2016 RS Canadian cars were automatically shipped with Forged wheels and Pilot Sport Cup 2 235/35ZR19 tires. While an excellent tire for track use, I was not impressed with the ride for a street tire, even with pressures reduced to 42F, 40R. The sidewall on the PSC2 tire is particularly stiff. And the PSC2 tires tend to wear quickly. After some research, I decided to go with a TSW Chicane 18 x 8.5 offset 43mm wheel in Matt Gunmetal and Michelin PSS 265/35ZR18 for a daily driver setup. My thanks to @zommer79 for his extensive research on fitment for a similar setup using OZ 19 x 8.5 offset 45mm and PSS 265/30ZR19.
An offset tool gave me the following:
The choice of 18 inch over 19 inch was prompted by several factors:
1) A taller sidewall was likely to improve the ride characteristics.
2) The PSS 265/35/ZR18 at 25.3" diameter is very close to the OEM PSC2 235/35ZR19 at 25.5".
3) The TSW Chicane 18 x 8.5 is relatively light at about 21 lbs. Overall, I managed to shed about 1.5 lbs per corner.
4) Pricing is more favorable on 18 inch setups than 19 inch.
Discount Tire Direct was very helpful in suggesting operating pressures for the tire in question; they suggested a minimum of 35 PSI, based on the load rating of 91 (1356 lbs) for the 235/35ZR19 versus 97 (1609 lbs) for the 265/35ZR18.
I came at it from a slightly different angle; the ratio of the load ratings 1356/1609 yields an 84% factor. Using OEM recommended PSI of 46 x 84% gives 38 PSI, and 42 PSI at 84% gives 35 PSI. But these numbers are close enough to DTD's suggestions.
Another interpretation is based on the comparative volume of air in the two tire sizes as a load carrying "cushion". The 235/35ZR19 has 1818 cubic inches of air, compared to 2110 cubic inches of air for the 265/35ZR18. This ratio is 81.3%.
In any event, this confirmed we should be okay to run a much lower operating pressure on a daily driver basis. Here are a few photos of the resulting setup:
Strut looks to have at least 1/2 inch clearance:
I did a quick road test for fitment confirmation and ride improvement, using pressures of 38F and 36R. No scraping issues so far and a much better ride.
Jacob.
Update: After about 10 miles, the TPMS warning light went on. I can confirm the following procedure and tool works:
One additional image after a few days' use:
JacobZ06
An offset tool gave me the following:

The choice of 18 inch over 19 inch was prompted by several factors:
1) A taller sidewall was likely to improve the ride characteristics.
2) The PSS 265/35/ZR18 at 25.3" diameter is very close to the OEM PSC2 235/35ZR19 at 25.5".
3) The TSW Chicane 18 x 8.5 is relatively light at about 21 lbs. Overall, I managed to shed about 1.5 lbs per corner.
4) Pricing is more favorable on 18 inch setups than 19 inch.
Discount Tire Direct was very helpful in suggesting operating pressures for the tire in question; they suggested a minimum of 35 PSI, based on the load rating of 91 (1356 lbs) for the 235/35ZR19 versus 97 (1609 lbs) for the 265/35ZR18.
I came at it from a slightly different angle; the ratio of the load ratings 1356/1609 yields an 84% factor. Using OEM recommended PSI of 46 x 84% gives 38 PSI, and 42 PSI at 84% gives 35 PSI. But these numbers are close enough to DTD's suggestions.
Another interpretation is based on the comparative volume of air in the two tire sizes as a load carrying "cushion". The 235/35ZR19 has 1818 cubic inches of air, compared to 2110 cubic inches of air for the 265/35ZR18. This ratio is 81.3%.
In any event, this confirmed we should be okay to run a much lower operating pressure on a daily driver basis. Here are a few photos of the resulting setup:









Strut looks to have at least 1/2 inch clearance:

I did a quick road test for fitment confirmation and ride improvement, using pressures of 38F and 36R. No scraping issues so far and a much better ride.
Jacob.
Update: After about 10 miles, the TPMS warning light went on. I can confirm the following procedure and tool works:

One additional image after a few days' use:

JacobZ06