i3Houston
Posts: 112
Joined: Thu Jul 12, 2018 2:30 pm

No Low Tire Pressure Warning?

Wed Nov 07, 2018 7:50 am

Just about 3 months ago i had replaced all 4 tires at costco, iDrive showed 44PSI. Yesterday[80F hot day] the front were down to 29PSI and rear were around 36PSI. Does anyone know why i3 is not showing a low tire pressure warning?
TM3 Reservation holder/ 2015 i3 Rex

nickp
Posts: 28
Joined: Tue Oct 02, 2018 7:40 am

Re: No Low Tire Pressure Warning?

Wed Nov 07, 2018 12:06 pm

I believe that's within the threshold of allowed tire pressure so no warning?

tjburbach
Posts: 35
Joined: Fri Oct 13, 2017 7:28 am
Location: Austin, TX

Re: No Low Tire Pressure Warning?

Wed Nov 07, 2018 12:16 pm

i3Houston wrote:Just about 3 months ago i had replaced all 4 tires at costco, iDrive showed 44PSI. Yesterday[80F hot day] the front were down to 29PSI and rear were around 36PSI. Does anyone know why i3 is not showing a low tire pressure warning?


From reading the i3 documentation the TPMS system warning occurs:
  • If the tire pressure deviates by more than 20% from the initialized nominal pressure
  • If the warning threshold value of 1.6 bar is undercut (23.2psi).
The 20% deviation warning is based on a tire pressure stored into the system when you do the manual TPMS initialization. So for example if the tire pressure was 30psi when the system was last initialized the warning would occur at <24psi.

You should set the tires to the correct pressure and then perform an initialization.

3.3.6. Initializing the tire pressure monitoring system (TPMS)
The TPMS is initialized via the iDrive menu.
The tire pressures must be initialized if:
  • The tire pressures have been changed
  • A tire change has been carried out
  • The tire pressure sensor have been exchanged.

jadnashuanh
Posts: 4165
Joined: Thu May 22, 2014 2:07 pm
Location: Nashua, NH USA

Re: No Low Tire Pressure Warning?

Wed Nov 07, 2018 2:22 pm

My guess, after installing the tires and pumping them way up, the TPMS was never reinitialized. The things look for a loss from the initialization value. If that value isn't set, the warning could come on at any pressure within limits.

To maintain good F/R balance and comfort, the recommended pressure seems pretty good to me. If anything, maybe a pound or two above. Keep in mind that the tire is also acting like a spring, and if the pressure is higher, an impact exerts lots more force on it and the chassis. Worst case, hitting a bump could cause damage. Way too low could also, as the carcass could get pinched and maybe even damage a rim, but the factory recommendation takes that into account when it is set.

But, in your case, where it lost about 15psi, that may indicate some other issue with the tire/wheel assembly. First, make sure that the valve cover is screwed down tight. Check the wheel for a crack. Temperature will account potentially for a little bit (1#/10-degrees F), but I'm sure it's not 150-degrees cooler now than it was!
Jim DeBruycker
2011 535i x-drive GT, 2014 i3 BEV

i3Houston
Posts: 112
Joined: Thu Jul 12, 2018 2:30 pm

Re: No Low Tire Pressure Warning?

Fri Nov 09, 2018 8:32 am

Is initialize different as "reset TPMS' on i3s iDrive menu?(Under settings > Vehicle Information)

I had reset a few times because i was really shocked to see 44PSI and thought it was too high and something was off with TPMS sensors.


Can someone please let know how TPMS can be re-initialized?
TM3 Reservation holder/ 2015 i3 Rex

jadnashuanh
Posts: 4165
Joined: Thu May 22, 2014 2:07 pm
Location: Nashua, NH USA

Re: No Low Tire Pressure Warning?

Fri Nov 09, 2018 9:57 am

Reset/reinitialize are the same thing. What that does is two things:
- makes the car 'look' for the TPMS sensors to place them at various corners
- sets the 'normal' pressure that then determines if the tire has lost pressure to give you a warning (going higher than when reset doesn't trigger a warning, only going lower beyond a computer determined delta value)

You need to do this only when you either:
- rotate your tires so that they can be placed properly in the computer
- swap tires/rims so it can look for different sensors (like if you swap from a set of summer tires to a totally new set with winter tires)

You wouldn't need to reset them to just put some air in them unless you wanted the car to know that a higher or lower value was now the 'normal' value. IOW, if you set the tire pressure to the factory setting and reset them, you may never need to reset them ever again. I have to do it twice a year when I swap between winter and summer wheels/tires.
Jim DeBruycker
2011 535i x-drive GT, 2014 i3 BEV

i3Houston
Posts: 112
Joined: Thu Jul 12, 2018 2:30 pm

Re: No Low Tire Pressure Warning?

Fri Nov 09, 2018 10:45 am

Great! thanks. I will have Costco inflate them again!

Also found a video that tells that the warning light comes on only if pressure drop below 30% the normal level.

https://www.youtube.com/watch?v=-GYIT1hiRKA


So that warning light should show at 31PSI. 44 -(44 * .3)
TM3 Reservation holder/ 2015 i3 Rex

alohart
Posts: 1434
Joined: Sat Nov 01, 2014 7:36 pm
Location: Honolulu, HI

Re: No Low Tire Pressure Warning?

Fri Nov 09, 2018 2:36 pm

i3Houston wrote:I will have Costco inflate them again!

The inflation pressure should be set when the tires are at ambient temperature. After you drive to Costco, your tires will be above ambient temperature. If Costco inflates them to 33 psi F/41 psi R before the tires cool to ambient temperature, the inflation pressure would be a bit low.

Besides saving time driving to Costco, you could use the 12 V air pump included with your i3 to increase the inflation pressures while parked at home with your tires at ambient temperature. I do this monthly. It's quick and easy to do. If you don't have an accurate tire inflation pressure gauge, the gauge on the air pump seems close enough.
Aloha,
Art

2014 BMW i3 Arravani Grey, Giga World, Tech + Driving Assist, Parking Assist, DC Fast Charging, JuiceBox EVSE

i3Houston
Posts: 112
Joined: Thu Jul 12, 2018 2:30 pm

Re: No Low Tire Pressure Warning?

Fri Nov 09, 2018 3:07 pm

alohart wrote:
i3Houston wrote:I will have Costco inflate them again!

The inflation pressure should be set when the tires are at ambient temperature. After you drive to Costco, your tires will be above ambient temperature. If Costco inflates them to 33 psi F/41 psi R before the tires cool to ambient temperature, the inflation pressure would be a bit low.

Besides saving time driving to Costco, you could use the 12 V air pump included with your i3 to increase the inflation pressures while parked at home with your tires at ambient temperature. I do this monthly. It's quick and easy to do. If you don't have an accurate tire inflation pressure gauge, the gauge on the air pump seems close enough.


I am surprised you say 33F/41R. Costco replaced the tires and filled all four to 44PSI, I will double check if tires are rated for that.

I do carry a tire inflator in the frunk but Costco fills Nitrogen :)
TM3 Reservation holder/ 2015 i3 Rex

alohart
Posts: 1434
Joined: Sat Nov 01, 2014 7:36 pm
Location: Honolulu, HI

Re: No Low Tire Pressure Warning?

Fri Nov 09, 2018 3:25 pm

i3Houston wrote:I am surprised you say 33F/41R. Costco replaced the tires and filled all four to 44PSI, I will double check if tires are rated for that.


I am surprised that you are surprised :D Look at the tire inflation pressure label in the driver door jamb.

The maximum inflation pressure for these tires as printed on their sidewalls is 51 psi. For ~5k miles, I ran 43F/51R to see whether the tread wear rate or the uneven wear pattern would be reduced. I couldn't measure any effect. However, the rolling resistance was noticeably less which resulted in longer range and the risk of tire and wheel damage was likely reduced. On the negative side, the tire contact patch was smaller which would reduce traction a bit, and road irregularities were a bit more noticeable.

i3Houston wrote:I do carry a tire inflator in the frunk but Costco fills Nitrogen :)

The i3's air pump pumps 78% nitrogen which is indistinguishable from 100% nitrogen in real life. A possible exception would be if an i3 is raced on the track. If Costco doesn't charge for nitrogen, your only cost would be your time to drive to Costco and to wait for your tires to be inflated and the cost of electricity for that drive.
Aloha,
Art

2014 BMW i3 Arravani Grey, Giga World, Tech + Driving Assist, Parking Assist, DC Fast Charging, JuiceBox EVSE

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