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Proper PSI for 155/80R13 tires
Topic Started: Mar 12 2015, 10:29 PM (1,677 Views)
TripleThreat


THANKS GMF!
Edited by TripleThreat, Mar 14 2015, 11:52 PM.
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Woodie
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myredvert
 
I would call "proper "anywhere from the car manufacturer's recommendation on the low end, to the maximum inflation rating of the tire itself on the high end.

I wouldn't exceed maximum inflation pressure unless you believe that safety margins are really determined by secretaries rolling dice with their eyes closed, and don't really apply to your tires... :O
:gp

This pretty much sums it up.
Coche Blanco
Mar 13 2015, 10:24 PM
This is not accurate.
At least half of what is posted in this thread is not accurate, or even worse.
DesmondGhostRider
Mar 13 2015, 06:22 PM
Over inflation and you wear out the center of tire. It will give you less tread actually touching the ground so it will mean less drag, but at the cost of control and braking.
With belted radials over or under inflation doesn't really wear the outside edges or center anymore. The tread is pretty stable because of the steel belts, inflation just mostly just effects the sidewalls. Back when I was crew for a national champion autocross team, we sometimes used up to 55 psi, it depends on a myriad of factors.
fireflyin
Mar 13 2015, 12:48 AM
working at a tire shop them you can run them at 40 but its safer at 35 since u will get longer life out of them
Pressure isn't going to effect tire life unless you have them so underinflated that they overheat and fail.




Edited by Woodie, Mar 14 2015, 04:13 AM.
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fireflyin


don't listen to a tire guy then what do i know i just change tires and follow the FS on doors
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yiffzer
Forgot His Manpurse

I run around 40 PSI, below my sidewall maximum of 44 PSI, to maintain good fuel efficiency. I have not seen my treads wear out unevenly. If it did, it would be due to your alignment.
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PA.metro,fixer,frames,ect
Frame Fixer

I also run 40 psi...
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BadTrip
FiLTHY McNASTYS
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Where do I get my hands on some 175 70 13 tires for a decent price? any sites? Or should I just get my tire guy that I generally go to, to order them?
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BadTrip
FiLTHY McNASTYS
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I had some tires/rims off of my '90 mazda 323 but I am pretty doubtful they will fit -- sorry if this is a dumb question : P185/65r14
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Woodie
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Anywhere you buy tires, I prefer this place, they've got free shipping: http://www.discounttiredirect.com/direct/searchTiresBySize.do?sortBy=prca&ar=70&fqs=true&rd=13&cs=175 There's a few choices from $45 to $65, delivered to your door. I'd buy the Falken myself, or maybe the GT Radial since it has the shortest warranty. The longer a tire lasts, the less grip it has.

Those tires are the right diameter for the newer GEN3 cars, they're going to throw off your odo/speedo. The speedometer drive gear from a car that came with 13" wheels will put it back right.
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DesmondGhostRider
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Coche Blanco
Mar 13 2015, 10:24 PM
DesmondGhostRider
Mar 13 2015, 06:22 PM
"proper" is what the sidewall of the tires say. The sticker on the car is for the tires that came with it.

This is not accurate.
Did some googling and you are right. Srry for posting wrong info, I thought I was right. :/

If you are running the exact same size tire as the recommended then you'd want to use the recommended psi.

The max psi on the tire is just the max it can handle. If anything filling it up to that would make it more prone to breaking when the tire heats up.

I think some of it is personal preference. I usually like my tires to be inflated closer to max. It seems to help a bit with clearance, but it certainly makes it a rougher ride. I usually run the Thunderer tires. One set that I bought was rated for 65psi and the other was rated for 55 psi. Now I'm wondering if I had just filled em to the 35 (or w.e. the sticker says) how much different they would have handled. They would probably have lasted longer since the lower pressure would have absorbed more of the vibrations and impacts from off roading. Also might have something to do with why I go through rims and bearings so quick.

The question is how do you know how much to fill them if you use different sized tires? My tracker is running oversized tires on aftermarket rims. Guess for that one I'd want to try them at a bit below max psi and see what feels best?


I always seem to learn something when I get on the forum :D
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BadTrip
FiLTHY McNASTYS
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"are the right diameter for the newer GEN3 cars" What do you mean by newer GEN3 cars? Thanks guys you are awesome, super helpful. I'm stoked to see that this forum is so active.
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Woodie
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GEN1
-MK1 85-88
GEN2
-MK2 89-91
-MK3 92-94
GEN3
-MK4 95-97
-MK5 98-01
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myredvert
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myredvert

Quote:
 
The max psi on the tire is just the max it can handle. If anything filling it up to that would make it more prone to breaking when the tire heats up.
The max sidewall pressure is the max it can handle with an engineered/calculated safety margin. And that pressure is almost never what the car designers had in mind when they chose the design pressures for some combination/compromise of ride vs. handling vs. coefficient of rolling resistance. the more sophisticated the computers become in terms of Stability Control Systems, ABS, traction control, etc, the more deviating from (vehicle) manufacturers' recommended tire inflation pressures can degrade the performance of those systems.

All other things remaining equal, inflating to higher pressures (within the limits) is easier on a tire from a heat perspective. Less sidewall flex = less heat buildup, and from that respect only less susceptible to blowouts. That doesn't consider the possiblity of blowout from impact forces with a stiffer sidewall. And, while "normal" pressure can result in better dry traction, higher inflation, even though it reduces the size of the contact patch will actually reduce hydroplaning speeds (which varies with the square root of the tire pressure). Wet and dry braking performance will also vary with higher and lower pressures and can not be so easily "guessed at." So while changing tire pressure will result in one or more performance aspects getting better, one or more may also get worse. Which is why manufacturers actually test all these aspects on their cars at the intended design pressure in order to determine what they consider the best case compromise for recommended pressure to be.
Quote:
 
I think some of it is personal preference.
Outside of the the real considerations between higher/lower inflation pressures, it is...

If there is one thing we could learn on the forum that would be more beneficial than all other things put together, it would be to become more aware of what we don't actually know and usually only guess at.
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wahoospa
Advanced Member
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I had 4 news 155/80R13 the other day. The receipt says the tech set them at 35 PSI. They seem to ride pretty good.
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