salimshah

There are two safety issues.

Max pressure (marked on the tire):
If pressure exceeds this number, permanant damage can happen. Damage includes steel belt broken/stretched, blow out etc. There may be margin built in, but dont count on it.
Note: Blowout while inflating will generally be fatal and while driving can be fatal.

Contact patch (based on inflated tire pressure):
This affects traction and braking which in turn may affect the safety of occupants and others on the road.


Salim

TunedRX300

Fern,
It is true car manufacturers can specific recommendation for one or two OEM tire, but the recommendation can not be applied across all tires.
Just take a look at tires carried by Tire Rack for RX300, there are 35 models. Each tire is unique in design: the weight of the tire, tread depth and pattern, rubber compound material used, wear rating, and maximum pressure. Tire makers, including Goodyear and Bridgestone, do not design tires for a specified car model, nor does Lexus has the ability to test all possible tires offered on the market.

For example, 30 psi in OEM Goodyear Integrity performs very differently than 30 psi in Avon Ranger, for the same 225/70/16 size.
From tire specfifications posted by Tire Rack:
http://www.tirerack.com/tires/Spec.j...e1=yes&place=8

http://www.tirerack.com/tires/Spec.j...1=yes&place=12

Avon is
1) 7 lbs per tire heavier, or 28%, over GY. This means in AWD, RX lost a lot of torque to spin additional 28lbs mounted at 20" moment arm (radius of the wheel) just because of the mass difference alone.
2) 3/32 longer in tread depth, or 30%, over GY. Long tread tend to squirm more than short tread, which affects traction, responsiveness, and handling. Road noise, odometer, and speedometer accuracy are also affected by tread depth as tires start to wear down, depending on tread wear rate and compound material used.
3) 9 PSI lower, or 20.5%, in maximum cold pressure than GY. 30 psi in a tire specified for 44 max psi performs and handles very differently than another tire specified for 35 max psi.
4) All tiremakers use different compound for different tire models. For example, Goodyear Eagle ResponsEdge line uses Carbon Fiber for lightweight yet stiff outboard wall and spirally wrapped Kevlar for wear resistance. Sidewall flex will be very different vs rubber compound in the Integrity, even when filled with the same 30 PSI pressure.

Fern

TunedRx300,

I've seen lots of your former posts and have never disagreed, but actually learned a lot from them ... until the tire pressure issue.

We are all entitled to our opinion and certainly our own tire pressure, its just that I'm having difficulty finding a correlation between "maximum tire pressure" allowed by a tire manufacturer against the "recommended tire pressure" suggested by the vehicle manufacturer.

Manufacturers of passenger vehicles and light trucks determine this number based on the vehicle's design load limit, that is, the greatest amount of weight a vehicle can safely carry and the vehicle's tire size. The proper tire pressure for your vehicle is referred to as the "recommended cold inflation pressure."

Because tires are designed to be used on more than one type of vehicle, tire manufacturers list the "maximum permissible inflation pressure" on the tire sidewall. This number is the greatest amount of air pressure that should ever be put in the tire under normal driving conditions. This figure is not to be missinterpreted as the ideal tire pressure to be used.

Just my $.02

salimshah

Vehicle manufacturer specs out a tire size.

Would the contact patch be the same among various tires from different brand as long as the pressure is kept at what is stated on the door jamb?
[Only consideration is area of contact]

Salim

HarrierAWD

The Goodyear Fortera TripleTred is not as smooth as the OEM Bridgestone. Its dry traction seems to be slightly less capable, but I need its superb snow/ice traction in Colorado so it's a trade-off. Handling is about the same.

Many people go ga-ga about expensive tires and knock OEM tires. I try my best to give a fair and balanced view.

TunedRX300

Fern,
~95% of the load is supported with compress air in the tire, ~5% is supported by the tire itself. A tire specified with max pressure of 44 psi is designed to hold more air and "ballon" a little differently than the one that is specificied for 35 psi. Even though it is difficult to see the difference of sidewall flex and the difference in contact patch (as Salim indicated in previous posting), the difference (road noise, handling, fuel economy etc) can be easily felt as the driver starts to pick up speed. See a good link I found that explains tire flexing.
http://www.landlinemag.com/Archives/...techniques.htm
Exactly how much flexing difference between a tire with high max pressure vs one with low max pressure, I don't know. But you can read what others did in this thread when they change tires - they have to change their personal optimum PSI due to tire difference.
You can see many members here (I am not saying it applied to you) uses 35 psi, that is the maximum pressure on my Yoko Geolander and I uses it for >30K miles, gives me better mpg, better handling, and better wear. My Yoko is good as new and never a sign of structure failure despite I ran it at 35 psi. Based on the tread wear, it is still good to go another 30K unless I change to 18" rim and tires to make room for my Rotora BBK.