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Safe tire pressures?

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by 86blazerk5, Nov 21, 2002.

  1. 86blazerk5

    86blazerk5 1/2 ton status

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    Hey guys, I know that running a hire PSI on the street is a good way to increase gas milage. However, I was just wondering what is the highest pressure you can run without putting your self in any danger, and without cuasing any uneven wear on your tires? In case it makes any difference. I am running 35X12.5 R15 BFGoodrich All Terains. I was running around 28 PSI, I increased it to 38 PSI and my gas mileage got significanty better. But is that too High? Thanks.
    Ike /forums/images/graemlins/k5.gif
     
  2. Bubba Ray Boudreaux

    Bubba Ray Boudreaux 1 ton status

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    Well, it would help to know what rim width you are running. If it's an 8" rim, then you will get the centers wearing out faster than the sides. Furthermore, there's ratings on the side of the tire, one is maximum psi when cold. Check that when the tire is cold, and air up to that psi. Furthermore, on the road, don't run less than 80% of the maximum psi rating.
     
  3. 86blazerk5

    86blazerk5 1/2 ton status

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    Thanks for the fast reply, I knew i was forgetting to mention something. My rims are 10 inches wide. I will check out the side walls in the morning and see what they say the maximum is cold. Other opinions...???
    Ike
     
  4. heavy4x4

    heavy4x4 1/2 ton status

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    I run my 33" BFG All-terrains at 33psi cold. I have very even wear on my tires, which I'm happy with. Gas mileage, well...it sucks, but I don't think it can all be attributed to the tires.
    Opinion - run them at 33-35psi cold.
     
  5. Grim-Reaper

    Grim-Reaper 3/4 ton status Author

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    My 35 inch KM's are only rated 35 PSI max. I thought the AT's were on the same carcus and would be rated the same. on my 35 KM's with 10 inch rims I found 30 PSI is about right. I seem to be getting even tire wear. When I pull my trailer I bump up to 31-32. This is to help combat the trailer bouncing the truck as it hit bumps.
    On my old set of tires that were BFG's they were rated 50PSI max and I ran those about 38psi on 8 inch rims and the wore dead even. The factory rally rims they were on was only rated 40PSI max but those tires had a higher weight rating and over 40 they were like bricks and you felt every crack in the pavement.
     
  6. imiceman44

    imiceman44 1 ton status

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    Sorry, but I cannot let this slide.
    The PSI rating on the side wall is a max pressure with a weight rating.
    If your truck has that much weight on the tires, then by all means.
    To get the right pressure, you should figure out how much weight you have on each tire and by interpolating, you can get the right pressure to use.
    For example, for an unloaded truck with a heavy engine your front should have higher Pressures. But loaded you might need equal or more.
    Read the markings on the tires, and notice the rating is always matched to the weight.
    I worked in the tires business for 15 years, and I saw so many people doing what bubba ray was suggesting, and you can damage the tire, as well as have a very harsh ride doing so.
    The same goes for underinflating.
    Try and weigh the truck on each wheel the way you intend to use it.
     
  7. 86blazerk5

    86blazerk5 1/2 ton status

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    I thought there was a weight rating that would make a difference in the mix. The tire says, (and I'm estimating becuase I dont have it in front of me) Maximum weight 2500 lbs, 35 PSI cold. Now, I realize that the weight is different from front to rear, however, estimating that the whole truck wieghs under 5000 lbs, then there is now way that there is 2500 lbs at each wheel. So I should be ok running 38 PSI except for the harsher ride quality. In fact, it may even be good to run say, 38 PSI up front, and say 35 PSI in the back to acount for the engin being in the front, and I usualy never have anything in the back. Lat me know if I'm on the right track now. Thanks.
    Ike
     
  8. Bubba Ray Boudreaux

    Bubba Ray Boudreaux 1 ton status

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    </font><blockquote><font class="small">In reply to:</font><hr />
    interpolating

    [/ QUOTE ]
    Now that's a $14 word if I ever saw one. Anyway, I'm just going off what I have learnt in school and doing time in a tire shop. As for what I do, I run tires with a 35 psi max rating, and I run 35 psi on roadtrips, and when the truck is around town, I air down to about 32% for ride quality. I currently have 5 years and 50K miles on my tires, so if my advice, which I use on my truck can be harmful, well I guess I should see the errors of my ways.
     
  9. imiceman44

    imiceman44 1 ton status

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    OK guys, sorry for the big words, but this is a tehnical word for applying a ratio.
    What it means is, a tire says MAX 2250lbs at 35 PSI
    If you have 1500lbs o each wheel, a good pressure should be 23 PSI.
    Now that is just an example.
    That is why if you see those bias ply tires that are meant for big trucks, need to go dow in the singe digits under a jeep to have enough flex in them.
    You can go more or less to regulate your ride but do not ecceed the max, and if you don't want a stiff ride don't go to the max.
    It is a max pressure not the recommended pressure.
    After this you can do what you feel like doing, but this is my experience with tires. 15 years of research and import, I took courses and I was the consultant for choice of tires, not a worker in the company. I talked to engineers from companies like goodyear.
    This not to say I am important /forums/images/graemlins/grin.gif just to say this is not my opinion here, it's what the engineers told me.
    And it makes sense.
    /forums/images/graemlins/thumb.gif
     
  10. Bubba Ray Boudreaux

    Bubba Ray Boudreaux 1 ton status

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    What about the heat buildup with the lower pressures while going down the road?
     
  11. 86blazerk5

    86blazerk5 1/2 ton status

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    Oh, ok, I had it backwards. I was thinking that the Max 2250 lbs at 35 PSI meant that if you had more than 2250 lbs per wheel, if you went over 35 PSI you were at risk of the tire exploding. No I realize that what id means is that the heacier the vehicle, the higher the tir pressure should be. Becuase its the weight on the tires that makes them plyable. And that means that 38 PSI is way to high for me to be running for my truck. I will air it down tomorrow. My gas mileage really did improve running 38 PSI, But thats not worth the safty risk, or the money it would cost to replace tires due to inproper tire wear. Thanks for the help. /forums/images/graemlins/wink.gif
     
  12. imiceman44

    imiceman44 1 ton status

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    Bubba Ray, it says cold pressure if you read on the tire, it's because they know the pressure rises when you get the tire hot.
    Usually between 3 and 5 more PSI.
    86Blazer: It's true that the higher the pressure, the better milage, but if not with the right load, you can ruin the tires by wearing off the center.
    GM experimented with higher pressures in their EV1 electric car, they had Michelin tires at 50PSI, they did however work on the suspension plus they had a heavy car full of batteries.
    Also part of Ford's problem with the firestones was the recomended pressure to meet EPA standards for fuel economie.
    Then they changed it too low to make the ride smoother, which made the tires heat up too much and cause the seperation.
     
  13. chevyfumes

    chevyfumes Court jester

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    Watch for the muzzleflash!
    Great now I'm even more confused than before /forums/images/graemlins/confused.gif /forums/images/graemlins/confused.gif /forums/images/graemlins/confused.gif /forums/images/graemlins/confused.gifSo if I'm running 33 10.5's with stock rallies what should I be running at.... Currently at 32PSI.... /forums/images/graemlins/1zhelp.gif /forums/images/graemlins/1zhelp.gif /forums/images/graemlins/1zhelp.gif /forums/images/graemlins/1zhelp.gif
     
  14. Bubba Ray Boudreaux

    Bubba Ray Boudreaux 1 ton status

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    So tell me, am I doing something wrong with the way I run pressures in my tires?
     
  15. imiceman44

    imiceman44 1 ton status

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    OK this is my last post on this.
    32 psi is fine as long as you are comfortable with the ride.
    It all depends on what you have in the truck, what kind of tire you have.
    Just to give you an idea, I have Procomp Xterrains 35x12.5x15, my engine is a heavy Perkins Turbo diesel which is 300lbs heavier than a BB Chevy, so I run 32 in the front, and 28 in the rear, and when I load it up for a camping trip, I put 30-32.
    On the trail, I run 20 front and 15 rear, and the front seams to have lower pressures.
    I have put more than 15000 miles on highway and about 10 trips off road, and they still look great, you can see them in my link Rubicon carnage.
    Just use common sense, and check often to see if your results are good.
    There is a way you can tell if you have the right pressure for the tire, put some chalk on the tire or shoe polish, and drive the car straight for a couple hundred feet.
    If the chalk wears of evenly from side to side, then you have the right pressure.
    If it wears out on the sides and not the middle you are underinflated, if it wears on the middle, then you are overinflated. /forums/images/graemlins/thumb.gif /forums/images/graemlins/deal.gif
     

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