Buying wheels and tires is so much fun. I must have looked at 40 wheels and another 40 tires in various combinations.
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I wanted to keep the gear ratios the same as the stock car, so I started with the stock tires that came with my donor:
5 spoke stock aluminum wheel 18"x7"
Toyo Proxes 4 plus 215/45r18, 25.6" high 7.75" wide.
Then looked for wheels and tires near that same 25.6" diameter.
I was looking for wide tires, and noticed that 17" Mustang wheels are cheap and 10.5" wide wheels.
Ended up choosing Nitto NT05R Drag Radial Tire - 315/35R17 which are 25.7" high.
The hard part is
calculating the wheel spacer width:
I didn't want the wheels to intrude closer to the car, and rub, so I started calculating spacers that would keep the inside edge of the wheel at the same location.
2006 CHEVROLET COBALT_SS 18"x7" Wheel
Bolt Pattern: 5x110mm
Hub Diameter: 65.1mm
Width 203.2mm (7" inside width where the tire bead touches. actual wheel is 8"(203.2mm) wide on the outside)
Offset 42mm
1998 Mustang 17"x10.5" Wheel
Bolt Pattern: 5x114.3mm
wheel center bore 70.3mm
Width 11.5" (10.5" inside width where the tire bead touches. actual wheel is 11.5" wide on the outside)
Offset: 27mm
Backspacing: 173mm
The spacer's thickness will be the Mustang wheel backspacing (173mm) less the stock wheel backspacing.
Since I only have the stock offset, I calculated the backspacing (203.2mm/2 + 42mm) = 143.6mm
So to keep the inside wheel rim at the same location, I need a 173-143.6 =
29.4mm thick spacer.
But the new tires overhang the wheel more than the original tire, so the tire might rub if I don't include that in my calculations.
So the stock 215mm tire overhangs the 7" wheel by (215-(7*25.4))/2 = 18.6mm
The new 315mm tire overhangs the 10.5" wheel by (315-(10.5*25.4))/2 = 24.15mm
So to keep the inside of the tire at the same location, I need a (24.15-18.6)+29.4 =
34.95mm thick spacer.
But the new tires have more sidewall thickness than the stock tires, so they will move more during cornering. I don't know how much more, but I did measure the Cobalt SS hub stud length is 38.6 mm long. Since I want to go a little wider, a
39mm thick spacer will save me from trimming all the stock studs shorter. So this is what I went with. (Later realized that the brake rotor thickness gets subtracted from the hub stud length, but no big deal, 39mm works)
Ordered from
http://motorsport-tech.com/ for custom made wheel adapters that are hub centric.
39mm thick wheel adapter.
from 5x110mm hub bolt pattern, Hub Diameter: 65.1mm
to 5x114.3mm wheel, center bore 70.3mm