Ross
Goblin Guru
Buying wheels and tires is so much fun. I must have looked at 40 wheels and another 40 tires in various combinations.
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: (But this tool helps make it easy: https://www.rimsntires.com/specspro.jsp )
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 Cobra 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
Here is the results with those 39mm adapters and the mustang cobra wheels. About 1.25" (32mm). The 275mm tire doesn't overlap the wheel when sitting still, but it will flex over during cornering, and I sometimes run 315mm tires, which do overlap the wheel. Oh, this is with the BC racing coil overs, and 0.5 degrees camber.
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: (But this tool helps make it easy: https://www.rimsntires.com/specspro.jsp )
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 Cobra 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
Here is the results with those 39mm adapters and the mustang cobra wheels. About 1.25" (32mm). The 275mm tire doesn't overlap the wheel when sitting still, but it will flex over during cornering, and I sometimes run 315mm tires, which do overlap the wheel. Oh, this is with the BC racing coil overs, and 0.5 degrees camber.
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