So I'll be buying in summer a set of 3 piece custom made wheels from England. Dimensions are:
17x8.5 et 30 in the front
17x8.5 et 25 in the rear

(anybody with similar dimensions and offset post your pics for comparison)

Upon asking the wheel makers their max size lip for the dimensions of my wheels I want, they want the dimensions of "D": refer to image attached.

I told my friend, he gave me this sheet: http://www.ccwheel.com/documents/BrakeMeasurements.pdf

Which dimension does the wheel maker want? I have no idea what the stock caliper dimensions he wants are. If anybody has them handy, please post.

Also, I will be lowering my 2006 r53 over 2 inches with these wheels on ST coils. Any fitment experts on here, could you tell me the range of danger in rubbing coils/brakes/anything else? Do you think my sizes are safe?

 

I like the CCW wheel measurement doc that you linked to. If you give those measurements to the wheel company they can figure out how much clearance your current brakes have. Front calipers are larger than rear brakes. You have the opposing piston caliper type.

Using OEM 17x7" et48 wheels for comparison-

17x8.5 et30 will be 1mm closer to the inner suspension and poke out 37.1mm which is a lot. combined with a 2" suspension drop and you will not have much clearance for the front tire without doing the following:
Opt for a really small tire diameter size less than OEM 24.4"
Opt for a stretched tire fit which combines a narrow tire for the 8.5" wide rim with small tire diameter.
Add front adjustable camber plates so that you can increase negative camber to -2 to -3 degrees so that the top of the tire can tilt inward to clear the plastic wheel arch.
Use a dremmel tool to remove plastic from the inner wheel arches to give more clearance.
Shave the outer treads of the tire just a bit to allow for clearance but this may reduce tire treadlift for street driving.
Use a tire with tread design that has a more rounded not square shoulder tread block.
Opt for less drop than 2" in the front to add some clearance.

For the rear
17x8.5" et25 compared to OEM, the new wheel is 3.9mm further from the inner suspension and pokes out 42.1mm more which is very large. You would need rear lower adjustable control arms to increase rear negative camber to -2 to -3 degrees which will wear out the inner tire treads more with street driving and increase tendency to oversteer when turning fast. Combined with a 2" drop it's likely you may rub during driving over dips or with a full load of passengers, but that depends on how you tuck in the tire shoulder under the wheel arch plastic. Since you have full ride height control consider lowering just enough to get the clearance you need front and rear.

What tire size were you thinking of using?

Do you have the ST coilovers installed already? If so,what wheels and tires do you have now and how much clearance do you have with that suspension mod?

Are your roads smooth or full of potholes? Low profile sidewalls are going to be very stiff riding for bad roads and combined with the 2" suspension drop and possible front camber plates, it could be very jarring on anything but smooth roads.

For compatible tire sizes for 17x8.5" wheels most tire companies don't make a wide range to fit the MINI.

But Yokohama S.Drive is an exception with sizes that allow for dropped suspensions and more clearance. There are sizes for stretched fit or extra wide sizes for wider rims like
225/35-17 fits 7.5-9" wide rim, perfect for 8" rim, 23.1" tire diameter is extra small but works for extra clearance. 35 series sidewall will be stiff.
235/40-17 fits 8-9.5" wide rim, perfect for 8.5" rim, 24.3" tire diameter is stock. Tire fits rim nicely with good proportion for wide rim but you need to tuck in the outer treads to get it to be flush.

see
http://www.tirerack.com/tires/tires....eModel=S.drive



Here is an example of a MINI with 15x8.5" wheels and stretched tires.

 

Thanks much for such a detailed response. I do not have the STs yet. I also live in New England. Bad roads, but not as bad as Massachusetts. I'm in New Hampshire. Everything you listed was what I was expecting which is good, that means I'm not totally clueless yet. As far as the offset, I'm trying to get pretty close to flush. You mentioned my rear wheels will be about 42mm outwards. Compared to stock wheels that are pretty tucked in, how close to flush do you think this is? Also, I intended on definitely getting stretched tires for clearance. I was thinking 195-40-17. Camber plates were a thought as well.

 

It is correct that the OEM wheel is not flush so that poking out is not as drastic as it might seem just from the difference I quoted. Roughly it will poke out 1.65 inches = 42mm.

Now look at the picture I used as an example, those are 8.5" wide rims and both front and rear have added negative camber and narrow stretched tires.
That front camber might even be maxed out for the suspension drop, roughly -3.0 degrees which will wear the inner treads out faster. Budgeting for front adjustable camber plates and rear adjustable control arms would be wise and you'd save labor costs to add those when installing the ST coilovers.

195/40-17 usually fits rims 6.5-7.5" wide, perfect for 7" wide rim, 23.2" tire diameter is more than 1" lower than OEM tire. Load rating is 81 and is about the lowest you could consider, I usually look for at least 84 for street use. In that size there are very few tires available, Yokohama S.Drive or Nankang AS1 being the two exceptions, but there can be others that are often used by shops for tire stretch fitments. Not all tires are suitable for stretch fit.



Some examples of 195/40-17 on 8.5" wide rim

When using a tire that is much smaller than stock for tire diameter you get some speedo and odometer error, less clearance for any road debris, more risk for scraping over dips, speed bumps or when cresting steep parking lot ramps.

My MINI is not as lowered as yours and with small diameter tires I won't be able to drive over an empty pepsi can laid on it's side. So just be careful.
I scrape on everything it seems, pretty hard not to.

 

look me up on instagram under the same name (@dropnstylez) and you can see how they fit. Im running 17x8.5 et 30 all the way around with 205/40/17. speedo is about 5mph off. im on bags but at ride height front camber is 2.6 and rear is 3.6. I could get away with a lot less rear camber but when I air out the lip sits flush with the flare. Ride height is I think (from ground to fender lip at center of rim) 23.5 up front and 23.75 rear. Tons of pics on instagram if any of them help.