For those with the stock 235/55R17 Pirelli P-Zero Neros, what tire pressure do you normally run for maximum fuel economy and treadlife? I normally use 32 PSI but since I'd have to get new tires every 6 years because of how the rubber dries out, I figure I can sacrifice longer treadlife for better fuel economy. In 6 years, I'll rack at MOST 36,000 miles and that is pushing it.

I was thinking about bumping it up to 33 psi or 34 psi cold.

 

Probably wont make a difference, given the amount of mileage you put on your car I dont think the minor increase in tire pressure will show up in meaningful way. I certainly didn't notice an increase in economy when the tire pressure increased due to temperature differences (I rotated my tires yesterday and the tire pressyre was up 3 pounds to 35 psi compared to when I last set them at 32 PSI during cooler weather).

 

Hi Metroplex,
It would be a very interesting experiment for you to run door-jamb recommended pressure over a certain loop of travel, with similar weather conditions (mainly it would have to be dry) and record your mileage. Then, run the same loop again, and similar speeds and vehicle loads, but this time with your tire pressure at the maximum allowed per the sidewall. Also, feel with your hand the sidewall just after the run to see if there is any apparent sidewall heating difference. Could you try this out? Maybe a week's worth of commuting to work?

 

Gearhead: I recorded the gas mileage since I bought the car, and it has always remained at about 20 MPG in combined city/hwy driving. With more highway driving, I can get as high as 23 MPG. I'll definitely keep an eye on it with the higher tire pressure!

 

Higher tire pressure should give you less rolling resistance, i.e. better fuel economy. The tire won't squat as much so you won't have as much of a contact patch with the road. Thats why cars like the prius and even road bicycles have skinny tires.

 

Too much pressure and you run the risk of tire-related control problems. Too little pressure and you lose fuel economy and performance. Why not just use the pressures recommended by the people who made the tire? It's not just a rubber tube that someone made a guess for, so unless you have some wildly unusual setup, those pressures are most likely just right.

 

Tires only last 6 years, whether you use them or not. For those that log very few miles a year, it might be worthwhile to consider a boost fuel economy and sacrificing tread life.

 

I remember on our original set of radial tires, they were very sensitive to tire pressure. They were also very bulgie in the sidewalls too at recommended door-jamb pressure. If you had too much pressure, the steering would wander side-to-side. I have not observed this since the sidewalls have been made stiffer, starting in about 1980. I believe that using maximum cold pressure will wear-out the center of the tread a little faster than the edges of the tread, but overall tire life probably wouldn't be that different. If drift is observed at maximum cold pressure, then for sure I would reduce it. But, this is a 1-week experiment to see if a change in MPG can be measured. I have heard of many safety problems with low tire pressure, but I've never heard of a premature tire failure from using the maximum allowed cold pressure. Also, I've never heard of air leaking into a tire, so I like to be on the high side of recommended door-jamb pressure anyway.

 

Like everything else on a factory Mustang, the recommended pressure (as listed on the door jamb by FORD) is a "safe" pressure that should be used by Mr. (or Mrs.) Every One. That recommended pressure has been tested by FORD to be generally safe under the wide range of conditions in which a Mustang can be driven from sub zero to over 100 degs F. Rain, snow, dirt, dry, asphault, etc. This presure, when maintained based on the relative outside temperature, results in a drive that is comfortable and responsive for MOST drivers. Adjusting the pressure up or down from there will affect the ride quality and tire wear but each individual driver may appreciate the resulting change in ride quality.

The maximum PSI listed by the tire manufacturer is the maximum safe pressure the tire can handle under all possible conditions without major tire wear or catastrophic failure. The tire manufacturer can not recommend a general optimum pressure because even one tire size can be used on many different cars of different styles, weights, RWD, AWL, WWD (wrong wheel drive ) and will fit a range of wheel widths.

So feel free to experiment within reason. Take notes and ultimately balance tire wear, road feel (control) and MPG.

For example, I put big-fat wheels and tires on an F-150 once and I had to actually adjust the tire pressures lower than recommended (by 5 pounds or more) when running around with an empty bed because otherwise they wore like they were over inflated (center tread wear). With the lower pressure, they still handled normally and controllably on the road.

 

Once, about 8 months ago, I accidentally put in slightly more PSI than the recommended. The car felt like I was hydroplaning. Not a good feeling when cruising through DC highways.

 

I always run what the tire says for max cold PSI on everything I own including my motorcycle, I never run what the door jam says.

 

Why not?

 

Well, I know there will be plenty of people who will argue this and I'm not going to debate it but I have always believed that the tire manufacturer knows there tires better than the car manufacturer does. Especially when the tires are replaced with non OEM brand. I have never-ever had a tire or wear problem running the pressure on the tire(which is almost always higher than the door sticker) even in the FL heat. Also we went on vacation last your and drove up to NC. I have an '07 vert and my parents have an '06 vert and other than the year they were both stock and identical. My dad runs the pressure on the door and I run the pressure on the tire and the entire trip I consistently got 2-3 MPG better than he did with 3 people in my car and 2 in his. I had more weight and better MPH. I cant guaranty that the tire pressure was the difference but it's the only difference in the two vehicles we could think of.