Most manufacturers recommend no larger than a 285/35-18 on an 18x9.5" wide wheel (recommended range 9.5 - 11.0"). Next size up is a 295/35-18, and that requires a 10" wide wheel.
Fred
381ci all-forged stroker - 10.8:1 - CNC LT4 heads/intake - CC solid roller - MoTeC engine management - 8 LS1 coils - 58mm TB - 78# injectors - 300-shot dry nitrous - TH400 - Gear Vendor O/D - Strange 12-bolt - 4.11's - AS&M headers - duals - Corbeau seat - AutoMeter gauges - roll bar - Spohn suspension - QA1 shocks - a few other odds 'n ends. 800HP/800lb-ft at the flywheel, on a 300-shot. 11.5 @ 117MPH straight motor
With the larger wheel, you're moving the center of mass toward the outside diameter of the wheel/tire combo, and that increases the energy needed to bring the wheel/tire mass up to rotating speed. Small loss of rear wheel HP, a little more resistance to acceleration from the front wheels. Probably hard to measure. The thinner/stiffer sidewall will probably reduce straight line traction slightly as well. Again, these changes are hard to quantify.
The speedo error will be less than 1%.
Fred
381ci all-forged stroker - 10.8:1 - CNC LT4 heads/intake - CC solid roller - MoTeC engine management - 8 LS1 coils - 58mm TB - 78# injectors - 300-shot dry nitrous - TH400 - Gear Vendor O/D - Strange 12-bolt - 4.11's - AS&M headers - duals - Corbeau seat - AutoMeter gauges - roll bar - Spohn suspension - QA1 shocks - a few other odds 'n ends. 800HP/800lb-ft at the flywheel, on a 300-shot. 11.5 @ 117MPH straight motor
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