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After picking up my 2019 MDX up from the dealership for a regular service, I noticed tires were set to about 35psi, which I understand is the recommended tire pressure when the car is cold.

It's summer here and the tires get up to about 40 psi while driving on the freeway. I know the numbers increase during normal usage, but at number does it become dangerous and at risk of blowing out?
 

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The sidewall of the tires normally have a max psi displayed.

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Continental tire on my Hybrid has max inflation pressure to 51 PSI.
 
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2018 Acura MDX Advance AWD, Modern Steel/Silverstone
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Underinflated tires are just as bad as overinflated tires. Read this:
https://m.tirerack.com/tires/tiretech/techpage.jsp?techid=1

Inflate your tires to the cold pressures specified on the sticker on the driver's door jamb and worry about the potholes, nails, and other road hazards that can damage your tires.
 

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I fill up my tires when hot to 40 PSI. You gotta play around with the PSI till you find the sweetspot that you like.

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Just follow the manufacturer's recommendation rather than trying to second guess the engineers and in the case of most MDXs it means inflating to 35psi cold - but I think the hybrid may have a different spec but it'll be indicated in the owner manual and probably the door sticker.

As per Boyle's law, the pressure will increase as it gets hotter, sometimes to more than 40psi, but don't be concerned about it - the tire and system are designed to handle that.

Since temperature isn't a constant throughout the year, it's important to every now and then do a 'reset' on this and set the tire pressure to 35psi cold again (different for a hybrid I think) - i.e. the dead of winter versus the dead of summer, even if the tire lost no air, would result in quite different pressures.
 

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It is 35 PSI front/rear for the hybrid OEM tire size (245/50/20). You would probably have to adjust to PSI if you went with an aftermarket tire or different size tire to get the OEM tire feel.

I usually do 1-2 PSI under the recommended in summer because it get pretty hot in the southwest (asphalt temp +135 degrees). I do 2-4 PSI cold over recommended in winter since early morning temps can make the PSI drop to make the TPMS alarm go off.

I also have the added issue of living/driving at 5000-6800 feet. The TPMS PSI is around 1.5-2 PSI off from a hand held gauge (hand help 34 PSI = 32 TPMS).
 

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It is 35 PSI front/rear for the hybrid OEM tire size (245/50/20).
What I was thinking of apparently wasn't the hybrid but rather, the 2019 A-Spec or with 360 camera in which case they say to inflate the rear to 32 and front to 35. The bottom line is to just go by the manual/door sticker for the particular model.
 

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Check the sticker on the frame by driver door, mine with 20's says 35 psi cold for front and 32 psi cold for rear. So slightly lower pressure recommended for rear then front tires

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All you care about is the COLD tire pressure!!!! Do NOT repeat do NOT adjust tire pressure when hot. EVEN IF IT IS ABOVE MAX. Tire mfg have taken that into account such that as long as cold is at or below max hot will not affect the tire. FWIW on my trailer 85psi cold will often go to near 100 when hot and driving, likewise on my truck.
 

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Realistically, not everyone has the ability to adjust tire pressures at home, so even a little drive to the nearest pump results in adjustment when hot.

Considering that though, common practice is to gauge your pressures when stone cold before moving the vehicle, note how much more pressure you need per tire, using the same gauge when you reach the pump to assess the difference, and add the necessary amount measured at cold to the current hot pressure. Or the lazy way of adding 4 psi to your door card pressure and filling to that pressure when the tires are already hot.

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Realistically, not everyone has the ability to adjust tire pressures at home, so even a little drive to the nearest pump results in adjustment when hot.

Considering that though, common practice is to gauge your pressures when stone cold before moving the vehicle, note how much more pressure you need per tire, using the same gauge when you reach the pump to assess the difference, and add the necessary amount measured at cold to the current hot pressure. Or the lazy way of adding 4 psi to your door card pressure and filling to that pressure when the tires are already hot.

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To that point I had mine topped off this winter when it was -20 to about 4 psi above cold temp knowing it would drop by that much outside at -20. So then even that cold the lowest pressure it hit was 35, otherwise it would drop closer to 30 or below which is too low. Mine was filled at 35 in summer but by winter at that temp it dropped below 30 and tripped the pressure sensors. Now it's around 45 hot with outside temp around 90 so still under 50 psi max.

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What I was thinking of apparently wasn't the hybrid but rather, the 2019 A-Spec or with 360 camera in which case they say to inflate the rear to 32 and front to 35. The bottom line is to just go by the manual/door sticker for the particular model.
Yes, always go by your door sticker .......... and for the 20 Advance AWD, the correct psi is 35 front, 32 rear .... cold.
5482E755-3D4C-48F6-BF27-73770F15BBB9.jpeg
 

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To that point I had mine topped off this winter when it was -20 to about 4 psi above cold temp knowing it would drop by that much outside at -20. So then even that cold the lowest pressure it hit was 35, otherwise it would drop closer to 30 or below which is too low. Mine was filled at 35 in summer but by winter at that temp it dropped below 30 and tripped the pressure sensors. Now it's around 45 hot with outside temp around 90 so still under 50 psi max.

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the 50 psi max is for COLD inflation, tire mfg have taken into account temp rise as the tire heats up so even if it is above 50psi hot nothing to worry about as long as cold is near where the car mfg recomends. Don't worry if hot temp psi rises 5-10 psi.

Boyles Law PV=rT, T= degrees kelvin (room temp is about 275 Kelvin) P= pressure. V= volume. Since tire volume is almost constant with pressure (for reasonable changes in pressure in a car tire) , P is pretty linearly related to temperature. so, "back of the envelope" calculation says a 27K temp change (about 45F) should cause about a 10% pressure change, or for "typical" car tires around 1psi for each 10-15F temp change. Or 35psi at "room temp" will certainly drop it below 30psi by -20F. And that internal tire temp can be 40F or more above outside when the tire is hot, a noticeable pressure increase after a drive on a hot day.
 

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Realistically, not everyone has the ability to adjust tire pressures at home, so even a little drive to the nearest pump results in adjustment when hot.

Considering that though, common practice is to gauge your pressures when stone cold before moving the vehicle, note how much more pressure you need per tire, using the same gauge when you reach the pump to assess the difference, and add the necessary amount measured at cold to the current hot pressure. Or the lazy way of adding 4 psi to your door card pressure and filling to that pressure when the tires are already hot.

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I find it hard to believe that a Bmw owner does not have at least a $30 air compressor.
 

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Sorry wrong forum. Same applies though.
 

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I find it hard to believe that a Bmw owner does not have at least a $30 air compressor.
Well yanno, some folks live in apartments or they aren't a diy type of person. Heck I'm a diy guy and i don't have an air compressor simply because my wife doesn't approve of more tools, nor do i have garage space. Plus i can just go and do it for free at Costco anyway.

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Not only do I have no problem at all finding a spot for a small compressor in my car but I also have a plug kit and a gauge.Tires and brakes are the most important part of the car.Do yourself a favor get a damm compressor and GOOD gauge.Keep your cold tire pressure according to the door sticker.Check your pressure at night or early morning or in your garage.Not when the sun is beating on one side of the car
 

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Well yanno, some folks live in apartments or they aren't a diy type of person. Heck I'm a diy guy and i don't have an air compressor simply because my wife doesn't approve of more tools, nor do i have garage space. Plus i can just go and do it for free at Costco anyway.

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The compressor stays in the car. It’s the size of a book. Remember those. I’m not diy but I have a compressor in each car.
 
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