Tire Pressure for a layman

At the risk of stirring up this thread again, here's something I saw in Consumer Reports. Me? I like 38/36 for handling reasons - seems a reasonable middle ground. YMMV.

"Is it wise to inflate tires to 110 percent of the recommended pressure?
Alan Paulding
Plymouth, MA
Inflating your tires to a higher pressure than the automaker's recommendation can reduce heat buildup and decrease rolling resistance, resulting in slightly better fuel economy. But it can reduce the tire's grip on the road and decrease ride comfort. Overinflating can also make the tread wear unevenly, shortening the life of the tire. For maximum performance and safety, keep your tires at the auto manufacturer's recommended pressure, which is usually found on a placard in a doorjamb, not on the tire's sidewall."

I can't post a link due to my having fewer than 5 posts, but it's in Feb. 2010 issue, and is viewable w/out subscription.

 

A) Never inflate your tires beyond the max pressure on the tire itself
B) Try to retain the pressure difference in the specs in the drivers door even if you change the actual pressure
C) On the 2009 Prius with Integrity tires, tire wear improves with more pressure, only ride quality suffers

 

That person's statement seems like the typical generic advice given to anyone with regards to tire pressures... good advice, but its not really saying all that much. For me, handling is improved with more front cornering traction when I have cold pressures at 40f/35r - basically a 5 psi different between front and back. When taking a corner hard, the rear actually swings out slight. I wouldn't recommend this to anyone however, as its generally safer if your car understeers/plows. But it definitely feels nicer.

 

This is just more like a observation than a reply or comment, I have checked my tire pressure using 4 different gauges its somewhat like choosing a thermometer, which one is giving the right reading?

 

This thread is great for people doing research on how tire pressure effects MPG.

 

Yes I have run into the same problem. At 40 psi my old gauge read about 5 psi lower than my new one. I bought another one and it was different than the other two .

I wish there was someplace to get them tested or buy one that has some kind of guaranteed accuracy.

 

I present to you all a question. If I want to rely on my tpms to remind me that I need to add air pressure (within a closer tolerance): Can I inflate to 3 psi over my target, then initialize the tpms, followed by a reduction of 3 psi? Would this method result in a tpms warning at about -2psi below my target psi? Sounds viable to me. Am I missing something? Dave

 

No I don' think you are missing anything, your procedure seems OK. But I'm not sure TPMS alarms at 5 psi below where it was set, I thought it was more like 7 or 8. If you want it that close you should test it first by setting it then deflate a tire and see where it alarms.

Also remember if you set it that close you may have alarms due to normal temperature changes while driving and ambient temperature changes, day to night etc. Those changes can cause a 5 or more psi difference. So be sure to set pressures and TPMS when cold, like a early morning.

 

"Overinflating can also make the tread wear unevenly"

That's the key phrase. I keep a close eye on tire wear. If I don't see an uneven tire wear pattern, then I'll continue to maintain the pressure up around max rated pressure.

 

I have 36K miles on my OEM Toyo tires. I have kept them around 45 to 48 psi for all of those miles. The tread wear is pretty even, maybe a little more wear on the edges from cornering forces.

The old adage of higher pressures wearing the tread out in the center may be true for bias ply tires but for modern radial ply tires it seems completely false. The belts under the tread are strong enough to prevent uneven wear.

I predict you will have no problems from running higher pressures.

 

I initialized the tpms while the tire pressures were set at 46/44. First thing in the morning and ambient temperatures were 29 f and no wind. I'm not sure if wind even makes any difference. I reduced the pressure to 42/40. I'll check the drop when the warning light comes on. According to what I've read here, that should be around 41/39. If it sounds at 2 psi below that, it will probably be better. (that is where the car may have the best compromise for comfort, fuel economy, saftey/handling, and tire longevity for my typical use) I'm still early on my learning curve. Thanks for your input. Dave

 

No one has mentioned the difference between 15-inch and 17-inch wheels, I have the latter on my Five (I guess it's not a V anymore). The ride starts out firmer, and gets more so with enhanced pressure, which I am running at a moderate level.

When I replace tires, all the factors (all-season, mileage, LRR, handling, noise, road comfort) will be factored in.

 

Keep in mind that tire pressure varies about 1 psi/10 degrees F temperature change and just give yourself the slack you need for the occasional short cold spell where you don't want to pump up your tires.:rockon:

 

Wow after reading the last six pages of posts I decided to chime in with my own experiences and opinion.

My last car had the same size tires as my new Prius P215/45R17, they both have the same b-pillar placard recommended inflation pressures of 33 PSI Front and 32 PSI Rear.

My last car was a Saab 9-2x Aero, AKA Subaru Impreza WRX wagon, it was a tad quicker than my new baby and AWD. It was driven hard, I mean spirited and I had kept Ultra High Performance Summer or Max Performance Summer tires on it. I had to replace them on average of every 20k miles totaling four sets. The door sill pressure seemed low to me and the tires showed signs of under-inflation wear. Somewhere around the middle of my third set of tires lifespan I noticed a section in the owners manual that said if you routinely go over XXX MPH or carry XXX amount of weight in the car daily increase the PSI of each tire by 3 PSI. I did that and the car felt better and the tires wore normally. I had just ended up servicing all for tires to 36 PSI.

Next I looked in the operators manual for my Wife's Toyota Tacoma for the same information and it was there. It Reads as follows: For sustained high speeds above 160km/h (100 mph), in countries where such speeds are permitted by law, add the tire inflation pressure given below to the front and rear tires, but never exceed the maximum cold tire inflation pressure on the tire side wall.

All Except P225/45R18 20 kPa (0.2 kgf/cm squared, 0.2 bar, 3 psi)
P255/45R18 30 kPa (0.3 kgf/cm squared, 0.4 bar, 4 psi)

Her tires are P265/70R16 so add 3 PSI, Placard Recommendations Front 29 PSI, Rear 32 PSI. Values with 3 PSI addition Front 32 PSI, Rear 35 PSI.

When I got my Prius I went straight into the book to see if I could find something similar there in regards to increasing tire pressure over the placard limit and no luck it was not there. So today after just shy of two weeks of ownership I decided to check my tire pressures they were set as follows LF 36 PSI, LR 36 PSI, RF 37 PSI, RR 35 PSI. The car felt good when driven so I decided to inflate them all to 40 PSI and see how it fells. If it does not feel/ride good, I will go back to 36 PSI or so and reevaluate that setting.

I would think that an under-inflated or overinflated tire will kill you before a tire kept at its recommended pressure or inflated as high as its max cold pressure.

Aloha, Ed

 

Thanks for sharing this. I've heard of these instructions on some foreign-market cars, and seen images of door placards displaying similar advice, but such manufacturer guidance tends to be lacking on U.S. market vehicles.

 

My other cars owners manual says this about high speed driving.

I don't plan on needing to do that.