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Old 02-19-2006, 05:35 PM   #1
FromAP1toSTI
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Default Tire Pressure for 18s

Quick question...what should the tire pressure (psi) be at on an STi with 18s? Thanks

Ryan
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Old 02-19-2006, 05:40 PM   #2
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what does the tire say? or when you bought the tires they will say reccomended psi right?
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Old 02-19-2006, 06:19 PM   #3
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Quote:
Originally Posted by MrH00nel2
what does the tire say? or when you bought the tires they will say reccomended psi right?


12345
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Old 02-19-2006, 06:34 PM   #4
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Doesn't the tire just say a maximum rated PSI? The PSI of the tires depends on the weight and weight distribution of the vehicle as well as the surface area of the tires desired to be in contact with the ground. In other words, I have no idea and I don't think anyone will be able to give you a truly good answer without knowing the dimensions of the tires (i.e. 225/40/18).
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Old 02-19-2006, 06:50 PM   #5
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max minus 4/5 psi. thats what i do.
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Old 02-19-2006, 07:05 PM   #6
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I'm speechless. Speechless. I am without speech. I have no speech.
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Old 02-19-2006, 07:07 PM   #7
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Quote:
Originally Posted by WR^2X
I am speechless. I'm without speech.
Please elaborate, cause I would hate for this guy to go place more air in his tires than they can handle.

btw, I think max minus 4-5 psi could be pretty dangerous assuming you are taking the pressure readings on cold tires like the readings are supposed to be because the expansion of the air molecules caused by heating up with easily increase your cold tire pressure by at least 4-5 psi.
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Old 02-19-2006, 07:17 PM   #8
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Quote:
Originally Posted by InvertedB
Please elaborate, cause I would hate for this guy to go place more air in his tires than they can handle.

btw, I think max minus 4-5 psi could be pretty dangerous assuming you are taking the pressure readings on cold tires like the readings are supposed to be because the expansion of the air molecules caused by heating up with easily increase your cold tire pressure by at least 4-5 psi.

could be. never been a problem...
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Old 02-19-2006, 07:31 PM   #9
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Quote:
Originally Posted by InvertedB
Please elaborate, cause I would hate for this guy to go place more air in his tires than they can handle.

btw, I think max minus 4-5 psi could be pretty dangerous assuming you are taking the pressure readings on cold tires like the readings are supposed to be because the expansion of the air molecules caused by heating up with easily increase your cold tire pressure by at least 4-5 psi.

yup, since most tires under normal operating temps increase about 8 psi or more. My dads real time tire pressure monitoring in his vette shows a 10psi increase one they get hot.

How about just going with whats on the sticker on the driver side door. I dont see why the diameter would effect what subaru recommends.
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Old 02-19-2006, 07:45 PM   #10
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Quote:
Originally Posted by Imprezive_04
yup, since most tires under normal operating temps increase about 8 psi or more. My dads real time tire pressure monitoring in his vette shows a 10psi increase one they get hot.

How about just going with whats on the sticker on the driver side door. I dont see why the diameter would effect what subaru recommends.

you know people do have tires other than stock right?
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Old 02-19-2006, 07:54 PM   #11
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Quote:
Originally Posted by wrxblubayou
you know people do have tires other than stock right?

right and if you dont have a clue and you have to ask in here and people recommend things like the max the tire says, which i believe the max on the tires on my sti right now is like 52 psi. Anyway then isnt it best to go with something close.

Or i dont know asking the tire manufacturer or whoe ever sold them to you. Instead of getting 3000 opinions from people are are pulling numbers out of their ass. Whats on the door is the least "i pulled it out of my butt" number you could go with and the safest choice to make if you dont have a clue.
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Old 02-19-2006, 07:59 PM   #12
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Quote:
Originally Posted by Imprezive_04
right and if you dont have a clue and you have to ask in here and people recommend things like the max the tire says, which i believe the max on the tires on my sti right now is like 52 psi. Anyway then isnt it best to go with something close.

Or i dont know asking the tire manufacturer or whoe ever sold them to you. Instead of getting 3000 opinions from people are are pulling numbers out of their ass. Whats on the door is the least "i pulled it out of my butt" number you could go with and the safest choice to make if you dont have a clue.

you know im not the OP right?
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Old 02-19-2006, 08:09 PM   #13
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I think it may have been a general "you" though this thread looks like it's taking the fast track to OT.
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Old 02-19-2006, 08:16 PM   #14
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I run 225/40/18 and I always keep my psi around 30 (+/- 3psi). I would not run anything under 25 and nothing over 40 psi. Hope this helps.
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Old 02-19-2006, 11:31 PM   #15
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I have 225/40/18 AVS100s and its max psi is 44psi. I run mine at 40psi. Just read the side wall and make an educated decision.
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Old 02-20-2006, 01:07 AM   #16
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Here's what subaru thinks the tire pressure of the WRX should be. Sti's probbaly wouldn't be different. It's only for 16 & 17's but you could see what changes from 16 to 17, and then do that again to get 18'' pressures.


forgot to mention this is out of a 2004 wrx service manual.

Last edited by tkarabian; 02-20-2006 at 05:43 AM.
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Old 02-20-2006, 01:08 AM   #17
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Check the tire sidewall, I usually start off with 5 psi below the max.
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Old 02-20-2006, 01:57 AM   #18
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Kind of weird how they have a higher rear psi on the 215/45/17's than the 225/45/17's given the other trends, anyone know why that is? Seems that a narrow tire on the same sized rim and thus a slightly smaller sidewall will require a higher pressure on the rears. I wish they had data on two different 16" wheels rather than the 15's. It would be interesting to plot the data and find the curve or linear progression.
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Old 02-20-2006, 02:16 AM   #19
shane86
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I usually say 35 PSI for street driving.
if it's a really low profile tire (below 40) i'd go a little higher to 38-40 just to help keep from banging up the rim.
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Old 02-20-2006, 08:58 AM   #20
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In my 215/40-18 I run 38 lbs in the front and 36 lbs in the rear.
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Old 02-20-2006, 09:02 AM   #21
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Quote:
Originally Posted by eltrouble
Check the tire sidewall, I usually start off with 5 psi below the max.
Thats pretty damn high for the street...let alone before the tire gets heated up. Might want to rethink that one....
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