Anonymous
Anonymous asked in Cars & TransportationMaintenance & Repairs · 1 month ago

What do I inflate my tires too ?

Quick question. I have a 2019 BMW 330i Xdrive.

My car is typically 225/45 R18 for my all season tires. 

There was a mixup with my winter tires and long story short ended up getting 225/50 R18 winters (which the dealership said was okay). 

Anyway, the manual says the tires should be inflated to 32PSI front, 35PSI rear, but That’s for the 225/45’s. the 225/50’s are not in the manual as an option. Does anyone know if I would inflate to the same PSI or something different ? 

Greatly appreciated. 

20 Answers

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  • 1 month ago

    The problem with the manufacturer tire pressure recommendations is that they are based more on comfort and not safety. If you check your tire pressure once a week then you will know that it is at the bare minimum pressure per those recommendations. 

    HOWEVER, if you look at the sidewall of the tires, maximum pressure might be 40PSI to 60PSI. So, if the car is loaded down with passengers and cargo, then you'd want something higher than the bare minimum. 

    If you rarely check your tire pressure then it will be lower than the minimum recommended pressure about a month after you air them up. The TPMS system will not alert you to low tire pressure until at least one tire is somewhere between 20-25PSI. The TPMS will also fail when the batteries inside the tire unit die. 

    So, the best tire pressure is usually around 35 PSI for most cars and trucks or about five PSI higher than the minimum recommended on the door sticker or in the owners manual. This allows a margin or cushion between checking tire pressure if you only check it a couple of times a year. My vehicles lose exactly 5 PSI when the temp's drop in November and can drop 10 PSI over a period of three months once we are in the dead of winter especially when temp's are in the single digits or lower. Even on a car or truck parked into the garage and is not driven during the winter months. 

    So, we either check often, once a week or once a month, or we create a margin of error for normal pressure loss that occurs over weeks and months. 

    Low profile tires are especially susceptible to road damage when the tire pressure isn't very firm. The wheel cuts the tire and the pothole damages the wheel so you end up with a tire and wheel that must be replaced which costs a staggering amount of money compared to a car that uses a 65-75 series tire that is properly inflated and sustains no damage from pothole strikes. 

    Good Luck! 

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  • Poppy
    Lv 7
    1 month ago

    The original tires( maybe the new ones) needed the 32 psi. The new ones may be different. Read the information stamped on the tires for the psi they need.

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  • Anonymous
    1 month ago

    The correct inflation rate can usually be found on the middle pillar when you open the driver's door. Failing that your owner's manual will provide the information. 

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    • Edna
      Lv 7
      1 month agoReport

      The psi in the owner's manual or on the door frame is the psi that was recommended for tires that were mounted on the car as original equipment when the car was manufactured. If you mount a different brand of tires on your car, the psi will be shown on the side rim of those particular tires.

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  • Anonymous
    1 month ago

    Almost all car tires, from the smallest 145's to the massive 355's use the same tire pressure range, somewhere between 30 to 35 psi. The tire pressures are irrelevant.

    The tire size difference is about 3.5%. If you think you're going 60 mph on your speedo, you'll actually be going 62 mph. Your odometer reading will also be off by 3.5% while using the snow tires.

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  • 1 month ago

    Go with the pressures in the manual, that'll be fine. There's little noticeable difference between those sizes and none that would require different pressures.

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  • 1 month ago

    With winter tires, you'd be good with anything from 30 to 35 PSI.  

    Don't worry so much about the BMW manual, because those are the recommended pressures for 'stock' all-season tires.  And don't use the number on the side of the tire, because that's the maximum safe pressure.  You don't want to max out your tire pressure on winter roads.

    Most mechanics agree that 35 PSI is the default pressure for any passenger / light truck tire they inflate.  They don't care which make or model, they don't care who made the tire or how 'specialized' it claims to be, they just inflate the dammed things to 35 PSI and be done with it.

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  • Joe
    Lv 7
    1 month ago

    Stick with the PSI in the manual.  the 225/45 and 225/50 will have exactly the same "footprint", which is what matters.

    PSI = "pounds per square inch".  That number, multiplied by the size of the footprint (in square inches), added up for all four tires, equals the weight of the car in pounds.

  • lj1
    Lv 7
    1 month ago

    Ignore the answers telling you to go by the numbers on the sidewall. That's the maximum tire pressure that the Tire can safely take. Stick with what BMW recommends. They make those recommendations to ensure maximum efficiency and safety.

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  • JetDoc
    Lv 7
    1 month ago

    There's not really that much difference between 225/45 and 225/50 tires. The factory recommended inflation pressures should be good.

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  • 1 month ago

    The tire pressure monitors are looking for that pressure or they will show up as low tire pressure on your dash. There is a recommended pressure on the sidewall of the tire and also on a sticker inside the door on the drivers side

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