Tires for 20" rims on 2008 535i
 

So I recently purchased a new set of rims for my 2008 535i. The wheels are 2 piece Work LS406 in 20x9 (+17) up front and 20x10 (+17) in the rear. The wheels have some curb rash and the chrome is pitting and peeling in areas, so I am planning on having them sandblasted, touched up and re-powdercoated. In the meantime however, I decided to throw them on and see how they fit. Immediately after going for a short drive, my dash lit up like a christmas tree with a whole plethora of ABS, traction control, passenger airbag lights and warnings.

I am assuming this is due to the larger diameter of the tires on the car. The fronts are not bad, 245/35/20 as opposed to the stock 245/40/18s that come on the car (Overall diameter is 26.75" as opposed to 25.72" stock), however the rears are way off: stretched 245/45/20s vs the stock 275/35/18s (Overall diameter of 28.68" vs stock OD of 25.58")

So my main question is this: are the warning lights due to the overall diameter of the tires being larger than stock, or is it caused by the OD of the rear tires being much larger than the fronts? And in either case, would going to a more reasonable rear tire size of say, 275/30/20 resolve the issue?

My apologies if this topic has been covered before. I tried searching but couldn't find much info about warning lights from larger sized tires. (it could also be that I suck at searching)