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The Tire Rack's Tire & Wheel Forum
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Old 01-14-2013, 01:52 PM   #1
Cali Chase
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tire pressure questions

so i have noticed some play in my steering wheel and decided it wolld be a good idea to check my tire pressure. My front tires, Kumho ecsta 225/40 r18 are at 27 psi and my rear dunlops, 255/34 r18 are at 28psi. That seemed normal to me being that i filll my tires to about 28 or 30 but the labels on the tires say to fill to 50 and 51 psi respectively. That seems way to high...
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Old 01-14-2013, 02:04 PM   #2
Poncho@home
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max PSI is typically around @50, however that is too high for normal driving.

under 30 is also a little low IMO. I normally run anywhere from 32 to 36, depending on car, tire ride quality.
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Old 01-14-2013, 04:34 PM   #3
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+1

I would not fill your tires up to 50 PSI, and 27-28 seems low. I believe the tire pressure info should be on the door jamb though if you'd like to run what's recommended for your car.
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Old 01-15-2013, 04:51 AM   #4
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For savety of the tires, you better keep the pressures high, mayby even higher then you have now. Comfort and gripp are bad then ,but you dont risk a blow out.
Tires with low aspect ratio ( further AR = the 35 in your 255/35 R 18 ) are to high calculated in their maximum load ( on the sidewall Loadindex or maximum load printed) by the tire-makers, and so deflect more then is save for them, when you put maximum load and reference-presssure on them.
This is a thing the tire-makers wont tell you.

If you give me the GAWR's front and behind and the maximum load or loadindex of the tires, and the type of tire, I can calculate a save pressure for fully loaded, what after 2000 is called normal use advice.
If you can produce empty weight or curb weigt and weight division front /back, and the way you normally load the car ( Persons and load), I can estimate the normal use axle loads and calculate an advice-pressure for that .

Reference pressure i mentioned is the pressure the maximum load can be carried ( according to calculations) up to the reference speed of probably 190km/??m/h for your W speedrated tires, without damaging the tires by driving alone. this is lower then the maximum pressure of that 50 and 51 psi that is only printed on P-tires/standard load and Extraload/XL/reinforced.
So search on the sidewall for the last ( XL etc).

American P-tires Pr ( referencepressure/maxloadpressure) 2,4bar/35psi
American XL tires Pr 2,8 bar/41psi.
Difference between Pr and Pmax is used for higher speed and camber-angle above 2 degrees ( alignment tires like this /-\ on the axle instead of this|-|)
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Old 01-15-2013, 05:46 PM   #5
Jim Clark
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Originally Posted by jadatis View Post
For savety of the tires, you better keep the pressures high, mayby even higher then you have now. Comfort and gripp are bad then ,but you dont risk a blow out.
Tires with low aspect ratio ( further AR = the 35 in your 255/35 R 18 ) are to high calculated in their maximum load ( on the sidewall Loadindex or maximum load printed) by the tire-makers, and so deflect more then is save for them, when you put maximum load and reference-presssure on them.
This is a thing the tire-makers wont tell you.

If you give me the GAWR's front and behind and the maximum load or loadindex of the tires, and the type of tire, I can calculate a save pressure for fully loaded, what after 2000 is called normal use advice.
If you can produce empty weight or curb weigt and weight division front /back, and the way you normally load the car ( Persons and load), I can estimate the normal use axle loads and calculate an advice-pressure for that .

Reference pressure i mentioned is the pressure the maximum load can be carried ( according to calculations) up to the reference speed of probably 190km/??m/h for your W speedrated tires, without damaging the tires by driving alone. this is lower then the maximum pressure of that 50 and 51 psi that is only printed on P-tires/standard load and Extraload/XL/reinforced.
So search on the sidewall for the last ( XL etc).

American P-tires Pr ( referencepressure/maxloadpressure) 2,4bar/35psi
American XL tires Pr 2,8 bar/41psi.
Difference between Pr and Pmax is used for higher speed and camber-angle above 2 degrees ( alignment tires like this /-\ on the axle instead of this|-|)
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