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      07-19-2021, 04:59 PM   #1
SoftShoe
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Recommended tire pressure WTF

After some (very little) experimentation, I’ve decided that the recommended (stickered) pressures suck (are very much not to my liking).

My ‘19 rwd lists 38-45 (front-rear) on the door.

I’m running stock-sized non-run-flat Michelin 4S.

My opinion is that the car feels very unsettled, darty, and nervous, with zero on-center feel at these settings. This inspires me to feel the exact same way … plus sad about how crappy it feels.

Just now I tried 34-36 and was quite impressed.
• The steering was heavier and deliberate.
• The ride was noticeably more comfortable, steady, and confidence inspiring.
Everything about this was better from a seat of the pants perspective.
I may actually add a couple of pounds and see how that is.

But, generally, is BMW recommending only for better mpg?
Or am I somehow destroying my car or tires as I make it much better (IMO) to drive by setting significantly (percentage-wise) lower-than-recommended pressures?

Also, the in-car monitor differs from my hand-held gauge by about 3 pounds. Is that normal? Yes, I’ll check with another gauge, but am curious if that’s a common condition.

Last edited by SoftShoe; 07-19-2021 at 05:59 PM..
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      07-19-2021, 06:41 PM   #2
dradernh
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Quote:
Originally Posted by SoftShoe View Post
My ‘19 rwd lists 38-45 (front-rear) on the door. I’m running stock-sized non-run-flat Michelin 4S.

...is BMW recommending only for better mpg?

Or am I somehow destroying my car or tires as I make it much better (IMO) to drive by setting significantly (percentage-wise) lower-than-recommended pressures?

Also, the in-car monitor differs from my hand-held gauge by about 3 pounds. Is that normal? Yes, I’ll check with another gauge, but am curious if that’s a common condition.
1) Interesting, because my 2017 RWD shows 39 R & 35 F on the door sticker. It came with Michelin Pilot Super Sport tires, the predecessors to the 4S'.

While I've been too lazy to bother with changing from the OEM-suggested TPs, if I wanted to fully-exercise my car on public back roads I'd start with 34 psi front and rear.

2) It would seem so.

3) That's quite unlikely.

4) I don't even look at the in-car TPs. I use a very expensive digital gauge that I acquired when doing competitive events and the differences are significant.

I use a race shop for day-to-day maintenance work and asked them last week about TPMS read-outs. The shop owner said there's a +/- 3 psi variation in what the typical DOT-approved TPMS sensor reads out. IOW, they're not particularly useful unless you're a typical owner who expects the car to save him from himself. Welcome to modern "life"?
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      07-19-2021, 09:17 PM   #3
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I find the M240i feels best with the same pressure all around, I normally use 2.4 bar / 35 PSI.
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      07-20-2021, 05:14 PM   #4
SoftShoe
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That makes me comfortable.
I’ll watch the shoulders on the fronts for any suggestions about upping the pressure (or increasing camber). But unless they speak up, I’ll stick with what feels right.
Will also try running even at all corners to see how that fits with the driving I do.

Thank you, both.
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      07-20-2021, 08:51 PM   #5
elliswyatt
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Hmm, the door placard on my 2021 reads 35/41. Came with Michelin PSS.
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      07-21-2021, 12:49 AM   #6
SoftShoe
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FWIW, my door numbers don’t match anything in the owner’s manual.

They match pressures for a 17” fitment.
Meanwhile, the door sticker lists 18” tires.

Looking at the book for 18”, the closest match to the pressures on the door fall under the “high-speed tuning feature.”

So again, WTF, and also, whatever.
I’ll fill them however drives best (to me).
But it would be nice if BMW explained this a little more in the book.
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Last edited by SoftShoe; 07-21-2021 at 09:26 PM..
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      07-21-2021, 10:55 AM   #7
aerobod
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My tire pressure sticker, for a 2017 M240i:
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      07-21-2021, 01:14 PM   #8
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I configured my 2018 M240i vert with non RFTs (Michelin Pilot Super Sport) which also got me the increased top speed limiter/high speed synchronization (840). My tire pressure sticker (front 33 psi, back 41 psi) does match the manual for “tire inflation pressures up to 100 mph/160 km/h.”

What gets me though is that the recommended pressures are different even though it seems like we are similarly configured.

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