up?

I use the chalk test to come up with a good guideline, and then print my own label for the door jamb. Manufacturers recommendations, I've found, are generally on the low side, for a more comfortable ride. And the max pressure printed on the sidewall is often too much, except when you are loaded down. I use the chalk test results for everyday use, and yes, I do adjust them twice a year for summer and winter pressures. I use the same chalk test pressures, but the tires "shrink" in winter and "expand" in summer. Our winters are generally in the 60-70 degree range, while our summers are 90-105. The chalk test yields a nice ride and maximum wear.
 
For LT tires (which I have on my Tacoma, which are able to hold a much higher pressure), I only up the pressure for carrying heavy loads. Our garage is completely plumbed with black pipe from a Quincy QT-5, and using a good gauge in the shade of the garage captures a pretty good reading for the ambient "cold" pressure for the season.
 
Our tires may change a bit between seasonal adjustments, but they are alway all 4 the same pressure, which feels good there is no leak in one.
 

Whatever the door jamb sticker says, maybe a few under.

quote:

Originally posted by mindustrial:
Max psi for max load is listed at 40psi... so I run 38-39. 2012 Nissan Altima. Do the same for my wife’s accord too.

Perfect example where it sounds like you must be reading the sidewall, not the door jamb. Does Nissan actually recommend that pressure? Seems incredible.

I have found that rental car companies have begun to err FAR on the high side, presumably either to give latitude for slow leaks and avoid blowouts, or because of stoopid air jockeys at the rental centers. Or both.

I'll ignore for a day rental, but if there's a TPMS readout and I'm in the car for a week or so I'll bleed them down closer to recommended. Wow - suddenly the car's not so dart-y!!!

quote:

Originally posted by CaptainMike:
I start at the recommended pressure, take a spirited drive to get the tires up to temperature, then use a laser pyrometer to measure the temperatures across the tread:
Hotter in the center> reduce pressure
Hotter on the edges>increase pressure
significantly hotter on inner or outer edge>adjust toe or camber.

Whoa! Is your name Ray Evernham?

quote:

Originally posted by TMats:

quote:

Originally posted by CaptainMike:
I start at the recommended pressure, take a spirited drive to get the tires up to temperature, then use a laser pyrometer to measure the temperatures across the tread:
Hotter in the center> reduce pressure
Hotter on the edges>increase pressure
significantly hotter on inner or outer edge>adjust toe or camber.

Whoa! Is your name Ray Evernham?

Nope, but two amateur comedians in a police cruiser once had an argument over whether I reminded them more of Mario Andretti or AJ Foyt while they were debating on whether to arrest me for reckless driving or release me with a mere citation. (personally I think I look a bit more Dan Gurneyish but whatever-I didn't go to jail)

I autocrossed for a lot of years and moderated a large tire and wheel forum on teh intrawebz for a while. These days I drive a pickup but old habits die hard.

quote:

Originally posted by sns3guppy:

quote:

Originally posted by radioman:

quote:

Originally posted by sns3guppy:

The tire will hydroplane at 9X the square root of the tire pressure.

not doubting you, but, I don't understand how this equation is used in real life, if say I change my pressure by 4 lbs.
Where does the equation come from? Does it vary with surface type or slickness?

Look it up yourself, but it's evident that you missed the point.

Oh that was useful.

quote:

tire will hydroplane at 9X the square root of the tire pressure

Yeah, that may be some nifty plane stuff but it would indicate that a tire at 30PSI hydroplanes at 34MPH. So, I've never not been in a hundreds mile controlled slide in the rain.

Done a lot of track days on 4 wheels and 2. Tires are a massive deal to me. They are the most important thing on the car (as well as brakes), truck, or motorcycle.

On my DD I run OEM pressure (door jamb on the car) or several psi higher. I want the efficiency. My performance car I absolutely do not run OEM recommended PSI as it is too high at 46 psi. I run 41/42 front and 38 on the rears since the majority weight is on the front. What’s funny is this is the OEM recommended pressure on the Australian delivered cars. Here in the USDM 46 psi for some reason.

Bike tire pressure is 36 front 42 rear OEM recommended and I will only run that if loaded down with panniers and a top box. Twisties I run 34 front 36 rear. Track pressures a few psi less.

Don’t skimp on tires. Buy the best available for your application. All the tire manufacturers run a special twice a year. Usually in the form of a prepaid Visa card. I just bought a set of Continental PureContact LS for my DD. Got $75 prepaid visa from Continental coming as a manufacturers rebate. On top of that last week prior to the holiday Discount Tire had a $100 rebate through them so in total $175 back in my pocket. Made the tires $500 a set with lifetime road hazard replacement and rebalancing, etc.

Equally important is rotation. On my DD I rotate them every 3k, not 5k per recommendation. I get more life out of them rotating at shorter intervals. Whatever mileage you decide to rotate just be religious about it. I keep a spreadsheet for my vehicles, and write all this stuff down. I check it when I pay bills each month so I don’t forget.

I need to check if the owners manual recommends the same pressure as the National Highway Traffic Safety Administration-mandated sticker on the door frame. If not, I will go with what the owners manual says.

quote:

Originally posted by DMF:
My preference is not in your poll. I use the pressure that maximizes safety.

Same here. If inflating tires above the manual recommendations shortens braking distance, I'm all for it. As an added benefit, handling and mpg usually improves as well.

quote:

Originally posted by John Steed:
If inflating tires above the manual recommendations shortens braking distance, I'm all for it. As an added benefit, handling and mpg usually improves as well.

Can I ask how this works? Now I usually run my tires a few psi above the door sticker, but I fail to see how inflating them higher equates to shorter braking distances. Braking is a function of the friction between the tire and the ground (not the pad and rotor. You can get 100% friction there, tire locked up, and still not stop). So how does decreasing tire contact patch with a higher pressure DECREASE your stopping distance? It seems to me less area on the ground will lead to a GREATER stopping distance.

A vehicle with low air pressure is harder to move than a vehicle with a higher air pressure. More friction between the tire and the pavement. Vehicles with low air in the tires get worse gas mileage than those with higher pressures due to greater friction with the ground.

Honest question.