Tire Sizes
If you don't
understand tire sizes, I whipped up some info
that might help.
The following is a chart of various tire sizes that might fit on our
cars. Anything 235 or narrower will fit. 245 and wider tires may rub. Up to
255-wide tires seem to fit fine on 2nd-gen W-body cars, such as the 97+ Grand
Prix GTP. Some people have been able to wedge 245-wide tires onto first-gen
W-body cars, but sometimes they rub a little. So far, most people who have put
245-wide rubber on their first-gen W-body cars have also used tires with a slightly
smaller than stock overall diameter (245/50-16, for example, which is almost
1" smaller in diameter than the standard 225/60-16).
I have also listed any cars I know of that use a particular tire size as factory
equipment. That way, you can look up that type of car or something and possibly
visualize how wheels/tires of that size would look on your car. The Lowest Price
column lists the lowest price I've found for that size tire either from Tire
Rack or Discount
Tire Direct. As you can see, they get a lot more expensive as the
rim diameter gets bigger.
| Tire Size | Diameter (mm) |
Change
in Diameter (mm) |
Circumference (mm) |
rev/mile | Speedometer Error |
Lowest Price |
OEM Tire on... |
| 16" Rim Diameter | |||||||
| 245/50-16 | 651.4 | -25.0 | 2046.43 | 786.41 | -3.70% | $90 | 1989-90 Pontiac Grand Prix Turbo |
| 225/55-16 | 653.9 | -22.5 | 2054.29 | 783.41 | -3.33% | $103 | |
| 215/60-16 | 664.4 | -12.0 | 2087.27 | 771.03 | -1.77% | $54 | |
| 235/55-16 | 664.9 | -11.5 | 2088.84 | 770.45 | -1.70% | $77 | |
| 225/60-16 | 676.4 | 0.0 | 2124.97 | 757.35 | 0.00% | $50 | All W-body w/16" wheels |
| 17" Rim Diameter | |||||||
| 235/45-17 | 643.3 | -33.1 | 2020.99 | 796.32 | -4.89% | $117 | |
| 245/45-17 | 652.3 | -24.1 | 2049.26 | 785.33 | -3.56% | $112 | 1994+ Ford Mustang GT/Cobra |
| 225/50-17 | 656.8 | -19.6 | 2063.40 | 779.95 | -2.90% | $158 | |
| 235/50-17 | 666.8 | -9.6 | 2094.81 | 768.25 | -1.42% | $196 | 2000 Jaguar S-Type |
| 245/50-17 | 676.8 | 0.4 | 2126.23 | 756.90 | 0.06% | $129 | 1999 Jaguar XK8 |
| 225/55-17 | 679.3 | 2.9 | 2134.08 | 754.11 | 0.43% | $96 | 1998+ Chrysler 300M w/o PHP |
| 18" Rim Diameter | |||||||
| 225/40-18 | 637.2 | -39.2 | 2001.82 | 803.94 | -5.80% | $140 | |
| 235/40-18 | 645.2 | -31.2 | 2026.96 | 793.97 | -4.61% | $165 | |
| 245/40-18 | 653.2 | -23.2 | 2052.09 | 784.25 | -3.43% | $165 | 1999+ Mercedes Benz SL-class |
| 225/45-18 | 659.7 | -16.7 | 2072.51 | 776.52 | -2.47% | ||
| 235/45-18 | 668.7 | -7.7 | 2100.78 | 766.07 | -1.14% | $246 | |
| 245/45-18 | 677.7 | 1.3 | 2129.06 | 755.90 | 0.19% | $174 | 1999+ Audi S8 |
| 235/50-18 | 692.2 | 15.8 | 2174.61 | 740.06 | 2.34% | $208 | |
| 19" Rim Diameter | |||||||
| 245/35-19 | 654.1 | -22.3 | 2054.92 | 783.17 | -3.30% | $281 | |
| 255/35-19 | 661.1 | -15.3 | 2076.91 | 774.88 | -2.26% | $275 | |
| 255/40-19 | 686.6 | 10.2 | 2157.02 | 746.10 | 1.51% | $245 | |
| 20" Rim Diameter | |||||||
| 255/35-20 | 686.5 | 10.1 | 2156.70 | 746.21 | 1.49% | $316 | |
A positive speedometer error
means your speedo will say you are going slower than you really are.
A negative speedometer error means your speedo will say you are going faster
than you really are.
To do speedo error calculations, use this formula: ActualMPH = SpeedoMPH+(SpeedoMPH*SpeedometerError%)
Be sure to observe whether the SpeedometerError figure has a negative sign or
not!
An easier way for the mathematically challenged would be simply to use Palo Alto's Speedometer Error Calculator.