After years of extensive testing and measuring, I finally fit 305-width Michelin Cup 2 (240)s under the rear of an NSX, mounted on a set of custom Forgeline GA1R wheels.
I am a big fan of Michelin. I’ve raced on their tires in the 24 Hours of LeMans driving the No.66 Ford GT and worked with them to create bespoke Cup 2 tires for cars like the Ford GT, Shelby GT350-R and GT500. This experience has made me desperately want the level of on-track grip, comfort, quietness, refinement, and overall performance of the Cup 2 for my NSX.
Unfortunately, the Cup 2 was never offered in NSX-friendly 17” or 18” sizes. With the help of the wider fenders that we installed in Part 8, and after a significant amount of testing and measuring on 18/19” wheels, I finally figured out how to stuff modern sportscar-width Cup 2 tires fit on an NSX.
I decided on a 245/35-18 front tire, and a massive 305/30-19 rear tire. This happens to the staggered width of most modern track-focused Porsches, McLarens, and Ferraris. The new Michelin Cup 2 (240) “Connect” tire is the second-generation Cup 2 that I talked about in my article Not All Cup 2 Tires Are Created Equal.
In order to do this, we needed a set of custom width and offset wheels. Forgeline stepped up the plate with their GA1R Open Lug wheel. I’ve won a lot of races on this exact wheel design, which features an open center lug design that helped make pit stops faster on the GS-class Roush Performance Mustang race cars that I competed in. This was a game-changing competitive advantage in the pit lane, and a special design feature I’m proud to have on Project NSX.
Now this has been a long journey that started with testing the 18/19” wheel stagger on the NSX using Advan RSii wheels. This large wheel setup has historically been reserved for the “big-wheel” NSX crowd that didn’t care much for what rubber they stretched around their blingy wheels. But as the saying goes: necessity drives innovation; and as 17/17 and 17/18 tire options started to dwindle, I looked for a solution in larger sizes.
I first tested 235/40-18 and 275/35-19 tires which are an extremely common, modern size that virtually every tire that matters are available in. Including the Michelin Cup 2. I chose the Nitto NT05 in these sizes to push the limits of the platform and see what it takes to make them work. This was the tire that I set a really fast time at Buttonwillow using the standard 17/18 tire stagger and my goal was to compare 17/18 vs 18/19 using the same tire.
Unfortunately, after months of testing this setup and modifying the car, the 25.5” front outer diameter of the 235/40-18 tire was just too large to work in a wheel well designed for a 23” diameter 205/50-15 tire. Plus, it raised the ride height by over an inch, which is not good for looks, handling, or performance.
From the knowledge in my article How to PROPERLY select and size TIRES for PERFORMANCE, it’s crucial to start by choosing and sizing a tire before selecting a wheel. Since I wanted the Cup 2, and my testing determined that 235/40-18 was too large, I decided on a 245/35-18 which is 0.7” smaller in diameter and is a popular size that’s available in other high performance tire models. This size is a full 1” larger than the OEM-sized 215/40-17 front tire, which is far more reasonable than trying to stuff a tire that’s 1.7” larger.
Out back, I chose a 305/30-19 rear tire to have a more modern supercar tire stagger, to stay within the ABS tolerance of the NSX, and increase rear grip which is usually the limiting factor of the NSX. This rear tire has a 11.0” treadwidth and based on my general rule of thumb of sizing a wheel 0.5” wider than the tread width for the best handling and grip, we would need an 11.5” rear wheel and a 9” front wheel for the 8.6” wide front tire.