Othello09

Okay, the time has come when the only mod left for me to do is a new set of rims (currently using the stock 18" 123's).

So my question becomes is there anything I need to be aware of with regard to the onboard FTM in iDrive when changing to non-OEM rims? My manual says I have a FTM, not TPMS. I don't understand FTM enough to understand the ramifications of switching to non-OEM. Is it a non-issue and just a matter of re-initialization in iDrive?

Can anyone help or point to a good tutorial on this topic. Also, if I move from 18" wheel to 20" is there anything I need to be aware of in terms of the functional driving/handling of the car? Cons of bigger wheel?

Thanks in advance for your help.

pjinca

All you have to do is reset the pressure in the iDrive, that's what I did. Whenever you change wheels you will get an FTM error, just reset the pressure (there are no sensors on the wheels) and drive away happy.

theXman

+1 on what pjinca said. I don't think I've ever resetted the pressure in iDrive when I change wheels. I thought it was all calculations done inside iDrive based on the spin rates of all 4 wheels and compare to see if anyone change significantly (hence, flat tire spins at slower rate).

pjinca

+1 This true, I however reset it just because. Since the pressure in my new wheels (as well as size, meaning rotational mass) were different than the stock ones I got an error which went away as soon as I did the reset. Other than that you should be fine.

Othello09

pjinca & theXman thanks! You guys rock. I notice you both choose to go to 19" rims versus 20". Is there a reason for that?

Also, did you notice any cons in handling/performance of the car by increasing your wheel size?

pjinca

Handling? Not really - performance? yes, the 20" are larger heavier wheels and have greater rotational mass so stopping is slower and brakes wear a little faster, but with only a one inch difference that's negligible. I chose 19's mainly because I didn't want paper thin tires, a little cushion is better. Some people don't mind but I do (some people also have super hard coilovers, but I would prefer to keep from losing my fillings too)

or_550i

It's quite simple... The ABS system keeps track of the number of rotations of each wheel. If one starts spinning faster than the others, its diameter is less than that of the other wheels and therefor alerts you that you have a flat.

When you reset FTM in iDrive it calibrates the rotation of each wheel and then knows what a 'normal' rotation is.

theXman

20" definitely look nice and aggressive, but I'm always scared of hitting potholes and getting curb rash. You will feel the bumps on the road, even a tiny one. So, 19" is my limit. I haven't noticed any cons in handling or performance. Actually, it got better comparing to OEM 17". GL with your search.