Make sure the wheel you are looking at is 4x100 bolt pattern. With stock suspension there is enough clearance for no rubbing if going straight. Not certain with full turn since wheel and tire are both very wide.

Compared to OEM 17" wheel and tire the 17x9 will be 7.6mm further from inner suspension and poke out 58.4 mm more or about 2 inches.

Usually using wide wheels like that do a few things not for the better. You add a lot of weight for wheel and tire without that much gain. Tire selection can be a problem depending on your tire needs. Cost is usually higher for wide wheels and tires. In general when you increase track you put more stress on the wheel bearings if used on the track. For street use it isn't that bad.

Normally for 9" wide rims you would want tire sizes that are 255mm wide (but tire diameter will be too tall) but 245/40-17 is OK and has tire diameter of 24.8" which is about 0.4" taller than OEM.
235/40-17 is an alternative size that fits the wheel and has tire diameter of 24.5" which is close to OEM. This tire size has some good summer performance tires. Extreme Summer like Dunlop Direzza III is streetable but will wear out faster. Streetable track tires like Toyo Proxes R888R also available

 

 

Problem with your plan is "same exact setup" is not the same when going from 15x9 to 17x9. It's a different setup but only with extra wide wheels and tires.

Why? because 15x9 is a small wheel which gives you small tire diameter sizes giving you much more clearance for turning the extra wide tire and rim. Tire diameter for 245/40-15 is a scant 22.7" or a little less than 2" smaller. This is great for lowered gearing when racing so it is a common track solution and doesn't require a lowered suspension to work although there is enough clearance for a 1/2 to 3/4" drop.

17x9 and the larger tire size give you essentially an OEM tire diameter or larger which gives you reduced clearance and all the problems of the wide tire moving when turning.

Wheel spacers? You're poking out 58mm, wheel spacers would increase the poke. Not the exact setup, wheel offset is the difference.

 

OK, took a look at that video. Those wheels poke out about 50mm which is too far without adding fender flares or a wide fender kit. Using larger 17" tire sizes in that width would likely require some cutting of the plastic wheel arch trim if it rubs which can be over uneven roads and dips or with a full load in the rear seat depending on weight and your suspension (worn OEM will be soft). To adjust for just enough clearance you could go with fully adjustable coilovers which control ride height but add to cost and labor.

If you really like the poke out look and don't mind it, watch out for rock chips and mud which will fly up everywhere. In the video they used 20mm wheel spacers to clear the inner suspension parts and mentioned control arms. In my experience you need to clear the front brake for air flow and cooling and in the rear on the lower trailing arm for the R53. Even with 15x8 et36 I have to add 3mm spacer for clearance due to rubbing.

Another way to deal with the poke is to run more negative camber using front adjustable camber plates at the top of the shock tower and rear adjustable control arms (one pair). But more front negative camber will wear out the inner treads of the tires when street driving and rear negative camber beyond -1.4 degrees may increase tendency for understeer.

 

This is said wheel that I was looking into, a wheel with a wide *** fit for tires. I like the look of 245 and 255 on these wheels. Why 17x9 ET15? Because they're the best looking and the cheapest I have found out of the 1Xx9 wheels I have found. If It makes a difference I have removed the front fender liners for prep. if I do go wide. See Photo, from Mike Baker's channel using 235/50r15 on 15x8s I believe.

Ebay link is the wheels: https://www.ebay.com/itm/DRIFZ-308B-...4/183481726424
My overall question is not how it will look, affect ride (within being still safe). More if I can still use full turn upfront with 17x9 ET15 with 245/40r17s mounted, the rubbing in both front and rear, and how it may effect the braking when at full lock. Basically safety concerns over practicality. I am going for a ridiculous poke, ridiculous stance and ridiculous width. I also have installed flaps on all for rears to avoid kicking up into the side of the car.

 

You're getting 58.4mm of poke so it's unknown if you will get rubbing with full turn or under load. If you do then be prepared to cut the fenders. a wide fender kit or flares will give you more space for a wider wheel and tire. A wider wheel and tire will be heavier so handling and performance will be sluggish and there is more stress on braking.

 

Hey, could you send me some more pictures of which i assume is your car in the linked post. im looking for some et20 wheels on 235-245 possibly to big, but like you i like the look. if you could send me some more pictures possibly even some more insight it would be much appreciated.