Tire pressure vs ride

========

That's a good question. The recommended tire pressure in my manual for an '06 Camry LE is 29 psi. 29 psi also appears on the sticker in the door jam.

29 psi produces a nice, smooth ride. When I pumped up the stock P205/65R15 tires by 5 psi to 34 psi, I definitely experienced a rougher ride--could easily feel the bumps. Didn't like it much at all. But my gas mileage seemed to improve from 20 mpg city driving to 24 mpg city driving, a 20 percent improvement. 20 percent seems like a lot. Is that even possible? I was expecting 5 percent at most.

Anyway, I next pumped up the tires to 38 psi, 9 psi over the recommended 29 psi. The stock Goodyear Integrity tires have a maximum cold tire inflation pressure of 44 psi, according to the sidewall, so I'm within the safety margin. Well, I don't know if it's just in my mind, but 38 psi feels smoother to me than 34 psi--I don't feel the bumps as much, and I like the ride as much as at the recommended 29 psi.

I generally run our cars at about 5 psi (cold) below the maximum - the figure posted on the car is almost always too low for both fuel economy and a good safety margin. I get similar improvements in economy. As for ride, different vehicles seem to be affected differently. I suspect it may have something to do with shock/strut damping rates interacting with sidewall damping rates at various pressures, but that's only a guess. One other thing I've noticed: the increased wear I regularly get warned about never happens - we always take our tires off because of extreme age, with plenty of even tread left on them...

Yeah, I guess there's suppose to be balding that occurs with over-pumped tires (loss of tread in the middle of the tire). Nice to hear that's not necessarily so.

I was thinking of going back to 34 psi from 38 (29 being recommended by the manual), but now that I hear you're not experiencing problems, I might just leave'm at 38 psi.

I am using 31-32 psi. I never tried going more than that. Maybe I should try it too. However, many recommend lowering pressure in snow or wet roads, and its been raining in NJ for sometime now.

Wow....

Unlike some I seem to be reading the right 'books' and running tires fully loaded with air when the vehicle weight doesn't need that is not only wrong, it is dangerous.

When I overinflate my tires by as little as 8 psi, I only end up with 3

1/2" of tread in the center of the tire touching ground. They will then spin really easy and slide out easy. The U shape this causes also lets water under the edges of the tire so it hydroplanes like mad. Very Very unsafe!

When I run proper pressure for the load, in my case 28-29 psi around town and 32 loaded for highway trips, I then get a nice 7" of the available 7.5" of tread touching the ground and no issues in the rain. My tires will take 44 psi 'if' I put that kind of load on it to 'need' that much air.

I 'also' 'use' my tires, I don't change them from age, so I actually 'see' the wear patterns.

Proper inflation allows my $225.00 each, tires to wear all the way down evenly.

Mike

86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00 88 Cherokee 235 BFG AT's - Gone to the rust pile...

The more I think about this issue, the more it occurs to me that the automotive engineer who specified the tire pressure for my make and model of car and my tire size probably knows more about proper inflation than the wrench down the street who says to inflate to the maximum allowable pressure shown on the sidewall. So I look at the sticker behind the car door and inflate accordingly.

That's the thing on my truck - I feel my tires are WAY overinflated, but the ride and traction say otherwise. unfortunately, it's going to snow here soon, so I'll see how the grip compares vs normal pressures.

I've been meaning to do that in the winter anyway - run my tires at 5 pound increments from 20 to 50 and see if I can determine any difference in handling or traction. I know on my Trans Am, I can feel the difference between 30 and 35. The tradeoff is 35 gives a sharper turnin but there's more traction at 30 - the back tires spin easier at 35.

Ray

Very well said, I never thought of it that way. I tend to over inflate a few psi more because I imagine tire gauges have some reading inconsistencies and the fact that my tires still *looks* like it still needs some air. I'm thinking over inflation would have the lesser evil compared to a under inflated tire.

Except these people all have a say in the tire pressure: Marketing. "Dubs" for everyone! The people who mandate that the OEM tires last through the warranty period. The company lawyers who don't want a Ford/Firestone repeat. The fuel economy guys. The handling department. The NVH department.

No, I'm not smarter than the car company, but I'm also not bound by the same rules they are.

I like to use the cold air intake (intake lid) on my Trans Am. Aftermarket ones are worth 10hp. How can GM do such a lousy job? In this case, it's induction noise - the GM piece has a big honkin' resonator on it and the aftermarket ones don't. More air coming in = more noise. Also, the GM one probably cost them $15 or less, mine was $100. (FWIW, I also didn't want to cut up a factory piece when installing nitrous, and I can confirm the intake lid is worth a tenth at the strip.)

It's all a tradeoff.

Ray

_____________________ Me too. Only I overinflate the door pressure by 1-2lbs depending on the season and the handling of the car I'm driving. Just a tip on your tires *looking* like they need more air: Radials tend to look a little "flatter" than equivalent sized bias plies set to the same pressure.

-CC

Five lbs makes quite a difference in ride. I keep mine at five under max too, at around 30 lbs

I'd use the recommended pressure. No less. No more. Yeah, Fords/ Firestones were just too bad, unfortunately.

Michelin on tire life and air pressure:

I'd use specified pressure. No more, no less.

Michel> Mike Roma> > Proper inflation allows my $225.00 each, tires to wear all the way down > > evenly.

They say that to protect themselves against lawsuits, since changing the air pressure can have an adverse affect on rollover tendency of a vehicle, especially SUV's and trucks. Trust me, there are many rollover accidents and deaths each year, and some of those are with Michelin tires. If Michelin started recommending tire pressures different from the vehicle manufacturer, they would be sued for hundreds of millions of dollars each year as a result of the accidents and deaths.

With regard to their rotation diagram, it is clearly wrong since you never want to cross tire from one side to the other. It causes a horribly harsh ride when you do that.

Huh? Total BS.

Rather than compensate for an inaccurate gauge, I decided to slog around until I got a gauge I trust. I have a friend who's almost anal about tire pressure (yet who ignores the manufacturer's recommendations), and my gauge reads the same as his three favorite gauges.

Bought a cool new compressor from Costco a while back and just got around to trying it. The compressor is great, but the gauge on it is off by a lot; it read about 27 when I got the tire to 32PSI by my aforementioned tested gauge.

35 is fine if you aren't sure your readings are accurate. 38 is probably best of you can get it.

I sometimes drop the pressure in Winter, to maybe 34, but I think the tire itself matters more than the pressure.