Originally Posted by Lucky1
Are you sure this is a factor? BMW sold tires for the 128i in size ranges from 16" - 18" (16" square winter tires, 17" stock non-sport suspension and 18" sports suspension in Canada). I've had both 17" winter square setup and 18" summer tires on the car and have never had this issue. If it were tire diam between front and rear was an issue wouldn't all the non 1addict 1ers equipping their car with 16" winters would be traction lighting all over the place with DSC on?
I'm just thinking the DSC is very sensitive and it isn't getting the grip its comfortable with with the winter tires on and intervenes early. Does the problem happen in DTC mode?
Going from 265-35-19 to 245-40-18 rear results in a change of around 0.6" in tire diameter while changing the 245-35-19 fronts to 245-40-18 results in essentially the same diameter. This change (rear wheels are spinning quicker than the fronts vs normal conditions - one of the factors TC detects) plus a reduction in 20 mm in width definitely makes the TC come on quicker. I definitely notice TC come on very early with the winters even on mid throttle exits on mild radius corners (I have to punch it in on the same corners to get the traction control light to come on with the summer staggered setup).
I am sure the Alpine PA3 rubber is also not as grippy as the PS2s but the TC comes on way before I feel any slip with the winters. This is not always the case with the summers!