Unconventional CT4V-BW wheel fitment (Apex)

[Yllwwgn]

Hi, thought I’d share with the group… absolutely love the CT4V-BW and have never been a domestic guy (mostly German), but the handling, steering, and precision of the car absolutely sold me. Since I’ve never kept anything stock, I wanted to tailor the wheel setup more to my liking. I’m old school and like some sidewall to my cars, and didn’t want to sacrifice our car’s purpose, but also wanted to fill out the wheel wells a little more. The front oem 18” sizing is spot on, but the rears always looked a bit “small” to me. I got some Apex wheels but still wasn’t happy with the look… it was good, but I wanted SYMMETRY. Symmetry front to back, in terms of sidewall height, tire-to-fender-gap, and width ratio front-to-back. Again I didn’t want to compromise handling, and some trial and error and lots of calculations… here you go. Turns out GM designed the rear fender wells exactly 1” larger in diameter than the fronts… hence why 18’s look fine up front but small in the back.

The goal here was subtlety… hopefully hard to spot until I point it out.

Sorry for the multiple “similar” pics… wanted to show it under different lighting to be fully transparent. Yes, 255/35R18 front, 285/30R19 rear . Looks even more subtle in person. And before anyone asks, the PS4 rear in that size happens to have the same tread width as the oem 275/35R19 BW-spec PS4… so the cornering balance/grip balance has stayed the same.

 

[JLayer]

Any problems with speedometer or warning lights running staggered. I know your running 35 fronts and 30 rears but I didn't know if the newer ecms would throw a fit or not.

 

[Yllwwgn]

Zero issues whatsoever; the overall diameters of the oem rear setup vs the new rear setup are almost the same.
I tried a 295/30R19 for a few days and didn’t like it… the back was almost too planted mid corner at 9/10ths and felt almost more sluggish/sloppier is the best I can describe it.

 

[Melon]

It's nice finally seeing 19's on the CT4. I want to go to 19's F & R, but man, this setup looks excellent.

 

[1Evil55]

Bravo. That looks great. I did a similar setup years ago on a GS400. It really looks made for it.

 

[dwduck]

Thanks a lot for the post! I was actually thinking the same thing for so long about the rear tire looking smaller and wanted to run a similar setup as you with the flow formed vs5 but was afraid of all the possible PTM error codes that could happen or a difference in the handling feel. There was no difference at all in handling or acceleration? What do you think about a 265 tire in the front will that cause any rubbing? Also did you lower it or change the alignment or camber?

 

[Yllwwgn]

Thanks a lot for the post! I was actually thinking the same thing for so long about the rear tire looking smaller and wanted to run a similar setup as you with the flow formed vs5 but was afraid of all the possible PTM error codes that could happen or a difference in the handling feel. There was no difference at all in handling or acceleration? What do you think about a 265 tire in the front will that cause any rubbing? Also did you lower it or change the alignment or camber?

I had originally tried a 295/30R19 in the PS4 in the rear and it was WIIIIDE… like more wide than most 295’s. Turns out Michelin uses the 305 casing for the 295 as well. And unfortunately the 285 PS4 runs narrow (go figure)… Michelin uses the same casing for the 275 as it does the 285. The 295 for perspective was 28mm wider than the 285, when it should only be 10mm wider.

Besides that the 295 gave me too much rear end grip when running the factory 255 up front… I didn’t like how it promoted understeer. My car also exhibited occasional weird shifts (10spd auto) when floored… I believe it to have been a PTM issue.

With the 285 I have had ZERO issues whatsoever, and because it runs narrow, the handling balance is the same as OEM. Suspension is oem btw. And a 265 up front would be fine, but visually it would negate the symmetric look I was looking for (sidewall, fender gap, overall diameter, etc.)

 

[dwduck]

I had originally tried a 295/30R19 in the PS4 in the rear and it was WIIIIDE… like more wide than most 295’s. Turns out Michelin uses the 305 casing for the 295 as well. And unfortunately the 285 PS4 runs narrow (go figure)… Michelin uses the same casing for the 275 as it does the 285. The 295 for perspective was 28mm wider than the 285, when it should only be 10mm wider.

Besides that the 295 gave me too much rear end grip when running the factory 255 up front… I didn’t like how it promoted understeer. My car also exhibited occasional weird shifts (10spd auto) when floored… I believe it to have been a PTM issue.

With the 285 I have had ZERO issues whatsoever, and because it runs narrow, the handling balance is the same as OEM. Suspension is oem btw. And a 265 up front would be fine, but visually it would negate the symmetric look I was looking for (sidewall, fender gap, overall diameter, etc.)

I was initially thinking of running 18x265 all around on a square setup so that I can rotate the tires and not have to change them so frequently.. Keep going back and forth between running square setup and an aesthetic/performance oriented setup like yours. Do you feel any extra harshness in the back due to the 19 inch wheel? Since it is heavier than the 18 wouldn't it slow down your acceleration by a small amount?

 

[Yllwwgn]

I considered going square at first as well, and running 275 all around. If I tracked it more often I would consider it, but I don’t. I drive like a goon more often than not anyway, and consider rear tires to be 100% a wear and tear item that I usually replace 2x as often as I do the front tires regardless.
I too thought I’d feel slightly more sluggish, but I don’t at all. Also my acceleration times have stayed the same. Have not observed any more harshness at all; probably because Magnaride is just THAT good on these cars.

 

[dwduck]

any reason you went with 10.5 width over 9.5? Is it traction related or does it just sit more flush with the rear fender?

 

[Yllwwgn]

I went with the 10.5 because the plan was to fill the rear fenders up with a 295. Having gone with a 285, I’d ideally prefer a 10” wide wheel; the 285 on the 10.5 has a slight stretch… but it’s minimal and fine.

 

[dwduck]

Makes sense I really wish apex would make a 10 for our car but they don't.. Knowing this now would you opt for a 19x9.5 or 19x10.5?

 

[Yllwwgn]

I like the 285 on a 10.5 more than a 9.5 rim. So no regrets.