Over inflation

Messages
1,251
Location
Austin, TX
On my 02 Camry SE (stiffer suspension setup compared to LE and XLE trims), the book calls for a blanket 29 PSI of inflation, but says if you drive over 100 MPH, inflate it to 35 PSI. Truth is I don't do 100 MPH but I like the way the car handles at 35 PSI, it corners flatter, and the steering is more responsive. I don't drive on rough roads at all, so comfort is not an issue. Anyone see a problem with leaving it at 35 PSI?
 
Messages
1,001
Location
Baltimore
My wife has the '02 Camry. It came with Continentals which expired at around 20k miles using 30psi. I replaced them with Yokahomas and took them to 35psi. I then checked them at 500 mile intervals with a tread wear gauge and increased the pressure until the wear evened. At the moment it's got 39psi in the left front and 37psi in the right front. The rears are at 35psi. Your upper limit is on the sidewall of the tire, around 44psi generally. 29psi is plain too low. The reason why it corners better and steers more responsively is that raising the pressure decreases the slip angle. That's the same thing you get when you change from one tire profile to a lower profile, such as a 65 to a 60. Since the front tires have more of the load and do more of the work than the rear, putting more air in the front makes sense. Also, since these cars tend to understeer, putting more air in the front reduces the Camry's understeer, since a larger slip angle in the rear vis a vis the front moves the car towards oversteer. http://www.auto-ware.com/setup/slp_hndl.htm (his use of "looser" and "tighter" is a bit confusing) .
 
Messages
40,732
Location
Great Lakes
I'm guessing Toyota recommends the lower PSI for two reasons: 1. Better comfort 2. Decreased center of gravity to minimize rollovers (kind of like Explorer + Firestone) For better steering response, I don't see a problem adding a few PSI like you did.
 
Messages
1,001
Location
Baltimore
The lower air pressure actually increases the tendency to roll over. It allows sidewall flex which causes the tire to "twist under". .
 
Messages
1,001
Location
Baltimore
Jonny Z:
quote:
MM, why higher on the left front? Because the tranny puts more weight on the left?
That gave me even wear. I think what's happening is that when she hits the gas the right front tire is trying to lift, and the additional air in the left is preloading it. She tends to "stomp" the gas when she takes off from a stop. At least that's the theory I'm working under at the moment. .
 
Messages
6,171
Location
Santa Barbara, CA
I've settled on 35psi also for 195/60/15 tires. Way better gas mileage and improved handling. I remember reading in motor trend advice from a tire guy saying that it was better to over inflate than be even 1psi under recommended. They showed the footprint of a tire driving over plexiglass in the snow. The tire with higher psi made full contact all the way across, while the slightly lower psi tire had areas of less tread contact.
 
Messages
783
Location
Austin Texas
Truth is that different driving styles (using the same car) will want slightly different air pressures. Different (aftermarket) tires change the desired a pressures, heck even aging of tires can desired air pressure upwards or dwonwards. Secondly, once the optimal air pressure is found that maximizes traction, there is a significantly wide pressure interval surrounding this optimal point; that 2PSI down from optimal might give one driver a better ride he desires, while 2 PSI up from optimal might give another driver the steering response he desires. There is not one pressure that can satisfy all drivers and their preferences--let alone the miriad of changes drivers can do to cars {after market wheels and different tire sizes, brake pads, springs and shock changes, ride hehight adjustments, suspension aligments,...}. So use the tire pressure indicator in the door jamb as a starting point guess, and work you way up and down until you like the way the car feels. However, there is a little device that can tell 'any' driver if his tires are operating at the correct pressures for 'him'. This device is called a probe tipped pyrometer. It is easy to use, and only requires a few seoncds of time after a long drive in order to ascertain if the tires, pressures, alignments,... are proper for that driver, on that drive in those temperatures and condistions.
 
Messages
23,591
I'd say use the carmaker's recommendation as the low end of recommended pressure. My Audi specs about 32 psi with the vehicle carrying only 2 occupants, but I run consistently 36-39 psi, depending on where I drive. If your tires wear too much in the center, tire pressure is indeed to high.
 

Kestas

Staff member
Messages
13,959
Location
The Motor City
Over the 30 years I've maintained my personal fleet, I have never had a tire with an overinflation wear pattern. Conversely, I've had plenty of tires with an underinflation wear pattern. Since I've gone to 35 psi across the board for all my fleet, I now have tires wear with an even wear pattern.
 
Messages
43,667
Location
'Stralia
[Off Topic!] working in a service station about 20 years ago, an Indian guy with an HQ Holden came in and told me that he'd pumped up his tyres yesterday, and the car wasn't handling...could I help him ? I looked out, and it looked like a matchbox car, almost perfectly roundtyres, with no inkling of flattening against the road. He reckons he just ran air until it stopped (Plenty of cyclists did the same, as evidenced by loud bangs and clouds of talk) Taking the innard out of the valve stems was rather frightening.
 
Messages
1,001
Location
Baltimore
Mitch Alsup
quote:
However, there is a little device that can tell 'any' driver if his tires are operating at the correct pressures for 'him'. This device is called a probe tipped pyrometer.
If I recollect those correctly, you measure the tread temperature across the width. When you've got an even contact patch, you'll get the same temperature reading all the way across. It's the very fast version of my approach, which measures the tire wear over some months. Who makes them and what do they sell for? .
 
Messages
2,324
Location
Baltimore, MD
my neon door says 32 psi and the tire says 44 psi. i have settled on about 38 psi. as long as you are between the door pressure and the sidewall pressure you are fine. remember that all tires are to be adjusted cold and if the pressure is a few psi higher than the sidewall pressure when the tire is hot then it is probably fine.
 
Messages
709
Location
CT
Johny Z, no problem keeping it at the manual's maximum, even if you're not going 100MPH. 29 PSI provides full contact patch and a comfortable ride. However, 35 PSI does two things. It reduces heat build-up and increases the load capacity fo the tire. So it's not unsual for a manual to show a higher pressure recommendation than the door placard if you engaed in high speed driving and/or carry more than the addition of 1 passenger. If you can live with the firmer ride, go for it. My wife Honda CR-V show 26 PSI (not a typo) and 35 PSI for >85 MPH driving. I use 29 PSI as anything higher it jarring (Honda isn't known for great suspension). On my Saab 9-5, I use 41 PSI (versus 32 PSI) which is the spec for high loads or speeds above 120 MPH with no ride comfort issues at all.
 
Messages
2,364
Location
sebring, florida
personally i like to use 35psi on the fronts and 30 on the rears, unless im hauling something in the boot. i find that with most front engined cars, using 35 and 30 still results in more front sidewall deflection in the front of the car compared to the rear, when measured with a tape measure. you can all do a relatively simple test that costs nothing, only takes a minute and gives you something to think and type about. go out to youre cars and properly inflate youre tyres. then measure the distance from the wheels to the ground on the front and rear wheels. next, try and alter the front and rear tyre pressure to make the distance the same, while trying to keep the tyres pressure within 10% of factory spec. i normally find that the front wheels on most vehicles are closer to the ground than the rears. i dont know quite what that means but its just something to think about. i use 35 on the front and 30 in the rear to try and keep the sidewall deflection close.
 
Messages
23,591
quote:
my neon door says 32 psi and the tire says 44 psi
It's good that your tires know on what vehicle they're mounted. [Wink]
 
Messages
1,856
Location
PA
If you really want to get your tire pressure right, cold, then you should inflate to a pressure and drive over a wet part of your driveway and measure the tread width of the tire and compare it to the tread width on the pavement. My Camaro recommends 30psi all around, but honestly I run Z rated high quality tires on it with a maxiumum spec of 51psi. I run my fronts around 37-38psi and the rears at 35 for everyday driving. On my snow tires though, 225/60R16s, I run them about 32 front and back because they can handle more sidewall movement. As long as the increase in pressure doesn't reduce the contact patch, you're fine. I run my tires up to the highest tolerable pressure without decreasing my contact patch. For me, thats about 38psi in the front... 30psi actually wears the outside of the tire badly and makes it corner poorly in all weather conditions. For most vehicles that run good tires spec'd to 44 or 51psi, I start at 35.
 

Jonny Z

Thread starter
Messages
1,251
Location
Austin, TX
My passenger front is always the first one to spin out - I have done it in second gear @3.5K RPM (I have a manual) hitting a patch of wet pavement. I always thought that my fat a$$ (215 lbs) gives the driver side more traction. [LOL!] I don't have the fancy gears - I am going to leave all four at 35 PSI, so far so good.
 
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