With the very limited performance tires available for our cars with 19" wheels, I'm wondering if anyone has downsized to 18" wheels for more tire options. Do we have clearance for 18s? Anyone done this? If so, what wheel specs and tire sizes are you running?

 

By default, the calipers are too big to fit 18 inch wheels. I believe, some people have found either very limited wheels that are thin enough to clear the calipers. I believe, one member even had custom 18 inch wheels built for his RCF. You might be able to find some, but they are very rare and hard to find.

 

18's. mostly the forged ones, with the right offset, will work. I had 18' Volk te37's (18x10 +34, 18x10.5 +22) with no fitment issues. tires were 265/40, 285/40 IIRC. Forged wheels tend to not have too much material in the inner barrels so big brakes fit in them. This is not to say all 18's forged wheels will fit though. One other brand I know fit the front brakes are Apex forged VS-5RS, 18x10 +40 fit with plenty of clearance, also ze40's 18x9.5 +45 and 18x10 +39 fit. These are wheels that I have tried and verified to clear the front brakes. You’re most likely looking to get a square setup, I know a couple people that track with 18x10 +35 volks ZE40’s.

 

As I have come to understand it, the 2015 STI has the same calipers as the RC-F. The Offsets will be different, but there are plenty of 18" wheels covered in this thread...

https://forums.nasioc.com/forums/sho...18034&page=301

 

Are you sure? STI’s have 13 in. front rotors and calipers are 4-piston.

 

EDITED.
The year I first used was incorrect. The 2018+ STi was offered with six piston calipers, with smaller rotor. In reply to your response I dug in more and it appears I was incorrect. They are the same as the 2008-2014 IS-F though.

 

We sell and run the Wedssport TC105X for the RCF in 18x10 square. We happen to have 1 set in stock at the moment. We torture Wedssport wheels on our shop car while we're testing products and have never had a failure. It's a great set of wheels

-Justin
RR Racing

 

What colour are these? I have it in my head they are bronze. Also, in an 18x10 what tire size would you recommend for a square setup?

 

These are Gunmetal grey. I have the hardest time trying to capture wheel color in this shop sometimes. Here's a picture in the box. I would probably run a 275/40 front and maybe 285-295/35 rear tire on these. That depends on the tire and the use for the vehicle though.

-Justin
RR Racing

 

I've been going to the track enough lately that I think I've finally 'outgrown' stock street tires, so I'm actually going down a rabbit hole looking into fitments and specs. Surprisingly finding a lot of 18" setups when I search the FB groups.

Generally all 18" wheels that DO fit are forged options that specifically advertise being designed for large caliper clearance. For example I can confirm that 18" Enkei RPF1s do NOT fit. I'm looking for a square setup so I can rotate tires, currently roasted two sets of fronts and rears are still kicking.

Here's my notes so far.

Stock Specs, used for online calculator comparisons:
19x9 +50 (+35 w/ 15mm spacers) 27.7lbs
19x10 +41 (+26 w/ 15mm spacers) 29.4lbs
5x114.3 60.1 bore

Wheel options, based on sizing listed on manufacture websites as of Nov, 2022. I mention that because some posts inline spec offsets that aren't listed. So I don't know if those are typos, or if wheel manufactures change available specs often.

Most common sizing option for square: 18x10 +40
When cross referencing this size, it appears to be a very common spec for a Mustang. As such, typically will need hub rings for the RCF.

Wheels available in this size:

Apex VS-5RS
18x10" +40 all around
https://www.apexraceparts.com/our-wh...ed-vs5rs.html/

Titan7 has T-S5 and T-R10 forged in this size, but caliper clearance not confirmed yet. Full 18x10 set costs about $800 cheaper then their RCF specific staggered 19" T-S5 setup as well.
https://titan-7.com/collections/wheels

Volk Racing (Rays) ZE40
18x10 +40
https://www.rayswheels.co.jp/product...=en&wheel=ZE40

Advan RS-DF Progressive
18x10 +35
https://www.yokohamawheel.jp/brand/a...ssive_jpn.html

WedsSport TC105X
18x10 +35
https://www.weds.co.jp/english/wedssport/tc105x/
https://www.weds.co.jp/english/wedssport/tc105xforged/

Tires:
I'm not sure what to run just yet, but seems like 275/35R18 and 295/30R18 are common enough to have a wide selection of options in the "extreme performance summer" category on tirerack (aka 200tw tires).

Misc:
Poking around with calculators, "good fitment" specs in 18" or 19" to aim for are:
9.5 +35 (front)
10 +40 (square)
10.5 +35 (rear) +40 (front)
11 +40 (rear)

10.5 +22 is super common size from all manufacturers, but need a lot of camber in the rear to avoid rubbing.

 

I'm thinking of making a set of custom rims (monoblock forged, >750kg load rating, under a grand), this is the size I'm thinking, anyone think it'll fit?

18x9.5 et35
18x11.5 et57

Open to thoughts

 

This is REALLY good info.

Can anyone confirm that running a square 18x10 +40 setup on 275/40s will not rub in front or rear at stock ride height?

Also, if going staggered, in theory we should be able to do 18x9 up front with +45 or +50 to get close to stock fitment if wheels are available with that offset? Thinking something like 18x9 +45 up front and 18x10 +40 in rear.

 

I guess I didn't think to circle back to this post. I picked up the Apex VS-5RS wheels in square 18x10 +40 with 275/35R18 tires. I did put a set of 10mm spacers on the rear so they didn't seem too sunk in (considering stock is a 10 +41 offset wheel and i normally run 15mm spacers). I'm on Swift springs and no issues.

 

Thank you for following up and that looks like a super clean setup! The 18x10 +40 looks like a really solid fitment all around. Now I just have to figure out which wheels I want and in which color...