Lowered 1.25 and want a dedicated track wheel set
 

I have a 2011 SS running 1.25 lowered BMR springs and a bunch of BMR suspension mods. I've upgraded rotors, pads, lines and fluid for the track and the car delivers 675 to the wheels. My current 20 inch NT05's are manageable (315 rear and 275 front) but I'd like to get a dedicated set of wheels and tires for track days. I need advice before I buy on sizes, offsets and potential spacing. Here's what I'm leaning towards so far:

19x11ET25 Apex PS-7's on all 4 corners
Nitto NT01 305/30ZR19 (102Y) XL on all 4 wheels

18x11ET25 Apex PS-7's on all 4 corners
Nitto NT01 305/35ZR18 101W on all 4 wheels

What I notice is that tire widths are about the same as my current rear setup at 12.4 inches but I all cases the tire diameter shrinks considerably by about 2.5 inches. Is this what most people are doing or am I missing something? This will alter top speed and the speedometer accuracy but will it change any other calculated items?

Should I be running 18 inch wheels instead of the 19's to allow for greater tire selection down the road?

Current front wheel is 10.79 inches wide. Will the 12.3 inch wide 305's rub because of my 1.25 inch drop?

Will I need spacers or adapters of any kind to mount these?

Thanks in advance for the feedback and shared wisdom.

I run the Apex PS-7 19x10.5 with Nitto NT-01 285/35/19 tires. I like it a lot, they work well but brake cooling becomes a MAJOR issue with the stickier tires. I went with the 10.5-inch wheels and 285s because I don't like the idea of running a spacer on the track. I'm pretty sure 305s and 11-inch wheels require a spacer. Also, I'm pretty sure that most 18s don't fit over the Brembos. I had a hard time getting my questions answered on that so I went the safe route and got the 19s and the 10.5 inch wheels. Wish I could give you a better answer but I recently went through the same thing and I got a lot of back and forth and I didn't want to take any chances. As to the gearing change, I have a different transmission and rear end than you but the smaller diameter wheels changed my final drive to about 4.05ish and I prefer it over the stock gearing on the track. It helps a little with drive out of 3rd gear turns but you have 250 more hp than me so I'm sure that isn't a concern for you.

I have a set of Forgelines for sale 19x11 square set up. See my thread on it if interested.

Notilloc thanks for your reply. Having done some additional reading here's what I think I'm learning:

The stock Brembo pads have "roller skates" which act as harmonic balancers. They stick out an extra inch and prevent the mounting of 18's in some cases. I (and I assume you as well) are running a set of track brake pads and have removed those things. Which now should allow 18's to mount fine.

10.5 is the key width to avoid the need for spacers. This is cool because 305's require a 10-12 inch rim and so it's right in the ballpark. If I go 11 I then need a spacer to clear the strut. That then leads to extended thread wheel lug nuts or potentially even swapping wheel studs out of the spindles for longer ones.

The smaller diameter tire will result in less rotating mass and potentially faster acceleration. It will also run me through the gears faster but on a road course I'll never run out of gears. Speedo will be inaccurate but who cares.

Your point about hot brakes is an important one. I'm running drilled and slotted Baer rotors, braided lines, Motul RBF 600 DOT-4 fluid and Carbotech pads that squeal like a pig. Short of venting the system, so far so good at the track. Oil temps have been the main issue I've been dealing with and so I just finished a big oil cooler project which this weekend I'll see how well it works.

It's not just the roller skates, I was feeling around back there and on my car there is a part of the strut or something that sticks out into the wheel well and with wheel weights on it barely clears. I don't really know how to explain it but that's something that was brought up in other posts I've read too. If you get the 18s and they fit I'll be super jealous though haha.

I got the 18s today. The wheels look awesome, they totally clear the rotors BUT they do just barely hit the strut. it's the bare upper aluminum block portion, right above where there is a threaded hole that nothing appears to thread into.

Now with that said, this can be fixed one of two ways - the first is simply when I buy the centering ring conversion from 72.56 to 66.9 I buy one with 8 mm (1/4 inch) of spacer built into it and then get the extended lug nuts that drop 1/4 inch further into the hole and neutralize the lost clamping force. The second and simplest in my opinion is to shave down that bare aluminum knuckle where it touches and be done with it. I will opt for a bit of clearancing on that edge of the strut corner and all the other things should fall into place.

Some of the aftermarket wheel barrels are such that the inner portion will hit the upright (sometimes called a knuckle). Mine fit the wheel, but but the clearance was so low it hit the wheel weights in that location, had to move them outboard on the wheel. I think structurally you're at fairly low to no risk to do some massaging there to get them to fit. The wheel weights in question were ~1/8" thick so it's not much material if that what it takes to get them on.

Great info from both of you. I'll keep my 19s because that just sounds like a bit of a headache. Good luck, I'm sure you'll get it figured out!

It's 30 seconds with a grinder on each sides knuckle to cure the problem, not a big deal. The threaded hole with nothing in it is beneficial for setting camber, even more helpful if disassembling your suspension at home and a bolt set in there will keep you close to where you were prior to strut removal. I keep 2 bolts in my tool box for it since my car is apart more than together. Somehow I need to explain it to every shop I've ever taken the car to for an alignment. Last time was a nightmare between 4 shops before one could "figure it out".

Understand this thread is a bit old, but I have recently installed the BMR/KoniV2 kit and noticed that clearance is tight back there as well. I want to install a set of 18 inch wheels for AutoX purposes, and have come just short of smashing my head in the desk trying to math out the clearances. I am trying to go for a square setup like a 285/40r18 all the way around.
Does anyone have any experience with this? I feel like an 18x10 with a +20 offset would work all the way around.
Suggestions? Comments?

I'll sell you my APEX PS-7 19"x11" +25 spin forged wheels. They don't make them anymore. Let me know!

What are you looking to get for them? Toss me a PM.
Also, with a smaller diameter wheel/tire combo, does anyone have issues with the car being too low? I have about 4" of ground clearance under the car before I start dragging my rear subframe braces.