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tire pressure


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18 replies to this topic

#1 monk50

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Posted 30 October 2003 - 09:53 AM

Just bought a set of new WRX wheels and tires for my 95 legacy. the stock tires have about 1000 miles on them and really dress up the car.

Question: What is the recommended tire pressure for these tires? The max tire pressure on the tire itself states to not inflate over 44 #.

I drive in piedmont of NC and up to the Blue Ridge mountains.

Any idea?

Thanks:-\

#2 mtsmiths

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Posted 30 October 2003 - 10:36 AM

We run at 36psi for normal driving (whitefish, Montana, definately mountain driving). When we take a long trip on the interstate we up to 38.

With the studded tires we go down to 32.

#3 monk50

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Posted 30 October 2003 - 10:55 AM

Thanks,
I think I will run them at around 35 per your suggestions and push them higher when I go to the mountains.
Thanks
gerald

#4 1 Lucky Texan

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Posted 30 October 2003 - 11:24 AM

Short term - start with about 2psi over the 'door post' recommendation - adjust for ride/handling/load - BUT monitor tire wear closely.

As a general rule - for the same vehicle weight, going to larger tires means a bigger 'patch' on the road and lower pressures. But there are a lot of variables like sidewall stiffness, centrifugal forces at high speed, changing loads etc.

good luck

#5 monk50

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Posted 30 October 2003 - 11:30 AM

Thanks,
That sound like a good plan but appreciate any experience out there.
monk

#6 mtsmiths

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Posted 30 October 2003 - 11:38 AM

Raise 'em for the interstate and long highway driving. The studs are at 32 to give better 'squish' and bigger footprint on ice.

#7 Commuter

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Posted 30 October 2003 - 01:10 PM

Tire contact patch area is a function of the tire pressure and the weight on that tire (wheel). It's a balance of forces. It does not change with the tire profile. What does change is the shape of the contact patch.

For starters, use the recommended tire pressure for your car. If the wear is even, then this is the correct pressure. If you don't care about even wear, or you want different handling characteristics, then adjust accordingly. Within reason and safety limits of course. As mentioned, sidewall stiffness etc will affect the required pressure. I recall one set of tires I had where I had to bump up about 6 psi !! to get even wear. (It was a semi no-name brand... )

I have found that running a couple psi over recommended works out well. But this is more a function of the fact that tires slowly lose air (they never gain) as opposed to any performance reasons. By the time you check, you may be a couple of psi low, hence, one ends up with even wear overall.

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#8 Suzam

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Posted 30 October 2003 - 09:38 PM

I have found that 2-3 lbs over recommended pressure works well for me. I put 90 miles per day at mostly 65-70+MPH on the highway with the same setup as you have. Over 10k on the tires and wear is very even.
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#9 sprintman

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Posted 31 October 2003 - 12:09 AM

Outback 36 psi all round on Yokohama Geolandars (OEM tyre) with Nitrogen fill. I run 38-40 psi in the Mazda turbo also Nitrogen fill.

#10 Setright

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Posted 31 October 2003 - 02:24 AM

How can you discuss tyre pressure without mentioning tyre size??


Wider road tyres actually tend to need higher pressure because otherwise the carcass doesn't excert enough force on the central part of the contact patch. Also, more air in the tyre gives better thermal stability.


(Race tyres have a much harder carcass and pressure be lowered as they get wider.)

#11 gotsubarus

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Posted 02 November 2003 - 09:33 PM

Living here in NC running the roads from WNC to Piedmont every week for the last 14 years, and numerouse times to Atlanta and TN...I run 40 in the front and 39 in rear and have had no problems.

The only time I lower it will be when and if it snows or there is chance of ice.

The advantage of higher preasure is that the tire is harder and will last longer and wear more even. The disadvantage is handling on curvy winding mountain roads ( 2 lane road or parkway ) at high rate of speeds but no problem on the Highway.

but i also run higher tread wear tires such as 580 tread wear or more rather than the lower soft rubber tires for racing

#12 gotsubarus

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Posted 02 November 2003 - 10:23 PM

Living here in NC running the roads from WNC to Piedmont every week for the last 14 years, and numerouse times to Atlanta and TN...I run 40 in the front and 39 in rear and have had no problems.

The only time I lower it will be when and if it snows or there is chance of ice.

The advantage of higher preasure is that the tire is harder and will last longer and wear more even. The disadvantage is handling on curvy winding mountain roads ( 2 lane road or parkway ) at high rate of speeds but no problem on the Highway.

but i also run higher tread wear tires such as 580 tread wear or more rather than the lower soft rubber tires for racing

#13 monk50

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Posted 03 November 2003 - 07:43 AM

Rode to Boone and area this weekend with 35# front and rear. Good ride and handled well.

Will go up some on pressure.

Running 40 and 30 does that not cause your tires to wear in the middle?

Thanks for your input.
monk

#14 gotsubarus

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Posted 03 November 2003 - 12:20 PM

No, they wear very well that way and will last you longer.... Alot of tires running with 35 PSI in the Mountain areas will wear on the outer edges. Especialy when driving harder than a person should be driving in the curves.

Like i said i run 40 in front and 38 - 39 in rear because of the weight difference from fron to rear of the the vehical. And i Also run higher tread wear tires such as 580 tread wear, traction A temperature B.

#15 monk50

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Posted 03 November 2003 - 02:04 PM

Thanks Shane

#16 electryc_monk

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Posted 03 November 2003 - 03:37 PM

what ever the "stamped PSI rating is for max. i usually set it there for around the town and what have you.but, for the roadtrips... I usually go 2-5 over currently the 185/70r13 has a SI max of 35 so its at 35 now..... for the raodtrip they usually get 38-40 all around. but i don't let it go over 5+ max... persona preference....

your results may vary.

#17 DaveWV

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Posted 03 November 2003 - 06:17 PM

What size are the tires? If they are 205/55/16 like on my 99 Legacy GT, I run 32f and 30r like the door jamb says. Works and rides perfectly.

#18 subyroo

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Posted 04 November 2003 - 04:53 AM

I have 215/60 R16 Yokohama Geolander's on my 03 XS Forester and I'm running 36psi in them and I rotate - balance & align them at every service interval.

They are currently wearing very even from an eye perspective the aligner & balancer may say otherwise as they are due for their 1st rotation in another 1,200kms.

I have always run 36psi in the tyres on all my cars and have never had a problem.
However, NEVER NEVER go below 32psi on Steel Belted Radials or you may end up having tread seperation. That information was passed onto me by a Bridgestone Tyre Technician when Steel Belted Radials first appeared in Australia, the reason being that the steel belts may overheat and fracture causing the seperation or a blowout.
The main reason some people deflate their steel belted tyres below the 32psi is because the ride is too harsh for them, those people should remain using "cloth radials" if they desire a softer ride.

#19 DaveWV

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Posted 04 November 2003 - 02:21 PM

When were steel belted tires introduced to Austrailia? 20 years ago? A lot has changed since then. It used to be with steel belted radials, you couldn't swap tires side to side. Thats even recommened by tire manufactures now. All these years after the introduction of steel belted tires, there ar a lot of myths.

The best PSI for you tires(if they are a recommended size for the car) is what the CAR manufacturer has stated in the owners mannual or stamped somewhere on the car.

In most cases, tire makers don't know what particular tire is going on what make of car. The car maker does many miles of testing and knows what tire and psi will work best for the intended purpose of the car.

To make a blanket statement of what psi to run in every tire regaurdless of car make and tire size is based purley on personal experience or ignorance, however it may work out.

There are exceptions to this, and many you have probably had great results in adjusting the psi in your tires to suit your needs and experiences. Good for you. I'll stick to Subaru's recommendation for tire pressures.




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