With this particular Brembo kit, an 18-in wheel is the smallest we could go. But before we gave iForged the okay to start the manufacturing process we had to decide on what tire widths we would use. After researching available tire sizes for both street and track use, we chose 18x9.5 for the front and 18x11 for the rear. The fronts will comfortably accommodate anything from a 245mm to a 265mm wide tire. The 11-inch rears can be easily wrapped with widths ranging from 275mm to 305mm.
To clear the front and rear calipers, iForged built the wheels with custom offsets, +45mm in the front and +48mm in the rear. With such large offsets you may want to convert to longer wheel studs, which we may do in the near future. We can still get seven full turns per lug nut. If a sanctioned race event requires the studs clear each nut all the way through then we'll need to convert to longer studs for sure. But for now we'll use the stock wheel studs.
The wheels arrived a few weeks after we placed our order. As beautiful as they are, we knew that there would be some gain in unsprung weight due to the size difference over stock. One of the disadvantages of running a multi-piece wheel is that it's usually heavier than a one-piece. However, along with a more aggressive look comes a much smaller price tag when you ding a wheel at the track or on a pothole, which in this case would cost a modest $200. Much cheaper than replacing an entire,$1,000 wheel!
The respective weights are 24-lb for the front and 25-lb for the rears. Although not the lightest, we aren't too concerned-the trade off from the small amount of added weight versus the gobs of extra grip in every direction will be worth it. In fact, at the time of this writing the Supra has already been re-dynoed since the last intake manifold install. Thankfully, not one horsepower was lost through the wheels as a result of the heavier running gear.
The tire of choice was once again the Bridgestone Potenza S-03. The fronts are outfitted with 255/35-18s and the rears with 285/30-18s, the widest tire offered in the S-03 line-up. Bridgestone was chosen for its exceptional grip in dry weather, something we Southern Californians see year-round. Its cornering, acceleration and braking grip outshines the majority of the competition, and the S-03 proved itself worthy last time we hit the road course.
Although getting wheels installed is a brainless act, things still can go wrong. I stripped one stud completely. Worst of all, it was on the corner that would be getting the most abuse on the road course, the front-left. Thankfully after a quick trip to Under Pressure Fabrication and Distribution, the Supra had all five studs holding the wheel on for better piece of mind.
The new wheel and tire combo, coupled with the increased braking power, is nothing short of awesome. The new brakes are so powerful that using stock tire sizes would only have the car frequenting the ABS department at fifty-percent pedal effort. With the increased tire sizes in both the front and rear, braking performance has increased dramatically. We should have some numbers soon.
Along with cornering performance, an increase in acceleration grip is another benefit with these tires. However, going wider up front has caused a new problem we must tackle. The extra grip from the wider tires causes the car to lean instead of slide, bringing the edge of the tire in contact with the outer edge of the wheelwell under hard cornering. Even with the Supra's adjustable coil-over system set to full stiff (more on that next time) the car rubs under hard cornering. We need to dial in some negative front camber-something this Supra needs anyways. We'll also try to remedy the problem with a set of stiffer anti-roll bars.
In the next couple of installments we'll talk about a new suspension system, test an intercooler kit, and re-dyno the stock twins with more ignition timing and boost. We'll hopefully have another track day under our belt with this setup and R-compound tires as well. After that we will really start diving into the engine for some serious, Suprasonic power. Stay tuned.
Author's note: Special thanks to Doug of Big O Tires in San Bernardino for having these tires mounted and balanced on such short notice.