[dave_P]

Hi all, my first post :-)

I have a 2017 M240i with 19" 405M wheels (Pirelli runflats). From time to time I get low pressure warnings and reduced pressure in the front tyres. Every time i get them checked at a trusted tyre place they find no air leaks, but resealing the tyres seems to temporarily resolve the issue.

Seems like hitting bumps / potholes on the road (not really hard) might be the cause.

Has anyone else experienced this, it's becoming annoying.

Thanks in advance.

[Sportstick]

Originally Posted by dave_P

Hi all, my first post :-)

I have a 2017 M240i with 19" 405M wheels (Pirelli runflats). From time to time I get low pressure warnings and reduced pressure in the front tyres. Every time i get them checked at a trusted tyre place they find no air leaks, but resealing the tyres seems to temporarily resolve the issue.

Seems like hitting bumps / potholes on the road (not really hard) might be the cause.

Has anyone else experienced this, it's becoming annoying.

Thanks in advance.

Not a new problem, nor question, but you are new, so welcome and best wishes for your new 2!

A moderate solution are 18s.
A superior solution are 17s, and some do fit over the blue MSport calipers.

[dave_P]

Thank you 👍

[Kernel Kurtz]

If you don't need new wheels and tires right away you could get the tire shop to apply some bead sealer when they reseat them.

[Shovelman]

Have never had this problem with 17's on my 230 with 60,000 miles and second set of tires.

OTOH, it is normal to need a little air once or twice a year on almost any vehicle.

[msej449]

Hi @dave_P I'm on the South Coast near Brighton. What you describe seems odd to a UK owner. I'm on 18" runflats and haven't ever seen this problem. In the US they have a lot of issues with poor roads and their Pirellis don't seem to be great at handling this. Runflat-ness often gets 100% of the blame, but I think it's also a lot to do with the choice of OE brand.

As far as I knew, BMW UK didn't use Pirelli as original equipment (OE), but that may have changed with the M240i - what Pirelli are they? PZeros? I ask because the PZero isn't really the optimal tyre for our cars - it's designed for a heaver performance vehicle, to my mind. Certainly , the PZero runflat has a bad reputation in the US.

Generally, 18" are more tolerant of poor road surfaces than 19" and at the moment, I'm on my winter 17" (Pirelli Winter Sottozero S3). The softer ride is noticeable. But I don't think I'd want 17" on in summer - the 18" seem a good summer compromise. Most 235i UK forum owners seem to go for Michelin PS4/PS4S, or stay with the Bridgestone S001 that were OE.

[XutvJet]

Runflats are absolutely terrible. Kill them with fire.

[nazali]

my TPMS sensors are notoriusly inaccurate, and unreliable, (not for the first 3 months) my digital tire gauge is balls on

Originally Posted by dave_P

Hi all, my first post :-)

I have a 2017 M240i with 19" 405M wheels (Pirelli runflats). From time to time I get low pressure warnings and reduced pressure in the front tyres. Every time i get them checked at a trusted tyre place they find no air leaks, but resealing the tyres seems to temporarily resolve the issue.

Seems like hitting bumps / potholes on the road (not really hard) might be the cause.

Has anyone else experienced this, it's becoming annoying.

Thanks in advance.

[aerobod]

Originally Posted by nazali

my TPMS sensors are notoriusly inaccurate, and unreliable, (not for the first 3 months) my digital tire gauge is balls on

One of the things to take into account with TPM Sensors is that they operate in general on absolute pressure, not relative pressure, as they don't have a reference outside the tyre to ambient pressure. Unless altitude is taken into account in the displayed values (which could be done if altitude info from the nav system or an ambient pressure sensor is used), then TPMS displayed pressure will only be accurate at sea level under standard atmospheric conditions.

On our Macan (we only have FTM on the M240i), at my houses's 1250m altitude the TPMS displays pressure 0.3 bar (4.5PSI) below what the actual pressure is when measured with an accurate tyre pressure gauge (that measures relative pressure). When in Vancouver at sea level the TPMS and pressure gauge read the same. The TPMS is basically displaying internal tyre pressure minus 1 bar (14.7PSI) / 1 standard atmosphere of pressure.

[Sportstick]

Originally Posted by msej449

But I don't think I'd want 17" on in summer - the 18" seem a good summer compromise.

Someday, try a set of 17" Michelin PS4S and see how great they are at performance without punishment or notable risk of damage on compromised surfaces. Somewhere in Florida, a fellow forum member is enjoying the 18s that originally came on my car.

[aerobod]

Originally Posted by Sportstick

Someday, try a set of 17" Michelin PS4S and see how great they are at performance without punishment or notable risk of damage on compromised surfaces. Somewhere in Florida, a fellow forum member is enjoying the 18s that originally came on my car.

Other than generally better looks with the larger wheels, I agree the smallest you can fit will typically give the better overall performance. Standard rule I use is fit the largest brakes to the car that it needs to give the required stopping performance, fit the smallest wheels over those brakes, then use the widest tyres that will fit without rubbing.

On my Caterham the 6x13" front & 8x13" rear track wheels just fit over the AP front brakes and rear suspension tube with 2mm to spare, with 185/60-13 front and 235/45-13 rear tyres. The lower performance 6.5x15" wheels are fine for the road with 195/45-15 tyres all around (now having to use 195/50-15 tyres due to lack of decent tyres in the 195/45-15 size). You can notice the extra feel and better conforming tread that gives a much better grip profile with the 13" tyres compared with the 15" ones, with no appreciable loss in turn-in sharpness due to the higher sidewalls.

[freakystyly]

Not all 17" are the same for fitting over the "blue brakes". The Apex Arc-8 wheels for instance need the vibration damper on the brake pad trimmed off so as not to rub against the barrel of the wheel. And I hear they have a more open barrel than some other brands...

18's would be a guaranteed fit.

On my e90 I ran 17s in the summer and 18s in the winter and it was night and day with the weight savings alone.

[Sportstick]

Originally Posted by freakystyly

Not all 17" are the same for fitting over the "blue brakes". The Apex Arc-8 wheels for instance need the vibration damper on the brake pad trimmed off so as not to rub against the barrel of the wheel. And I hear they have a more open barrel than some other brands...

18's would be a guaranteed fit.

On my e90 I ran 17s in the summer and 18s in the winter and it was night and day with the weight savings alone.

But, why deprive oneself of the benefits for the lack of a generalized guarantee? Even modest research will find compatible 17" solutions. Tire Rack actually test fits the wheels and they will guarantee fit if they show it as compatible. That is where I found my BBS wheels, no modifications required, and despite the concerns of some about 17", I have been quite pleased with the appearance.