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post #1 of (permalink) Old 09-11-2003, 09:21 AM Thread Starter
 
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Tire Air Pressure

Yesterday I had a set of Goodyear Wrangler AT/S 285/75R16 put on stock rims which is on a stock '97 Z71. The recommended air pressure for stock tires(265/75R16) on the truck is 35 psi. My question is, with the bigger tires 35 psi sounds too low, what would everyone recommend? I think the tire shop said they put around 45 psi. Just curious. Thanks to all.
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post #2 of (permalink) Old 09-11-2003, 10:17 AM
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Re: Tire Air Pressure

I always run around 45psi in my 265s. When I had 285s I ran 50psi. 50psi it probably a little high though, so I would go with what the tire shop wants to put in there (45). If the pressure is too low the edges will wear and if it is too high the center will wear.
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post #3 of (permalink) Old 09-11-2003, 12:49 PM
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Re: Tire Air Pressure

I don't know why the shop put 10 psi more than the recommended tire pressure. There is a reason the tire maker wanted it to be at 35. When you drive the tire heats up and expandes the air inside the tire. It is going to put you at risk of having a blowout vs. a flat if you hit something on the road. It could be that they want you to wear out your tires sooner so that you come back and buy more.

I always stay about 5 psi under the pressure listed on the sidewall. Another thing to remember is that the sidewall listed psi is almost always the MAX.

Like box said, too much air wears the center, and too low wears the outer edges. Your also going to have a much stiffer ride with the extra 10 psi. Also, always check the pressure when the tires are cool to get an accurate reading.

I recommend that you run 30, but that's just me. Rotate at about every 3000 miles and you should get plenty of life from your tires. You will have much better contact on the road, and a much nicer ride quality.
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post #4 of (permalink) Old 09-11-2003, 12:55 PM Thread Starter
 
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Re: Tire Air Pressure

Actually, the label on the truck recommends running 35 psi and the max pressure on the tire is 50 psi. With them putting 5 lbs less than the max tire pressure, that is what bothers me. I may knock it down to 35 psi and just see how they wear till the next rotation.
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post #5 of (permalink) Old 09-11-2003, 12:56 PM
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Re: Tire Air Pressure

Folks, remember that the MAX tire pressure on the tire and the RECOMMENDED tire pressure on the vehicle placard are two completely different things. I believe the original post referred to the RECOMMENDED pressure on the placard of 35psi. This is for the stock tires, and will probably not be applicable for larger tires. You'll probably have to experiment some to see where you should run the larger tires. I'm running 285 BFG A/T's on my '97 at about 38psi front and 36psi rear. I'm getting good wear out of them and found at higher pressures the ride suffers pretty dramatically. Keep in mind these are BFG LT tires, and the example may not apply to the Goodyears.
post #6 of (permalink) Old 09-11-2003, 01:06 PM
 
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Re: Tire Air Pressure

I run BFGs and experimented with 50,45 40 and 35 psi. I found them to be too hard and 35 seemed to alleviate the bumpiness. Rotating them frequently should help them wear more evenly, although I am more concerned about my comfort than the tire's lifetime.

Good luck
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post #7 of (permalink) Old 09-11-2003, 01:20 PM
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Re: Tire Air Pressure

just do the chalk line test on them...make sure they're riding even.
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post #8 of (permalink) Old 09-11-2003, 03:18 PM
 
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Re: Tire Air Pressure

I keep my 285's at around 58lbs because of the highway driving..... Max tire pressure is 65lbs.
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post #9 of (permalink) Old 09-11-2003, 04:34 PM
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Re: Tire Air Pressure

I would keep it between 40 and 50, whatever they wear at the best. Ignore the rating on the door, that was only valid with the smaller, lighter stock tires. 285s will need at least 40 to 45, in my experience. Too little air will cause the tires to not only wear funny but to heat up with highway driving, accelerating wear and causing potentially dangerous situations. Too much (above 50) can cause the tires to burst easier if a rock or stick is run over on the road.
The tire shop had it right with 45lbs.
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post #10 of (permalink) Old 09-11-2003, 05:13 PM
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Re: Tire Air Pressure

I wish I could find Tims post. He posted some really good info [img]images/graemlins/frown.gif[/img]

Lotsa this has already been touched on but since I am typing this in word since my spelling sucks and I don't remember everything that was said you guys can just deal with it [img]images/graemlins/tongue.gif[/img]

Anywho......the pressure on the tire is for max the max load the tire is rated at. Go by whats on the tire and forget the door. As a tire rotates it flexes and this flexing causes heat. Heat kills tires and then you get things like the firestone fiasco happening. The more load you put on a tire the more it will flex too. The more air you have in your tire the less it flexes and the less heat it builds. This doesn't mean that if your tire says it will carry 3k# at 50psig then it will take 6k# at 100psig though. Everything said next will basically hold true as an inverse, if more increases mileage then less will decrease. There is also a point of "diminishing returns" Meaning sometimes in drag racing for example 10# might give less traction than 12#. Also you wont notice a change in some of these unless you change air pressure drastically or if you are doing something very demanding of your tire. Your not running a risk of popping a bead for instance if you run 30# instead of 35#. Back to the more air= less flex. Less flex=less rolling resistance. This means fuel mileage goes up. It will ride firmer. More pressure can cause the middle of the tire to kind of bulge out so the center of the tire wears quicker. Less air will make it a bit harder to steer(you wont notice unless you have manual steering and the air is pretty low). It increases your foot print or contact patch meaning more rubber is on the ground. This means better traction and flotation. More side wall flex will mean you don't feel bumps as bad but way aired down makes things feel squishy. Less air means more side wall flex laterally and can pop beads or cause the vehicle kinda squirm in hard corners. So we want to balance things so they handle how we want them too. In a truck especially we might need to alter the tire pressure quite a bit(not as much in the back generally unless we go to haul a load or pull a trailer for instance) In the winter I will run the tires at max inflation since I will have 1000# of ballast in the back and a plow up front. In the summer I run what ever I feel comfortable with ride wise and set that pressure cold. Then after I drive it a bit and get the tires hot I check em again and make sure the pressure don't jump more than 5#. This would show that the tire is flexing lots and building heat and causing the air to expand. I stole this idea from Tim. Remember that especially in a truck front to back will probably be pretty different. Don't forget when you rotate.

I dont think that running high pressure(as long as it isnt above the spec wil casue thigs to kerspload.
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