Hello, has anyone had issues fitting e21 front brake calipers under stock wheel specs? I know this is a pretty common “ upgrade” but I was quite shocked the find my calipers rubbing on the inside of the stock 15 inch steel wheels. What’s the best solution? Convert to wheel studs and run spacers? New wheels? Any advice and experience would be greatly appreciated.

Never seen that. What year is the car? Did you use Ate or Girling calipers? Were they machined as needed for late ones? I have sold several sets of both on late cars without problems.
And those wheels look very rusty.

Ate caliper drilled to fit on a later car. Yes wheels have a good amount of service rust I plan to clean them up for before the car goes back on the road. What wheels did you run with your calipers?

Drilled or machined .125" off the mounting pad? They should work with stock wheels. Maybe a picture of the whole caliper would shed some light on the problem. Even 944 turbo brakes clear stock wheels.

I am running the E21 brakes on my early car with Fuchs. Whomever mounted and balanced the tires did a horrible job. There is a massive amount of weights on three of the wheels. I have to keep two of the wheels on the back because the weights don't clear the calipers on the front. I have an appt tomorrow to have the tires unmounted, flipped and remounted and balanced.

Best solution is put the stock calipers back on....

I would not be surprised if the steel wheels have a slightly smaller ID, as this is the first I've heard of both the BMW calipers and steel wheels used at the same time.
The lighter alloy wheels are a better first upgrade.

I have E21 calipers on the stock steel wheels on a ‘74. They are Ate calipers (not Girling)

As Bruce Stone said, they need machining on the mounting face to centre the calipers over the rotor. Any machinist can do this.There is a thread about this on this forum somewhere.

It’s a worthwhile upgrade and don’t be deflected.

If this is a street driven car stock brakes will be fine unless you've done big HP upgrades and/or added large sticky tires like and Autocross or Track tire.

Tire grip has the largest determination upon braking distances not the type of brake caliper. 2nd up from that would be the brake pad friction determined by the pad compounding itself.

Also the steel wheel setup will run hotter brake temperatures than an aluminum wheel that offers more airflow cooling to the rotor and the thermal mass effect of having a nice big aluminum mass attached to it to suck heat out of the rotors.

Not trying to disuade you if you know what you want and why you want it. Just laying out food for thought.