The car showed a 0.15sec acceleration advantage in just a 30mph window (increased from 25-55mph). And the lower the rpm, the bigger the gain. Granted, it's at an engine speed you'll never see while drag racing, but it would help in everyday driving, or when powering out of a tight turn (because we're talking about engine speeds between 1800-4100rpm).
Since we have several goals for this project car, we're glad we didn't buy larger, heavier wheels. And unless you've installed huge brakes, or are having serious traction problems with forced induction, you should probably think twice about upgrading your running gear with bigger, heavier parts - assuming you care about your car's complete performance.
Alternatively, those of you wishing to upgrade your wheels and tires could argue that, providing you don't go with huge sizes, the penalty is pretty small. It really depends whether you're building a pure track day car or just want something quick for the weekends.
Power/torque vs MPH: When testing power against vehicle speed, it brought gearing into the equation. It looks like our 1% gearing reduction helped power output throughout the rev range, making the car slightly quicker through the rpm sweep. Peak gains are 5whp and 9 lb/ft at around 31mph, but the torque drops sooner as the car now sees about 100rpm higher with the 235/40-17 tires | 
Power/torque vs RPM: With 7.5 lb less per corner, we expected to see a wheel horsepower difference from the new wheels and tires. They provided up to 4 lb-ft gain as the torque ramps up from 1800-2300rpm, but after that it was even | 
MPH vs time: Speed plotted against time will give us acceleration, and more tangible, real-world results. From 25-80mph, our car is now nearly 0.2sec quicker in third gear, with most of the gains happening in the first 30mph (1800-4100rpm). Where the stock set up took 4.73sec, the SSR/Sumitomo combo took 4.58sec |