Next, the Wheelrite is rotated...
Next, the Wheelrite is rotated around the circumference of the wheelwell to check for clearance issues relative to the inner fender lip. A torpedo level is placed against the fender lip as a reference point to measure the clearance from the lip to the wire (9/16 inch). A measurement is then taken from the frame to the inner portion of the wire simulator. Steve DuSold recorded 15/16 inch.
The YearOne wheels were ordered to allow for 0.5-inch of clearance in the front and rear based on a maximum section width of 298.45 mm. Anything below that figure provides additional clearance. Conversely, a section width that exceeds it reduces clearance and increases the potential for wheelwell/lip or frame contact when under hard-cornering or braking conditions.
| MANUFACTURERS’ TIRE SPECIFICATIONS |
| Size | 285/40ZR18 | 295/40ZR18 | 295/45ZR18 |
| Diameter | 26.97 | 27.29 | 28.45 |
| Rim Size Range | 9.5-11 | 10-11.5 | 9.5-11 |
| Recommended Rim Size | 10.00 | 10.50 | 10.00 |
| Section Width (mm) | 285 | 295 | 295 |
Tools And Supplies
Percy's Wheelrite
Tape measures-inches and millimeters
Torpedo Level
Jacks and jackstands
Standard sockets and socket wrenches
Conclusion
Given the vast choices, wheel and tire fitment has never been more challenging than it is today. Thankfully, Percy's Wheelrite has answered the call for an easier method by which a hobbyist can science out a wheel/tire combo that will fit properly before he places an order.
Whether your car is a classic GTO or Firebird, a brand new G8 GT or Solstice, or any model in between, using this tool to make the calculations means you no longer have to seek out an enthusiast with a proven wheel/tire combination to copy in order to get it right the first time.
Having determined that a 285/40ZR18...
Having determined that a 285/40ZR18 tire mounted on a 10-inch-wide wheel would fit easily, the Wheelrite was used to set up both the frame and fender lip clearances at equal distances of 0.50 inch (giving us the maximum section width potential of 298.45 mm). This resulted in 6 inches of backspacing (backspacing read right on the Percy's Wheelrite).
The rear wheels were installed,...
The rear wheels were installed, and setting up the front-end measurement commenced using the same procedure as the rear, except the stock upper and lower control arms and spring were removed and replaced with the Global West upper and lower control arms. Compared to the stock control arm on the right, the Global West LCA has a black powdercoated finish and an advanced tubular design for added strength. Special sway-bar end-link and greasable Del-A-lum bushings show that it's engineered to sustain high stress loads and eliminate unwanted suspension flex.
We then adjust the total length...
We then adjust the total length of the Wheelrite from 26.97 inches up to an overall diameter of 28.45 inches (295/45ZR18 tire) to make sure the calculations can be simulated. To get the added 1.48-inch-diameter increase, the Wheelrite is raised 1 inch, the tire wire is stretched 0.48 inches, and the wire is adjusted for a 295mm section width. The Wheelrite is then rotated, and we verified that the calculations and real-world simulation were dead on. Even the wheelwell clearance closest to the door was only marginally diminished, from 2.75 to 2.01 inches.
To measure accurately, the...
To measure accurately, the shock and spring must be removed. To simulate a maximum suspension travel, the assembly was raised until the bumpstop of the control arm contacted the frame. The Wheelrite was installed and set to a tire diameter of 26.97 inches. All other measurements remained the same. The existing 6 inches of backspacing and the 295mm section width proved to be too wide, as the wire simulator is directly below the lip of the front wheelwell.
Adjustments were necessary...
Adjustments were necessary to provide adequate tire clearance, so the section width is reduced to 285mm and the backspacing is adjusted to 5.5 inches to establish the same 0.5-inch of clearance from the fender and frame that was established on the rear. Look close and you will notice that the fender lip has a 0.25-inch clearance!
After double-checking the...
After double-checking the clearances and backspacing, the rotor is swiveled to the left to ensure that the Wheelrite clears both the back edge of the fender and the frame. The rotor is then moved in all ranges of motion on the left side to simulate what the wheel would do with varying degrees of steering-wheel input turning the car to the right.
The same range of motion is...
The same range of motion is then checked with the wheel to the left. Seen here is the angle in which the Wheelrite is simulated at the bottom of the arc as it goes toward the frame. Even the front of the fender has nearly 2 inches of clearance. From a wheel/tire simulation standpoint, a 10-inch rim with 5.5 inches of backspace should provide adequate clearance for a 285/40ZR18 tire. All that's left to do now is place the order and admire the results!
YearOne billet Snowflakes...
YearOne billet Snowflakes began life as 18x10-inch wheels with brushed centers (PN BNW18180) and built to the specifications detailed in the article. The owner then powdercoated the inside Cameo White.
The KORE3 '73-'77 A-body front...
The KORE3 '73-'77 A-body front brake kit (Retail $1,102 with options shown) utilizes a Corvette C6 Z51 PBR twin-piston caliper and 340mm x 32mm [13.4 x 1.26-inch] GM drilled rotors with ACDelco Durastop semi-metallic pads.