Tire over inflation?


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Old 06-27-22, 04:49 PM
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Tire over inflation?

Is there a generic guide to over inflating tires to compensate for weight? A lot of tire manufactures say to consult your owners manual but mine only covers stock tire sizes and im running larger than stock sizes.

my car weighs about 900lbs more than stock unloaded and at the factory spec 32psi there is a lot of sidewall buldging
 
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Old 06-27-22, 05:25 PM
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Most vehicles have an info sticker in the drivers doorway with suggested tire pressures.
In any event.... you would never want to put more air in the tire over the max stated pressure.
Typically you run a few pounds under to keep the ride from becoming too hard.

There should be a maximum weight rating on the tire..... are you exceeding that ?
 
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Old 06-27-22, 05:59 PM
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Pj, the vehicle is 15 years old and the door jam sticker is no longer legible.

I donít think im overloading the max weight which is 1030kg per tire. Stock vehicle is 1960kg + 450 kg in additional weight. So I should have quite a bit of margin. The tireís maximum pressure is 50psi according to the sidewall so at 35 (which theyre at now and buldging) im pretty far away from that. Im just wondering if theres a way to know how much I should inflate beyond the manuals recommended 32psi to compensate the increased weight.

 
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Old 06-27-22, 06:14 PM
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You're not supposed to exceed the suggested maximum pressure of the manufacturer but that presupposes that you are using the exact size and specified tire. On a tire rated 50psi I'd be running at least 40psi.

The tires on my van are rated to carry more than the mfg specified tires.
I run them five psi under the tire mfg's specs even though though the van specifies less.
 
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Old 06-28-22, 04:42 PM
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Year, make and model of vehicle - too much vague information here.
What does "there is a lot of sidewall buldging" mean??
What does "im running larger than stock sizes." mean ??
 
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Old 06-29-22, 03:41 AM
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A vehicle modified by increasing stock weight by 900 lbs and adding larger tires is not stock and any vehicle manufacturers recommended tire pressures are useless. Is the 900 lbs dispersed so each wheel supports a quarter of the added weight?
 
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Old 06-29-22, 04:44 AM
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I generally go with about 10% below the max pressure stated on the tire, although I run the wrecker right at the 80 psi max.
 
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Old 06-29-22, 08:42 AM
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Year, make and model of vehicle - too much vague information here.
2005 SsangYong Musso 2.9D
What does "there is a lot of sidewall buldging" mean??
https://1drv.ms/u/s!ApGASKs9NMHbgYgu...ZT2Bw?e=Nv0nF0
https://1drv.ms/u/s!ApGASKs9NMHbgYgs...lYZFA?e=vwyQWH
What does "im running larger than stock sizes." mean ??
31x10.5R15
I believe stock was 235/75R15

Is the 900 lbs dispersed so each wheel supports a quarter of the added weight?
Pretty much.

A vehicle modified by increasing stock weight by 900 lbs and adding larger tires is not stock and any vehicle manufacturers recommended tire pressures are useless.
This was the motivation for my post. Most of what I've found on the internet says to check the manufacturers recommendations.
 
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Old 06-29-22, 11:16 AM
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Check the tire manufacturers recommendations. Read this:https://www.tirerack.com/tires/tiret...jsp?techid=195
 
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Old 06-30-22, 06:15 AM
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As example:
  • Let the chart tell youIf your truck has not been substantially modified, outside of the larger tires, you can use your tire inflation placard and a load inflation chart to identify a tire pressure.

    The first step is to find the chart that goes with your stock tires. Locate the pressure that relates to the recommended pressure on the tire inflation placard. Then, look for the weight the tire should bear at that level of pressure. Next, get the chart for your new tires. Look for the same weight there. If that specific weight isn’t listed, select the next highest weight and record the recommended pressure.

    Let’s go through an example, using a 2005 F-150HD that originally had 245/70R x 17D Load Range D tires.
    • According to the tire placard, at maximum load, the tire pressure should be 50 psi in the front and 60 psi in the back.
    • When you locate that tire at those pressures on the load inflation chart, the rated loads are 2,205 lbs. and 2,469 lbs.
    • The proposed new tires are 285/70R x 17D Mickey Thompson MTX Load Range D tires. The closest numbers on the load inflation chart for those tires is 2,340 lbs. and 2,540 lbs. These equate to 40 psi and 45 psi, respectively.
    If you need to adjust for differences in the pressure or weight between the charts, you can do it using this formula:
    • Tire weight/tire pressure = Load capacity pounds per psi
    You would start with the load and pressure closest to the original tire, adding or subtracting to find the proper adjusted pressure. In this example, the calculation would be:
    • Original tire: 2,205/50 = 44.1 pounds per psi
    • New tire: 2,130/35 = 60.8 pounds per psi
    To determine how much tire pressure to add, subtract the weight of the new tire at pressure from the weight of the old tire at pressure. In our example, this results in 75, or 2,205 minus 2,130. Next, take that result and divide it by the pounds per psi of the new tire. This equates to 1.23, or 75 divided 60.8. Adding the 1.23 psi to our front tires would amount to 36.23 psi, which we rounded up to 37.

    For the rear tires, the old tire had a slightly lower capacity than the new one. In this case, you could go with the 45 psi or let out some air to reach 43.6 psi.
  • Let the chalk tell youYou can also “calculate” your tire pressure with the chalk method. This involves coloring a section of your tire with chalk to see how much tread is making contact with the ground. Start by finding a flat road surface. Concrete is actually the best choice, but you can also do this on asphalt. Make a mark with soft chalk that goes all the way across your tread. Then, gradually drive your truck forward about 50 feet and then backwards 50 feet.

    Analyze the chalk on the tire. If the chalk is only worn off on the center of the tire, reduce the tire pressure slightly and go through the process again. With the adjustment, you should see the chalk wear off more broadly. Keep making tiny adjustments in the tire pressure until the chalk wears off evenly and all the way across the tread.

    You will have to complete this process for each of your four tires. Once you’ve found the right street pressure, add 10% to all four tires. Then, measure the tires and add pressure to balance them. As explained above, you need to measure from the wheel to the ground. Start by balancing the profiles of the front tires with each other. Then, balance the front tires again with the rear tires. Always adjust the tires with the smaller profiles by adding air.

    The advantages and disadvantages of this method are the same as those involved in the second method above. If you go through the process correctly, you end up with the ideal tire pressure. But, this method is tedious and there’s a reasonable chance that you will make a mistake.
 
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Old 06-30-22, 06:17 AM
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SILCA Pro Tire Pressure Calculator

https://silca.cc/pages/sppc-form
 
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Old 07-10-22, 08:30 AM
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Quick related question, when filling tires with a compressor that has a pressure gauge, the needle will mark a higher pressure when squeezing the trigger and filling the tire and then it will drop down when you stop. Is the pressure in the tire what the gauge marks when youíre filling or when youíre not filling.
 
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Old 07-10-22, 11:20 AM
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Not filling
 
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Old 03-21-23, 03:19 PM
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Bumping this because I bought new tires and they were fairly pricey so I really donít want to damage them by under inflating.

this is 40psi, does this look good or too low (or too high)?
 
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Old 03-22-23, 01:51 AM
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Tire pressures shouldn't change much from one set of tires to another. If you got even wear with the old tires/pressure I'd use that as a starting point for the new. If the old tires wore more on the outer portions of the tread, I'd bump up the pressure.
 
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Old 03-22-23, 04:19 AM
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Also if cold in the pic, you'll get slightly more pressure when warmed up.
 
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Old 03-22-23, 07:14 PM
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This is the first SUV Iíve ever owned my previous cars have all been sports sedans with a relatively low sidewall profiles which is maybe playing tricks on my eyes making me think itíd squishing more than it is
 
 

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