[Aircooler]

My 2009 E91 330D has the tyre pressure monitor display on the i-drive. I'll be installing a new set of alloys with winter tyres (non-RFTs) for a couple of months. Will I get any kind of error light on the dash/i-drive since there won't be any sensors on the new wheels?

Maybe I'm missing something obvious and it won't be a problem but I don't know much about the car yet - only had it a few hours and then put it in the garage for a work trip abroad.

[Em135eye]

The TPMS works off the ABS sensor so it will be fine.

[Aircooler]

Originally Posted by 335diesel

The TPMS works off the ABS sensor so it will be fine.

really? how does that check the pressure in the tyres? I always thought there was some kind of transmitter in the tyre valve assembly or similar.

[Em135eye]

Nope - it's to do with wheel rotation speed. A flatter tyre spins faster (I think) due to the reduction in diameter - or something like that.

It uses (nicked from xenon - lord of BMW facts!) the Hall effect (magnets) to work it out.

The wheel has nothing in it at all - just need to reset the TPMS every time you change the pressures - very simple to do.

[xenon]

Generally only on the US models. On the UK model the ABS sensors compare rotational speed - a tyre with low pressure rotates slightly quickers (as its diameter is smaller) and the warning light comes on. Doesn't detect a very gradual loss so you're wise to check the old fashioned way from time to time.

Edit - crossed post with 335d who gave the same answer.

[Aircooler]

ok, thanks guys - much appreciated. Im used to air/oil cooled 911s, so lots to learn about all this new technology