what is the largest rim width the 840ci will accomodate at the front?
will a 19x8 fit without spacers?...
any info appreciated....

I have the Hamann HM2 wheels on my '97 840Ci with 19 x 8.5 in the front and 19 x 10 in the rear. No spacers needed.

Hi
If you size the tire to match the factory original tire rolling diameter it doesn't matter what diameter wheel that you use. Your neck may not forgive you if you get down to about 25 series tires though:)

Offset aka ET is very important. The original offset is 15 mm and any more will run the tire into the lower spring perch. That leaves out anything that fits the 3 series.

My 8.5 x 18 OZs on the fron have an offset of 6 mm and I have had 265/35 tires in the wheel well with no rub. Currently running 245/45 x 18 in the front. With 19s you would need 245/40 to be the right tire diameter.

As a caution--you need to be less than 3% different in rolling diameter from front to rear tires or the ABS will constantly trip out.