06-11-2019, 12:13 PM | #1 |
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Tire pressure system & recommendation?
Anybody understand the TPMS display in their M40i? And can explain it to me?
Yesterday early evening, after standing on a parking lot the whole day (so tire temps where in the 90’s on one side, around 80 on the other), the display tells me front recommended pressure is 36 psi, rear 35 psi. This morning, fresh out of the garage, tire temps about 70, it tells me both front and rear recommended pressure 34 psi??? They actually happen to be all at 34 psi (according to car TPMS). Tire recognition is set to automatic. |
06-11-2019, 01:09 PM | #2 |
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Yes, I have noticed this a well. I think the recommended tyre pressures are adjusted relative to the ambient temperature. The hotter the tyres are the higher the recommended pressure.
34 psi seems to be the normal recommended pressure front and rear at base ambient temperature. I am guessing that will be about 70F. I am also guessing that at 80F it will be 35psi and at 90F 36psi and so forth. Just my thoughts. Not sure though. Correction: 32psi is the recommended tyre pressure according to the door sticker. I set mine 2psi higher, ie 34psi Last edited by Jim S; 06-12-2019 at 11:37 AM.. |
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06-11-2019, 02:33 PM | #4 |
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06-11-2019, 03:27 PM | #5 |
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06-11-2019, 03:43 PM | #6 |
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Yes, it is very unusual and one of the new additions in iDrive v7. The target temperature is adjusted to compensate for the increase, or decrease, in tyre temperature.
You will know that in very hot temps the tyre pressure increases quite a lot. Great new addition in the G29. |
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06-11-2019, 03:52 PM | #7 |
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I should also add that the target tyre pressure also changes when you drive the car and the tyres heat up.
Also, it measures each of the four tyres but only sets the target temp for the front pair and the rear pair. Last edited by Jim S; 06-11-2019 at 04:04 PM.. |
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06-11-2019, 09:42 PM | #8 | |
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The manual does a very poor job explaining this. And I am a bit skeptical. I never heard about increasing tire pressure to account for higher temps. Except for tracking. |
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06-12-2019, 02:33 AM | #9 | |
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I would set my tyre pressures either inside your garage on a cool morning or in the shade if this is not possible. I wouldn't read too much into what the pressures should be at various temperatures. Just set the pressures at the recommended settings and let the car do the rest of the calculations. My opinion, for what it is worth. Hope you are enjoying your car. My car is great, just a pity about the problem with the brakes. Hoping this will be resolved and I can go on my merry way without having to worry about getting stuck in a remote place. |
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06-12-2019, 05:51 AM | #10 |
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Ok, thanks, I think I get it now. The recommended adjust for temps so that the tire will be at recommended when cold. If I had to add air while hot I don’t have to guess as to how much I have to add, or have to worry about bleeding the tire during hot summer months when pressure is higher even in ‘cold’ tire.
Even though in the past I would consider ‘cold’ after standing in garage over night and adjust then to recommended. |
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06-12-2019, 06:05 AM | #11 |
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Yes, I think you can consider cold as you say, in garage overnight. That will be your base “cold” setting.
Happy motoring. |
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06-12-2019, 09:50 AM | #12 |
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This morning, the tires had ambient temp of about 72F and 34psi. System recommended 32psi for both front and rear.
Yesterday morning tires were about 70F and it recommended 34psi. I'll take German's recommendation he gave me in another forum: just ignore it. |
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06-12-2019, 11:03 AM | #13 | |
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Quote:
Personally, I run my tyres about 2psi over the recommended pressure, so that is 34psi. Set in my garage after overnight parking. Today when I was driving, the tyres were showing 70F temp and 35psi pressure front and rear. The recommended was 33psi front and rear. The outside temp was about 60F. Last edited by Jim S; 06-12-2019 at 11:39 AM.. |
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